Meiosis with Mitosis Review and Comparison (Chapters 8 and 10)

Recall Mitosis ** Mitosis is asexual reproduction & occurs ONLY in regular old body cells called SOMATIC CELLS (skin, nails, your pancreas, etc..) NOT sperm and eggs  ** Produces two identical diploid (2n) cells

Diploid Chromosomes We call somatic cells diploid (2n) meaning you have 2 copies of each chromosome (1/2 from mom and ½ from dad) Autosomal chromosomes are non-sex chromosomes These contain genes that have nothing to do with determining your sex Each of your cells contain 44 autosomal chromosomes and 2 sex chromosomes (XX for female and XY for male) for a total of 46 chromosomes in each nuclei of your cells

Cell Cycle – Diploid (2n), Somatic Cells (Body Cells)

Mitosis Produces Identical, Diploid Daughter Cells (46 chromosomes in the nuclei of the cells) Replicates Above are Homologous Chromosomes - Same chromosome with same types of genes on each chromosome, just different variations from each parent

Meiosis and The Human Life Cycle FROM MOM FROM DAD

Meiosis Overview **Required for Sexual Reproduction **Diploid cells divide twice to produce haploid (n) sperm or egg (each have 23 chromosomes) **Produced in the ovaries (females) and testes (male) **Results in 4 NON-IDENTICAL haploid (n) cells Genetic recombination creates genetic variability in either sperm or egg For each meiotic division, 4 sperm are produced but typically only 1 egg survives

Meiosis Phases **After interphase (DNA replication phase) **Meiosis I  Prophase I, Metaphase I, Anaphase I, telophase I **Meiosis II  Prophase II, Metaphase II, Anaphase II, Telophase II and cytokinesis **4 cells, the gametes!!

Fertilization When egg and sperm fuse we say the egg is fertilized creating one, single diploid cell called a zygote Although numerous sperm attempt to fertilize the egg, only one will succeed Diploid zygote – will undergo mitosis

Sex Chromosomes Male = XY Female = XX

Meiosis occurs in 2 phases Meiosis occurs in 2 phases. Meiosis 1 and Meiosis 2 with cytokinesis following. The process results in 4 non-identical haploid cells After Meiosis 2 occurs the result is 4, non-identical haploid sperm or egg cells called gametes After Meiosis 1 From your From your Dad Mom Replication Homologous chromosomes – SAME chromosome type (have the same types of genes) A tetrad is formed Crossing Over between non-sister chromatids During Prophase 1 of Meiosis 1 – Results in genetic recombination

Meiosis I

Meiosis II

Genetic Recombination

Genetic Recombination During Meiosis ** A reassortment of chromosomes and genetic information they carry **crossing over between non-sister chromatids during Prophase 1 **independent assortment of homologous chromosomes

Crossing Over **Pink is from your mom, blue from your dad **Non-sister chromatids exchange genetic information

Sister Chromatids of Homologous Chromosomes Cross Over

Independent Assortment leads to genetic variability- homologous chromosomes are sorted before shipment to gametes independently of how the other pairs were sorted

Meiosis Square Dance

Problems During Meiosis

Non-Disjunction **chromosomes of a homologous pair (tetrad) fail to separate and move to the same pole of the cell. Some gametes may have an extra chromosome while others lacking ** Down syndrome occurs because of this. Called trisomy 21, there are 3 of chromosome #21 rather than a pair!

Karyotypes – Pictures of a person’s Chromosomes – Show Abnormalities Male with no chromosomal abnormalities

Abnormal Karyotype Trisomy 18 – Due to Non-disjunction

Compare Mitosis to Meiosis

Mitosis (asexual reproduction) vs. Meiosis (sexual Reproduction) Occurs in 2 stages Produces 4 genetically different haploid cells (genetic recombination) For Sexual Reproduction Produces genetically variability due to recombination Occurs in sex cells called gametes or germ cells and four haploid cells (sperm and egg) n=23  22 autosomal chromosomes and 1 sex chromosome Forms a tetrad Mitosis Occurs in 1 stage Produces 2 genetically identical diploid cells It is Asexual Reproduction Produces “clones” with no genetic variability Occurs in body cells (autosomal) and creates two diploid cells 2n=46  22 pair of autosomal chromosomes and 1 pair sex chromosomes

Mitosis Meiosis