Meiosis: Stages, Variability, and Human Chromosome Disorders

What is meiosis?

A special type of cell division that produces gametes for sexual reproduction.

What is the chromosome number of gametes produced by meiosis?

Gametes are haploid (n), containing half the chromosome number of diploid (2n) somatic cells.

What are the two types of gametes in humans?

Oocytes (female) and sperm (male).

What is the outcome of meiosis?

Meiosis results in four haploid cells from one diploid cell.

What are the phases of meiosis?

Meiosis I and Meiosis II.

What occurs during Meiosis I?

Separation of homologous chromosomes and reduction of chromosome number by half.

What occurs during Meiosis II?

Separation of sister chromatids, similar to mitosis.

What is the significance of crossing over?

It creates genetic variability by exchanging genetic material between non-sister chromatids.

What is independent assortment?

The random arrangement of chromosomes during metaphase I, leading to genetic variation.

What is random fertilization?

The combination of any sperm with any egg, leading to a vast number of possible genetic combinations.

What is gametogenesis?

The process of forming haploid gametes from diploid cells.

What is spermatogenesis?

The process of forming sperm cells by meiosis in the testes.

What is oogenesis?

The process of forming an ovum (egg) by meiosis in the ovaries.

What is nondisjunction?

The failure of chromosomes to separate properly during meiosis, leading to gametes with abnormal chromosome numbers.

What is Trisomy 21?

A condition where a person has three copies of chromosome 21, leading to Down syndrome.

What are the characteristic features of Trisomy 21?

Short stature, round face, heart defects, flattened nose bridge, and small irregular teeth.

How does meiosis differ from mitosis?

Meiosis results in four genetically diverse haploid cells, while mitosis produces two identical diploid cells.

What is the diploid number of chromosomes in humans?

46 chromosomes (2n = 46).

What is the haploid number of chromosomes in humans?

23 chromosomes (n = 23).

What happens during fertilization?

A sperm and egg combine to form a diploid zygote (2n = 46).

What is the role of shugoshin in meiosis?

It prevents sister chromatid separation during Meiosis I.

What is the result of nondisjunction during Meiosis I?

All four gametes will have incorrect chromosome numbers.

What is the result of nondisjunction during Meiosis II?

Two gametes with incorrect numbers and two normal gametes.