Mastering Biology Exam 3 part 2

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Meiosis involves two sequential cellular divisions.

Meiosis I and Meiosis II

meiosis I,

homologous chromosomes pair and then separate. Thus, although the parent cell is diploid (containing two chromosome sets, one maternal and one paternal), each of the two daughter cells is haploid (containing only a single chromosome set).

meiosis II

the sister chromatids separate. The four daughter cells that result are haploid.

Crossing over

Crossing over occurs during prophase I when homologous chromosomes loosely pair up along their lengths. Crossing over occurs only between nonsister chromatids within a homologous pair of chromosomes, not between the sister chromatids of a replicated chromosome. Only segments near the ends of the chromatids, not segments nearest the centromeres, can exchange DNA.

Which statement correctly describes how cellular DNA content and ploidy levels change during meiosis I and meiosis II?

DNA content is halved in both meiosis I and meiosis II. Ploidy level changes from diploid to haploid in meiosis I, and remains haploid in meiosis II.

Anaphase and mieosis

During anaphase of both meiosis I and meiosis II, the DNA content (number of copies of chromosomes) in a cell is halved. However, the ploidy level changes only when the number of unique chromosome sets in the cell changes. This occurs only in meiosis I (where separation of homologous chromosomes decreases the ploidy level from 2n to n and produces daughter cells with a single chromosome set).

What is the ploidy of organisms that have two sets of chromosomes?

2n An organism that has two sets of chromosomes has a ploidy of 2n.

What information can not be obtained from an individual’s karyotype?

The sequence of bases of a particular gene Karyotypes only give information about the chromosomes in an individual.

True or false? A haploid organism has one pair of homologous chromosomes

A haploid organism only has one set of chromosomes, so it has no homologous chromosomes. False

If a cell has 24 chromosomes, how many chromosomes would each of its four daughter cells have after meiosis?

12 Meiosis is a reduction division that reduces the number of chromosomes passed on to daughter cells by one-half.

Which of the following statements about meiosis and mitosis is true?

Meiosis II is similar to mitosis in that sister chromatids of each chromosome separate.Both meiosis II and mitosis are cell divisions involving the separation of sister chromatids.

Which structure is directly correlated with the production of genetic variability in the daughter cells produced during meiosis?

Chiasma is an X-shaped structure formed from the crossing over of homologous chromosomes, which can then exchange segments at the crossover sites.

What is the composition of a tetrad at the beginning of prophase I?

One pair of homologous chromosomes One chromosome in a tetrad is paternally inherited, while the other is maternally inherited. Each chromosome consists of two chromatids.

Which statement is correct concerning the relationship between chromosomes and chromatids?

A replicated chromosome contains two sister chromatids

Which event makes meiosis a reduction division and why?

separation of homologs in meiosis I because it produces 2 haploid (n) daughter cells from a single diploid (2n) parent cell.Separation of homologs results in a reduction in chromosome number.

In an organism in which 2n = 6, how many chromosomes will be in each gamete?

3

Which of the following processes contributes directly to genetic variation?

meiosis

Homologous chromosomes are separated during _____.

anaphase I

What is a major difference between mitosis and meiosis I?

Sister chromatids separate in mitosis, and homologues separate in meiosis I.

Crossover, the exchange of segments of homologous chromosomes, takes place during which of the following processes?

synapsis

Homologous chromosomes _____.

carry information for the same traits

For the duration of meiosis I, each chromosome is _____.

two sister chromatids joined by a centromere

Chromosomes and their homologues align at the equator of the cell during _____.

metaphase I

Centromeres split and sister chromosomes migrate to opposite poles in _____.

anaphase II

Chromosome number of hexaploid wheat, Triticum aestivum, can be represented by which of the following?

6n

At what stage of meiosis does DNA replication take place?

None. DNA replication occurs before meiosis I begins.

The diploid number of a roundworm species is 4. You have a male and a female roundworm that are planning a family. Assuming there is no crossover, and random segregation of homologues during meiosis, how many different possible combinations of chromosomes might there be in the offspring?`

16

Normal human gametes carry _____ chromosomes.

23

A diploid organism whose somatic (nonsex) cells each contain 32 chromosomes produces gametes containing _____ chromosomes.

