Genetics: The patterns of inheritance and Human Inheritance

1. Genetics: The patterns of inheritance and Human Inheritance Chapter 9

2. Do you look like your parents? • Perhaps the mailman? • You get your genes from your parents. • You can thank them, or blame them!

3. What is genetics? • It is the study of inheritance. • Discovered by Gregor Mendel. • He bred 24,034 pea plants between 1857-1863. • Meticulous experiments using lots of math! • Discovered that information went to offspring. • He could “predict” what the offspring would be. • His research was rediscovered in 1901.

4. Humans have actually studied genetics for thousands of years.

6. How could Mendel predict what offspring would be made? • Genes are located on each of the chromosome pairs. • You get one of the pair from your father, and one from your mother. • These genes are in alternate forms called “alleles.” • The alleles separate into each gamete. • Remember, Mendel did not know anything about chromosomes, mitosis or meiosis. • Meiosis explains genetics.

7. How did Mendel perform the experiments? • He chose what pea plants he wanted to mix. • He manually pollinated each pair. • He conducted his crosses to determine the traits. • Based on the traits he chose, he could predict the offspring!

8. What traits did Mendel study?

9. Mendel’s results formed two “laws” of genetics. • Law of Segregation • Genes separate into each gamete. • If you have two genes for freckles, one will go into each of your eggs or sperm. • This follows two traits at once. • Law of Independent Assortment • Each trait is completely independent of all others. • Your eye color has nothing to do with whether you have dimples or not. • Many traits you will study follow this rule. There are others that do not, however.

10. Law of Segregation These genes separate into these gametes, contributing to this offspring.

11. How did Mendel predict that 75% of offspring could have a trait? • He conducted so many experiments that these numbers, although not perfect, are statistically valid. • He could predict, with great certainty, how traits would be passed. This is where the 3:1 ratio (on average) comes from.

12. Rules of Probability • “Probability” is the math of statistics. • Mendel discovered that predicted offspring are like rolling dice: • 50/50 chance? • 75% chance? 25% chance? • 3:1 ratio? • When meiosis was figured out, then Mendel’s laws were explained. • Why do think this is the case?

13. The Punnet Square • A very convenient tool used in genetics. • Steps: • 1. Determine the parents gametes. • This may be the most important step. • 2. Match the gametes, and form possible offspring. • 3. Determine the chances of each type of offspring.

14. A basic Punnet square: • Notice that the mother and father are both heterozygous. • If the dominant sperm fertilizes the dominant egg, then the offspring would be TT. • There is a 25% chance of this occurring. • 1 out of 4 will be this.

15. Scientists use a “test cross” if they don’t know what the genotype of an individual is. • What is the: • Phenotype of a purple pea plant? • Phenotype of a white pea plant? • Genotype of a white pea plant? • Genotype of a purple pea plant? • How can you find out the unknown genotype of an individual? • You would want to breed a “known” genotype against your “unknown.” • The offspring will tell you what the “unknown” is.

16. Monohybrid cross • When only one trait is studied at a time. • This is the easiest cross to determine gametes and offspring. • When two heterozygous individuals are crossed: • 1:2:1 genotypic ratio • 3:1 phenotypic ratio

17. Other examples of monohybrid crosses:

18. Dihybrid crossDemonstrates the law of independent assortment. When two independent traits are studied at once. Trihybrid? Notice that each trait is independent of the other. Can you see the 9:3:3:1 phenotypic ratio of the offspring?

19. Mendel studied basic dominant and recessive traits. • There are many examples of traits that do not follow Mendel’s ratios. • These could not have been discovered without Mendel learning the basic foundations of genetics. • Most genes aren’t this simple.

20. Many human traits are controlled by a single gene. • Recessive disorders • The individual needs to be homozygous recessive. • Albanism, cystic fibrosis, sickle-cell disease, phenylketonuria, Tay-Sachs disease. • Dominant disorders • The individual only needs one dominant gene. • Achondroplasia, Huntington’s disease, hypercholesterolemia, Alzheimers (???). • How do these genetic disorders cause actual disease? • Which could be “worse” – dominant or recessive disorders? Why?

21. Incomplete Dominance • This is an example of how dominant and recessive traits may not be simple. • The heterozygous condition actually has its own phenotype. • Usually a mixture of each parent.

22. SnapdragonsExcellent example of incomplete dominance. • RR = red • WW = white • RW or WR = pink • What gametes would a RR individual make? • WW? • RW?

