The Legacy of Gregor Mendel: Foundations of Genetics and Inheritance Patterns

1. Genetics Chapter 11

2. Gregor Mendel • “Father” of genetics • Austrian monk, mid-1800s • Researched pea plant inheritance • Easy to grow, fast reproduction • Studied plant height, pea shape/color, pod color, etc.

4. Pea Plant Reproduction • Self-pollination • Male gametes (pollen) fertilize egg of same flower • Produces pure-bred offspring • True-breeding: produce offspring identical to parent when self-pollinated

5. Pea Plant Reproduction • Cross-pollination • Pollen from one plant fertilizes egg of another plant • Offspring have two parents

6. Mendel’s Experiments • P = Parent generation • F1 = First filial generation • F2 = Second filial generation (F1 X F1) P Pure Green X Pure Yellow F1 All Green F2 3 Green:1 Yellow

8. Mendel’s Conclusions • Law of Dominance – one allele (form of a gene) is dominant, one is recessive • Recessive trait was hidden in F1 generation • Green = dominant • Yellow = recessive

9. Mendel’s Conclusions • Law of Segregation: alleles for a gene separate when gametes form (meiosis I) • Each gamete gets one copy of each gene

10. Some Vocab. • Genotype – allele combination • Capital letter = dominant allele • Lowercase letter = recessive allele • Ex – AA, Aa, aa • Phenotype – physical appearance • Ex – green, yellow

11. Some Vocab. • Homozygous – two alleles same • Homozygous dominant: AA • Homozygous recessive: aa • Heterozygous – two alleles different • Aa

12. Punnett Squares • First must determine possible gametes • Heterozygous tall plant = Tt • Half of gametes will get ‘T’, other half will get ‘t’ • Homozygous tall plant = TT • All gametes will get ‘T’

13. Monohybrid cross Cross involving one trait Gametes go on the top and side Combine gametes to find possible offspring Punnett Squares Tt X Tt

14. Punnett Squares Tt X Tt • Genotype ratio 1TT: 2Tt: 1tt • Phenotype ratio 3 tall: 1 short

15. Probability • Punnett squares are used to predict the probability of certain traits in offspring of genetic crosses • Tt X Tt • ½ chance of getting ‘t’ from mom, ½ chance of getting ‘t’ from dad • ½ X ½ = ¼ tt in offspring

16. Dihybrid Cross • Mendel looked at the inheritance patterns of two traits • Seed shape and seed color • Found that the traits were inherited independently of each other • Law of Independent Assortment • Genes on separate chromosomes are inherited at random • Due to random chromosome shuffling in Metaphase I

17. Independent Assortment Metaphase I

19. Non-Mendelian Genetics • Not all traits follow Mendel’s Law of Dominance • Four Variations • Incomplete Dominance (blending) • Codominance (two phenotypes) • Multiple Alleles • Polygenic Traits

20. Incomplete Dominance • Neither allele is dominant, both produce a protein • Heterozygous phenotype is a blend of both homozygous phenotypes • Ex – wavy hair, pink flowers

21. Incomplete Dominance

22. Codominance • Neither allele dominates the other, both produce a protein • Heterozygous phenotype is a combination of both homozygous phenotypes • Ex – checkered chicken, human blood types,

24. Multiple Alleles • Some genes have more than two alleles • Each individual only gets two, but there are more than two in the population • Ex – Rabbit fur color

25. Multiple Alleles • Rabbit fur alleles (in order of dominance) • C: dark gray • cch: chinchilla • ch: himalayan • c: albino

26. Multiple Alleles

27. Polygenic Traits • Many traits are controlled by more than one gene • Traits show wide variation • Ex – human height, IQ, bell pepper colors