1. Mendelian Genetics

2. Playing with Peas Gregor Mendel Why Peas?
Austrian Monk who lived in the 1800’s
researched heredity in pea plants
Why Peas?
Avaliable in many varieties
Can control mating

3. Mendel’s Terminology Character Trait True-bred Hybridization
heritable feature, i.e., fur color
Trait
variant for a character, i.e., brown
True-bred
all offspring of same variety
Hybridization
crossing of 2 different true-breds
Generations
P- parents
F1 (first filial)- 1st generation of offspring
F2 (second filial)- offspring of F1 generation

4. Patterns of Inheritance
Purple x purple purple offspring
White x white white offspring
Purple plant x white plant all purple offspring
Two F1 generation (purple plants) crossed3:1 ratio of purple to white

5. The Law of Segregation
Alternative versions of genes (alleles) account for variations in inherited characteristics
For each character, an organism inherits 2 alleles, one from each parent
dominant allele- fully expressed in the organism’s appearance
recessive allele- has no noticeable effect on the organism’s appearance when a dominant allele is present
The alleles for each character segregate (separate) during gamete production (meiosis).

6. Alleles Somatic cells have 2 copies of each chromosome
Could have 2 of the same or 2 different alleles
If a dominant allele is present, it will be expressed
Recessive alleles are only expressed when there are no dominant alleles
Homozygous: pair of the same alleles
Heterozygous: two different alleles for a gene

7. Genotype vs. Phenotype Phenotype an organism’s traits Genotype
an organism’s genetic makeup

8. Punnett Squares Gametes on top and left sides
Combine to predict possible offspring
Monohybrid cross
one contrasting trait
4 boxes
Dihybrid cross
two contrasting traits
16 boxes

9. Testcross
When there is a dominant phenotype, cross with a homozygous recessive to determine genotype
All dominant offspring homozygous dominant
½ dominant, ½ recessive heterozygous

10. The Law of Independent Assortment
When there is more than one trait, they will sort independently of each other
Traits are not tied together just because they came from the same parent
In a dihybrid cross, every seed shape allele combines with every seed color allele.

11. Laws of Probability
Multiply probabilities of allele segregation possibilities to get probability of each result
Add probabilities of mutually exclusive events to get probability that one or the other will occur

12. Special Cases
Incomplete dominance: appearance between the phenotypes of the 2 parents. Ex: snapdragons
Codominance: two alleles affect the phenotype in separate, distinguishable ways. Ex: M and N blood groups

13. Not all traits are simple to figure out…
Multiple alleles: more than 2 possible alleles for a gene Ex: human blood types
Pleiotropy: genes with multiple phenotypic effects Ex: sickle-cell anemia

14. Multiple genes for one trait
Epistasis: a gene at one locus (chromosomal location) affects the phenotypic expression of a gene at a second locus. Ex: mice coat color
Polygenic Inheritance: two or more genes affect the phenotypic character Ex: human skin pigmentation
Quantitative characters (blending)

15. Nature vs. Nurture Some phenotypes are multifactorial
Genetics and the environment both influence the phenotype
Ex: Soil pH determines hydrangea color

16. Pedigree Analysis Can trace traits throughout a family tree
Males =  Females = O
Lines between males and females= mating
Children in order of birth from left to right

17. Genetic Disorders Recessive disorders: Dominant disorders:
Cystic fibrosis
Tay-Sachs
Sickle-cell Anemia
Dominant disorders:
Huntington’s
Polydactyly
Achondroplasia
Testing: •amniocentesis •chorionic villus sampling (CVS)