When a heterozygote for a particular gene locus A is selfed, the probability of obtaining an aa offspring is 1/4, and the probability of obtaining an Aa offspring is 1/2. Similarly, when a double heterozygote AaBb is selfed, the probability of obtaining an AaBB offspring is:
Answers
Explanation:
A plant with orange-spotted flowers was grown in the greenhouse from a seed collected in the wild. The plant was self-pollinated and gave rise to the following progeny: 88 plants with orange-spotted flowers, 34 plants with yellow-spotted flowers, 32 plants with solid orange flowers, and 8 plants with solid yellow flowers.
a. (1 point) What can you conclude about the dominance relationships of the alleles responsible for flower color and pattern? How many genes are involved?
There are two genes involved, one for flower color and one for flower pattern. There are two alleles for the flower color gene, with the orange allele (Y) dominant to the yellow allele (y). There are two alleles for the flower pattern gene, with the spotted allele (R) dominant to the unspotted allele (r).
b. (1 point) What was the genotype of the original plant with orange-spotted flowers?
the original plant was heterozygous for both genes: YyRr
c. (3 points) On a separate sheet of paper, draw a diagram that illustrates what happened to these alleles during meiosis in the original plant. Clearly label:
(a) the meiotic divisions (i.e. meiosis I and meiosis II)
(b) the homologous chromosomes, sister chromatids, genes and alleles
(c) all the genetically different gametes that could form and how frequently each type should be observed.
2. (1 point) In pigs, when a pure-breeding red is crossed to a pure-breeding white the F1 progeny are all red. However, when the red F1 individuals are interbred, the F2 shows 9/16 red, 1/16 white, and 6/16 are a new color, sandy. Explain how color is inherited in pigs, and how the sandy color comes about.
Two genes are involved, e.g. R and P. Dominant for BOTH color genes gives red pig (R-P-); dominant for ONE color gene (and recessive for other; R-pp or rrP-) gives sandy pig; dominant for NO color genes (i.e. double homozygous recessive, rrpp) gives white pig. 9:3:3:1 --> 9:6:1
3. Consider the following pedigree in answering this question.
a. (1 point) What is the most likely mode of inheritance for this trait? Explain your reasoning.
X-linked recessive. Males are more likely to be affected that females, thus likelihood of X-linked, and trait skips generations, thus recessive. Original mom is first generation must have been a carrier, with her first daughter (on left) not a carrier and her second daughter (on right) a carrier. Individuals mating into the family are not carriers.
b. (1 point) What is the probability that individual A is a carrier of this trait? What is the probability that individual B is a carrier of this trait?
Probability that A is a carrier = 0.5. Since she has brothers with the trait and unaffected parents, her mother must be a carrier. Therefore, she has a 50% chance of inheriting the recessive allele and being a carrier.
Probability that B is a carrier = 0. If he had the recessive allele, he would be affected.
4. Use the flower tutorial program (downloaded from the website) to answer the following questions. Remember that this program is also available from the P drive at P:data/biology/biol111/flower.exe, and will only work on a PC (no Mac).
a. (1 point) Describe how flower-center color is inherited. In formulating your answer, consider these questions: How many phenotypes can you observe? How many genes are involved? How many alleles are involved, and what are their dominance relationships to one another?
Flower center color is inherited in simple Mendelian fashion. There are two phenotypes that can be observed, yellow (or tan/brown for some of you) and white. This trait in inherited due to two alleles for a single gene, with the yellow allele dominant to the white allele.
b. (1 point) Inheritance of flower petal color is relatively complex in this system. What is the relationship of the r”ed” allele to the “pink allele”? What is the relationship of the “red” allele to the “dark blue” allele? On what evidence do you base your answers?
Flower petal color is inherited also do to a single gene, but there are multiple alleles for this gene in the population. The pink allele is dominant to the red allele; crosses between pure-breeding pink and pure-breeding red give pink individuals, and test crosses with these F1’s give a 1:1 ratio of pink and red. Similarly, the dark blue allele is dominant to the red allele; crosses between pure-breeding dark blue and pure-breeding red give dark blue individuals, and test crosses with these F1’s give a 1:1 ratio of dark blue and red.