Question

Can you help me with this problem:

5. In an organism where 2N = 20, how many unique gametes could be produced due to independent assortment alone (not considering crossing over)? Briefly explain. 6. One of the autosomal loci controlling eye color in fruit flies has two alleles, one for brown eyes and the other for red eyes. Fruit flies from a true-breeding line with brown eyes were crossed with flies form a true-breeding line with red eyes. The Fı flies had red eyes. a. Write the genotypes of each parent and the F1 offspring. b. Predict the results of an F1 intercross in terms of genotype and phenotype. c. If the F1 flies were mated with brown-eyed flies, what phenotypes would you expect the offspring to have? In what proportions would these phenotypes occur? d. What type of cross is described in part c?||

Answer 1

Answer 5:

In an organism where 2N = 20

So, N = 20/2 = 10

We know that, the number of unique gametes could be produced due to independent assortment alone from an organism = 2^N, where N = haploid number of chromosomes.

Thus, the number of unique gametes could be produced due to independent assortment alone from an organism = 2^N = 2¹⁰ = 1024 (as, here N = 10)

Answer 6:

One of the autosomal loci controlling eye color in fruit flies has two alleles, one for brown eyes and the other for red eyes. Fruit flies from a true-breeding line with brown eyes were crossed with flies form a true-breeding line with red eyes. The F1 flies had red eyes.

We assume that the allele producing red eye is denoted by R and the allele producing brown eye is r and R is dominant over r. So, for two alleles the possible genotypes are— RR (homozygous dominant), Rr (heterozygous) and rr (homozygous recessive). RR and Rr produces red eye as phenotype and rr produce brown eye as phenotype.

(a) The genotypes of red eyes parent is RR and the genotypes of brown eyes parent is rr and the genotypes of the F1 offspring is Rr.

(b) If F1 red eyes offsprings (Rr, heterozygous) are self-crossed the result come in F2 generation—

Gametes for Rr are R and r.

	R	r
R	RR (red eyes)	Rr (red eyes)
r	Rr (red eyes)	rr (brown eyes)

Genotypic ratio in F2 generation— RR:Rr:rr = 1:2:1

Phenotype ratio in F2 generation— red eyes : brown eyes = 3:1

(c) If the F1 red eyes flies (Rr, heterozygous) were mated with brown-eyed flies (rr, homozygous recessive), the result come in the next generation—

Gametes for Rr are R and r and gametes for rr are r and r.

	R	r
r	Rr (red eyes)	rr (brown eyes)
r	Rr (red eyes)	rr (brown eyes)

Genotypic ratio in next generation—Rr:rr = 2:2 = 1:1

Phenotype ratio in F2 generation— red eyes : brown eyes = 2:2 = 1:1

(d) The type of cross is described in part c is back cross. A back cross is a type of cross where a F1 hybrid offspring is crossed with either any of its parents or similar to the genotype of the either parents. Here F1 hybrid red eyes flies (Rr, heterozygous) were mated with brown-eyed flies (rr, homozygous recessive) which is similar to one of the parent genotype. Thus, it is a back cross.