1. Genetics & Heredity
Mendel and His Peas

3. Gregor Mendel
Heredity – the passing of traits from parents to offspring
Gregor Mendel – “father of genetics”
Austrian monk
performed experiments on peas to help answer questions about genetics
Genetics – the study of how traits are passed from parents to offspring

4. Mendel’s First Pea Experiment
Cross-pollinated
Purple flowers x purple flowers = all purple flowers
White flowers x white flowers = all white flowers
Purple flowers x white flowers = all purple flowers

5. Mendel’s Second Pea Experiment
Self-pollinated the hybrid flowers from the first generation (the offspring that were a result of the purple flowers x white flowers)
Results:
some offspring were purple and some were white

6. Mendel’s Conclusions Dominant and Recessive Dominant Trait
a genetic factor that blocks another genetic factor (ex. purple color (P))
Recessive Trait
a genetic factor that is blocked by the presence of a dominant factor (ex. white color (p))
recessive trait is observed only when two recessive genetic factors are present in offspring (pp)

7. Ratios A comparison of two numbers or quantities by division Try it:
The ratio of purple to white flowers in Mendel’s second experiment is 3 to 1 or 3:1 or 3/1
Try it:
There are 14 girls and 7 boys in a classroom. What is the ratio of girls to boys? Boys to girls?

8. Inheritance

9. Genes & Alleles
Gene – a section on a chromosome that has genetic information for one trait
ex. flower color
Allele – the different forms of a gene
ex. purple, white

10. Genotype & Phenotype Phenotype – how a trait appears, or is expressed
ex. purple flowers, blue eyes, red hair
Genotype – the two alleles that control the phenotype of a trait
expressed as letters
uppercase for dominant
lowercase for recessive

11. Homozygous and Heterozygous
Homozygous – when the two alleles of a gene are the same
homozygous dominant - purple flowers (PP)
homozygous recessive - white flowers (pp)
Heterozygous – when the two alleles of a gene are different
ex. purple flowers (Pp)

12. Punnett Squares
Punnett square – a model used to predict possible genotypes and phenotypes of offspring
expressed as a probability (percent chance)
Phenotype:
Green = 75%
Yellow= 25%
Genotype:
GG = 25%
Gg = 50%
Gg = 25%

13. Punnett Square Examples

14. Draw a Punnett square for the following breeding pair of frogs: Gg x Gg
If green skin (G) is dominant to yellow skin (g), what is the probability of the offspring being green?

15. Try Some Punnett Squares:
Brown eyes (BB) x Blue eyes (bb)
Freckles (Ff) x no freckles (ff)

16. Pedigree
Pedigree – a chart that shows phenotypes of genetically related family members
Symbols:
MALE
FEMALE
Homozygous Dominant
Heterozygous
Homozygous recessive

17. Pedigree Example

18. Patterns of Inheritance

19. Types of Dominance
Incomplete Dominance – when the phenotype of an offspring is a combination of the parents’ phenotype
ex. white flower x red flower = pink flower
Codominance – when two alleles can be observed in a phenotype
ex. white cow x black cow = spotted cow

20. Other Patterns of Inheritance
Multiple Alleles
genes with more than two alleles
ex. blood type (A, B, AB, O)
Sex-linked Traits
alleles found on the sex chromosomes (X, Y)
Polygenic Inheritance
when multiple genes determine the phenotype of a trait
ex. height