Section 11-1: The work of Gregor Mendel

1. Section 11-1: The work of Gregor Mendel Or, what peas have to do with your eye color

2. Who was Gregor Mendel? • Priest • Worked in the monastery garden • Grew some peas

3. Mendel’s traits

4. What about plant sex? • Every plant has male and female parts • Sperm=pollen • Egg located at flower base • Plants normally self-pollinate—breed with themselves

5. True-breeding plants • All the seeds that Mendel had to work with were true-breeding • Meant that offspring produced from these plants would be identical in appearance to their parent plant • Ex: Seed from a tall pea plant would only make tall offspring plants

6. Mendel the mad scientist

7. Mendel the mad scientist • He cross-bred the plants • Bred two true-breed plants together • Cut off male part, transferred sperm from different male plant to female part

8. Some quick vocab • P= parental generation • F1 = first filial generation • “children” of the P generation • Hybrid= offspring produced by cross-breeding the in the P generation

9. Hybrids • What did the hybrids look like? • Would they be a blend of the two parents like mixing paint?

10. Hybrids • Only one parental trait was visible • What happened? • How did Mendel explain it?

11. Mendel’s conclusions • Biological inheritance is determined by factors passed down from one generation to next • We now know these “factors” are genes • Each form of a trait is called an allele • Principle of Dominance- some alleles are dominant and some are recessive

12. Dominant and recessive? • Basically, dominant alleles (and the traits they code for) will mask a recessive trait • In humans, having attached earlobes is recessive. If even ONE allele for free earlobes is present, the person will have the appearance of free earlobes

13. Dominant and recessive • For Mendel’s pea plants, which allele—tall or short—was dominant? • Which was recessive?

14. The fate of the recessive allele • What happened to the recessive allele? • Was it hiding? • Did it disappear forever? • Mendel allowed the F1 generation to self-pollinate to see what would happen

15. The fate of the recessive allele

16. The fate of the recessive allele • Mendel believed that at some point, the alleles separate • Called it “segregation” • Occurs during gametogenesis (in meiosis) • Each gamete only carries one allele for each gene

17. Probability, Punnett Squares and Mendelian Genetics Sections 11-2 & 11-3

18. Genetic Vocabulary • Homozygous- organisms that have 2 identical alleles for the same trait • Heterozygous- organisms that have 2 different alleles for the same trait • Phenotype- physical characteristics • Genotype- genetic makeup

19. Genetic Vocab continued… • Hybrid – an individual that results from the cross of two different pure bred organisms • SAME AS HETEROZYGOUS • Pure bred/True bred – an individual that would produce offspring identical to themselves, if self-pollinated • SAME AS HOMOZYGOUS

20. Even More Vocab!!! • Phenotypic ratio – a comparison of the various phenotypes that result from genetic crosses • Genotypic ratio – a comparison of the various genotypes that result from genetic crosses

21. Just a little more… • Cross - breeding different traits together • Single-factor cross / monohybrid • Only looks at one trait • Two-factor cross / dihybrid • Looks at two different traits simultaneously • Are traits coordinated/connected?

22. Probability • Likelihood that an event is going to happen • What are the odds of having two boys in a row? • What is the chance of flipping three tails in a row? • What are the odds of flipping one heads on a coin? • What are the chances of pulling a queen in a deck of cards?

23. Probability • To calculate the probability of the results of a genetic cross, we use Punnett Squares

24. Punnett Squares • Valuable tool for genetics problems • Shows types of gametes from each parent • Can predict and compare genetic variation in offspring

25. Dihybrid Crosses • Mendel did a 2-factor cross to determine if different genes were coordinated • Cross-bred two different plants • Mendel’s Cross • Round yellow (RRYY) • Homozygous dominant for both traits • Green wrinkled (rryy) • Homozygous recessive for both traits

26. Dihybrid Cross • What does the F1 generation “look” like? • Genotype • ______ • Phenotype • Texture ______ • Color ______

27. Dihybrid Cross • Mendel had to go on to the F2 generation • Let F1 self-pollinate • What will they look like?

28. Dihybrid Cross • Some round and yellow (R_Y_) • Some green and wrinkled (rryy) • Sound round and green (R_yy) • Some yellow and wrinkled (rrY_) • 9:3:3:1 Phenotypic ratio WHY DID THIS HAPPEN?!?!

29. Dihybrid Cross • Genes for different traits segregated separately from each other • Called independent assortment **This is why even if you mom has brown hair and blue eyes and your dad has blonde hair and brown eyes you can have any combination of hair and eye color**

30. And now it gets messy… • Not all traits work with a definite dominate, a definite recessive, and only two alleles • Incomplete dominance • Codominance • Multiple alleles • Polygenic traits

31. Incomplete dominance • Occurs in four o’clock plants • No allele is completely dominant—mix of the two traits

32. Codominance • Both alleles contribute • Chicken feather varieties

33. Codominance • Both alleles contribute • ABO blood types

34. Multiple alleles • Genes that have 2+ alleles AVAILABLE • Can only have 2 at a time though • Rabbit coloration

35. Polygenic traits • More than one gene controls the phenotype • 4+ genes control skin pigmentation