manny notes 2

Flashcards based on lecture notes covering meiosis, mitosis, and sexual reproduction.

Mitosis in Asexual Reproduction

Cell division that produces cells with the same information; identical daughter cells; exact copies; clones; same amount of DNA; same number of chromosomes; same genetic information

Examples of Single-Celled and Simple Multicellular Eukaryotes that reproduce asexually

Yeasts (fungi), Protists (Paramecium, Amoeba), Simple multicellular eukaryotes (Hydra).

Sexual Reproduction

Joining of egg + sperm

Karyotype

A display of the chromosome pairs of a cell arranged by size and shape.

Homologous Chromosomes

Paired chromosomes that carry matching genes controlling the same inherited characters.

Why Meiosis is Necessary for Sexual Reproduction

To reduce 46 chromosomes → 23; to half the number of chromosomes in gametes.

Meiosis: Production of Gametes

Chromosome number must be reduced; diploid → haploid; 2n → n; humans: 46 → 23

Meiosis: Reduction Division

A special cell division in sexually reproducing organisms that reduces 2n → 1n (diploid → haploid) to make gametes (sperm, eggs).

First Step of Meiosis

Duplication of DNA

Meiosis 1 Function

First division of meiosis separates homologous pairs.

Meiosis 2 Function

Second division of meiosis separates sister chromatids.

Steps of Meiosis 1

Interphase, Prophase 1, Metaphase 1, Anaphase 1, Telophase 1

Steps of Meiosis 2

Prophase 2, Metaphase 2, Anaphase 2, Telophase 2

Crossing Over

During Prophase 1, sister chromatids intertwine, homologous pairs swap pieces of chromosome; DNA breaks & re-attaches.

Steps of Crossing Over

Cross over, breakage of DNA, re-fusing of DNA.

Mitosis

1 division; daughter cells genetically identical to parent cell; produces 2 cells; 2n → 2n; produces cells for growth & repair; no crossing over.

Meiosis

2 divisions; daughter cells genetically different from parent; produces 4 cells; 2n → 1n; produces gametes; crossing over.

Value of Sexual Reproduction

Sexual reproduction introduces genetic variation; genetic recombination during meiosis, independent assortment of chromosomes, crossing over, random fertilization; drives evolution; variation for natural selection

Independent Assortment of Chromosomes

Meiosis introduces genetic variation; gametes of offspring do not have same combination of genes as gametes from parents; random assortment in humans produces 2^23 (8,388,608) different combinations in gametes.

Variation from Random Fertilization

Sperm + Egg = ?; any 2 parents will produce a zygote with over 70 trillion (2^23 x 2^23) possible diploid combinations.

Spermatogenesis

Continuous & prolific process; each ejaculation = 100-600 million sperm.

Oogenesis

Eggs in ovaries halted before Anaphase 1; Meiosis 1 completed during maturation; Meiosis 2 completed after fertilization; 1 egg + 2 polar bodies

Advantage of Unequal Division in Oogenesis

The advantage is to concentrate cytoplasm and resources in the egg, ensuring the zygote has ample nutrients and cellular machinery for early development.

Differences Across Kingdoms in Meiosis

Not all organisms use haploid & diploid stages in same way; which one is dominant (2n or n) differs; but still alternate between haploid & diploid.

Meiosis

produces 4 cells