16 its half of 32

How would genetic variation be affected if during meiosis I maternal chromosomes always lined up together on one side of the metaphase plate and paternal chromosomes always lined up on the other side (ignoring the effects of crossing over)?

Gametes would contain either maternal chromosomes only or paternal chromosomes only. All maternal chromosomes would go to one daughter cell and all paternal chromosomes to the other, so different combinations would not be produced in gametes.

Which form of reproduction results in the highest degree of genetic variation among offspring?

out crossing It combines chromosomes from different individuals, which are likely to contain different alleles.

Which statement is FALSE concerning gametes produced by meiosis?

Gametes contain nonrandom combinations of maternal and paternal chromosomes. Gametes receive a random assortment of maternal and paternal chromosomes when homologs separate in meiosis I.

In a haploid organism, how many different alleles can there be for each gene?

1

Crossing over occurs _____.

during synapsis of homologous chromosomes

Which of the following creates different combinations of maternal and paternal chromosomes in gametes?

independent assortment

Which of the following creates new combinations of alleles along one chromosome?

crossing over

If meiosis produces haploid cells, how is the diploid number restored for those organisms that spend most of their life cycle in the diploid state?

fertilization

The bulldog ant has a diploid number of two chromosomes. Therefore, following meiosis, each daughter cell will have a single chromosome. There is/are _____ different possible combination(s) of genes in the daughter cells of meiosis because _____.

more than 2; the two homologues cross over

Asexual reproduction takes place by which of the following processes?

mitosis

The variation among offspring, and the fact that they are genetically different from their parents, is not due to which of the following?

random alignment of homologues during prophase I

An advantage of sexual reproduction is hypothesized to be _____.

avoiding the transmission of harmful alleles to offspring

Adaptation to a changing environment occurs most efficiently through which of the following processes?

sexual reproduction

What is a nondisjunction?

Nondisjunction refers to the failure of pairs of chromosomes or sister chromatids to separate during meiosis or mitosis.

When can nondisjunction occur? Choose the best answer.

All three answers are correct. In meiosis, when sister chromatids fail to separate In meiosis, when homologous chromosomes fail to separate In mitosis, when sister chromatids fail to separate Nondisjunction errors can occur in meiosis I, when homologous chromosomes fail to separate, or in either mitosis or meiosis II, when sister chromatids fail to separate.

Which syndrome is characterized by the XO chromosome abnormality?

Turner syndrome is characterized by a chromosome pattern of XO, or one X chromosome and no Y chromosome.

What kind of cell results when a diploid and a haploid gamete fuse during fertilization?

A triploid cell has three sets of chromosomes: the two from the diploid gamete and the one from the haploid gamete.

Of the following chromosomal abnormalities, which type is most likely to be viable in humans?

Trisomy Some trisomies are viable in humans, but they result in developmental abnormalities, such as Down syndrome (trisomy 21). Only humans with trisomies of the small chromosomes (13, 18, or 21) or the sex chromosomes survive past birth.

If a diploid cell undergoes meiosis and produces two gametes that are normal, and one with n − 1 chromosomes, and one with n + 1 chromosomes, what type of error occurred?

A nondisjunction error occurred in meiosis II, in which both sister chromatids of a chromosome migrated to the same pole of the cell.

If a diploid cell undergoes meiosis and produces two gametes with n + 1 chromosomes and two gametes with n− 1 chromosomes, what type of error occurred?

A nondisjunction error occurred in meiosis I, in which both members of a homologous pair migrated to the same pole of the cell. When this type of error occurs, half of the gametes receive one too many chromosomes, and the other half receive one too few. When all of the gametes are affected, the error probably occurred in meiosis I.

Nondisjunction in meiosis produces _____.

aneuploids

Which of the following would enable you to detect aneuploidy?

karyotyping

Which of the following is an example of monosomy?

Turner’s syndrome

In 1985 Hassold and Chiu found that the likelihood of miscarriage increased with maternal age. What is the most likely explanation for the relationship between age and miscarriage?

Ova are arrested in meiosis until ovulation. As a result, completion of meiosis in the older woman is more likely to result in aneuploidy or other chromosomal abnormalities.

A couple has three boys. What are the chances of them having a fourth boy?

1/2 The chance of having a boy as a single event is 1 out of 2 regardless of the sex of any previous children.

