1. Natural Science
Genetics

2. Genetics
Genetics refers to how parents pass on traits to their offspring through genes.

3. Genotype vs. Phenotype
Genotype: the genetic code for a particular trait (the genes)
Phenotype: the expression of the trait (the appearance)

4. Human Genetics A human being’s DNA has 46 chromosomes, in pairs of 23.
You get 23 chromosomes from your mother’s egg and 23 from your father’s sperm.

5. Human Genetics
These chromosomes combine so that you will likely have some genetic traits that you share with your father and some that you share with your mother.

6. Human Genetics
Because you have genes from 2 parents, you have some traits in your DNA that may not actually display.
For example, if your parents have different eye colors from one another, you will have genetic information for both possibilities, but your eyes will actually show up as one color or the other.

7. Dominant and Recessive Traits
Some traits are more likely to show up as the visible phenotype than others.
We call these dominant traits because they overpower the recessive, or hidden, traits.

8. Dominant and Recessive Traits
DOMINANT TRAITS ARE REPRESENTED WITH CAPITAL LETTERS.
recessive traits are represented with lowercase letters.

9. Heterozygous versus Homozygous
Heterozygous means you have two different kinds of genes (called alleles).
Homozygous means you have two of the same kind of genes (called alleles).

10. H h The gene for “hair” in a guinea pig is dominant.
The gene for “no hair” in a guinea pig is recessive. H h

11. HH Hh hh

12. Hh Hh

13. The Punnett Square
One common way of looking at how traits are inherited is through a Punnett square.
These charts show the possible combinations for the traits of offspring based on the parents’ genes.

14. H h H H H h H H h h h h

15. H h H H H h H H h h h h Probability Phenotype: Hair: 3 out of 4 = 75%
No Hair: 1 out of 4 = 25% H h h h
Genotype:
HH: 1 out of 4 = 25%
Hh: 2 out of 4 = 50%
hh: 1 out of 4 = 25% h

16. HH hh

17. h h H h H h H H h H h H

18. h h H h H h H H h H h H Probability Phenotype: Hair: 4 out of 4 = 100%
No Hair: 0 out of 4 = 0%
Genotype:
HH: 0 out of 4 = 0%
Hh: 4 out of 4 = 100%
hh: 0 out of 4 = 0% H h H h H

19. Homework: Punnett Square Practice!