23. Many genes have more than one allele.“Multiple Alleles” • There are examples of genes that are present in more than a simple dominant or recessive form. • Think about “I” being dominant to “i”. • But, there could be different kind of “I”. • IA and IB. • This could make a phenotype interesting.

24. Multiple Alleles Notice that you can be homozygous IAIA, or heterozygous IAi. Both of these have “Type A” blood though. If you cross someone who is type A, but you don’t know whether they are homozygous or heterozygous, always assume they are heterozygous. Why do you think I ask you to do this?

25. Here is what your blood looks like. • This is how a biologist can find out what your blood type is. • Your blood reacts to special chemicals or not, depending on the kind of blood cell you have. • How do you think this works? Reaction No reaction.

26. Go home and try these crosses: • Question: If your blood type is “A”, are you heterozygous or homozygous? How could you tell? How would you set up your own Punnet square? • Try these crosses at home: • Type “A” x Type “O” • Type “A” x Type “B” • Type “AB” x Type “B” • Type “AB” x Type “AB” • Type “AB” x Type “O” • Use your own blood type, come up with some on your own, and give them a try! Find out what kind of babies you can have!

27. Sometimes its not just the genes! • The environment can also influence what genes are expressed. • The mouthparts will become either legs or antennae, depending on temperature. • Interesting???

28. The environment can change other kinds of organisms as well. • Some turtle and tortoise embryos can change their sex… • While developing in the egg… • Prior to hatching… • Depending on the environment.

29. Temperature can change what genes are expressed.

30. Why do you think this is important? • If species react to their environment, that means that species change with a changing environment. • This is one of the key aspects of evolutionary study. • As we learn more about individuals and species, and how they live in their environment, we also learn more about ourselves.

31. Many traits you are familiar with aren’t determined by one gene. • Body height depends on many factors. • This is called Polygenic Inheritance. • Many genes involved.

32. Skin tone is another example of polygenic inheritance.

33. Polygenetic Inheritance • If you noticed, both examples of polygenetic inheritance resulted in a “bell-shaped” curve. • This is because of the many genes involved. • Most individuals would cluster around an average, with fewer towards the extremes.

34. The Human Genome Project • Scientists have mapped the human genome. • This allowed the discovery of the genes that make humans unique. • This also allowed the discovery of genes that are shared with other organisms.

35. PleiotropyWhen one gene affects many traits.

36. EpistasisOne gene masking another. • Blood types may not always show the correct results. • If there is a mutant gene, antigens cannot attach. • A person may show “O” even though it is another blood type. • This could cause confusion looking at blood types among families.

37. Other issues involving blood type genetics: • Universal donor and universal recipient. • Paternity tests • “Rh factor”

38. Sex-linked crosses • Autosomes versus sex chromosomes. • The “X” chromosome carries genes that the “Y” chromosome does not. • A good example of a sex-linked cross is colorblindness. • The colorblind gene is located on the “X.” • C = normal vision. • c = colorblind vision. • Why do you think there are more colorblind men than women? • Is it possible for a woman to be colorbind?

39. What do you see?

40. Cross a normal male (XCY) and a normal carrier female (XCXc). XC Y G.R. = 1:1:1:1 P.R. = 2:1:1 XC Can you see why? Xc

41. Think about this… • Remember “the birds and the bees?” • Don’t laugh but many students try to cross two XY individuals or two XX individuals. • Could two normal people have a colorblind child? • What would its sex be? • Try these crosses at home. Make up some more! • A normal male and a colorblind female. • A colorblind male and a carrier female. • A colorblind male and a colorblind female.

42. Some interesting genetic facts: • Some genes are dominant, but don’t always express themselves. • The environment can also impact how genes express themselves. • Many traits have so many genes, that you can’t isolate one.

43. Traits that are on the autosomes can be dominant or recessive. • Table 11.1 in your text goes over different human disorders. • Take a look at both dominant and recessive traits.

44. Polydactyly is an autosomal dominant trait.

45. Autosomal Dominance Inheritance • This pedigree shows a father who is affected, and his five children. • You can follow the trait through the generations.

46. AlbinismAn autosomal recessive trait.

47. Autosomal Recessive Inheritance • Both parents here do not show the trait. • Half of their children are carriers. • One child has expresses the trait. • One child does not carry the trait.