There are five dice in the game of Yahtzee®. What are the chances that a player will roll five ones (1) on the first roll?

1/7776This is the chance of having the same number on all five dice.

In humans, the allele for freckles (F) is dominant over the allele for no freckles (f). What is the chance of a heterozygous couple (Ff) having a boy without freckles?

1/8 Multiply the probability of the homozygote recessive times the chance of producing a boy.

In humans, the allele for freckles (F) is dominant over the allele for no freckles (f). What is the chance of a heterozygous couple (Ff) having a girl with freckles?

3/8 The either-or rule applies to the genotype (add 1/4 + 1/2), and this is multiplied by the chance of having a girl (1/2).

Four o’clock flower color is determined by two alleles: R (red) and r (white). RR flowers are red, rr flowers are white, and Rr flowers are pink, indicating incomplete dominance. Two pink-flowered plants were crossed. What is the probability of producing a homozygous plant?

This is the sum of the two homozygous probabilities, 1/4 + 1/4.

What would be the outcome of meiosis I if none of the homologous chromosomes separate at anaphase?

One daughter cell would be 2n; the other would have no chromosomes. All chromosomes from the diploid (2n) parent cell would go to one of the two daughter cells.

Meiosis I produces _____ cells, each of which is _____.

two … haploidAt the end of meiosis I there are two haploid cells.

Meiosis II typically produces _____ cells, each of which is _____.

four … haploidAt the end of meiosis II there are typically 4 haploid cells.

During anaphase II sister chromatids separate and migrate to opposite poles.

The events of prophase II are essentially the same as those of mitotic prophase except that prophase II cells are haploid.

Four haploid cells are present at the end of telophase II and cytokinesis.

Anaphase II is essentially the same as mitotic anaphase except that the cell is haploid.

At the end of telophase I and cytokinesis, there are two haploid cells with chromosomes that consist of two sister chromatids each.

Homologous chromosomes pair during prophase I..

Metaphase II is essentially the same as mitotic metaphase except that the cells are haploid.

During metaphase I tetrads align along the metaphase plate.

Synapsis occurs during _____.

Synapsis, the pairing of homologous chromosomes, occurs during prophase I.

Homologous chromosomes migrate to opposite poles during _____.

During anaphase I sister chromatids remain attached at their centromeres, and homologous chromosomes move to opposite poles.

During _____ chromosomes align single file along the equator of a haploid cell.

Metaphase II is essentially the same as mitotic metaphase except that the cell is haploid.

During anaphase I homologous chromosomes, consisting of sister chromatids, migrate to opposite poles.

During interphase the centrosome duplicates and the chromosomes are not condensed.

At the end of _____ and cytokinesis there are four haploid cells.

At the end of telophase II and cytokinesis there are four haploid cells.

During _____ a spindle forms in a haploid cell.

Prophase II is essentially the same as mitotic prophase except that the cells are haploid.

interphase

During interphase the centrosome duplicates and the chromosomes are not condensed.

Which event makes meiosis a reductional division and why?

Separation of homologs in meiosis I, because it produces 2 haploid (n) daughter cells from a single diploid (2n) parent cell separation of homologs results in a reduction in chromosome number.

The process of uniting sperm and egg is called _____.

Fertilization Fertilization is the union of the male gamete (sperm) with the female gamete (egg).

A species has ten distinct types of chromosomes. A haploid cell of this species contains how many chromosomes?

10 Haploid cells only contain one copy of each chromosome.

Which of the following is a difference between mitosis and meiosis?

Only in meiosis do homologous chromosomes pair up. In prophase I of meiosis homologs pair, and then separate to form haploid daughter cells.

Sister chromatids separate during which stage of meiosis?

Anaphase II Homologs separate during anaphase I to produce haploid cells with replicated chromosomes. The sister chromatids separate during meiosis II.

sexual reproduction takes place by which of the following processes?

mitosis

The variation among offspring, and the fact that they are genetically different from their parents, is not due to which of the following?

random alignment of homologues during prophase I

Mendel crossed yellow-seeded and green-seeded pea plants and then allowed the offspring to self-pollinate to produce an F2 generation. The results were as follows: 6022 yellow and 2001 green (8023 total). The allele for green seeds has what relationship to the allele for yellow seeds?

recessive

Different ratios occur in crosses with single gene pairs or two gene pairs. What types of ratios are likely to occur in crosses dealing with a single gene pair?

