Chapter 11, Problem 13A

Summary Introduction

Introduction :

Each cell in the human contains 46 chromosomes or 23 pairs of chromosomes. 22 pairs of these chromosomes are the autosomes and 1pair is the sex chromosomesthatdetermines the gender of an individual.

Answer to Problem 13A

Correct answer :

A correct answer is an option (A),the X and Y chromosome.

Explanation of Solution

Explanation/justification for the correct answer :

Option (A) s the X and Y chromosome. Theoffspring gender is determined by the combination of sex chromosomes in the egg and sperm cell. If fusing sperm having a Y chromosome, the gender will be male and if fusing sperm having an X chromosome, the gender will be female. Thus, the correct answer is an option (A).

The explanation for the incorrect answer :

Option (B) chromosome 21. Chromosome 21 is an autosome. It does not participate in sex determination. Thus, this is an incorrect option.

Option (C) codominance. In a heterozygous organism, if both alleles are expressed, it is called codominance. For example, sickle-cell disease follows codominant inheritance. Thus, this is an incorrect answer.

Option (D) epistasis. Epistasis is a form of interaction between non-allelic genes in which one combination of such genes has a dominant effect over other combinations. This phenomenon does not determine sex of the gender.Thus, this is an incorrect answer.