1. Mendelian Genetics

2. A Little History (no notes)
Pangenesis
A theory that started as far back as ancient Greece.
All body parts contribute “particles” to the sperm or egg.
Believed up until the nineteenth century (Darwin)
Leeuwenhoek’s idea (mini-human sperm)
De Graaf – mini-human egg
What are the big problems with these theories?

3. Mendel comes along Austrian Monk
Discovered patterns of inheritance (used pea plants)
Gave him strict control (changing one variable at a time)

4. Mendel’s controlled breeding
Allowed self pollination to assure true breeding.
Then crossed two true bred plants for one trait.
P = parent generation
F1 = first filial
First generation

5. Then he crossed the F1 generation to obtain the F2 generation.
F2 = second generation
He found that 3 out of 4 plants produced made yellow seeds and the 4th made green seeds.

6. Some definitions
Monohybrid cross – a cross between parents that differ in one trait.
Dominant – a trait that will be expressed over another.
Recessive – a trait that will be masked if the dominant trait is present.
Allele – a trait (including it’s different forms) In other words, the different forms of a gene.
Homozygous – if the alleles of a trait are the same
Heterozygous – if the alleles of a trait are different

10. More Definitions
Phenotype – Observable trait that shows up.
Genotype – The genetic makeup.
Punnett Square – a diagram that show the result of a cross.
Dihybrid Cross – Crossing for two traits at once.

11. Try making a couple of squares
F1 (gametes)= AA x Aa
Genotypes and Phenotypes
Ratio
F1 = Aa x aa

12. Mendel’s Principals apply to Humans
Pedigree: a family tree that records and traces the occurrence of a trait in a family.
The genotypes of most of the individuals in this pedigree can be determined by examining the pattern in which the trait occurs.

13. Disorders Inherited ~ Recessive
Pedigree analysis is a more serious matter when the alleles in question cause disabling or lethal disorders.
Examples:
Albinism (lack of skin pigment)
Tay-Sachs (nerve damage)
Carrier: individual that has one allele for a disorder, but is heterozygous, and trait does not show in phenotype.

14. Disorders Inherited ~ Dominant
Affects humans much less because of dominance of disorder.
Examples:
Achondroplasia (dwarfism)
Huntington’s (nervous system)
Carrier: Individuals carry on either allele, dominant, so shows up in Homozygous Dominant or Heterozygous.

15. Disorders Inherited ~ Sex-Linked
Sex-linked disorders are only found on the x-chromosome. (Only males have Y)
Examples:
Red Green Color blindness
Muscular Dystrophy
Carrier: On the x chromosome, automatically shows up in Males, females can be carriers and never know it. Only shows if on both X’s.