3:1, 1:1, 1:2:1

start ch 14

Gray seed color in peas is dominant to white. Assume that Mendel conducted a series of experiments where plants with gray seeds were crossed among themselves, and the following progeny were produced: 302 gray and 98 white. (a) What is the most probable genotype of each parent? (b) Based on your answer in (a) above, what genotypic and phenotypic ratios are expected in these progeny? (Assume the following symbols: G = gray and g = white.)

(a) Gg × Gg; (b) genotypic = 1:2:1, phenotypic = 3:1

From a cross of YY Yy Yy yy

what are the probabilities

What is the probability that F2 seed chosen at random will be yellow?

3/4

Waht is the probability that an f2 seed chosen at random from among the yellow seeds will breed true when selfed?

1/3 introduces the concept of conditional probability. Although there are two genotypes in the F2 that will breed true (YY and yy), only one of them is yellow. Thus, the question adds a new condition: Among yellow seeds only, 1/3 are true-breeding

what is the probabiulity that three f2 seeds chosed at random will include at least ione yellow seed

63/64 there are seven possible groupings that have at least one yellow seed (shown in blue in the table); the sum of their individual probabilities yields the final answer (63/64). Note that you could have also calculated this answer by subtracting the probability of the one category that doesn’t fit the criterion (Green, Green, Green) from the total probability (1 – 1/64 = 63/64).

what is the probability that three f2 seeds chosen at random will include one green seed and two yellow seeds

27/64

In peas, the allele for yellow seeds (Y) is dominant to the allele for green seeds (y). What would be the genotype and phenotype ratios of offspring from a cross between Yy and yy individuals?

Genotype: ½ Yy : ½ yy; Phenotype: ½ yellow : ½ green

does the type of gamete affect the inheritance of the traits?

no the domionancewill be the same whether from a mother or a father gamete

Which theory was disproved when Mendel observed that the F1 generation of a monohybrid cross resembled one of the parents?

the theory of blending inheritance

When do you first learn which trait is dominant?

when observing the F1 generation of a monohybrid cross

If flower color in peas is genetically determined and you’re speaking about the hereditary determinant that produces white instead of purple flowers, you’re speaking about _____.

an allele

In constructing a Punnett square, what do you fill in along the horizontal row on the top of the diagram?

the unique gamete genotypes produced by one parent

All of the plants have yellow pea pods (the recessive trait), except for one, which has green pea pods (the dominant trait). How could the botanist best determine whether the genotype of the green-pod plant is homozygous or heterozygous?

`Cross the green-pod plant with a yellow-pod plant.

What is the difference between heterozygous and homozygous individuals?

All of the gametes from a homozygote carry the same version of the gene while those of a heterozygote will differ.

When constructing a Punnett square, the symbols on the outside of the boxes represent _______, while those inside the boxes represent _______.

gametes, progeny

The same phenotype can be produced by more than one genotype.

true

In diploid organisms, a dominant phenotype will only be expressed if the individual is homozygous dominant for that trait.

false

If an organism with the genotype AaBb produces gametes, what proportion of the gametes would be Bb?

None

Two mice are heterozygous for albinism (Aa) . The dominant allele (A) codes for normal pigmentation, and the recessive allele (a) codes for no pigmentation. What percentage of their offspring would have an albino phenotype?

25 The offspring would be in a 3:1 ratio of normally pigmented mice to albino mice

A tall, purple-flowered pea plant (TtPp) is allowed to self-pollinate. (The recessive alleles code for short plants and white flowers.) The phenotypic ratio of the resulting offspring is 9:3:3:1. What is the genotype of the plant whose phenotype appeared once out of every 16 offspring (the "1" in the 9:3:3:1 ratio)?

ttpp

Assuming independent assortment, an individual of genotype SsYyAa would produce gametes of what genotypes (in their correct proportions)?

1/8 SYA, 1/8 SYa, 1/8 SyA, 1/8 Sya, 1/8 sYA, 1/8 sYa, 1/8 syA, 1/8 sya Because of independent assortment, all possible allele combinations would occur in equal proportions.

A man and woman are both of normal pigmentation, but both have one parent who is albino (without melanin pigmentation). Albinism is an autosomal (not sex-linked) recessive trait. What is the probability that their first child will be an albino?

