Question

What are homologous chromosomes? Contrast the genetic makeup of sister chromatids with non-sister chromatids.

Answer 1

Chromosomes are thread-like structures present in the nucleus of the cell and are made up of deoxyribonucleic acid molecules and proteins. It is transferred from parent to offspring and is the source of genetic material.

Complete answer:
The term chromosome means coloured bodies and this term was given by a German scientist von Waldeyer Hartz. Chromosomes are present in definite numbers which are unique for each species as human beings have 46 chromosomes which are present in 23 pairs, a dog has 78 chromosomes which are arranged in 39 pairs and this way the number of chromosomes differ from species to species. Chromosomes consist of packaging proteins called histones that are responsible for their condensed structure. Chromosomes are divided into sex chromosomes and autosomes. Sex chromosomes are responsible for the transfer of genetic characteristics from parent to offspring.
Homologous chromosomes are two similar pairs of chromosomes in diploid organisms and each one in the pair comes from each parent. A diploid organism is formed by the contribution of half chromosomes from the male parent and half from the female parent. Cells in human beings have chromosomes present in copies. This means a cell will produce two versions of a protein that is encoded by the DNA present in the chromosomes. Two different versions of a homologous chromosome produces variety in the population. Genes have alleles which are divided into dominant and recessive amongst which dominant allele suppresses the expression of recessive allele and expresses itself. The speciality of homologous chromosomes is that they consist of the same genes in the same order across their chromosomal arms.
Sister chromatids are the identical copies of chromatids formed after DNA replication which are joined together by centromere. Dyad is a pair of sister chromatids. Sister chromatids have similar alleles whereas non-sister chromatids are also just like sister chromatids but they don’t have similar alleles.

Note: Sister chromatids of the homologous chromosomes are involved in restoring the integrity of DNA by its capability of DNA repair. Cohesion of sister chromatids is also important for the correct distribution of genetic information between the newly formed daughter cells.