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 truebreeding 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 Aabb
AaBb x AaBb
AaBB x aaBb
AaBb x aabb
Probabilities
Calculate the probabilities of the
production of the offspring for
each cross
AAbb x aaBB
AaBB
AaBbCc x AaBbCc
AAbbCc
AABBCC
AaBbCc
aabbcc
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:
Double Mutant:
Black – Normal:
Grey – Vestigial:
750
764
120
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