2. Mendelian Heredity (Fundamentals of Genetics) Chapter 9

3. Heredity The transmission of characteristics from parent to offspring.
Trait (allele)- 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 (alleles)
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 (allele) 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 A cross in which only one characteristic is tracked
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

17. Using Probability Likelihood that a specific event will occur
Probability = # of one kind of possible outcomes
total # of all possible outcomes
Probability of a specific allele in a gamete
Represented as a fraction or ratio

18. Punnett Square Practice
1. Homozygous x Homozygous
Cross between a pea plant homozygous for purple flower color (PP) and a pea plant homozygous for white flower (pp)
2. Homozygous x Herterozygous
Cross between a guinea pig that is homozygous dominant for the trait of black coat color (BB) and a guinea pig that is heterozygous for this trait (Bb)
3. Heterozygous x Heterozygous
Cross between two rabbits that are heterozygous for coat color. In rabbits, the allele for black coat color (B) is dominant over the allele for brown coat color (b).

19. Many Genes, Many Alleles
Polygenic Inheritance
Example: Eye Color
Several genes affect the characteristic
Relative greenness or brownness, blue eyes are recessive
Incomplete Dominance
Intermediate between traits
Example: Snapdragon (red and white = pink)

20. Many Genes, Many Alleles
Codominance
Both alleles for the same gene are fully expressed
Example: Roan Shorthorn Cattle
Multiple Alleles
3 or more possible alleles, only two alleles for a gene can be present
Complex dominance
Example: Blood types and Labrador coat color

21. Heredity & The Environment
Genes can be affected by the environment
Nutrients and temperature
Personality and behavior

22. Uses for Heredity Pedigrees Several generations
Determine genetic disorders or diseases that can be inherited
Can answer questions about the three factors of inheritance
Sex-linked genes
Dominant or Recessive
Heterozygous or Homozygous