1. Mendel and Heredity Chapter 8 Ms. Hogg, Biology

2. The Origins of Genetics Heredity – the passing of characteristics from parent to offspring – Before DNA and chromosomes were discovered, heredity was one of the greatest mysteries of science!

3. Gregor Mendel The scientific study of heredity began with Gregor Mendel – Austrian monk – Carried out experiments with garden peas – He was the 1 st to develop rules that accurately predict patterns of heredity. – “Father of Genetics”

4. Pea Plant

6. 7 Characteristics Mendel Studied:

8. Pollen Transfer in Mendel’s Experiments

9. Mendel’s Hypotheses #1 For each inherited characteristic, an individual has two copies of the gene – one from each parent.

10. Mendel’s Hypotheses #2 There are alternative versions of genes. – These different “versions” are called alleles. – An individual receives one allele from each parent.

11. Mendel’s Hypotheses #3 When two different alleles occur together, one of them may be completely expressed, while the other may have no observable affect on the organisms appearance. – Dominant = expressed trait – Recessive = trait that is NOT expressed

13. Mendel’s Hypotheses #4 When gametes are formed, the alleles for each gene in an individual separate independently of one another.

14. Terms of Genetics Homozygous = two alleles of a gene are the SAME – Example: BB or bb Heterozygous = two alleles of a gene are DIFFERENT – Example: Bb

15. Genotype = the set of alleles that an individual has for a trait – Example: BB Phenotype = the physical appearance of a characteristic – Example = Brown hair Terms of Genetics

16. Punnett Square A punnett square is a diagram that predicts the outcome of a genetic cross Monohybrid cross:

18. The Hardy-Weinberg Principle p 2 + 2pq + q 2 = 1 You can use this equation to predict genotype frequencies in a population.

19. The Hardy-Weinberg Principle p 2 + 2pq + q 2 = 1 The sum of allele frequencies must always equal 1. p + q = 1

21. Exceptions… The Hardy-Weinberg principle holds true for any population as long as evolutionary forces are not acting… – Mutations – Gene flow – Nonrandom mating – Genetic drift – Natural selection

22. A Review… Monohybrid Cross

23. A Review… Dihybrid Cross NOTE: Must use the “FOIL” method to correctly set up the parent genotype combinations on the Punnett Square

24. Incomplete Dominance An organism can display a phenotype that is intermediate between the two parents Example: Snapdragon flowers RR = red Rr = pink rr = white

25. Incomplete Dominance

26. Codominance Two dominant alleles can be expressed at the same time Example: Human Blood groups (ABO blood groups) Type A = I A I A or I A i Type B = I B I B or I B i Type AB = I A I B (Universal Recipient) Type O = ii(Universal Donor)

27. Codominance – ABO Blood Groups

28. Rh Factor Source: NobelPrize.org

29. Human Blood Type Frequency Source: RedCrossBlood.org

30. Sex-linked Traits In sex-linked inheritance, the gene responsible for the disease is located on the X chromosome. Usually, the abnormal gene is recessive. – For these reasons, the resultant disorder is called an X-linked recessive disease

31. Sex-linked Disorders Color blindness – A person with the most common form of color blindness cannot distinguish red from green hues. Hemophilia – In hemophilia, the blood does not clot properly.

32. Color blindness Tests

33. Hemophilia

34. Pedigrees

35. Polygenic Traits Polygenic traits are controlled by two or more genes, usually on different chromosomes. Examples of Polygenic Traits: – Height, skin color, weight, – Many common diseases, such as heart disease, are caused by polygenic genes and environmental factors (Lifestyle choices such as diet and exercise)

36. Human skin color is controlled by at least eight different loci on different chromosomes...