Biology 302: Mendelian Genetics and Drosophila Development
Terms in this set (4)
Round (R) seed shape is dominant to wrinkled (r) seed shape in pea plants. If an RR plant is crossed with an rr plant, what is the frequency of phenotypes in the F2 generation?
A) All round seeds
B) 3 round seeds, 1 wrinkled seed
C) All wrinkled seeds
D) ¼ RR, ½ Rr, ¼ rr
B), since the F1 generation would have the genotype Rr, so crossing two heterozygotes would result in 3 plants with round seeds and 1 plant with wrinkled seeds.
If a yellow pea plant with round seeds that has the genotype GgWw is crossed to itself, what proportion of the offspring will be green with round seeds (Warning: G is a dominant allele for the yellow color, while g is a recessive allele for green)?
A), this is the probability of offspring that are either green with round seeds or yellow with wrinkled seeds.
In mice, agouti fur is a dominant trait resulting in individual hairs having a light band of pigment on an otherwise dark hair shaft. A mouse with agouti fur is shown here, along with a mouse with solid color fur, which is the recessive phenotype (A = agouti; a = solid color).
A separate gene, which is not linked to the agouti gene, can result in either a dominant black pigment or a recessive brown pigment (B = black; b = brown).
A litter of mice from the mating of two agouti black parents includes offspring with the following fur colors:
-solid color, black
-solid color, brown (sometimes called chocolate)
-agouti brown (sometimes called cinnamon)
What would be the expected frequency of agouti brown offspring in the litter?
F) not enough information given
A), because the two traits are determined by unlinked genes, they assort independently. As a result, you need to use the multiplication rule to calculate the probability of agouti brown offspring (A_ bb) from AaBb parents. The probability of A_offspring is 3/4, and the probability of bb offspring is 1/4. The combined probability is therefore 3/4 x 1/4 = 3/16.
In addition to A and a, the "agouti" gene has a third allele, AY . Here is some information about the inheritance of the AY allele:
-The AY allele is dominant to both A and a.
-The homozygous genotype (AYAY ) results in lethality before birth.
-The heterozygous genotypes (AYA or AYa) result in yellow fur color, regardless of which alleles are present for the B/b gene. (This effect exhibited by the AY allele is known as epistasis--when the expression of one gene masks the expression of a second gene.)
In a mating of mice with the genotypes AYaBb x AYaBb , what is the probability that a live-born offspring will have yellow fur?
Express your answer as a fraction using the slash symbol and no spaces (for example, 1/16).
2/3, because the presence of the AY allele is epistatic to (masks expression of) the B/b gene, the B/b gene does not need to be taken into consideration in this problem. For the AYa x AYa cross, 1/4 of the offspring would have the AYAY genotype, which is lethal before birth. For the live-born offspring, 2/3 would be AYa, and thus have yellow fur.