Exam 6: Gene Interaction

In chickens,the dominant allele Cr produces the creeper phenotype (having extremely short legs).However,the creeper allele is lethal in the homozygous condition.If two creepers are mated,what proportion of the living progeny will be creepers?

In loppins (fictitious diploid invertebrates),ear shape is controlled by two genes with two alleles each;upright ears (F)is dominant to floppy ears (f),and double-pointed ears (P)is dominant to single-pointed ears (p).Moreover,due to genetic interactions,floppy ears are always single-pointed.A loppin with floppy ears is crossed to a loppin with upright single-pointed ears,and the phenotypic ratios in the offspring are 2 floppy : 1 double-pointed upright : 1 single-pointed upright.What are the genotypes of the parents?

On an illegal wolf ranch in Wyoming,cowboys breed gray wolves and sell them illegally.A mutation was identified,generating a beautiful gray "speckled" coat color.The speckled wolves were particularly popular with buyers.The breeders struggled to keep up with demand.They noticed that when two speckled wolves were bred,their pups always contained some normal gray and some speckled gray pups.In one typical season of interbreeding the speckled wolves,they cumulatively generated 82 speckled and 38 gray pups.State a clear genetic explanation for the pattern illustrated.

An A/a;B/b dihybrid is testcrossed,and about ¾ of the progeny phenotypically resembles the dihybrid parent,while ¼ resembles the tester parent.If the dihybrid parent was selfed,what would be the expected phenotypic ratio in the progeny?

In the multiple-allele series that determines coat color in rabbits,c⁺ encodes agouti,c^ch encodes chinchilla,and c^h encodes Himalayan.Dominance within this allelic series is c⁺>c^ch > c^h.In a cross of c⁺/c^h $\times$ c^ch/c^h,what proportion of progeny will be chinchilla?

The following non-complementing E.coli mutants were tested for growth on four known precursors of thymine,compounds A-D.The data provided in the table to reveal a simple linear biosynthetic pathway of the four precursors and the end product,thymine.In what order do the enzymes appear in this pathway (designate by their mutant number)? Mutant A B C D Thymine 9 + - + - + 10 - - + - + 14 + + + - + 21 - - - - +

In the purple penguin,an allelic series occurs at the p locus on an autosome.All alleles affect the color of feathers: p^d = dark-purple,p^m = medium-purple,p^l = light-purple,and p^vl = very pale purple.The order of dominance is p^d > p^m > p^l > p^vl.If a p^l/p^vl female is crossed to a p^d/p^mmale,the ratio of phenotypes expected among the baby penguins would be:

In humans,the ABO blood type is determined mainly by four alleles of one gene,defined by the following allelic series: I^A = I^B > i.(I^A is codominant to I^B,and i/i results in blood type O).What matings can potentially produce children of any of the four blood types?

In sweet peas,the allele C is needed for color expression (c results in white).The precise color expressed is determined by the alleles R (red)and r (blue).A cross between certain red and blue plants resulted in progeny as follows: 3/8 red,3/8 blue,1/4 white.What were the genotypes of the plants crossed?

In a certain breed of dog,the alleles B and b determine black and brown coats,respectively.However,the allele Q of an unlinked gene is epistatic to the B and b color alleles,resulting in a gray coat (q has no effect on color).If animals of genotype B/b;Q/q are intercrossed,what phenotypic ratio is expected in the progeny?

Remember that,in Labrador retrievers,B (black coat)is dominant to b (brown coat)and homozygosity for the recessive epistatic allele e always results in a yellow coat.A brown female is crossed to a yellow male,and their progeny consists of six black puppies.Interestingly,when one of the F₁ females is crossed to her yellow father,she gives birth to seven puppies: three yellow,three black,and one brown. What are the most likely genotypes of the original brown female and yellow male?

