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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