2. Mendelian Heredity (Fundamentals of Genetics) Chapter 9

3. Heredity The transmission of characteristics from parent to offspring.
Trait- variant of a characteristic
Mendel observed 7 characteristics of pea plants.

4. Characters vs. Traits

5. Mendel’s Methods
Mendel observed traits by controlling how pea plants were pollinated.
Pollination occurs when pollen grains (male) are transferred to the stigma (female.
Normally, self-pollination occurs
Mendel utilized cross-pollination, prevented self- pollination
The offspring of a “cross” will have characteristics from both “parents”
Hybrid

6. Manual Cross-Pollination

7. Mendel’s Experiments
Used pea plants, easy to grow and quick to reproduce
Began by growing true-breeding (purebred) plants
Always produce offspring with that trait when they self- pollinate
Cross-pollinated pairs of plants that were true-breeding for contrasting traits of a single characteristic
Parents were P generation
Offspring were F1 generation
F1 offspring then self-pollinated  F2 generation

9. Mendel’s Laws of Heredity
Each trait is controlled by a pair of factors
Dominant (Capital letter)
Recessive (Lowercase letter)
Law of Dominance - One factor (trait) in a pair may mask the effect of the other.

11. Mendel’s Laws of Heredity
Each reproductive cell gets one factor of each pair
When two gametes combine, the offspring has two factors for each characteristic
Law of Segregation - The two traits for a characteristic separate during the formation of eggs and sperm.

12. Mendel’s Laws of Heredity
Factors for individual characteristics are not connected (Anaphase I)
Ex. Flower color vs. seed color (Green pods on a white plant)
Law of Independent Assortment - The traits for different characteristics are distributed to reproductive cells independently.

13. Genotype and Phenotype
Genotype- organism’s genetic makeup
Ex. Genotype of a white-flowering plant consists of two recessive alleles for white color, pp.
Ex. Genotype of a purple-flowering plant can either be PP or Pp.
Phenotype- organism’s appearance
Ex. Phenotype of a PP or Pp pea plant is purple flowers.
Ex. Phenotype of a pp pea plant is white flowers.

14. Genetic Terms Homozygous- both alleles of a pair are alike
Dominant PP
Recessive pp
Heterozygous- two alleles in the pair are different
Heterozygous for flower color- Pp (Purple)

15. Using Punnett Squares Punnett Square
Model that predicts the likely outcomes of a genetic cross with the alleles taken from the parents
Shows all the genotypes that could result from a given cross

16. Monohybrid Cross Contrasting traits (purple vs white flower)
Homozygous Cross (PP or pp)
Heterozygous Cross (Pp)
Paternal alleles across the top
Maternal alleles down the left side