1/4

A man and woman are both of normal pigmentation, but both have one parent who is albino (without melanin pigmentation). Albinism is an autosomal (not sex-linked) recessive trait. What is the probability that their first female child will have albinism?

1/4 probability of having a female child by that of an albino

A man and woman are both of normal pigmentation and have a one child out of three who is albino (without melanin pigmentation). Albinism is an autosomal (not sex-linked) recessive trait. What are the genotypes of the albino’s parents?

Both parents must be heterozygous.

In tigers, a recessive allele causes a white tiger (absence of fur pigmentation). If one phenotypically normal tiger that is heterozygous is mated to another that is phenotypically white, what percentage of their offspring is expected to be white?

50%

A man has extra digits (six fingers on each hand and six toes on each foot). His wife and their daughter have a normal number of digits. Having extra digits is a dominant trait. The couple’s second child has extra digits. What is the probability that their next (third) child will have extra digits?

1/2

Phenylketonuria is an inherited disease caused by a recessive autosomal allele. If a woman and her husband are both carriers, what is the probability that their first child will be a phenotypically normal girl?

3/8This problem blends the results of a monohybrid cross with the likelihood of having a girl.

Assuming independent assortment for all gene pairs, what is the probability that the following parents, AABbCc × AaBbCc, will produce an AaBbCc offspring?

1/8, 2^n = #

When Mendel crossed yellow-seeded and green-seeded pea plants, all the offspring were yellow seeded. When he took these F1 yellow-seeded plants and crossed them to green-seeded plants, what genotypic ratio is expected?

1:1 This is a typical testcross situation.

In rabbits, the homozygous CC is normal, Cc results in deformed legs, and cc results in very short legs. The genotype BB produces black fur, Bb brown fur, and bb white fur. If a cross is made between brown rabbits with deformed legs and white rabbits with deformed legs, what percentage of the offspring would be expected to have deformed legs and white fur?

25%This is a typical dihybrid situation

In Drosophila melanogaster, vestigial (short) wings (vg) are caused by a recessive allele of a gene that independently assorts with a gene pair that influences body hair. Hairy (h) results in a hairy body. A cross is made between a fly with normal (wild) wings and a hairy body and a fly with vestigial wings and a normal (wild) body. The phenotypically normal F1 flies were crossed among each other, and 1024 F2 flies were reared. What phenotypes would you expect in the F2, and in what actual numbers (not ratios) would you expect to find them?

phenotypes-wild, vestigial, hairy, vestigial hairy; numbers expected-wild (576), vestigial (192), hairy (192), vestigial hairy (64)

Alleles segregate during _____

meiosis I

Eye color in Drosophila is an X-linked trait. Which of the following is NOT possible?

a male homozygous for the white eye allele

A recessive allele on the X chromosome is responsible for red-green color blindness in humans. A woman with normal vision whose father is color blind marries a color-blind male. What is the probability that this couple’s first son will be color blind?

50%

Hemophilia is caused by several genetic factors; one, a recessive allele of an X-linked gene, is the subject of this problem. Assume that a man with hemophilia marries a normal woman whose father had hemophilia. What is the probability that their first child will be a girl with hemophilia?

1/4he probability of having a daughter in their computation of the final probability.

Hemophilia is caused by several genetic factors; one, a recessive allele of an X-linked gene, is the subject of this problem. Assume that a man with hemophilia marries a normal woman whose father had hemophilia. What is the probability that their first son will have hemophilia?

1/2When the sex of the child is fixed (first son) as in this problem, then one does not multiply by 1/2 to determine the final probability.

A man who carries an allele of an X-linked gene will pass it on to _____.

all of his daughters

Glucose-6-phosphate dehydrogenase deficiency (G6PD) is inherited as a recessive allele of an X-linked gene in humans. A woman whose father suffered from G6PD marries a normal man. (a) What proportion of their sons is expected to be G6PD? (b) If the husband was not normal but was G6PD deficient, would you change your answer in part (a)?

a) 1/2; (b) no

The inheritance of wheat kernel color shown in Figure 13.21 in the textbook is an example of _____.

polygenic inheritance Several genes are involved and have an additive effect on kernel color.

Which statement most accurately describes the pattern of inheritance for a human disease caused by a dominant allele on the X chromosome (assuming the disease allele is rare)?

