Question

In a species of carrots, two genes control a couple of desirable traits. The Y/y gene controls carrot color, where the “Y” allele that makes yellow carrots is dominant over the “y” allele which makes plain-old orange carrots. Additionally, the L/l gene controls carrot length, where the “L” allele that produces long carrots is dominant over the “l” allele which produces short carrots. A. A carrot farmer performs a dihybrid cross with two true-breeding species of carrots. The first carrot is true-breeding for being yellow and short. The second is true-breeding for being orange and long. Knowing this, what are the genotypes for each of these carrot plants?

B. For the two different carrot plants described in "A" above, what are all of the different types of gametes that each of them can produce?

C. Knowing all this, predict all of the possible genotypes that their offspring can have and in what percentages. (You can use a Punnett square to figure this out, but you do not need to show a Punnett square in your answer.)

D. Choose any of the offspring that were produced in "C". For this individual, explain how EITHER (pick one!) the Law of Segregation OR the Law of Independent Assortment can be seen in the gametes that this offspring will produce in the future. Your answer should include a clear statement of the Law itself and use alleles (ex. "y" or "L") to justify your answer.

Answer 1

A. The genotypes of the above mentioned carrot plants are YYll and yyLL. True breeding species means homozygous for that trait.

B. Yl and yL are the only possible gametes that each parent can produce, since both are true breeding species.

C. YYll, YyLl and yyLL are the all three possible genotypes that the offspring can have in the 1:2:1 or in the percentages 25,50,25 respectively.

D. Mendal's law of segregation states that a diplod organism passes a randomly selected allele for a trait to its offspring, such that the offspring receives one allele from each parent.

Let us consider YyLl is the offspring chosen to explain the the law of segregation, only one (either Y or y) of the two gene copies (gene responsible for color) present in a carrot species is distributed randomly to each gamete irrespective of the sex (egg or sperm cell) that it produce in future.