1. Chapter 8 Heredity

2. Basis of Genetics Gregor Johann Mendel
An Austrian monk that studied the heredity of pea plants in 1860’s.

3. Mendel’s Studies
Mendel chose peas because they have many simple traits with two phenotypes.
He studied one trait at a time.

4. Mendel’s Studies
Mendel crossed a purple flower with a white flower (P generation) and all offspring had purple flowers (F1 generation)

5. Mendel’s Studies
Mendel crossed two of the purple flowers from the F1 generation and found a 3:1 ratio of purple to white flowered plants (F2 generation)

6. Mendel’s Hypotheses
An individual has two copies of each gene. (One from each parent)
There are alternative versions of genes called alleles.
When two different alleles occur together one may be dominant and expressed completely. The masked allele is recessive.
Gametes carry only one allele for each trait.

7. Modern Terms Genotype – set of alleles (Pp)
Phenotype – expressed trait (purple)
Homozygous – two identical alleles for trait
Heterozygous – two different alleles for trait

8. Genotype Vs. Phenotype
Genotype – Phenotype – Actual genes Appearance

9. Laws of Heredity
Law of Segregation – During gamete formation, alleles for the same gene separate
Law of Independent Assortment – During gamete formation, alleles of different genes separate independently of one another (chromosomes)

10. Studying Heredity
Punnett Square – a diagram that predicts the outcome of a genetic cross.

11. Studying Heredity
Test cross – organism of dominant phenotype (but unknown genotype) is crossed with a recessive individual.
If any recessive offspring are created, parent was heterozygous.
If only dominant phenotype offspring, parent was homozygous.

12. Studying Heredity
Double Punnett square – Two traits are predicted at the same time.

13. Studying Heredity - Pedigrees
Pedigree – a family history that shows how a trait is inherited over several generations
- Helpful in families with genetic disorders.

14. Studying Heredity - Pedigrees
Pedigrees can be used to tell if a disorder is dominant or recessive
- Dominant will show up every generation
- Recessive will “skip” generations

15. Studying Heredity - Pedigrees
Pedigrees can be used to tell if a disorder is autosomal or sex-linked
- Autosomal will affect both males and females
- Sex-linked will affect mostly males

17. Probability
Probability – the likelihood that a specific event will occur

18. Patterns of Heredity
Polygenic Traits – influenced by more than one pair of genes
Skin
Hair color
Height
Intelligence
Body build

19. Incomplete Dominance Intermediate between the two phenotypes
Cross of red flower and white flower produces pink offspring

20. Codominance Both traits are expressed Roan horse – has both red
and white hair

21. Multiple Alleles Three or more alleles for a trait
ABO human blood types (also codominant)

22. Factors that Affect Gene Expression:
pH (flowers)
Diet (height)
Temperature (arctic fox or Siamese cat)
Amount of sex hormones (male pattern baldness)