1. Meiosis and Karyotypes

2. Somatic Cells v. Gametes
Somatic – body cells
Ex. Skin, liver, eyeballs
Gametes – sex cells
Ex. Egg or sperm (DNA here gets passed on to your kids!)

3. We have 46 total.
We get 23 from mom, 23 from dad – so we have two pairs of 23. Get it?
Each pair in the set is genetically identical, unless a mutation occurs.
Homologous chromosomes – two chromosomes (one from ma, one from pop) that look the same, are the same length and HAVE THE SAME GENES.

4. Autosome v. Sex Chromosome
Autosomes – Contain genes not directly related to your sex.
Humans have 44 (Chromosome pairs 1-22)
Sex chromosomes – directly control development of sexual characteristics
Pair #23
Humans have two options: X, Y
XX = female
XY = male

5. Sexual Reproduction v. Asexual Reproduction
Remember we called mitosis a form of asexual reproduction. The cells are identical. We use it for growth and repair all the time!!
Sexual reproduction involves fusing two gametes to make a genetic MIXTURE of both parents.
When human gametes fuse we call it fertilization.
The nucleus of the egg (23 chromosomes) fuses with the nucleus of the sperm (23 chromosomes) to make a new nucleus for a new individual (23+23 = ??)

6. Diploid v. Haploid Diploid – cell has two copies of the chromosomes
Also known as 2N
In humans, 2N or diploid = 46
Somatic cells are diploid
Mitosis
Haploid – cell has ONE copy of the chromosome
Also known as 1N
In humans, 1N or haploid = 23
Gametes are haploid
Meiosis

7. Meiosis! Two cell divisions
Dividing the nucleus to make four HAPLOID cells that are all genetically different
Involved in sexual reproduction
During Prophase 1 of meiosis crossing over (the exchange of genetic material between homologous chromosomes) occurs.
Crossing over helps ensure genetic diversity

8. Homologous chromosomes v. sister chromatids
Homologous chromosomes – get one from mom and one from dad
Similar length, carry same genes
NOT copies of each other
Divided in Meiosis 1
Sister chromatid – chromatids attached by a centromere
Divided in Meiosis 2

9. Karyotype
Picture of all the chromosomes in a cell, used to study chromosomes, help determine where genes are on chromosomes
Show changes in chromosomes – like too many or too few
Sometimes chromosomes don’t separate properly, this is called nondisjunction
Down Syndrome – extra copy of chromosome #21
Can have extra chromosomes on any pair, even sex chromosomes