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Exam 4: Modification of Mendelian Ratios

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Question 1

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Genomic imprinting occurs when one allele converts another.

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B) False

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Question 2

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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?

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females wi...

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Question 3

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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)?

"Gain of function" mutations are generally dominant because one copy in a diploid organism is sufficient to alter the normal phenotype.

A conditional mutant is one whose expression is influenced by some environmental condition.

A particular cross gives a modified dihybrid ratio of 9:7.What phenotypic ratio would you expect in a testcross of the fully heterozygous F₁ crossed with the fully recessive type? Diagram the testcross using A,a,B,b as symbol sets.

Assume that a dihybrid F₂ ratio,resulting from epistasis,was 15:1.If a double heterozygote is crossed with the fully recessive type,what phenotypic ratio is expected among the offspring?

The presence of more than two alternative forms of a given gene would be called ________.

Many of the color varieties of summer squash are determined by several interacting loci: AA or Aa gives white,aaBB or aaBb gives yellow,and aabb produces green.Assume that two fully heterozygous plants are crossed.Give the phenotypes (with frequencies)of the offspring.

Genomic anticipation refers to observations that a genetic disorder occurs at an earlier age in successive generations,whereas genetic imprinting occurs when gene expression varies depending on parental origin.

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

In a mating between individuals with the genotypes I^AIB X I^OIO,what percentage of the offspring are expected to have the O blood type?

The trait for medium-sized leaves in iris is determined by the genetic condition PP'.Plants with large leaves are PP,whereas plants with small leaves are P'P'.The trait for red flowers is controlled by the genes RR,pink by RR',and white by R'R'.A cross is made between two plants each with medium-sized leaves and pink flowers.If they produce 320 seedlings,what would be the expected phenotypes,and in what numbers would they be expected? Assume no linkage.

Mice have a set of multiple alleles of a gene for coat color.Four of those alleles are as follows: C= full color (wild) c^ch= chinchilla c^d = dilution c = albino Given that the gene locus is not sex-linked and that each allele is dominant to those lower in the list,diagram the crosses indicated below and give the phenotypic ratios expected from each. (a)wild (heterozygous for dilution)X chinchilla (heterozygous for albino) (b)chinchilla (heterozygous for albino)X albino

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

One result of X-linkage is a crisscross pattern of inheritance in which sons express recessive genes of their fathers and daughters express recessive genes of their mothers.

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?

The genes for zeste eyes and forked bristles are located on the X chromosome in Drosophila melanogaster.Both genes are recessive.A cross is made between a zeste-eyed female and a forked-bristled male. (a)If 200 offspring from this cross were obtained,present the expected number,sex,genotype,and phenotype in each class of the F₁. (b)If the F₁ offspring were crossed to produce 800 flies of an F₂ generation,present the expected number,sex,and phenotype in each class.Assume no crossing over.

The term expressivity defines the percentage of individuals who show at least some degree of expression of a mutant genotype.

What distinguishes sex-limited from sex-influenced inheritance?