Download Hershey-Genetics Introduction

GENETICS INTRODUCTION
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r.- lgti".ur, tallness is dominant to shortness. What type of ptarrt would result if a pure tall plant
were crossed with a short one?
2.
Whdt types would result if the F1 generation'from problem I were inbred? Give both
pheno(ypic and genotypic ratios.
3.
ln rats, black coat color is dominant to white coat color. What types of offspring would
result if a heterozygous black.rat were mated with a white rat?
4.
ln sheep, white is due to a dominant gene, and black to its recessive allele. A white ewe
. mated to a white ram produced. a black lamb. lf they produce another offspring, could it
white? What is the possible lenotype of the parents?
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5.
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ln guinea pigs, the coat may be rough or smooth. Certain rough-coated guinea pigs, when
. crossed with smooth-coated ones, produce all rough-coated offspring- Other rough-coated
guinea pigs when crossed with smooth-coated ones produce equal numbers of rough-coated
and smooth-coated offlspring. Explain tl-rese results. Write the genotypes for all animals
concerned in these crosses.
6.
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ln guinea pigs, black coat color is dominant over white coat color. Using this plus the
information you obtained from question 5, what would be the genotypes and phenotypes of
the Fr of the mating of a guinea pig homozygous for both black and rough coat with a white
smooth-coated guinea pig?
7. ryhat would be the g.noiyp",
and phenotypes and the genotypic and phenotypic ratios in
the F2 generation of the animdls of question 6?
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8.
ln dogs, the tendenry,to bark while trailing is due to a dominant gene while the trait to be
silent while trailing is recessive. Erect ears are dominant over drooping ears. Show the
offspring expected from a crois betw€en two erect-eared barkers who are heterorygous for
oglh genes.
9.
ln the domestic fowl, there are two pairs of genes affecting the comb. When homozygous for
the recessive forms of both genes, the fowlwill have a single (normal) comb. A dominant
allele of one of these genes, P, causes a pea comb. A dominant allele of the other, R., causes a
rose comb- However, if a fowl has at least one.of both dominant, P-R_, the comb will be a
walnut, a result of the combined action of both dominant genes. Show the expected
offspring of a cross between two walnut-combed fowl, both heterozygous for both genes.
10.
The chestnut color of horses is due to a recessive gene, while the dominant allele rezults in
black. The pacing gait is due to a recessive gene, whereas the dominant allele results in the
trotting gait- Show the types of offspring which could result from a cross of a black trotter,
n"t..o4ftous for both genes, crossed with a chestnut pacer. i,' .- '- ' , I ' .
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brown mink crossed with a silverblue mink produced all brown offspring. \)Uhen these F1
mink weie crossed amo,ng themselves, they produced forty-seven brown animals and fifteen
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silverblue animals. Which of these characteristics is dependent upon a dominant gene?
12.
Yellow guinea pigs crossed with white ones always produce cream-colored offspring. Two
cream guinea pigs when crossed produce yellow, cream and white offspring in the ratio of 1
yellow: 2 cream: 1 white. How are these colors inherited?
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ln radishes the shape may be long or round or oval. Crosses between long and oval gave 159
long, 156 oval. Crosses between round and oval gave 199 round, 203 oval. Crosses between
long and round produced 576 oval- Crosses between oval and oval resulted in 112 long,243
oval, 119 round. What type of inheritance is involved?
14. Gray squirrels are more common in nature than black ones.
a. What conclusions concerning the heredity of color in squirrels can be drawn from this
statement?
b. Assume that gray coloration is due to a dominant gene. Explain how you would
determine whether a gray squirrel is pure gray or hybrid gray.
State three crosses in which all the offspring will appear gray.
c.
15. ln foxes, a prair of alleles, P and p, interact as follows: PP is lethal, usually killing during
embryonic life; Pp results in platinum color; pp produces silver foxes. Could a fox breeder
establish a true-breeding variety of platinum foxes?
16. lf
two
individuals from problem #1O above were mated (pick any two), what types of
offspring could they produce and in what proportions?
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