Question

1. A species has a diploid chromosome number of 10. In cells undergoing meiosis the number of chromosomes present in one of the two cells produced after the first division of meiosis is a) 5 b) 10 c) 15 d) 20 d) 40.

2.You cross an Aa Bb Cc individual with an individual of genotype Aa Bb cc: The expected proportion of offspring of genotype Aa BB cc is a) 1/2 b) 1/4 c) 1/8 d) 1/16 e) 1/32.

3.In tomato plants hairy stems are produced by a dominant allele, H and nonhairy stems arise from the expression of its recessive allele, h. For the trait of plant height, a dominant allele D, produces tall plants while the recessive allele, d, produces dwarf plants. The loci assort independently. You cross a hairy stem tall plant of unknown genotype to a nonhairy dwarf plant and observe that half of the offspring plants are hairy short and half are hairy tall. The genotype of the hairy tall parent plant is

         a) HH DD b) Hh DD c) HH Dd d) Hh Dd e) any of the genotypes above is possible.

4.Tay-Sachs disease is caused by an autosomal allele, t, that is recessive to the normal allele, T. A normal man and normal woman have three children, a normal son, a normal daughter, and a daughter with the disease. The probability that the normal son is a Tt carrier of the disease is

a) 2/3 b) 1/3 c) 1/2 d) 1/4

5.The I^A and I^B alleles of the ABO blood group are codominant, and both are dominant to the i allele. An I^A I^B heterozygote marries an individual of blood type O. What phenotypes of offspring are possible in this family?

         a) A & B only b) A & AB only c) A, B & O only d) A, B, & AB only e) A, B, AB & O

6.If the B allele is dominant to the b allele, a 1:1 phenotypic ratio is expected in which of the following crosses? a) BB x BB b) BB x Bb c) Bb x Bb d) Bb x bb e) bb x bb.

                   

Answer 1

1. a) 5

First division of meiosis (meiosis I) is known as reductional division. Since there are 10 diploid chromosomes it will have 20 chromatids. During meiosis I, they are replicated to form 10 chromosomes (with 40 chromatids). Each chromosome pair is segregated so that each daughter cell receives 5 chromosomes (with a total of 10 chromatids) during meiosis I.

2. d) 1/16

3. C) HH Dd

Since there are no non-hairy plants in the offspring, parent with dominant hairy stream phenotype must have both the homozygous alleles (HH). Also, dwarf and tall both appeared in offspring, it indicates Dd genotype of parent with Tall phenotype.

4. C) 1/2

5. A) A & B only.

6. D) Bb x bb.