1. Patterns of Inheritance

2. Ancestry and Obesity In The News

3. Historical Views of Inheritance
Hippocrates (~ 400 B.C.)
Particles given off from bodies of father and mother
Offspring was mixture
Homonuculus (pre-1900)
Each sperm contained a tiny human

4. Gregor Mendel Austrian Monk Worked with garden peas
Discovered process of heredity

5. Suitability for Using Peas
Each flower has male & female parts
Sex organs are enclosed & protected
Pollination can be controlled

6. True-breeding
Generations of self-fertilization produce consistent offspring
Mendel used true-breeding varieties

7. Mendel’s Experiments Artificially crossed true-breeding plants
Recorded offspring from cross-fertilization

8. Characters Used by Mendel
7 true-breeding traits
Monohybrid crosses

10. Mendel’s Crosses Example: Tall plant crossed with short plant
Hybrid offspring (F1) were not intermediate
Resembled only one parent

11. F1 of Hybrid Cross Dominant – form expressed in F1
Recessive – form not expressed in F1

12. Mendel’s Next Step Allowed F1 to self fertilize
F2 expressed dominant & recessive forms
Ratio in F2 = 3:1 (dominant:recessive)

13. Mendel’s Monohybrid Crosses

14. Conclusions of Mendel’s Work
Traits are inherited as genes
Alleles are alternate forms of genes
Gametes receive only 1 allele of each pair
Alleles may differ or may be identical

15. Mendel’s Law of Segregation
Each gamete receives only one of an organisms pair of alleles, and which one it receives is determined by chance

16. Alleles of an Individual
Homozygous – identical alleles for a trait
Heterozygous – different alleles for a trait

17. Genotype An organisms allelic makeup
Dominant designated by capital letter
Recessive designated by small letter

18. Phenotype
Expression of alleles
Dominant gene is expressed if present

20. Punnet Square
Diagram to predict possible combinations

21. Test Cross Determining Genotype

22. Dihybrid Crosses Are Traits Linked?

23. Law of Independent Assortment
The transmission of alleles for one trait into gametes does not affect the transmission of alleles for other traits

26. Location of Mendel’s Factors
Mendel did not know where traits were located
Chromosomes were discovered 22 years after Mendel’s work was published
Walter Sutton suggested that Mendel’s factors were on chromosomes

27. Thomas Hunt Morgan Studied fruit flies, Drosophila melanogaster
Discovered different traits in flies
Experiments to test Mendelian inheritance

28. Morgan’s Cross White-eyed male Red-eyed female (normal eye color)
Eye color followed Mendel’s 3:1 ratio
However, all white-eyed F2 were males

30. Conclusion of Morgan’s Experiment
White eyes were linked to males
Trait was found on Y chromosome
Females do not have Y chromosome

31. Conclusion of Morgan’s Experiment
Traits are located on chromosomes
Some traits are sex-linked

32. End chapter 13