1. Mendel’s Laws of Heredity
Why we look the way we look...

2. What is genetics?
Genetics is the study of heredity, how traits are passed from parent to offspring

3. The father of Genetics Gregor Mendel
His most famous experiment was done with pea plants.
Was an Austrian Monk that lived in the mid 1800s
Mendel observed that the height of pea plants varied
Mendel crossed different size plants to see if he could predict the height of the offspring

4. Mendel’s cross between tall pea plants yielded all tall pea plants
Mendel’s cross between tall pea plants yielded all tall pea plants. His cross between small pea plants yielded all small pea plants.
Mendels’ cross between tall pea plants and small pea plants yielded all tall pea plants. X = x

5. Mendel then crossed these second generation tall pea plants and ended up with 1 out 4 being small.x =

6. Lets Start heredity

7. These are my parents, who do I look like?

8. My dad?

9. My Mom?

10. What is heredity?
The passing on of characteristics (traits) from parents to offspring
Genetics is the study of heredity

11. Mendel used peas... They reproduce sexually
They have two distinct, male and female, sex cells
Their traits are easy to isolate

12. Mendel crossed them
Fertilization - the uniting of male and female gametes
Cross - combining gametes from parents with different traits

13. Questions What did Mendel cross? What are traits? What are gametes?
What is fertilization?
What is heredity?
What is genetics?

14. Rule of Unit Factors Each organism has two alleles for each trait
Alleles - different forms of the same gene
Genes - located on chromosomes, they control how an organism develops

15. Rule of Dominance
The trait that is observed in the offspring is the dominant trait (uppercase)
The trait that disappears in the offspring is the recessive trait (lowercase)

16. Law of Segregation
A parent randomly passes only one allele for each trait to each offspring

17. Questions... How many alleles are there for each trait?
What is an allele?
How many alleles does a parent pass on to each offspring for each trait

18. Questions... What do we call the trait that is observed?
What case (upper or lower) is it written in?
What about the one that disappears?
What case is it written in?

19. Phenotype & Genotype Phenotype - the way an organism looks
red hair or brown hair
genotype - the gene combination of an organism
AA or Aa or aa

20. Heterozygous & Homozygous
Heterozygous - if the two alleles for a trait are different (Aa)
Homozygous - if the two alleles for a trait are the same (AA or aa)

21. Monohybrid
Monohybrid Cross - crossing parents who differ in only one trait (AA with aa)

22. Questions... What is the phenotype? What is the genotype?
What is homozygous?
What is heterozygous?
What is monohybrid crossing?

23. Let’s Practice –Take a look at the genetics behind getting a widows peak
Dominant and Recessive Genes
A dominant gene will always mask a recessive gene.
A “widows peak” is dominant, not having a widows peak is recessive.
If one parent contributes a gene for a widows peak, and the other parent doesn’t, the off spring will have a widows peak.
Widows Peak
This is lily Munster

24. Genetics
All organisms have two copies of each gene, one contributed by the father, the other contributed by the mother.
Homozygous - Two copies of the same gene
Heterozygous - Two different genes

25. Genetics For the widows peak:
WW - has a widows peak Homozygous dominant
Ww - has a widows peak Heterozygous
ww - no widows peak Homozygous recessive

26. Genetics
Since Herman has no widows peak, he must be “ww”, since Lilly has a widows peak she could be either “WW” or “Ww”
Definitely ww Homozygous
recessive
Either Ww Heterozygous
or WW Homozygous dominant

27. Genetics
We can use a “Punnet Square” to determine what pairs of genes Lilly has
A Punnet Square begins with a box 2 x 2
One gene is called an “allele”
One parents pair is split into alleles on top, the other along the side
Each allele is crossed with the other allele to predict the traits of the offspring
Assume Lilly is heterozygous Ww W w
Assume Herman is homoozygous recessive ww w Ww ww w Ww ww

28. Genetics
Notice that when Lilly is crossed with Herman, we would predict that half the offspring would be “Ww”, the other half would be “ww”
Half “Ww”, Heterozygous, and will have a widows peak
Half “ww”, Homozygous, and will not have a widows peak W w w Ww ww w Ww ww

29. Genetics
Another possibility is that Lilly might be “WW”, homozygous dominant.
Assume Lilly is homozygous dominant WW W W
Assume Herman is homoozygous ww
Notice that all the offspring are heterozygous and will have a widows peak w Ww Ww w Ww Ww