Bio chapter 11

Meiosis and production of genetically unique daughter cells

cell division that produces gametes with half the number of chromosomes as the original cell; sexual reproduction; unique daughter cells= randomization

Differences between sexual and asexual reproduction

Sexual reproduction: genetically unique offerings; 2 parents; involves gametes; meiosis

Asexual reproduction: genetically identical offsprings (CLONES o0o); 1 parent; mitosis

Homologous chromosomes

pairs of matching chromosomes, one inherited from each parent; found in diploid cells

Haploid

sex cells (gametes)

What is crossing over and when does it occur?

DNA exchange in Prophase I of meiosis I between homologous chromosomes; Happens at points called chiasmata; Produces new combinations of alleles (genetic variation)

How is chromosome number reduced from diploid to haploid in meiosis?

homologous chromosome pairs are separated in Meiosis I

When do homologous chromosomes separate vs sister chromatids?

Homologous chromosomes: separates in meiosis I; One chromosome from each pair goes to opposite poles

sister chromatids: separates in meiosis II; Chromatids split apart after being identical copies

Stages of meiosis I vs meiosis II

meiosis I: Homologous chromosomes pair up (synapsis); Produces 2 haploid cells (n)

meiosis II: No DNA replication before it starts; Produces 4 haploid, genetically unique cells

Stages of Meiosis

prophase→ metaphase→ anaphase→ telophase

What processes increase genetic diversity in meiosis?

crossing over, independent assortment of chromosomes, and random fertilization

What are tetrads and when do they form?

paired homologous chromosomes (4 chromatids) formed in Prophase I; Essential for genetic recombination

What is nondisjunction and what are its effects on chromosomes?

chromosomes fail to separate, producing gametes with too many or too few chromosomes, can lead to abnormalities