1. Mendel and Heredity
Chapter 10 and 12

2. Key Terms Heredity – The passing of traits from parents to offspring
Genetics – the branch of science that studies heredity
Gene – the unit of heredity – codes for a specific trait
Gregor Mendel – the father of modern genetics
Gametes – male and female sex cells
Zygote – forms when the sperm and egg meet

3. Summary of Mendel’s Experiments
Why peas?
Characters exist in two clear forms (tall or short, purple or white flowers, etc.)
Self-fertilization is possible
Small plant
Grows easily
Matures quickly
Many offspring

4. What did Mendel do?
He self pollinated the pea plants until they were “true-breeding”
Had only one version of a trait in their genes
Only genes for purple flowers, or for being tall
This made the “P-generation” (parent generation)
He then crossed 2 different true-breeding plants and recording the results. This made the F1 generation (filial 1). These are hybrids.
Finally, he crossed 2 members of the F1 generation making the F2 generation (filial 2)

6. What was the result of Mendel’s experiment?
All members of the F1 generation displayed the dominant traits
Seemed as if one trait had disappeared!
The members of the F2 generation displayed a 3:1 ratio of dominant to recessive
The trait reappeared!

7. The Result of Mendel’s Experiments.
Mendel’s Hypotheses:
For each inherited character, a person has 2 copies of the gene – one from each parent
There are alternative versions of genes (tall/short, wrinkled/round, etc.)
When 2 alternative versions occur in the same individual, one is expressed and the other is hidden

8. Genetic Rules Rule of Unit Factor: Rule of Dominance
There are genes on chromosomes that control traits and at least 2 versions of each trait exists
Rule of Dominance
One trait is dominant to the other and masks the other gene when it is present
Law of Segregation
Traits are inherited independent of each other
Law of Independent Assortment
Homologous chromosomes sort into the gametes independently of each other

9. Some more terms Alleles –different versions of a gene
Dominant – the gene that is always expressed if it is present – capital letter
Recessive – must have 2 copies to be expressed, otherwise it is hidden by the dominant gene – lower-case letter
Homozygous – person has 2 of the same allele – TT or BB or tt or bb
Heterozygous – person has 2 different alleles – Tt or Bb

10. Phenotype
The way an organism looks
Only reveals the genotype if the recessive trait is displayed
Genotype
The genes that an organism possesses
Homozygous
Heterozygous

11. How do we determine the genotype and phenotype of the offspring
Punnett Squares!
Used to determine probability
Monohybrid
Dihybrid
Trihybrid

12. More Complex Inheritance
Incomplete Dominance – the heterozygote has a blend of the 2 traits
Codominance – both traits occur equally
Multiple Alleles – more than two alleles for a trait
Polygenic Inheritance – more than one gene controls the trait – usually shows a wide range of variation – skin color and height

13. Nature vs. Nurture The effect of the environment
Environmental effects can determine if a gene is expressed
Chemicals, stress, sunlight, nutrition, etc
Internal environment can also determine if a gene is expressed
Gender, weight, hormone imbalances

14. Sex-linked Genes On the X or Y Chromosome
Examples: Color-blindness, hemophilia, duchene’s muscular dystrophy
Disorders occur more frequently in males

16. Codominance

17. Incomplete Dominance

19. Multiple alleles

20. Semi Dominance