1. Probability and Punnett Squares

2. Probability
Probability a number that describes how likely it is something will happen
Can be expressed as a ratio, fraction, or percentage
When you flip a coin, you have what probability of getting heads?
1 out of 2
1 : 2 (ratio)
½ (fraction)
50% (percentage)

3. Asexual Reproduction One parent
Produces offspring that are clones, or identical, to the parent and each other
The offspring get an exact copy of the parents DNA

4. Sexual Reproduction Involves two parents
Each parent gives ONE copy of each chromosome to the offspring
Result is offspring with a genetic combination of the two parents

5. Formation of Sex Cells & Fertilization
When the sex cells are produced, they only receive one chromosome at random from each pair of chromosomes.
This results in different combinations of alleles in each sex cell.
The sex cells combine to produce offspring with one full set of chromosomes.
This leads to variation in the traits of the offspring due to different combinations of the chromosomes

6. Punnett Squares
Chart that shows all the possible outcomes of a genetic cross – allows you to determine the probability

7. Determining genotype and phenotype ratios from a Punnett square
Genotype Ratios
1 GG : 2 Gg : 1 gg
25% GG, 50% Gg, 25% gg
Phenotype Ratios
3 Green : 1 white
75% Green, 25% white

8. Practice!!! In humans, brown eyes are dominant to blue eyes.
Cross a heterozygous brown eyed female with a blue eyed male. Give genotype and phenotype ratios
Genotypes : 50 % Bb , 50 % bb
Phenotypes: 50% Brown, 50 % blue

9. A heterozygous black rabbit (Bb) is crossed with a homozygous black rabbit (BB). What are the possible genotypes of this cross?
B b
Possible Genotypes = B

10. Two heterozygous parents for hair type have children (Ss x Ss)
Two heterozygous parents for hair type have children (Ss x Ss). What is the probability the children will have straight hair? What is the probability they will have curly hair?
S s
Straight Hair=
Curly Hair= S s

11. A heterozygous yellow pea plant (Yy) is crossed with a green pea plant (yy). How many of the offspring are homozygous recessive? How many are heterozygous?
Y y
Homozygous recessive=
Heterozygous= y