Question

What are chromosomes? Explain how in sexually reproducing organisms the number of chromosomes in the progeny is maintained.

Answer 1

Chromosomes:

1. Chromosomes are a collection of thread-like structures that come in a variety of lengths and forms.
2. DNA and proteins (mainly histones) make up chromosomes.
3. Genes are carried on chromosomes.
4. They are located in the nuclei of eukaryotic cells.
5. Chromosomes in humans can be divided into Autosomes and Sex chromosomes.
6. Humans have 22 pairs of autosomes and one pair of sex chromosomes.

Maintaining the number of chromosomes in the progeny of sexually reproducing organisms:

1. Meiosis sustains the number of chromosomes in the progeny in sexually reproducing organisms.
2. The fusion of two gametes, each with a complete haploid set of chromosomes, is required for sexual reproduction to produce offspring.
3. Meiosis produces gametes (sperm and ova in humans) from specialized diploid cells in the reproductive organs.
4. Meiosis results in the formation of haploid daughter cells by halving the number of chromosomes.
5. Meiosis ensures haploid phase generation, while fertilization restores the diploid phase.
6. Meiosis is the process through which sexually reproducing organisms maintain their particular chromosomal numbers from generation to generation.
7. In humans, meiosis generates sperm and eggs, each having 23 chromosomes. By fertilizing sperm and ova, the chromosome number is restored in the zygote (46 chromosomes).