Mendelian Genetics Practice
1) EXAMPLE: Use a Punnett square to predict the genotypic and phenotypic
outcome (offspring) of a cross between two heterozygous/hybrid tall (Tt) pea
plants.
Keytrait: height
T = tall, t = short
T
T
Tt
t
Tt
t
Tt
Tt
All offspring have the Tt genotype and the Tall phenotype
2) In pea plants, yellow peas are dominant over green peas.
Use a Punnett square to predict the phenotypic and genotypic outcome
(offspring) of a cross between a plant heterozygous/hybrid for yellow (Yy) peas
and a plant homozygous/purebred for green (yy) peas.
3) In silkworms a single gene determines the color of the cocoon. The yellow
cocoon allele is dominant. It is indicated by "C". The white allele is recessive,
and indicated by "c". Complete the following Punnett Square assuming a
homozygous dominant male (CC) fertilizes a homozygous recessive female
(cc).
4) In mice a single gene determines the color of the eyes. The black eyes allele is
dominant. It is indicated by "E". The red allele is recessive, and indicated by
"e". Complete the following Punnett Square assuming a heterozygous male (Ee)
fertilizes a heterozygous female (Ee).
5) The length of fur in guinea pigs is controlled by a single gene. The dominant
allele "F" produces short fur. The recessive allele "f" produces long fur.
Complete the following Punnett Square assuming a heterozygous male (Ff)
fertilizes a homozygous recessive female (ff).
6) In guinea pigs, black coat color is dominant over white, short hair is dominant
over long, and rough coat is dominant over smooth. Show the Punnett Square for a
cross between a homozygous black, short-haired, rough coat guinea pig and a
homozygous white, long-haired, smooth coat guinea pig. What do the offspring
look like?
7) In race horses, black hair (F) and a trotting gait (G) are dominant traits.
Recessive traits are chestnut hair (f) and a pacing gait (g). The genes for hair color
and gait are on two differnet chromosomes. Use a Punnett Square to determine the
possible offspring from a cross between two heterozygous black trotters (FfGg).
8) In fruit flies the allele for normal size wings (W) is dominant over the allele for
vestigial wings (w). The allele for normal size eyes (E) is dominant over the allele
for small eyes (e). The genes for wing size and eye size are on different
chromosomes. Use a Punnett Square to predict the results of a cross between an
individual heterozygous for both traits and one that is homozygous recessive for
both traits.
9) In Mountain Boomers, the genes for length of tail exhibit "incomplete"
dominance. Use a Punnett Square to predict the result of a cross between a
homozygous Long-tailed and a homozygous Short-tailed Mountain Boomer. What
do the offspring look like?
10) In a certain flower, color is determined by genes showing “co-dominance”.
Plants are either solid white, solid black, or checker-board white and black. Show
a cross between a heterozygous plant and a homozygous white plant.
“No human investigation can be called real
science if it cannot be demonstrated
mathematically” Leonardo da Vinci, (1452-1519