Question

16. Use the following information to answer the questions below.
Drosophila (fruit flies) usually have long wings (+) but mutations in two different genes can result in bent wings (bt) or vestigial wings (vg).
If a homozygous bent wing fly is mated with a homozygous vestigial wing fly, which of the following offspring would you expect?

a. 1/2 bent and vestigial to 1/2 normal

b. 1/2 bent and 1/2 vestigial flies

c. 3/4 bent to 1/4 vestigial ratio

d. all +bt +vg heterozygotes

e. all homozygous + flies

25. The term hemizygous refers to

a. X-linked characteristics expressed in mammalian males.

b. incomplete dominance of phenotypic traits.

c. having two different alleles on the loci of polyploidal species.

d. X-linked characteristics in mammalian females resulting from Barr body silencing.

e. autosomal characteristics in diploid populations.

29. Which of these descriptions of the behaviour of chromosomes during meiosis explains Mendel’s law of independent assortment?

a. Crossing over causes the alleles to switch between chromosomes.

b. The arrangement of each pair of homologous chromosomes on the metaphase plate during metaphase I is random with respect to the arrangements of other pairs.

c. Sister chromatids separate during anaphase II.

d. The two alleles for each gene separate as homologous chromosomes move apart during anaphase I.

Answer 1

Question:If a homozygous bent wing fly is mated with a homozygous vestigial wing fly, which of the following offspring would you expect?

Answer: d. all +bt +vg heterozygotes

NOTE homozygous bent wing fly's genotype would be +bt +bt

homozygous vestigial wing fly's genotype would be +vg

If they are crossed all the offsprings would be +bt+vg

Question: The term hemizygous refers to

Ans:a. X-linked characteristics expressed in mammalian males.

NOTE: Mammals are diploid so they will have pairs of chromosomes which are homologous, but male will have one pair of chromosome which would not be homologous. That is, a male will have a single X chromosome on which there will be genes which will not have any allele on Y chromosome. This is hemizygosity

Question:Which of these descriptions of the behaviour of chromosomes during meiosis explains Mendel’s law of independent assortment?

a. Crossing over causes the alleles to switch between chromosomes.

NOTE: Mendel's law of independent assortment says that the genes move independent of each other when they enter the gamates.

And now we know that if the genes are apart from each other on the same chromosome,in Meiosis I there is a recombination or crossing over taking place between homologous chromosome which will lead to different combinations of alleles on the chromosome entering into the gamate. (possibility of two genes on the same chromosome entering together i.e. linkage depends upon the distance between them)