Meiosis Creating Gamete Cells MEIOSIS a process by
Meiosis Creating Gamete Cells
MEIOSIS: a process by which the number of homologous chromosomes per cell is reduced by half the number and is referred to as haploid cells (n).
46 chromosomes Human female karyotype 23 pairs Meiosis only happens in Gametes ( sex cells – egg or sperm)
46 chromosomes 23 pairs Human male karyotype
What are homologous chromosomes? a similar pair of chromosomes, one from the father & one from the mother
What is a Diploid Cell? A cell that contains 2 complete sets of homologous chromosomes is said to be diploid or 2 n Brain cells Blood cells Somatic (body cells) are diploid cells. Nerve cells Liver cells
What is a Haploid Cell? A cell that contains 1 complete set of chromosomes. These are called gametes or sex cells (egg or sperm)
Meiosis: production of gametes • Alternating stages – chromosome number must be reduced • diploid haploid • 2 n n haploid – humans: 46 23 • meiosis reduces chromosome number • makes gametes – fertilization restores chromosome number • haploid diploid • n 2 n diploid
There are 2 distinct divisions of meiosis: Meiosis I Interphase I Prophase I and Metaphase I Meiosis II Anaphase I resulting in 4 haploid daughter cells with “n” number of chromosomes Telophase I Metaphase II Telephase II and Cytokinesis
Each chromosome pairs with its corresponding homologous chromosome to form a structure called a tetrad. Meiosis I - Prophase I There are 4 chromatids in a tetrad.
Overview of meiosis I. P. M. A. T 2 n = 4 interphase 1 prophase 1 metaphase 1 anaphase 1 n=2 prophase 2 metaphase 2 anaphase 2 telophase 2 n=2 telophase 1
As homologous chromosomes pair up, they exchange genetic information in a process called crossing over producing new combinations of alleles – accounting for variation among species.
Sexual reproduction creates variability Sexual reproduction allows us to maintain both genetic similarity & differences. Jonas Brothers Baldwin brothers Martin & Charlie Sheen, Emilio Estevez
Gamete Formation in Meiosis 2 n 2 n 2 n n n Sperm - male n 2 n n Polar Bodies Egg- female
Human Sperm + Human Egg Fertilization Human Zygote 23 23 46 N N 2 N Mitosis Cells Examples Meiosis Somatic (body) Gametes (sex) Skin, Blood Sperm, Egg 2 n Chromosomes Found ? All over body Cytokinesis Once n Testes, Ovaries Twice
MITOSIS MEIOSIS 2 n 2 n 2 n n n n
- Slides: 16