Genetics Practice Problems

Ratios

1. What would be the genotypic and phenotypic ratios be for a cross between a true-breeding

tall pea plant and a true-breeding short pea plant?

2. What would be the phenotypic ratio be for the

following cross:Tt x tt

3. What would be the genotypic and phenotypic ratio for the

following cross:

Tt x Tt

4. What would be the genotypic and phenotypic ratios for the

following cross:

TTAA x ttaa

5. What would be the phenotypic ratio for the following

cross:

TtAa x ttaa

6. What would be the genotypic and phenotypic ratios for the

following cross:

TtAa x TtAa

7. In cows, roan coat color is caused by having one red allele

(R) and one white allele (W). What is the genotypic ratio of

the following cross:RR x WW

8. What is the phenotypic and genotypic ratio of the following

cross:

RW x RW

9. In snapdragons, red flower color (R) is incompletely dominant to

white flower color (R’), what is the phenotypic and genotypic ratio for

the following cross:

RR x R’R’

10. What are the phenotypic and genotypic ratios of the

following cross:

RR’ x RR’

11. In Guinea Pigs, 2 genes control coat color. One gene controls whether they will be colored (A) or albino (a). The other gene determines if they will be black (B) or brown (b).

What type of inheritance pattern is this?

12. What will be the phenotypic ratio of the following crosses:

AaBB x AabbAaBb x AaBbAaBB x aaBbAaBb x aabb

Probabilities

Calculate the probabilities of the production of the offspring for

each cross

AAbb x aaBB

AaBB

AaBbCc x AaBbCc

AAbbCcAABBCCAaBbCcaabbcc

Non-Mendelian Inheritance Patterns

Many genes control the expression of one trait.

One gene has many phenotypic effects.

In a heterozygote, both alleles are expressed individually.

In a heterozygote, the phenotype expressed is blended between

what the alleles actually code for.

2 genes affect one trait, but one gene controls the expression of

the 2nd gene.

Spermatogenesis and Oogenesis

How many gametes are produced during oogenesis?

What is the scientific name for the gamete?

When does spermatogenesis begin?

How many gametes are produced during spermatogenesis?

When does oogenesis begin?

Gene Mapping

b+bvg+vg x bbvgvg

• Wild Type: 750

• Double Mutant: 764

• Black – Normal: 120

• Grey – Vestigial: 166

• What is the recombination frequency?

Linkage Map

• A-B = 23 mu

• A-C = 12 mu

• B-C = 11 mu

Linkage Map

• A-B = 10

• A-C =5

• A-D = 18

• B-C = 15

• B-D = 8

• C-D = 23