1. The genetic passing of characteristics from parent to offspring
Heredity
The genetic passing of characteristics from parent to offspring
Eye color
Hair color and texture
Facial features
Height

2. It’s all in the DNA…. DNA – DeoxyriboNucleic Acid Gene
Unique individual sequence of nucleotides
Only identical twins have the same sequence
Gene
A segment of DNA that codes for a protein
Humans are estimated to have 50,000 genes

3. Chromosomes the pairs are called: Homologous Chromosomes
DNA wrapped around proteins
Contain genes
Humans have 46 chromosomes in somatic (body) cells
That equals 23 pairs of chromosomes
the pairs are called:
Homologous Chromosomes

4. Homologous Chromosomes
Pairs of chromosomes with the same genes on each individual in the pair Which means….. We have two copies of each gene Those copies of the genes are called alleles

5. Where do we get our chromosomes?
We inherit 23 chromosomes from each parent
But…somatic cells have 46 chromosomes…..if two somatic cells from our parents are put together that would be 96 chromosomes!
Gametes are the solution!
Sex cells (eggs and sperm)
Have 23 chromosomes
When two gametes are put together = 46 chromosomes!
Created during Meiosis – a reduction division

6. Karyotype A visualization of the chromosomes of a somatic cell.
Used as part of amniocentesis tests
Cells are “caught” with their chromosomes condensed and duplicated during prophase.
Chromosomes are matched by size
Can see chromosome disorders using a karyotype

9. Special Names for the Number of Chromosomes
Diploid
A cell with a double set of chromosomes
All somatic cells are diploid
46 chromosomes in humans 2n
Haploid
A cell with a single set of chromosomes
All gametes are haploid
23 chromosomes in humans n

10. Diploid Cells Pair of chromosomes – 2n
Each individual of the pair has a copy of the same set of genes
We all have two alleles (copies) of a single gene
We got one allele from Mom and one from Dad

11. Can’t use Mitosis to get a haploid cell!
Meiosis
Cell division that reduces the number of chromosomes – Reduction Division
Involves two consecutive cell divisions called Meiosis I and Meiosis II

12. Meiosis I Interphase Prophase I Metaphase I Anaphase I Telophase I
Carrying out metabolic processes
Replicating DNA – condensing it into chrmosomes
Prophase I
Metaphase I
Anaphase I
Telophase I

13. Prophase I Chromosomes appear Synapsis Crossing over
sister chromatids are joined in the middle
Synapsis
Replicated homologous chromosomes pair up and form bonds
Crossing over
Chromosome segments are exchanged between homologous chromosomes
Results in greater genetic variation

14. Metaphase I
Homologous chromosomes and their sister chromatids line up on the equator (middle) of cell
Spindle fibers attach

15. Anaphase I Homologous chromosomes separate
Sister chromatids go to the poles of the cell

16. Telophase I Sister chromatids reach poles
Only one of the original homologous chromosome pair (and it’s sister chromatid –the replicated DNA is still attached) are a part of this cell
Creates two haploid cells

18. Meiosis II
During the Interphase between Meiosis I and Meiosis II –The DNA does not replicate
The cell undergoes another round of phases:
Prophase II
Metaphase II – sister chromatids line up on equator
Anaphase II – sister chromatids pull apart
Telophase II – 4 haploid cells all genetically different are created