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GENETIC CROSS PROBLEM SET MONOHYBRID CROSSES Note: work all crosses through the F2 generation if the F1 is 100% heterozygous. See the text for help in setting up these crosses. 1. In peas, round seeds (R) are dominant over wrinkled seeds (r). A plant that is homozygous dominant (RR) is crossed with one that is homozygous recessive (rr). a. Work the Punnett Square for the F1 cross below. R R r Rr Rr b. List the genotype of the parents: RR & rr c. List the phenotype of the parents: Round & Wrinkled d. Work the Punnett Square for the F2 generation below showing a self-fertilization of an F1 individual. R r R RR Rr r Rr rr e. What percentage of the F2 offspring will have round seed? 75% Wrinkled seeds? 25% What percentage will be homozygous? 50% What percentage will be heterozygous? 50% f. Give the phenotypic ratio - 3:1 g. Give the genotypic ratio - 1:2:1 DIHYBRID CROSSES Note: work all crosses through the F2 generation if the F1 is 100% heterozygous. See the text for help in setting up these crosses. Consider a cross in which a male fruit fly with white eyes (rr) and shriveled wings (ss) is crossed with a female that is homozygous dominant for both traits (red and straight - RRSS). Work the F1 generation cross to answer the following questions. When listing the parent’s genes on the cross, make sure each R is paired with each S. There will be four possible combinations of genes. See the text for an example. Male gene → RS Female gene ↓ rs rs rs rs F1 generation a. What is the phenotype of all members of the F1 generation? Red and straight b. Work the F2 generation Punnett Square to show self-fertilization of one individual. Male gene → RS Female gene ↓ RS RS RS RS F2 generation c. List the phenotypes present in the F2 generation: Red and straight, red and shriveled, white and straight, white and shriveled d. Give the phenotypic ratio observed: 9:3:3:1 e. Which of the laws governing genetics account for the phenotypic ratio observed (hint: it is the law that accounts for new and novel combinations of genes in offspring)? Law of Independent Assortment

GENETIC CROSS PROBLEM SET
MONOHYBRID CROSSES
Note: work all crosses through the F2 generation if the F1 is 100% heterozygous. See the text for help in setting up these crosses.

1. In peas, round seeds (R) are dominant over wrinkled seeds (r). A plant that is homozygous dominant (RR) is crossed with one that is homozygous recessive (rr).

a. Work the Punnett Square for the F1 cross below.

R R
r Rr Rr

b. List the genotype of the parents: RR & rr
c. List the phenotype of the parents: Round & Wrinkled
d. Work the Punnett Square for the F2 generation below showing a self-fertilization of an F1 individual.

R r
R RR Rr
r Rr rr

e. What percentage of the F2 offspring will have round seed? 75%
Wrinkled seeds? 25%
What percentage will be homozygous? 50%
What percentage will be heterozygous? 50%

f. Give the phenotypic ratio - 3:1
g. Give the genotypic ratio - 1:2:1

DIHYBRID CROSSES
Note: work all crosses through the F2 generation if the F1 is 100% heterozygous. See the text for help in setting up these crosses.

Consider a cross in which a male fruit fly with white eyes (rr) and shriveled wings (ss) is crossed with a female that is homozygous dominant for both traits (red and straight - RRSS). Work the F1 generation cross to answer the following questions. When listing the parent’s genes on the cross, make sure each R is paired with each S. There will be four possible combinations of genes. See the text for an example.

Male gene → RS
Female gene ↓

F1 generation

a. What is the phenotype of all members of the F1 generation? Red and straight
b. Work the F2 generation Punnett Square to show self-fertilization of one individual.

Male gene → RS
Female gene ↓

F2 generation

c. List the phenotypes present in the F2 generation: Red and straight, red and shriveled, white and straight, white and shriveled
d. Give the phenotypic ratio observed: 9:3:3:1
e. Which of the laws governing genetics account for the phenotypic ratio observed (hint: it is the law that accounts for new and novel combinations of genes in offspring)? Law of Independent Assortment

Added by Lisa S.

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