Affected fathers have all affected daughters, but no affected sons.

If two carriers of an autosomal recessive genetic disease have children, what is the chance that their first child will be a carrier?

½

http://session.masteringbiology.com/problemAsset/1234167/2/13-1.jpg

(a) recessive; (b) X-linked

In humans, blue eyes are inherited as a recessive autosomal trait and color blindness is an X-linked recessive trait. A woman with blue eyes and normal color vision whose father was color blind marries a man who also has normal color vision. He has brown eyes, but his mother had blue eyes. Which of the following do you expect to be true for their sons?

One-fourth of their sons will be color blind and have blue eyes, 1/4 of their sons will be color blind and have brown eyes, 1/4 of their sons will have normal color vision and blue eyes, 1/4 of their sons will have normal color vision and brown eyes.Independent assortment applies when one of the genes is X-linked and other is not. The sons have a 50% chance of inheriting the allele for color blindness from their mother.

Regarding an allelic pair for flower color in snapdragons, heterozygotes have pink flowers, whereas the two homozygotes have red flowers or white flowers. When plants with red flowers are crossed with plants with white flowers, what proportion of the offspring is expected to have pink flowers?

100%

In humans, ABO blood types refer to glyocproteins in the membranes of red blood cells. There are three alleles for this autosomal gene: IA, IB, and i. The IA allele codes for the A glycoprotein, The IB allele codes for the B glycoprotein, and the i allele doesn’t code for any membrane glycoprotein. IA and IB are codominant, and i is recessive to both IA and IB. People with A type blood have the genotypes IAIA or IAi, people with type B blood are IBIB or IBi, people with type AB blood are IAIB, and people with O type blood are ii. If a woman with type AB blood marries a man with type O blood, which of the following blood types could their children possibly have?

A and B

Which event in meiosis accounts for Mendel’s principal of segregation?

separation of homologs at anaphase IThe physical separation of alleles on the two homologs in anaphase of meiosis I explains why each gamete contains one allele of each gene.

Which event in meiosis accounts for Mendel’s principle of independent assortment?

Nonhomologous chromosomes line up independently during meiosis I.This event explains why alleles on nonhomologous (different) chromosomes assort independently, and explains why gametes contain random assortments of maternal and paternal chromosomes.

In peas, the allele for round seeds (R) is dominant to the allele for wrinkled seeds (r). What would be the genotype and phenotype ratios of offspring from a cross between Rr and rr individuals?

Genotype: 1/2 Rr: 1/2 rr; Phenotype: 1/2 Round: 1/2 Wrinkled

Which theory was disproved when Mendel observed that the F1 generation of a monohybrid cross resembled one of the parents?

blending inheritance Blending inheritance predicts that the F1 generation should have a phenotype intermediate to that of the parents. This is not what was observed.

The dominant allele ____.

determines the phenotype in a heterozygote

Assuming independent assortment, an individual of genotype SsYyAa would produce gametes of genotypes (in their correct proportions) _____.

1/8 SYA, 1/8 SYa, 1/8 SyA, 1/8 Sya, 1/8 sYA, 1/8 sYa, 1/8 syA, and 1/8 sya Because of independent assortment, all possible allele combinations would occur in equal proportions.

AaBb × AaBb is an example of ____.

a dihybrid cross

Which result led Mendel to the principle of independent assortment?

He observed a 9:3:3:1 ratio in the offspring of a dihybrid cross

Which chromosomal event in meiosis explains Mendel’s principal of segregation?

Separation of homologs at anaphase I The physical separation of alleles on the two homologs in anaphase of meiosis I explains why each gamete contains one allele of each gene.

Which chromosomal event in meiosis explains Mendel’s principle of independent assortment?

Nonhomologous chromosomes line up independently during meiosis I This event explains why alleles on nonhomologous (different) chromosomes assort independently, and explains why gametes contain random assortments of maternal and paternal chromosomes.

What is the mechanism behind Mendel’s principle of segregation?

the separation of homologous chromosomes during meiosis I During anaphase of meiosis I, the two alleles of each gene are separated.

In Drosophila the gene for eye color is located on ____.

the X chromosome Eye color in Drosophila is an X-linked trait.

