1. Probability & Punnett Squares

2. Genetics & Probability
When Mendel crossed two hybrid plants for height, Tt, he found that ¾ of the offspring were tall, and ¼ were short.
Probability can be used to explain the results of genetic crosses.

3. What is Probability? Probability: the chance that an event will occur.
If you flip a coin, you have a 50% chance of landing on heads.
If you flip three times, each time you have a 50% chance, or ½.
The probability of landing on heads three times in a row is:
½ x ½ x ½ = 1/8
Genetic segregation is random, like flipping a coin.
The principles of probability can be used to predict the outcomes of genetic crosses.

4. Punnett Squares
Diagrams used to determine the gene combinations from a genetic cross.
The letters represent alleles.
Can be used to predict and compare the genetic variations in the cross results.

5. Example

7. Homozygous vs. Heterozygous
Homozygous: have two identical alleles for a trait.
TT, aa, ZZ, uu
Heterozygous: have two different alleles for the same trait.
Tt, Aa, Ww, Cc
Homozygous: true breeding
Heterozygous: hybrids

8. Red Flowers Ratio: 1Rr:1rr

9. Phenotype vs. Genotype Phenotype: physical characteristic.
Tall, yellow, Freckled
Genotype: genetic makeup
Tt, yy, FF
Two organisms may have the same phenotype, but not the same genotype.
Genotypes Phenotype
TT, Tt Tall

10. Ear Length on Goats L l Ll ll

11. Questions What are the phenotypes of the parents?
Long and Short
What are the genotype of the parents?
Ll & ll
What is the phenotype ratio for the offspring?
1 Long: 1 Short
What is the genotype ratios of the offspring?
1 Ll: 1ll