Question

A cell has two pairs of submetacentric chromosomes, which we will call chromosomes IA, IB, IIA, and IIB (chromosomes IA and I B are homologs, and chromosomes IIA and IIB are homologs). Allele M is located on the long arm of chromosome IA and allele m is located at the same position on chromosome IB. Allele P is located on the short arm of chromosome IA, and allele p is located at the same position on chromosome IB. Allele R is located on chromosome IIA and allele r is located at the same position on chromosome IIB.

A. Draw these chromosomes, identifying alleles M, m, P, p, R, and r as they would appear in metaphase I of meiosis. Assume there is no crossing over.

B. Taking into consideration the random separation of chromosomes in anaphase I, draw the possible types of gametes that might result from this cell’s undergoing meiosis. Assume that there is no crossing over.

Answer 1

A) Allelic position in the chromosomes:

IA ----------M------------:-----------P----

IB ----------m------------:-----------p----

IIA -----------------R--------------------:---------------------

IIB -----------------r---------------------:---------------------

B) Types of gametes (assuming there is no crossing over):

MPR; MPr; mpR; mpr.

Step-by-step explanation:

In submetacentric chromosomes, the centromere is located near to the middle of the chromosomes.

Since these two pairs of homologous chromosomes do not undergo crossover, the resulting gametes after meiosis may have four (4) allele combinations.