BIO chp10

Two copies of each chromosome (one from each parent)

Human cells are diploid

• Making sex cells
• (egg and sperm...often referred as "gametes")

• Gametes have half the genetic information,
• they are haploid (one copy of each chromosome)

The diploid result when a haploid sperm and haploid egg fuse together

• one round of chromosome duplication
• followed by two rounds of cell division (Meiosis I and Meiosis II)

• Cells start off as diploid & Chromosomes have been duplicated:
• -Prophase I
• -Metaphase I
• -Anaphase I
• -Telephase I

Result: 2 haploid cells

• homologous chromosomes exhange reciprocal sections
• Takes place in Prophase I

Microtubles move homologuous chromosomes to metaphase plate (different than metaphase in mitosis!!)

• Microtubles separate homologous chromosomes
• --Sister chromatids remain together!

• Nuclear envelope reforms
• spindle dissasembles
• 2 cells result from cytokinesis

• Another Round of division
• -2 daugher cells made in Meiosis I divide again
• -this time, no DNA replication in between

This time, sister chromatids separate


Result: 4 haploid daughter cells

Gametes created by meiosis are genetically different from each other

• 2 Events:
• Crossing Over (formation of tetrads)
• Independent Assortment

Random distribution of homologous chromosome pairs during Metaphase I

• ensures offspring will be unique
• more genomes for natural selection to choose from
• depedent on mutation or "horizontal" gene transfer (bacteria clonal strains)

• Males: Spermatogonium
• Females: Ooogonium

Spermatogenesis starts at puberty and continues through life

• Spermatogonium - "stem" sex cells:
• -- can go on to make sperm
• OR
• --can go on to make more spermatogonia

• All or most potential gametes produced before birth
• meiotic divisions unequal, leading to formation of polar bodies
• puberty releases the "arrested state" of primary oocytes, leading to ovulation
• Meiosis II does not occur until fertilization of 2nd oocyte
• Ovulation and reproduction naturally end during menopause

reproduction that does not require sex


NOTE: only birds and mammals are ALL strictly sexually producing types of organisms..

Parthenogenesis: embryo develops from unfertilized egg

• Binary Fission: cell division resulting in 2 single-celled organisms
• --Different from meosis, two new cellls, not similar cells

• Vegetative reproduction: in plants, new individuals are made without seeds.
• **in animals: regeneration

• Have both male and female reproductive parts
• Variation on sexual reproduction

• Example:
• Pea plants
• Earthworms

• Mitosis:
• diploid
• all the same
• all other cells

• Meiosis:
• haploid
• sex cells
• all different