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

** 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

Recall MitosisRecall Mitosis

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)

Above are Homologous Chromosomes - Same chromosome with same types of genes on each chromosome, just different variations from each parent

Replicates

Meiosis and The Human Life Cycle

FROM MOM

FROM DAD

Meiosis Overview**Required for Sexual Reproduction

**Results in 4 NON-IDENTICAL haploid (n) cellsGenetic recombination creates genetic variability in

either sperm or egg For each meiotic division, 4 sperm are produced

but typically only 1 egg survives

**Produced in the ovaries (females) and testes (male)

**Diploid cells divide twice to produce haploid (n) sperm or egg (each have 23 chromosomes)

Meiosis Phases

**Meiosis II Prophase II, Metaphase II, Anaphase II, Telophase II and cytokinesis

**4 cells, the gametes!!

**Meiosis I Prophase I, Metaphase I, Anaphase I, telophase I

**After interphase (DNA replication phase)

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

From your From yourDad 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

After Meiosis 1 After M

eiosis 2 o

ccurs th

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no

n-id

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aplo

id sp

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r egg

cells called

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etes

Meiosis occurs in 2 phases. Meiosis 1 and Meiosis 2 with cytokinesis following. The process results in 4 non-identical haploid cells

Meiosis I

Meiosis II

Genetic Recombination

Genetic Recombination During Meiosis

**independent assortment of homologous chromosomes

** A reassortment of chromosomes and genetic information they carry

**crossing over between non-sister chromatids during Prophase 1

Crossing Over

**Non-sister chromatids exchange

genetic information

**Pink is from your mom, blue

from your dad

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• 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

Meiosis • 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 (asexual reproduction) vs. Meiosis (sexual Reproduction)

MitosisMeiosis