BIOL 2300 MasteringGen Ch. 4

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A mutation in a gene often results in a reduction of the product of that gene. The term for this type of mutation is ________.

loss of function or null (in the case of complete loss)

A gain-of-function mutation _______.

results in an increased quantity of the normal gene product

Typically, when one wishes to represent a gene, the symbol used is _________.

in italics

Which of the following symbols indicates a wild-type allele?


Part A: Assume that a cross is made between two organisms that are both heterozygous for a gene that shows incomplete dominance. What genotypic ratio is expected in the offspring?
_____ AA : ____ Aa : ____ aa

Part B: What phenotypic ratio is expected in the offspring?

A: 1:2:1 B: 1:2:1

A situation in which there are more than two alternative forms of a given gene would be called ________.

multiple alleles

Why is it necessary to survey a large number of individuals to study multiple alleles?

Any individual diploid organism can have, at most, two different alleles at a single locus.

In a mating between individuals with the genotypes I^AI^B × ii, what percentage of the offspring would be expected to have the O blood type?


Part A: Determining relationships between alleles
You decide to conduct a genetic analysis of these mutant lines by crossing each with a pure-breeding wild-type line. The numbers in the F2 indicate the number of progeny in each phenotypic class.

Part B: Crossing the forked and pale mutants
You continue your genetic analysis by crossing the forked and pale mutant lines with each other. The leaves of the F1 are light green (intermediate between pale and wild-type leaves) and forked. The F2 has six phenotypic classes:
You designate the forked mutant allele as F (wild type = f+ ) and the pale mutant allele as p (wild type = P).

Part C: Crossing the forked and twist mutants
You continue your analysis by crossing the forked and twist lines. Your results are as follows:

Part D – Assigning genotypes for codominant alleles
You decide to designate the twist allele as FT to distinguish it from the forked allele F.

A: twist- The mutant allele is dominant to its corresponding wild-type allele forked- the mutant allele is dominant to its corresponding wild-type allele pale- The mutant allele is neither dominant nor completely recessive to its corresponding wild-type allele B: a- PP b- F_ c- Pp d- F_ e- pp f- F_ g- PP h- f^+f^+ i- Pp j- f^+f^+ k- pp l- f^+f^+ C: The forked mutation and the twist mutation are codominant alleles of the same locus. D: F^TF^T. FF. FF^T

Part A: What would be the expected frequency of agouti brown offspring in the litter?

Part B: Lethal alleles and epistasis
In a mating of mice with the genotypes AYaBb x AYaBb , what is the probability that a live-born offspring will have yellow fur?

Part C: The effect of a third gene on fur color
Match the phenotypes on the labels at left to the genotypes listed below. Labels can be used once, more than once, or not at all.

Part D: The effect of a fourth gene on fur color
In a cross between two mice that are heterozygous for agouti, black, color, and piebaldism, what is the probability that offspring will have solid black fur along with large patches of white fur?

A: 3/16 B: 2/3 C: albino, agouti brown agouti black, solid color, black albino, albino D: 9/256

Part A: Crossing lines with the same recessive phenotype
You continue your analysis by crossing the Aberdeen White and Victoria White lines. This time you count the actual numbers of progeny in the two F2 phenotypic classes.

Part B: Crossing lines with dissimilar recessive phenotypes
You continue your analysis by crossing the Aberdeen White and Kansas Yellow lines. Again, you count the actual numbers of progeny in the two F2 phenotypic classes.

Part C: A second cross between lines with dissimilar phenotypes
You complete your analysis by crossing the Victoria White and Kansas Yellow lines. Again, you count the actual numbers of progeny in the F2 phenotypic classes.

Part D: Assembling a genetic model
Based on your analysis so far, you assign the following allele symbols to the three lines:
Wild type = A_ V_
Aberdeen White = a a
Kansas Yellow = aYaY
Victoria White = v v

A: 1. true 2. independent assortment 3. 9:7 4. complementary gene action B: 1. false 2. failure to complement 3. 3:1 4. complete dominance C: 1. true 2. independent 3. 9:3:4 4. recessive epistasis D: a- aa b- VV c- AA d- vv e- Aa f- Vv g- wild type h- white i- white j- white k- AA l- vv m- a^Ya^Y n- VV o- Aa^Y p- Vv q- wild type r- yellow s- white t- white

Part A : The inheritance of a skin condition in humans
Consider the following family history:
Based on Bob and Eleanor’s family history, what inheritance pattern does the skin condition most likely follow?

Part B: A sex-linked gene for eye color in Drosophila
The inheritance of eye color in Drosophila is controlled by genes on each of the fly’s four chromosome pairs. One eye-color gene is on the fly’s X chromosome, so the trait is inherited in a sex-linked manner. For this sex-linked trait, the wild-type (brick red) allele is dominant over the mutant vermilion (bright red) allele.

Part C: The inheritance of both a sex-linked trait and an autosomal trait in humans
Red-green color blindness is due to an X-linked recessive allele in humans. A widow’s peak (a hairline that comes to a peak in the middle of the forehead) is due to an autosomal dominant allele.
Consider the following family history:

A: X-linked dominant B: all wild type all wild type all wild type 1/2 wild type, 1/2 vermillion C: 1/4 1/2 0 1

Part A – Construct a pedigree
John and Jane Jones’ newborn baby girl, Leah, has just been diagnosed with galactosemia. Prior to their genetic counseling appointment, they submitted this family history:

Part B: Identify the mode of inheritance
Look over the pedigree you constructed in Part A.
Based on the inheritance pattern, which mode of inheritance must be the cause of galactosemia?

Part C: Predicting the probability of inheritance
Jane and John are considering having another child. Given the pedigree you constructed and the mode of inheritance for galactosemia, what is the risk that their next child will have the disorder?

Part D: Genetic testing
If Jane and John want to have another child, they plan to see a genetic counselor to find out when it would be best to test for galactosemia. A newborn with galactosemia must be put on a lactose- and galactose-free diet as soon as possible after birth. Even on this diet, affected individuals may still suffer from learning disabilities, ovarian failure (in young women), late-onset cataracts, and early death.
Which of the following tests would be most useful for Jane and John to have?

A: I. Hanna’s father, Harry’s father II. Hilda, Hope, Holly, Hanna, Haryy III. Jen, Joe, Jane, John IV. Les, Lee, Leah(ONLY RED CIRCLE) B: autosomal recessive C: 1/4 (because they are both heterozygotes) D: newborn screening (either assaying for the GALT enzyme or measuring excess galactose in the newborn’s blood)

What is the blood type of individuals who cannot add the terminal sugar to the H substance?


What term is used to express the idea that several genes exert influence over the same characteristic?

gene interaction

Alleles that are masked by an epistatic locus are said to be hypostatic to the genes at that locus.


What would be a typical phenotypic monohybrid ratio in which a lethal allele is involved?


A gene in which a male heterozygote has a different phenotype compared to a female heterozygote is referred to as __________.


Some genes can be silenced so that they are not expressed depending on the sex of the parent from whom the gene is inherited. This phenomenon is known as __________.


The white-eye gene in Drosophila is recessive and sex-linked. Assume that a white-eyed female is mated to a wild-type male. What would be the phenotypes of the offspring?

wild type females, white-eyed males

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