How is this different from mitosis? Overview of Meiosis How is this different from mitosis?

Meiosis vs Mitosis Characteristics Mitosis Meiosis Purpose Growth, replacement, repair Sexual Reproduction Location Somatic (body) cells Sex cells (ovaries/testes) Number of Cells at end 2 4 Human (start) 46 Human (end) 23 # of c’somes Same as parents (diploid = 2n) Half of parents (haploid = n)

A karyotype is an organized picture of pairs of homologous chromosome Humans have 22 pairs of autosomes, one pair of sex c’some = 46 total

What are homologous chromosomes? matching pairs of chromosomes that carry the same types of genes one from the mother (maternal) and one from the father (paternal) may have different allele forms Example:

What can we learn from looking at karyotypes? Gender Chromosomal Disorders Let’s try it….Google: Biology Project Karyotype Can you diagnose patient A, B, and C?

Homologous vs. Sisters Don’t confuse homologous chromosomes with sister chromatids- identical copies of chromosome made during the S phase of interphase, must have same allele forms.

Human Reproduction Meiosis allows parents to pass on HALF of their chromosomes In Women – an egg is formed from the ovaries In Men – sperm is formed from the testes

Steps of Meiosis (in detail)

Chromosome Dance 5 boys; 5 girls: Homologous Chromosomes Line up at Metaphase I How many different ways can you line up? Crossing over…change shoes with your partner (you can hold them if you don’t want to wear them). Imagine these “chromosomes” are made of DNA. What does independent assortment do? Crossing over?

X X X X XX X X X X X X X X Meiosis Example (box is cell) Interphase (early) 2n = 6 2) Interphase (end) 3) Prophase I X X X X X X 4) Metaphase I homologous pairs line up next to each other vs. in a line during mitosis 5) Anaphase I *homologous pairs separate! Vs. sister chromatids in mitosis!!! 6) Telophase I/ Cytokinesis *2 new cells that are haploid n = 3 vs. 2 new cells diploid in mitosis XX X X X X X X X X X X X X X X

7) Prophase II 9) Anaphase II –chromosomes line up sister chromatids separate (like in anaphase in mitosis) X X 8) Metaphase II –chromosomes line up (Just like in Metaphase in Mitosis!) 10) Telophase II –ends with 4 new cells EACH with HALF CHROMOSOMES as original X X X X X X n = ____3`____