University:
University of Cincinnati
Course:
BIOL 1081 | Biology I
Academic year:

2023
Views:

214

Pages:

3
Author:

Patricia Pena

Meiosis & Sexual Reproduction Cell division / Asexual reproduction ▪ • o • o • o o Mitosis produce cells with same information identical daughter cells exact copies clones same amount of DNA same number of chromosomes same genetic information Asexual reproduction ▪ ▪ • • o o ▪ • Prokaryotes Single-celled eukaryotes yeast (fungi) Protists Paramecium Amoeba Simple multicellular eukaryotes Hydra How about the rest of us? ▪ • ▪ What if a complex multicellular organism (like us) wants to reproduce? joining of egg + sperm Do we make egg & sperm by mitosis? Homologous chromosomes ▪ • o o Paired chromosomes both chromosomes of a pair carry “matching” genes control same inherited characters homologous = same information How do we make sperm & eggs? ▪ Must reduce 46 chromosomes → 23 o must half the number of chromosomes Meiosis: production of gametes • o o o o o • o o chromosome number must be reduced diploid → haploid 2n → n humans: 46 → 23 meiosis reduces chromosome number makes gametes fertilization restores chromosome number haploid → diploid n → 2n Reduction Division • • • • • • special cell division in sexually reproducing organisms reduce 2n → 1n diploid → haploid “half” makes gametes sperm, eggs Double division of meiosis DNA replication 1st division of meiosis separates homologous pairs 2nd division of meiosis separates sister chromatids Trading pieces of DNA ▪ • o o o Crossing over during Prophase 1, sister chromatids intertwine synapsis homologous pairs swap pieces of chromosome DNA breaks & re-attaches The value of sexual reproduction ▪ • o o o • o ▪ • Sexual reproduction introduces genetic variation genetic recombination during meiosis independent assortment of chromosomes random alignment of homologous chromosomes in Meiosis 1 crossing over random fertilization which sperm fertilizes which egg? Driving evolution variation for natural selection Variation from genetic recombination ▪ • • o 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 223 (8,388,608) different combinations in gametes Variation from random fertilization ▪ • Sperm + Egg = ? any 2 parents will produce a zygote with over 70 trillion (223 x 223 ) possible diploid combinations Differences across kingdoms ▪ • • o Not all organisms use haploid & diploid stages in same way which one is dominant (2n or n) differs but still alternate between haploid & diploid must for sexual reproduction