The inheritance of wheat kernel color shown in Figure 14.21 is an example of _____.

polygenic inheritance Several genes are involved and have an additive effect on kernel color.

Imagine that you perform fruit fly crosses with different pairs of three X-linked traits specified by genes x, y, and z. You observe the following frequencies of recombinant offspring for the various gene pairs: xy= 6.9 percent yz= 7.6 percent xz= 0.7 percent What is the most likely gene order?

yxz This is the only order where the recombination distances between each gene pair (the physical distances along the linear chromosome that produce the observed recombinant frequencies) sum correctly.

Linked genes may violate Mendel’s ____.

principle of independent assortment Independent assortment says that alleles of different genes are transmitted to gametes independently of one another.

The IA and IB alleles of the ABO blood group gene I exhibit ____.

codominance Codominance is the simultaneous expression of the phenotype associated with each allele in a heterozygote. An AB individual expresses both the A and the B phenotypes.

A couple has three boys. What are the chances of them having a fourth boy?

1/2 The chance of having a boy as a single event is 1 out of 2 regardless of the sex of any previous children.

There are five dice in the game of Yahtzee®. What are the chances that a player will roll five ones (1) on the first roll?

1/7776

If color blindness is an X-linked recessive trait, what genotype in a father and a mother would be predicted to produce a 1:1 ratio of normal to color-blind offspring?

Affected father and carrier mother

A carrier is an individual who is ____.

heterozygous for a recessive disease allele Because the disease-causing allele is recessive, heterozygotes do not manifest the disease. They can, however, pass the allele to their offspring.

The alleles found in haploid organisms cannot be dominant or recessive.Why?

Dominance and recessiveness describe which allele is expressed in phenotype when different alleles occur in the same individual.

In studies of how traits are inherited, what makes certain species candidates for model organisms?

They are easy to maintain, have a short life cycle, produce many offspring, and yield data that are relevant to many other organisms

The artificial sweetener NutraSweet consists of a phenylalanine molecule linked to aspartic acid. The labels of diet sodas that contain NutraSweet include a warning to people with PKU. Why?

People with PKU have to avoid phenylalanine in their diet.

A plant with orange, spotted flowers was grown in the greenhouse from a seed collected in the wild. The plant was self-pollinated and gave rise to the following progeny: 88 orange with spots, 34 yellow with spots, 32 orange with no spots, and 8 yellow with no spots.

background info

What can you conclude about the dominance relationships of the alleles responsible for the spotted and unspotted phenotypes?

Spotted petal is the dominant allele.

For the orange and yellow phenotypes?

Orange petal is the dominant allele

What can you conclude about the genotype of the original plant that had orange, spotted flowers? (Let O stand for the allele for orange petals and o the allele for yellow petals; let S stand for the allele for spotted petals and s the allele for unspotted petals.)

OoSs

The smooth feathers on the back of the neck in pigeons can be reversed by a mutation to produce a "crested" appearance in which feathers form a distinctive spike at the back of the head. A pigeon breeder examined offspring produced by a single pair of non-crested birds and recorded the following: 22 non-crested and 7 crested. She then made a series of crosses using offspring from the first cross. When she crossed two of the crested birds, all 20 of the offspring were crested. When she crossed a non-crested bird with a crested bird, 7 offspring were non-crested and 6 were crested.

Background info

Which allele is dominant?

Non-crested (C) is the dominant allele.

Provide genotypes for parents and offspring for the cross 1.

non-crested (Cc) × non-crested (Cc) = 22 non-crested (C_); 7 crested (cc)

Provide genotypes for parents and offspring for the cross 2.

crested (cc) × crested (cc) = 20 crested (cc)

Provide genotypes for parents and offspring for the cross 3.

non-crested (Cc) × crested (cc) = 7 non-crested (Cc); 6 crested (cc)

According to these data, is the curved-wing allele autosomal recessive, autosomal dominant, sex-linked recessive, or sex-linked dominant?

autosomal recessive

Is the lozenge-eyed allele autosomal recessive, autosomal dominant, sex-linked recessive, or sex-linked dominant?

sex-linked recessive

What is the genotype of the female parent? Let L be the allele for long wings and l be the allele for curved wings; let XR be the allele for red eyes and Xr the allele for lozenge eyes.

