2Homologous Chromosomes Homologous chromosomes: pairs of chromosomes with genes for the same traits, but they can have different information about those traits
3HumansHumans have 46 chromosomes or 23 pairs of homologous chromosomes.Somatic (body) cells contain 46 chromosomes.46 is the diploid number for humans.- Diploid means that a cell has both homologs for each chromosomeSomatic cells reproduce by mitosis
4½ the chromosomes in a cell come from Mom, ½ the chromosomes in a cell come from Dad
6Reproductive CellsGametes(eggs and sperm) are called haploid because they contain one set of chromosomes.Eggs also called Ovum and sperm contain 23 chromosomes.@Eggs and sperm are produced by meiosis- a process that reduces chromosomes by
7What is Meiosis?A type of cell division where ONE diploid cell (46 chromosomes) become FOUR haploid cells(23 chromosomes each).The cells produced by meiosis are gametes (sex cells)4623232323
8Who does it? Plants Fungi Animals (including you) Males start meiosis at puberty.Females start meiosis in utero.
9Where does it occur? In your gonads Females- the ovary Males-the testicles
10Why does it occur? Genetic Variation Mixes genes from Mom and Dad to create a unique baby@Reduces the chromosome number byEnsures that each cell produced has one copy from each homologous pair of chromosomes23 in sperm + 23 in egg unite (fertilization) leads to a 46 zygote(baby)
11How does it occur? In two stages called Meiosis I and Meiosis II. Each stage contains 4 distinct phasesprophasemetaphaseanaphaseteleophasetelophase is followed by the division of cytoplasm known as cytokinesis.
12Prophase 1 Homologous chromosomes join to form a tetrad -chromosomes in the tetrad cross over and exchange genes
13Crossing Over @Crossing over produces new genetic combinations@ - It is another way to increasegenetic diversity
14Metaphase 1During Metaphase 1, the tetrads (groups of 4 homologous chromosomes) line up down the center of the cell- they assort independently-Chromosomes from eachparent line up independently of each other
15Anaphase IDuring anaphase I, spindle fibers pull each homologous chromosome pair toward opposite ends of the cell..
16Telophase I and Cytokinesis During telophase I, a nuclear membrane forms around each cluster of chromosomes.Cytokinesis follows telophase I, forming two new cells.
17Meiosis II@The two cells produced by meiosis I now enter a second meioticUnlike the first division, neither cell goes through a round of chromosome replication before entering meiosis II.
18Prophase IIAs the cells enter prophase II, their chromosomes—each consisting of two chromatids—become visible.The chromosomes do not pair to form tetrads, because the homologous pairs were already separated during meiosis I.
19Metaphase IIDuring metaphase of meiosis II, chromosomes line up in the middle of each cell.
20Anaphase IIAs the cell enters anaphase, the paired chromatids separate.
21Telophase II, and Cytokinesis These four daughter cells now contain the haploid number (N)—just two chromosomes each.
22Independent Assortment @Independent assortment increases genetic- There are 23 pairs of homologous chromosomesin humans- independent assortment ensures that there are223 possible combinations223= 8,388,608 combinations- When two gametes join to form the zygote in fertilization the possible number of combinations is223 X 223 = 64 trillion
27How is mitosis different from meiosis? Mitosis creates 2 daughter cells with same amount of chromosomesMeiosis creates 4 daughter cells with half amount of chromosomesMeiosis goes through 2 cyclesMitosis occurs in somatic cells, Meiosis in sex cells