1. Human Reproduction and Alleles
Genetics Week 2

2. I Can…
I Can#12: explain that sexual reproduction produces offspring that inherit half their DNA from each parent.
I Can#13: describe the difference between a diploid and a haploid cell.
I Can #14: explain how genes are carried from parents to their offspring on chromosomes

3. How many pairs of chromosomes does the human cell have?
Human Chromosomes
Within the nucleus of almost every human cell there are 46 chromosomes.
These chromosomes come in pairs.
How many pairs of chromosomes does the human cell have?
23 pairs

4. What is a diploid cell?
We say that cells with the full set of 23 pairs or 46 total chromosomes are DIPLOID.

5. Chromosomes and Life
When a child is missing a chromosome or has an extra chromosome serious complications can occur.
Example: Down Syndrome

6. Chromosomes and Reproduction
So, how do humans get the full set of 46 chromosomes?

7. Chromosomes and Reproduction
Because humans reproduce through sexual reproduction, they inherit half or 50% of their DNA from each parent.
SO, they inherit 23 chromosomes from each parent.
What if they mated ppt.?

8. Inheriting Chromosomes
But if human cells have 46 chromosomes each, how does the baby end up with the correct number of chromosomes? 92
46 from Dad
46 from Mom + =
YIKES!!

9. Sex Cells
Sex cells, the SPERM and the EGG, are special cells because each of these cells contains only 23 chromosomes.

10. Sex Cells
Because each sex cell has only 23 chromosomes we say they are HAPLOID (think “HAlf-diPLOID”
46/2= 23

11. What will the baby look like?
Because chromosomes carry genes, when the two sex cells meet and the chromosomes form pairs--the baby ends up with 2 alleles for each trait.
DAD’S
MOM’S

12. Girl or Boy?
SEX CHROMOSOMES: are one of the 23 pairs of chromosomes in each body cell.
The SEX CHROMOSOMES carry genes that determine whether a person is male or female.

13. XY It’s a BOY If you are a boy, your two sex chromosomes do not match.
One of them is an X chromosome, and the other is a Y chromosome. XY

14. XX It’s a GIRL If you are a girl, your two sex chromosomes match.
The two sex chromosomes are called X chromosomes. XX