1. Meiosis & Chromosomes
Chapter 10.1 and 11.3

2. Chromosome Structure
DNA coils around histones (proteins) to form nucleosomes,
This coils to form chromatin fibers.
The chromatin fibers supercoil to form chromosomes that are visible in the metaphase stage of mitosis.

3. How many chromosomes do we have in our cells?
Human body cells have 46 chromosomes
Each parent contributes 23 chromosomes
Homologous chromosomes - a pair of chromosomes that have the same genes

4. Homologous Chromosomes
-Same length
-Same centromere position (middle)
-One maternal and one paternal chromosome

5. Homologous Chromosomes
Carry the same genes that control the same inherited traits
Alleles are the variations of one gene
Ex: eye colors can brown, blue, green, hazel, etc….
You inherit one chromosome from each parent!

6. DO NOW
Label the following structures:

7. Pairs #1-23 23 pairs = 46 total chromosomes
These are your chromosomes! chromosome in each pair comes from your mother and father!

8. Unduplicated homologous chromosomes Duplicated homologous chromosomes

9. Karyotyping
A micrograph that shows pairs of homologous chromosomes in decreasing size
46 chromosomes, 23 pairs
Pairs # are autosomes
Pair #23 are the sex chromosomes
XX or XY

10. Karyotype

11. Chromosomal Mutations - nondisjunction
Monosomy – Results
in a sex cell with one
less chromosome
Trisomy – Results in a sex chromosome with one extra chromosome
Chromosomal Mutations - nondisjunction

12. Do Now 1. How many autosomes? 2. How many sex chromosomes?
3. What is the sex of this patient?
4. Monosomy, Trisomy?
5. Is this individual normal?

13. Before we start genetics, let's review the process of what makes us all look different compared to our siblings, family, and classmates!

14. Sexual Reproduction
Sexual reproduction creates genetic variability. That is why we all look different and you look different from your siblings!

15. Define the following words…
Meiosis:
Sexual reproduction-production of gametes
Gamete:
Sex Cells (egg = females & sperm = males)
contain half the number of chromosomes (23)
Somatic Cells:
Body Cells
Contain 46 chromsomes

16. Haploid:
Half the chromosome number (n)
1 of each pair of chromosomes (23)
Gametes are haploid
Diploid:
2 of each type of chromosome (2n)
Somatic cells are diploid
Fertilization:
Sperm enters egg
Zygote:
Fertilized egg (diploid)

17. Can you apply terms learned on the past few slides to this picture?
Think - Pair - Share
Can you apply terms learned on the past few slides to this picture?

18. Meiosis The sexual life cycle in animals involves meiosis
Meiosis produces gametes (23 chromosomes).
When gametes combine in fertilization, that creates a zygote.
A zygote has 46 chromosomes

20. Meiosis 2 Divisions Meiosis I - separation of homologous chromosomes
Meiosis II - separation of sister chromatids

21. DNA Replication before Meiosis 1
Before Meiosis begins, all DNA must be replicated

22. Meiosis 1
Crossing over occurs
Homologous chromosomes separate, randomly!
46 Duplicated
23 duplicated
Crossing over = the exchange of genes between homologous chromosomes, resulting in a mixture of parental characteristics in offspring.

23. Crossing over
The same genes “switch”, which allows for unique gametes to form, different from the exact chromosomes given from the mother and father.
Occurs during Meiosis 1, Prophase 1

25. Each gamete has a unique combination of genes!
Meiosis 2
Sister chromatids separate into 4 different gametes, randomly.
23 duplicated
Each gamete has a unique combination of genes!
23 unduplicated chromosomes in each gamete

27. Meiosis 1 & 2 - Females (Eggs) and Males (Sperm)

28. What creates genetic variability?
Crossing over - switching of genes during meiosis 1 creates a unique combination of genes
Independent Assortment - chromosomes separate into gametes randomly during meiosis 1 and meiosis 2
Random Fertilization - random sperm and egg combine to make a unique gamete