Below is a simplified version of the biochemical pathway responsible for fruit color in peppers.Suppose that gene A encodes enzyme 1,gene B encodes enzyme 2,gene C encodes enzyme 3,and that each gene only has two alleles: completely functioning (capital letters)and null (lower case letters).Note that red plus chlorophyll is brown,but yellow plus chlorophyll is green. a)A breeder crossed two pure lines of peppers and then selfed the resulting F₁.The F₂ was comprised of 351 plants with red peppers,115 with yellow peppers and 154 with colorless (white)peppers.What must have been the genotypes and phenotypes of the two original pure lines? b)A pure-breeding plant with green fruits is crossed to a pure-breeding plant that makes yellow fruits.All the F₁ plants make yellow fruits.The F₁ is selfed,and in F₂ we have 250 plants with yellow peppers,84 with colorless peppers,and 112 with green peppers.What must have been the genotypes and phenotypes of the original pure lines?

Domestic rats can have black,silver,or light-gray patches on their necks.A pure-breeding silver female was crossed to a pure-breeding black male,and the F₁ was comprised of black females and light-gray males.When F₁ brothers and sisters were mated,the resulting F₂ consisted of about ¼ black females,¼ black males,¼ silver females,and ¼ light-gray males. Propose a model for the mode of inheritance of patch color in domestic rats.

Crosses between two ducks with spread-out tail phenotype always produce ducklings with spread-out,normal,and pointy tails in a 2:1:1 ratio.In addition,normal-tailed ducks crossed to short-tailed ducks always produce only normal-tailed individuals,while crosses between pointy-tailed and short-tailed individuals always produce only pointy-tailed ducklings.If the tail shape phenotype is controlled by a single locus,what is the expected phenotypic ratio in the progeny of the cross spread-out tail × short tail?

In laboratory mice,the "short tail" phenotype is dominant to the wild-type ("long tail")phenotype.However,crosses between any two short-tailed mice always produce mixtures of short- and long-tailed offspring.Assuming that tail length is controlled by a single locus,a likely explanation for these results is that the "short tail" allele is:

The following four crosses all apply to diploid organisms.Assume that all the parents are true breeding.You are given the phenotypes of the parental generation and the phenotypic ratio of the F₂ generation.You must supply the following information. 1) genotypes of the parents 2) the phenotypic ratio expected for a testcross of the $F_{1}$ 3) a diagram of the chromosomes of the $F_{1}$ in cross (c) at metaphase I Define your symbols. a) Pcross Genotypes Phenotypic Testcross of of parents Ratio in (phenotypic ratio, Brown \times red Brown 9 red-brown 3 red Red 3 brown 1 white b) Pcross Genotypes Phenotypic Testcross of of parents Ratio in (phenotypic ratio, Red \times tall Red 1 red,tall 2 red, intermediate 2 pink, tall Tall 4 pink intermediate 2 pink, short 1 white, tall 2 white, intermediate 1 white, short c) Pcross Genotypes Phenotypic Testcross of of parents Ratio in (phenotypic ratio) albino 1\times albino 2 albino 1 9 wild type 7 albino albino 2 Diagram the chromosomes at metaphase I.Give all possible arrangements of the bivalents.Assume there is no crossing over between genes and centromeres.

A 15:1 phenotypic ratio in a typical F₂ data set would be consistent with _____________________ affecting a particular phenotype.

In a flowering plant, the a/a ; B/B genotype results in yellow flowers, and the A/A ; b/b genotype gives red flowers. Wild-type flowers are orange and are observed in plants with genotype A/A ; B/B. Two possibilities have been proposed for the biosynthetic pathways of flower color: 1. yellow pigment $\rightarrow$ red pigment $\rightarrow$ orange pigment 2. red pigment $\rightarrow$ yellow pigment $\rightarrow$ orange pigment Propose a genetic experiment that can determine which of the two possibilities is most likely correct, and explain how you would interpret your results.

A dihybrid plant is selfed,and the offspring shows a 13:3 phenotypic ratio for flower color.If the same dihybrid plant was testcrossed instead of being selfed,what would be the expected phenotypic ratio in the offspring?

In wheat,a cross between red-kernel and white-kernel strains yielded F₁ offspring with red kernels.When the F₁ were intercrossed,the F₂ plants had a ratio of 15 red-kernel : 1 white-kernel.A testcross of the red-kernel plants yielded 3 red-kernel : 1 white-kernel. a)What are the parental genotypes? b)What are the F₂ genotypes and phenotypes? c)What conclusions can be made about the allelic and gene interactions?