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Exam 4: Extensions of Mendelian Genetics

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Question 31

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

A) O
B) B
C) A
D) AB
E) Bombay phenotype

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Question 32

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With both incomplete dominance and codominance,one expects heterozygous and homozygous classes to be phenotypically identical.

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Question 33

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What distinguishes sex-limited from sex-influenced inheritance?

In a mating between individuals with the genotypes IᴬIᴮ × ii,what percentage of the offspring are expected to have the O blood type?

Assume that a dihybrid F₂ ratio,resulting from epistasis,was 9:3:4.If a double heterozygote was crossed with the fully recessive type,what phenotypic ratio is expected among the offspring?

The enzyme glucose-6-phosphate dehydrogenase deficiency (G6PD)is inherited as a recessive gene on the X chromosome in humans.A phenotypically normal woman (whose father had G6PD)is married to a normal man. a) What fraction of their sons would be expected to have G6PD? b) If the husband had G6PD,would it make a difference in your answer in part (a)?

Assume that a dihybrid cross (AaBb × AaBb)is made in which the gene loci are autosomal,independently assorting,and incompletely dominant.What phenotypic ratio would you expect from such a cross? Just provide the ratio,not the phenotypes.

With which of the following would hemizygosity most likely be associated?

The ABO blood group locus in humans provides an example of epistasis.

Assume that a mutation occurs in the gene responsible for the production of hexosaminidase A,such that only about 50% of the enzyme activity is found in the heterozygote compared with a homozygous normal individual.If heterozygotes are phenotypically normal,we would say that the mutant allele is recessive to its normal allele.

Regarding the ABO blood group system in humans,if an individual is genetically Iᴮᶦ and yet expresses the O blood type,which genotype is it likely to have?

Two forms of hemophilia are determined by genes on the X chromosome in humans.Assume that a phenotypically normal woman whose father had hemophilia is married to a normal man.What is the probability that their first daughter will have hemophilia?

Expressivity is the term used to describe the balanced genetic output from a hemizygous condition.

If an X-linked disorder is lethal to the affected individual prior to the age at which one reaches reproductive maturation,the lethality will be expressed only in males.Why is this so?

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

Typical ratios resulting from epistatic interactions in dihybrid crosses would be ________.

Name three modes of inheritance that are influenced by the sex of individuals.

How many different alleles can a gene have?

A condition in which one gene pair masks the expression of a nonallelic gene pair is called ________.

The following F₂ results occur from a typical dihybrid cross: purple: A_B_ 9/16 white: aaB_ 3/16 white: A_bb 3/16 white: aabb 1/1 If a double heterozygote (AaBb)is crossed with a fully recessive organism (aabb),what phenotypic ratio is expected in the offspring?