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.
Key-
trait: height
T = tall, t = short
T / tT / Tt / 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