1. Meiosis Basic Info

2. Who do we look like? Do you look like your mom or dad?
Why do people who are related to us have similar characteristics?

3. Genes Each chromosome contains hundreds of genes
Gene = a segment of DNA that determines characteristics and functions of a cell

4. Chromosomes
Each species has to have a certain number of chromosomes in its cells
Species size & complexity
does NOT determine
chromosome number
Two types of chromosomes:
Sex Chromosomes (X and Y)
Autosomal chromosomes (all others)

5. Diploid vs. Haploid 46 = diploid
Somatic cells (body cells) = diploid = 2n
2 copies of each chromosome
Gametes (sex cells) = haploid = 1n
1 copy of each chromosome
Fertilization – when two haploid gametes join to produce a diploid cell (zygote)
23 = haploid
23 = haploid
46 = diploid

6. Diploid vs. Haploid

7. Chromosome Numbers Organism Somatic Cell Gamete Fruit Fly 8 4 Corn 2010
Human 46 23
Dog 78 39
Adder’s tongue fern
1260
630

8. Homologous Chromosomes
In a diploid cell, there are 2 copies of each chromosome
Homologous Chromosomes = contain genes for the same trait, but can have different versions (alleles) of that trait
(same length & centromere position)
Homologous Chromosome Video End at 1:08

9. Homologous Chromosomes
Height
(short)
Height
(tall)
Hair type
(straight)
Hair type
(curly)
Eye color
(brown)
Eye color
(blue)
From Mom
From Dad
Earlobes
(attached)
Earlobes
(unattached)
Hair color
(blonde)
Hair color
(brown)

10. *Sister chromatids are identical *Homologous chromosomes are similar
What is the difference between sister chromatids and homologous chromosomes?
*Sister chromatids are identical
*Homologous chromosomes are similar

11. Mitosis vs. Meiosis Mitosis produces EXACT copies of cells
Meiosis produces cells that are genetic variations that have only HALF the number of chromosomes
Mitosis – produces 2 identical diploid somatic cells
Meiosis – produces 4 variations of haploid gametes

12. If cells tried to use mitosis to make gametes?
92! 46 46 +
egg
sperm
zygote
Doesn’t work!

13. Why do we need meiosis? 46 46 Must reduce 46 chromosomes  23 46
zygote
egg
meiosis 46 46
fertilization 23
sperm

14. Gametogenesis – when cells use meiosis to make gametes
Two Types
Spermatogenesis – males produce sperm
(about 250,000,000 sperm per day)
Oogenesis – females create eggs
produce 3 polar bodies and 1 egg
Polar bodies don’t develop due to unequal division of cytoplasm

16. Ovulation = egg released from ovary