Meiosis PPT

MeiosisProducing cells capable ofcombining to make a copy of anorganism

GameteForming Gametes Another name for a reproductive cell In order to end with a complete set ofchromosomes, cells must divide theirgenes into half sets One set in the male reproductive cell - sperm One set in the female reproductive cell - egg

Human reproductive cells Number of chromosomes in a normalhuman cell?46 Each reproductive cell contains 23chromosomes so that when they arecombined the will produce a cell with 46chromosomes

Haploid vs Diploid Haploid cells contain only one set ofchromosomes [half the required amount] Usually represented by the letter n n = 23 haploid human reproductive cell Diploid cells are complete cells. Eachhaving a complete set of chromosomes. 2n = 46 diploid = human organism

Haploid and Diploid cells Other Organismsfor other organismsHaploidDiploid Fruit Fly n = 4 2n = 8 Chicken n = 39 2n = Corn n = 10 2n = Pea n = 7 2n = White-tail tail Deer n = 35 2n =

A special process of cell division Meiosis A process where the number of chromosomesin the diploid cell is reduced by half to form ahaploid gamete. Similar to mitosis – meiosis 1; but nointerphase before the next division Therefore the chromatids don’t duplicate

Meiosis one Prophase 1Phases of Meiosis Chromosomes uncoil and spindle fibers form Metaphase 1 Chromosomes pair and line up in center of cell Paired chromosomes are called tetrad

Anaphase 1 Tetrads are pulled apart; one going towards eachend of the cell Crossing-over over can occur Telophase 1 Nuclear envelope reforms and cell begins to divide Two new cells begin to form But with different combinations of chromosomes End result is two haploid daughter cells

Meiosis II No DNA replication at the beginning of thisprocess Each cell contains a mixed set ofchromosomes The cell undergoes another division

Prophase II Nuclear envelope begins to dissolve Spindle fibers begin to form Metaphase II Chromosomes attach to fibers Chromosomes line up in center of cell Anaphase II Chromosome pairs split Spindle fibers begin to contract

Telophase II Two cells begin to divide Nuclear envelope begins to reform Four haploid cells produced Gametes Four haploid cells may form up to fourdaughter cells In male humans, all four develop into gametes In female humans, only one cell becomes agamete; the others are polar body’s