Mendel and Genetics

1. Chapter 14 Mendel and Genetics

2. Mendel and Heredity • Gregor Mendel – Austrian Munk • Worked with heredity in pea plants • Wanted to determine how characters and traits were passed from generation to generation • Advantages of pea plants: • Short generation • Large offspring production • “either or” traits • Self pollinating • True breeding

3. Mendel’s Cross Fertilization Experiments • Crossed 2 distinct versions • Created a hybrid • True breeding plants were P-generation • Offspring were the F1 • If F1 self pollinated the result was the F2

4. Monohybrid Cross • Four principles revealed: • Alternate versions of genes account for variations - alleles • For each character, organisms inherit 2 copies, one from each parent • Alleles may be dominant or recessive • Law of segregation

5. Punnett Square • Used as a predictive tool to show potential offspring • Alleles are combined to show possible genetic outcomes • Homozygous dominant • Heterozygous • Homozygous recessive

6. Test Cross • Used by current geneticists to determine genetype • Use of a homozygous recessive crossed with the unknown • P? x pp • If all purple – PP • If half purple, half white - Pp

7. Law of Independent Assortment • Do alleles tend to follow one another? • Mendel paired two traits together and crossed • AABB x aabb (F1) • The resulting heterozygotes were then allowed to self pollinate (F2) • Dihybrid cross • 9:3:3:1

8. Probability Rules • Probability scale – 0-1 • 1 = event is certain to occur • 0 = event is certain not to occur • Multiplication rule – used for two or more independent events (Ex. Chance of having 5 boys in a row) • ½ x ½x ½ x ½ x ½ = 1/32 • Addition rule – used for mutually exclusive events (Ex. Male vs. female) • ¼ = ¼ = ½

9. Degrees of Dominance • Alleles can show different degrees of dominance/recessive • Incomplete dominance is when neither allele is completely dominant (blended) • Codominance is when two alleles affect the individual in separate, distinguishable ways

10. Relationship Between Genotype and Phenotype • Alleles can looked at on three phenotipic levels • Ex. Tay Sachs disease • Only children that inherit two recessive alleles have the disease- organismal level is recessive • Heterozygotes produce enough of enzyme to be normal – biochemical level is incomplete dominance • Heterozygotes also produce equal numbers of normal and dysfunctional enzymes – molecular level is codomiance

11. Multiple Alleles and Pleitropy • Some genes exist with multiple alleles • Blood type • IA, IB, I • Also codominance • Some genes can have multiple phenotypic effects • Responsible for many symptoms associated with many genetic disorders

12. Epistasis • Phenotypic expression of one gene is affected by another gene • Ex. Labs

13. Polygenic Inheritance • Quantitative characters are the result of polygenic inheritance • Multiple genes determining the resulting phenotype • Ex. Height, skin color • Alleles have a cumulative affect

14. Human Traits and Pedigree • Geneticists can not manipulate traits in humans • To analyze they use a pedigree • Using information from family history about a particular trait

15. Autosomal Recessive Disorders • To get the disorder individual must inherit both recessive alleles • Heterozygotes are called carriers • When recessive disorders are rare, highly unlikely carriers will meet and mate

16. Autosomal Dominant Disorders • Individual must inherit only one dominant allele to have the disorder • Achondroplasia • Huntington’s disease

17. Genetic Testing and Counseling • Most recessive individuals come from normal parents 9carriers) • Problems with knowing? • Insurance • Loss of jobs • Types of testing • Amniocentesis • Chorionic villus sampling

18. Genetic Screening and Testing