Download General Genetics Problem Set #1

General Genetics Problem Set #1
Background: The possible gene combinations in the offspring that result from a genetic cross can be determined
by drawing a diagram known as a Punnett square. A Punnett square shows the genes in the gametes produced
by the parents along the top and left side of the square and the possible gene combinations in the offspring
within the square.
Rules for Working Genetic Problems Using a Punnett Square:
1. Use the letters given or choose a letter to represent the alleles in a cross.
2. Write the genotypes of the parents, P1.
3. Write the possible gametes that the parent can produce.
4. Enter possible gametes at the top and sides of the square.
5. Combine the gamete possibilities in the Punnett Square.
6. Determine the genotypic ratio.
7. Determine the phenotypic ratio.
A. The following letters represent gene pairs. Indicate which of the following pairs of genes are dominant (D),
recessive (R), homozygous (HO) and heterozygous (HE). Include ALL possibilities.
1. DD __________________
2. Dd __________________
3. Dd __________________ 5. ss __________________
4. Rr __________________ 6. Yy __________________
B. Use letters G and g to illustrate the following gene conditions in a pair of chromosomes.
7. Homozygous recessive ______________
8. Homozygous dominant ______________
9. Heterozygous ______________
10. hybrid ______________
C. Single Trait Problems.
*In pea plants, the gene for round seeds is dominant over the gene for wrinkled seeds.
11. What symbol will represent the gene for round seeds? (circle one) R or
r
12. What symbol will represent the gene for wrinkled seeds? (circle one) R
or
13. What is the genotype for a pea plant that is homozygous round? _________
14. What is the genotype for a pea plant that is heterozygous round? _________
15. What is the genotype for a pea plant with wrinkled seeds? _________
16. What is the phenotype for a pea plant with the genotype Rr? _________
17. What is the phenotype for a pea plant with the genotype RR? _________
18. What is the phenotype for a pea plant with the genotype rr? _________
r
19. If a pea plant that is heterozygous for round seeds is crossed with a pea plant with wrinkled seeds, what are
the expected genotypic and phenotypic ratios in the F1?
Parent Genotypes: ______ X _______
F1Genotypic Ratio: ________________________
F1Phenotypic Ratio: ________________________
20. Cross a pea plant that is homozygous for round seeds with a pea plant that is homozygous for wrinkled
seeds. What are the genotypes and phenotypes of the offspring of the F1 generation?
Parent Genotypes: ______ X _______
F1Genotypic percentage or ratio: ________________________
F1Phenotypic percentage or ratio: ________________________
21. Cross two of the F1generation from the previous cross to obtain the F2 generation. What are the expected
genotypic and phenotypic ratios in the F2 generation?
Parent Genotypes: ______ X _______
F2 Genotypic percentage or ratio: ________________________
F2 Phenotypic percentage or ratio: ________________________
* In foxes, red coat color is governed by a dominant allele B, silver-black coat color by a recessive allele b.
Determine the genotypic and phenotypic ratios expected from the following matings.
22. Cross a homozygous red fox and a heterozygous red fox.
Parent Genotypes: ______ X _______
Genotypic percentage or ratio: ________________________
Phenotypic percentage or ratio: ________________________
23. Cross a heterozygous red fox with a silver-black fox.
Parent Genotypes: ______ X _______
Genotypic percentage or ratio: ________________________
Phenotypic percentage or ratio: ________________________
24. Cross a homozygous red fox with a silver-black fox.
Parent Genotypes: ______ X _______
Genotypic percentage or ratio: ________________________
Phenotypic percentage or ratio: ________________________
25. Frosty the Snowman is homozygous dominant for a carrot nose. Mrs. Frosty is homozygous recessive and
does not have a carrot nose. She had to settle for a nose made out of coal. What will be the possible genotypic
and phenotypic ratios of their kids?
Parent Genotypes: ______ X _______
Genotypic percentage or ratio: ________________________
Phenotypic percentage or ratio: ________________________
26. After the Grinch joined all the Whos down in Whoville for Christmas one year, he married a Who by the
name of Peggy Lou. The Grinch is heterozygous dominant for green fur, but Peggy Lou is recessive and has
lovely purple fur. What will be the possible genotypic and phenotypic ratios of their little Whos?
Parent Genotypes: ______ X _______
Genotypic percentage or ratio: ________________________
Phenotypic percentage or ratio: ________________________
27. Mickey Mouse is recessive for big ears. Three of his children, Ricky, Vicky, and Nicky area also recessive
and have big ears like their famous father. One son, Ronald, however, has small ears. What must the genotype
of the children’s mother, Minnie, be?
Minnie’s Genotype: _________
28. Dumbo the elephant is homozygous dominant for big ears. His wife, Mumbo, is recessive and does not have
big ears (which, sadly means that she can’t fly). What will be the possible genotype of Baby Dumdodo?
Dumdodo’s Genotype: _________
29. Tarzan has normal skin, which is a dominant trait. He marries Jane, who is an albino (a recessive trait).
While swinging from tree to tree in the jungle, Tarzan and Jane realize they have left their son, Boy, “Home
Alone.” What are the genotypes of Tarzan, Jane and Boy? Oh, by the way, Boy looks just like his mother.
Tarzan’s genotype: _________
Jane’s genotype: _________
Boy’s genotype: _________
* In guinea pigs, black coat color is dominant to brown coat color. A brown guinea pig is crossed with a black
guinea pig of unknown genotype.
30. Because a known recessive guinea pig is crossed with an unknown black guinea pig, what kind of cross is
this? ___________________________
31. If any of the offspring are brown, what is the genotype of the black parent? _______
32. If, after many offspring, all offspring are black, what is the probable genotype of the black parent guinea
pig? _________