LlXRXr

What is the genotype of the male parent? Let L be the allele for long wings and l be the allele for curved wings; let XR be the allele for red eyes and Xr the allele for lozenge eyes.

LlXRY

Suppose a heterozygous woman with blood type A married a homozygous man with blood type B. What phenotypes and genotypes would you expect to observe in their offspring, and in what proportions?

1 : 1 IAIB (type AB) : IBi (type B)

Answer the same question for a heterozygous mother with blood type A and a heterozygous father with blood type B.

1 : 1 : 1 : 1 IAIB (type AB) : IAi (type A) : IBi (type B) : ii (type O)

If a heterozygous woman without hemophilia had children with a man with hemophilia, what is the chance that their first child will have the Recall that hemophilia is an X-linked recessive disease.disease?

50 %

What is the chance that their first child will be a carrier?

25 %

Mendel’s rules do not correctly predict patterns of inheritance for tightly linked genes or the inheritance of alleles that show incomplete dominance.Does this mean that his hypotheses are incorrect?

No, it just means that his hypotheses are limited to certain conditions.

The genes for the traits that Mendel worked with are either located on different chromosomes or so far apart on the same chromosome that crossing over almost always occurs between them. How did this circumstance help Mendel recognize the principle of independent assortment?

Otherwise, his dihybrid crosses would not have produced a 9 : 3 : 3 : 1 ratio of F2 phenotypes.

What is meant by the claim that Mendel worked with the simplest possible genetic system?

Discrete traits, two alleles, simple dominance and recessiveness, no sex chromosomes, and unlinked genes are the simplest situation known.

You are studying a human disease and find an affected father with six children: three unaffected sons and three affected daughters. What is the most likely mode of transmission for the disease?

X-linked dominant Daughters receive their father’s only X chromosome that carries the disease allele; sons receive his Y chromosome that does not.

How does crossing over break up linkage between alleles?

It involves a physical exchange of segments between homologous chromosomes. Because of crossing over, alleles originally located on the same chromosome can end up on different chromosomes and can be inherited independently (genetic recombination).

Why is the allele for wrinkled seed shape in garden peas considered recessive?

The trait associated with the allele is not expressed in heterozygotes

Two black female mice are crossed with a brown male. In several litters, female I produced 9 blacks and 9 browns; female II produced 57 blacks.What deductions can you make concerning the inheritance of black and brown coat color in mice?

black is dominant to brown

What are the genotypes of the parents in this case?

female I must be Bb; female II must be BB

If a purple-flowered, heterozygous plant were crossed with a white-flowered plant, what is the expected ratio of genotypes and phenotypes among the F1 offspring?

the ratio of genotypes is 1:1 (Aa:aa); the ratio of phenotypes is 1:1 (purple:white)

If two of the purple-flowered F1 offspring were randomly selected and crossed, what is the expected ratio of genotypes and phenotypes among the F2 offspring?

the ratio of genotypes is 1:2:1 (AA:Aa:aa); the ratio of phenotypes is 3:1 (purple:white)

Mendel studies seven different traits in the garden pea. What genetic term is used to describe an observable trait, such as those studied by Mendel?

phenotype

The work of Gregor Mendel provided an answer to two prevailing hypotheses popular at the time. What were these two hypotheses?

The two major hypotheses of the time were blending inheritance and inheritance of acquired characteristics.

A sexually reproducing animal has two unlinked genes, one for head shape (H) and one for tail length (T). Its genotype is HhTt. Which of the following genotypes is possible in a gamete from this organism?

HT

Albinism is an autosomal (not sex-linked) recessive trait. A man and woman are both of normal pigmentation, but both have one parent who is albino (without melanin pigmentation). What is the probability that their first child will be an albino?

1/4

How many unique gametes could be produced through independent assortment by an individual with the genotype AaBbCCDdEE?

8

Which of the following statements about independent assortment and segregation is correct?

The law of independent assortment requires describing two or more genes relative to one another.

Assuming independent assortment for all gene pairs, what is the probability that the following parents, AABbCc × AaBbCc, will produce an AaBbCc offspring?

1/8

In cattle, roan coat color (mixed red and white hairs) occurs in the heterozygous (Rr) offspring of red (RR) and white (rr) homozygotes. Which of the following crosses would produce offspring in the ratio of 1 red:2 roan:1 white?

roan × roan

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