Mendel’s Genetics

1. Mendel’s Genetics • Mendel’s research provided the groundwork for our understanding of inheritance of traits.

2. Mendel’s Conclusions • Mendel's four conclusions - although we know that there are exceptions, his conclusions apply to plants, animals and humans! Many of our deadly diseases are found to be carried on one recessive allele. • First Conclusion: biological inheritance is determined by factors that are passed form one generation to the next. Today we know these factors as genes. • Second Conclusion: Principle of dominance – Some alleles (forms of a gene) are dominant and some are recessive. An organism with a dominant allele for a particular form of a trait will always have that form.

3. Mendel’s Conclusions • Third Conclusion: Mendel's Law of Segregation = Each pea plant has 2 alleles (different forms of a gene) for each trait. One allele comes from each parent. This means, that during the formation of each gamete (egg and sperm), the two alleles must separate or segregate from each other. Each gamete only carries a single gene (allele). • Fourth Conclusion: Principle of Independent Assortment - genes for different traits can separate INDEPENDENTLY during the formation of gametes.

4. Real World Genetics • MOST traits are not inherited in such a simple manner as shown by Mendel. For example: • Many traits are controlled by more than one gene • Many alleles are neither completely recessive nor dominant • We now know a gene is actually a small section of a DNA molecule.

5. Exceptions to Mendel • Incomplete Dominance • Codominance • Multiple Alleles for a Trait • Multiple Genes for a Trait Jackalope = cross between a jack rabbit and an antelope

6. Exceptions to Mendel • Incomplete dominance – neither allele is dominant. • For example: Red + White sometimes makes …

7. Incomplete Dominance • What CONCEPT does red + white=pink appear to follow? __________________ • How does this differ from blending? • Genetics of four-o-clock flowers: • R = red allele • W = white allele RR = red flower, WW = white flower, RW = pink flower Blending

8. Incomplete Dominance • Draw a Punnett Square showing a cross between a red flowering four o’clock and a white flowering four o’clock. • What are the phenotypes and genotypes of the offspring?

9. Incomplete Dominance • Phenotype: All of the offspring are pink • Genotype: All of the offspring are RW • Draw a Punnett Square showing a cross between two pink flowering four o’clock. • What are the phenotypes and genotypes of the offspring?

10. Incomplete Dominance • Is this blending? • Why or why not? RW R W RRRW RW WW

11. Incomplete Dominance • Each allele in the example provides instructions to a cell for making an enzyme. • The R allele produces an enzyme necessary for the production of red pigment. • The W allele produces an enzyme necessary for the production of white pigment. • Both alleles are active in incomplete dominance.

12. Exceptions to Mendel • Codominance -neither allele is dominant or recessive. • Example: • variety of cattle with all red hair = RR • variety of cattle with all white hair = WW • A cross of a red cow with a white bull produces offspring (RW) that have both red and white hair

13. Codominance • Other examples: + =

14. Codominance • Other examples: +

15. Exceptions to Mendel • Multiple alleles: More than two alleles exist for a trait--however, each individual still only has two alleles.

16. Multiple Alleles for a Trait • Example: Variations of a tabby cat

17. Multiple Alleles for a Trait • Example: Human Blood Groups • Before the 1900’s people thought all blood was the same. Fatalities resulted from • Transfusions of animal blood into humans! • Transfusions of some human blood to other humans

18. Multiple Alleles for a Trait • It was then discovered there are different types of red blood cells. • Each type contains a different antigen. • Antigen = a substance (a protein or sugar) that triggers the production of antibodies. • Antibodies are part of the body’s defense for fighting off infection

19. Multiple Alleles for a Trait • Human Blood Groups – Three alleles • A = contains one type of antigen • B = contains a different type of antigen • O = does not contain an antigen

20. Multiple Alleles for a Trait • What are all of the possible genotypes using these three alleles? (Hint: Remember each person only has two alleles for a trait!!) AA AO BB BO AB OO

21. Multiple Alleles – Blood Types Genotypes Phenotypes • AA Blood Type A • AO Blood Type A • BB Blood Type B • BO Blood Type B • AB Blood Type AB • OO Blood Type O

22. Multiple Alleles – Blood Types • Which blood type shows codominance? _________ • Which blood type is the universal donor? _________ • Which blood type is the universal recipient? _________ AB O AB

23. Multiple Alleles – Blood Types • Blood types in the United States are more or less common based on race and ethnicity. • However, Type O is most common among all groups and Type AB is least common.

24. Multiple Alleles – Blood Types • Complete Reading on Blood Types • Discuss articles with your group • Answer questions

25. Exceptions to Mendel • Multiple genes for a single trait: • Example: height. Height is made up of the length of different sections of your body added together. Each section is controlled by a different gene. • Example: Eye color in humans. Controlled by interactions of at least 3 different genes.

26. Exceptions to Mendel Complete Worksheets in Groups