18 Background Information Chromosome NumbersHaploid or NHumans 23 Haploid number (N)Chromosomes are in pairsHumans have a total of 46 chromosomes or 2N (diploid)Meiosis reduces 2N to NThus when sperm and ova meet and combine at fertilization the resulting embryo will have 2N
19 How else do cells reproduce? Meiosis is the reproduction of animal sex cellsOva and spermHappens in two stagesTwo divisions of the cell compared to only one division in mitosisEnd up with four haploid cells
20 Stages of Meiosis I Prophase I Chromosomes thicken and becomes visible Chromosomes are present in homologous pairs
21 Stages of Meiosis I Metaphase I Homologous pairs line up on the axis of the dividing cell opposite from each other.
22 Stages of Meiosis I Anaphase I Homologous pairs of chromosomes leave each other and are pulled towards opposite poles by spindle fibers
23 Stages of Meiosis I Telophase I The cells physically divide Each daughter cell now contains one chromosome from each pairReduction DivisionNumber of chromosomes is reduced from diploid to haploid.
24 Stages of Meiosis II Prophase II Chromosomes still duplicated
25 Stages of Meiosis II Metaphase II Sister chromatids line up on the axis of the cell.
26 Stages of Meiosis II Anaphase II The sister chromatids are pulled apart at the centromere by spindle fiber
27 Stages of Meiosis II Telophase II Nuclear membrane reforms Each of the four final haploid cells or gametes contain one strand from the original homologous pair of chromosomes.