1. Meiosis with Mitosis Review and Comparison

2. Mitosis (asexual reproduction) vs
Mitosis (asexual reproduction) vs. Meiosis (sexual Reproduction) Overview
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
4 gametes , haploid cells (sperm and egg) formed
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

3. 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

4. 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

5. 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

6. Fertilization
A zygote is formed when one sperm and egg fuse to create a single diploid cell.
Although numerous sperm attempt to fertilize the egg, only one will succeed
Diploid zygote – will undergo mitosis

7. Sex Chromosomes
Male = XY
Female = XX

8. Meiosis I

9. Meiosis II

10. Genetic Recombination

11. Genetic Recombination: Crossing Over
A reassortment of chromosomes and genetic information they carry
**Pink is from your mom, blue from your dad
**Non-sister chromatids exchange genetic information

12. Problems During Meiosis

13. 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!

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

15. Abnormal Karyotype
Trisomy 18 – Due to Non-disjunction

16. Chromosomal Mutations
Affects an entire chromosome or chromosomes
Typically occur during meiosis (gamete formation) but can also occur during mitosis
Can lead to cancer some cases
Few harmful gene mutations are passed on to the next generation because the zygote usually dies. If it lives, the offspring may have birth defects.