Meiosis Basic Info

Who do we look like? Do you look like your mom or dad? Why do people who are related to us have similar characteristics?

Genes Each chromosome contains hundreds of genes Gene = a segment of DNA that determines characteristics and functions of a cell

Chromosomes Each species has to have a certain number of chromosomes in its cells Species size & complexity does NOT determine chromosome number Two types of chromosomes: Sex Chromosomes (X and Y) Autosomal chromosomes (all others)

Diploid vs. Haploid 46 = diploid Somatic cells (body cells) = diploid = 2n 2 copies of each chromosome Gametes (sex cells) = haploid = 1n 1 copy of each chromosome Fertilization – when two haploid gametes join to produce a diploid cell (zygote) 23 = haploid 23 = haploid 46 = diploid

Diploid vs. Haploid

Chromosome Numbers Organism Somatic Cell Gamete Fruit Fly 8 4 Corn 20 10 Human 46 23 Dog 78 39 Adder’s tongue fern 1260 630

Homologous Chromosomes In a diploid cell, there are 2 copies of each chromosome Homologous Chromosomes = contain genes for the same trait, but can have different versions (alleles) of that trait (same length & centromere position) Homologous Chromosome Video End at 1:08

Homologous Chromosomes Height (short) Height (tall) Hair type (straight) Hair type (curly) Eye color (brown) Eye color (blue) From Mom From Dad Earlobes (attached) Earlobes (unattached) Hair color (blonde) Hair color (brown)

*Sister chromatids are identical *Homologous chromosomes are similar What is the difference between sister chromatids and homologous chromosomes? *Sister chromatids are identical *Homologous chromosomes are similar

Mitosis vs. Meiosis Mitosis produces EXACT copies of cells Meiosis produces cells that are genetic variations that have only HALF the number of chromosomes Mitosis – produces 2 identical diploid somatic cells Meiosis – produces 4 variations of haploid gametes

If cells tried to use mitosis to make gametes? 92! 46 46 + egg sperm zygote Doesn’t work!

Why do we need meiosis? 46 46 Must reduce 46 chromosomes  23 46 zygote egg meiosis 46 46 fertilization 23 sperm

Gametogenesis – when cells use meiosis to make gametes Two Types Spermatogenesis – males produce sperm (about 250,000,000 sperm per day) Oogenesis – females create eggs produce 3 polar bodies and 1 egg Polar bodies don’t develop due to unequal division of cytoplasm

Ovulation = egg released from ovary