Chapter 5, Problem 1TQ

Summary Introduction

During fertilization, two gametes fuse and produce a single cell termed as the zygote. The zygote contains a set of haploid (n) chromosomes from each gamete and thus resulting in the formation of a diploid (2n) set of genetic material. Diploid cells consist of two sets of chromosomes (2n), one derived from the maternal origin and the other derived from the paternal origin. Human cells carry two copies of chromosomes (22 pairs of autosomes) and a single pair of sex chromosomes.

Answer to Problem 1TQ

Homologous chromosomes contain a pair of similar kind of chromosomes; each chromosome inherited from each parent (one from maternal and one from paternal). Therefore, option b is correct.

Explanation of Solution

Justify the reasons for the correct statement:

Each homologous pair of chromosomes present in the zygote contains a set of chromosomes, one derived from the mother and another from the father. The human genome contains twenty three (23) pairs of chromosomes. Homologous chromosomes carry a similar kind of genetic information in their corresponding loci. All pairs (22 pairs) of chromosomes carry the same genes or genetic information except X and Y chromosomes. The X and Y chromosomes are known as sex chromosomes and they are involved in the determination of sexual characteristics in human beings. The remaining 22 pairs of homologous chromosomes are called autosomes.

The homologous pair of chromosomes found to be similar according to their size, physical character, pattern, and gene content. Homologous chromosomes carry two forms of a gene in the same locus are called alleles (same gene but different alleles).

Option (b) is given as, “a pair of chromosomes of the same kind”.

Hence, the option (b) is correct.

Justify the reasons for the incorrect statements:

Option (a) is given as, “the same thing as sister chromatids”.

Two identical DNA molecules after replication are known as sister chromatids. These chromatids are attached at the centromere until metaphase of the cell cycle. When sister chromatids are attached, it will be considered as a single chromosome. Hence, it is a wrong answer.

Option (c) is given as, “identical copies of the same chromosome”.

Two identical DNA copies of the same chromosome are known as sister chromatids. Hence, it is a wrong answer.

Option (d) is given as, “always haploid”.

A single set of chromosomes is known as a haploid. Hence, it is a wrong answer.

Hence, options (a), (c), and (d) are incorrect.

Conclusion

The homologous chromosomes are a pair of a same kind of chromosomes. They are inherited from the parents, one from the mother and another from the father.