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Exam 4: Sex Determination and Sex-Linked Characteristics

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Question 31

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What is the role of the SRY gene in humans?

A) It initiates the X inactivation process in females.
B) It is located on the X chromosome and causes the X to pair with the Y chromosome during male meiosis.
C) It is located on the Y chromosome and initiates the developmental pathway toward the male phenotype.
D) It is located on an autosomal chromosome and represses expression of autosomal genes in order to balance their expression level with genes on the X chromosome.
E) None of the answers is correct.

F) D) and E)
G) A) and E)

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Question 32

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In domestic chickens, some males display a plumage pattern called cock feathering.Other males and all females display a pattern called hen feathering.Cock feathering is an autosomal recessive trait that is exhibited in males only.Two heterozygous birds are mated.What fraction of the female offspring is expected to exhibit cock feathering?

A) 0
B) 1/8
C) 1/4
D) 1/2
E) 3/4

F) B) and D)
G) A) and E)

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Question 33

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The SRY gene is located on the Y chromosome.This single gene encodes a protein called a transcription factor which binds to DNA and stimulates the transcription of other genes that lead to the development of male sex characteristics, including physical, biochemical, and behavioral phenotypes.What concept in genetics best describes this example?

A Barr body is a(n) :

If a male bird that is heterozygous for a recessive Z-linked mutation is crossed to a wild type female, what proportion of the progeny will be mutant males?

In purple people eaters, purple is dominant to white.A true-breeding white mutant is mated with a different true-breeding white mutant.All of the F₁ are purple.When the purple F₁ offspring mate with each other, their offspring occur in the ratio of 9 purple:7 white.Which phenomenon explains the purple F₁ offspring?

Women with Turner syndrome (XO) and normal women (XX) are clearly different phenotypically.In addition, the vast majority of XO conceptions abort before birth.However, both XO and XX women have one active X chromosome since the X in XO women remains active and one might expect that they would therefore have similar phenotypes.What is the MOST reasonable explanation for their different phenotypes?

In chickens, comb shape is determined by genes at two loci (R, r and P, p) .A walnut comb is produced when at least one dominant gene R is present at one locus and at least one dominant gene P is present at a second locus (genotype R_ P_) .A rose comb is produced when at least one dominant gene is present at the first locus and two recessive genes are present at the second locus (genotype R_ pp) .A pea comb is produced when two recessive genes are present at the first locus and at least one dominant gene is present at the second (genotype rr P_) .If two recessive genes are present at the first and the second locus (rr pp) , a single comb is produced.Give genotypes for comb shape of the parents in the following cross: pea crossed with single produces one single offspring.

You are studying body color in an African spider and have found that it is controlled by a single autosomal gene with four alleles: B (brown) , b^r (red) , b^g (green) , and b^y (yellow) .B is dominant to all the other alleles, and b^y is recessive to all the other alleles.The b^g allele is dominant to b^y but recessive to b^r.You cross a pure-breeding brown spider with a pure-breeding green spider.Predict the genotype of the progeny.

In a certain species of plant, flowers occur in three colors: blue, pink, and white.A pure-breeding pink plant is mated with a pure-breeding white plant.All of the F₁ are blue.When the blue F₁ plants are selfed, the F₂ occur in the ratio 9 blue:3 pink:4 white.The genotype that produces white is ww.The presence of one W allele allows pink or blue color to occur.The alleles at the hypostatic locus are B (blue) and b (pink) .What is the genotype of the white parent?

Women known to be heterozygous or carriers for the sex-linked recessive condition of hemophilia A were studied to determine the time required for their blood to clot.It was found that the time required for their blood to clot varied from individual to individual.The values obtained ranged from normal clotting at one extreme to clinical hemophilia at the other extreme.What is the most probable CORRECT explanation for these findings?

With the XX-XO sex determination system, generally:

Human males, with XY chromosomes are _____ and produce two different kinds of gametes, whereas females with XX chromosomes are _____ and produce only one kind.

A mother of blood type A gives birth to a child with blood type O.Which of the following could NOT be the blood type of the father?

The Lyon hypothesis helps us to understand which phenomenon in mammals?

Red-green color blindness is an X-linked recessive condition.Juliet has a bit of difficulty passing the red-green color distinction test when she tries to get her driver's license.Her husband is not color blind, and neither is her son, Henry, nor her daughter, Roxanne.Roxanne has a son who is color blind.What is Juliet's genotype for the color-blind allele? How would you explain her partial color blindness?

Which of the following human genotypes is associated with Klinefelter syndrome?

How does epistasis differ from Mendel's principle of dominance?

Coat color is determined by two loci in large cats.Two pink panthers fall in love and produce a large litter of baby panthers with the following phenotypic ratios: 12/16 pink; 3/16 black; and 1/16 white.What might be the genotype of the black progeny?

In a certain species of plant, flowers occur in three colors: blue, pink, and white.A pure-breeding pink plant is mated with a pure-breeding white plant.All of the F₁ are blue.When the blue F₁ plants are selfed, the F₂ occur in the ratio 9 blue:3 pink:4 white.How many gene pairs control the flower color phenotype?