Why is Gregor Mendel the GREATEST BIOLOGIST EVER ? Even though he wasn’t really a biologist

1. Why is Gregor Mendel theGREATEST BIOLOGIST EVER?Even though he wasn’t really a biologist

2. Ch 14 Mendelian Genetics

3. Pre-Mendel • Predominate belief in “blending”, child is a mix of parents • problem with this was traits skipping generations Terms early genetic study • Character = detectable, inherited feature, ex. color • Trait = variant of an inheritable character, ex. green or red color • True-Breeding = always produce plants with same traits as parents, self fertilization • Cross-Breeding = cross parents with different traits to create hybrids

4. Generations are named • P = parental • F1= results of PxP • F2= results of F1 x F1

5. Mendel’s experiment • Mendel looked at 7 characteristics, each had 1 alternate form that did not “blend” when cross-bred • His experiment– if a cross of purple & white P’s • gives all purple, then a cross between F1’s, self-pollinating, would produce white again in F2 generation • results – 3:1 ratio of purple to white flowers, • conclusions – ?

6. Mendel’s experiment • Mendel looked at 7 characteristics, each had 1 alternate form that did not “blend” when cross-bred • His experiment– if a cross of purple & white P’s • gives all purple, then a cross between F1’s, self-pollinating, would produce white again in F2 generation • results – 3:1 ratio of purple to white flowers, • conclusions • Heritable trait for whiteness is masked • Purple trait is dominant • Extension • If 2 purple P’s were mated, what ratio of traits would you expect to observe?

7. The ratio does not match the ideal. Create a plan to test if this difference is acceptable.

8. So… • there are alternate forms of the same gene = alleles, p265 • we inherit one allele from each parent • if alleles are different, one is dominant (noted by capital letter), one is recessive (lowercase letter) • When do alleles segregate?

9. So… • there are alternate forms of the same gene = alleles, p265 • we inherit one allele from each parent • if alleles are different, one is dominant (noted by capital letter), one is recessive (lowercase letter) • When do alleles segregate? Anaphase I

10. More Terms • homozygous – 2 identical alleles for a trait, ex. DD, dd • heterozygous – 2 different alleles for a trait, carrier, ex. Dd • phenotype – organism’s expressed traits, ex. color, height • genotype – organism’s genetic makeup, letters, ex. PP, Pp

11. Testcross – a cross between a recessive and an unknown • tells if it is homo or heterozygous • monohybrid cross – dealing with 1 trait • dihybrid cross – 2 traits • Trihybrid – 3 traits

12. Mendel’s first postulate:Law of Segregation • = allele pairs separate randomly during meiosis, p. 266 • There are 2 alleles for flower color, if 1 purple and 1 white: there is a 50% chance of getting either allele • Punnett square used to predict the results

13. Mendel’s secondpostulate:Law of Independent Assortment • when dealing with 2 or more traits, each allele of the different genes segregates independently of each other • WHY? • If cross 2 dihybrid heterozygotes, get 9:3:3:1 ratio

14. Probability = mathematical chance of an event happening • Rule of multiplication- probability of 2 events occurring at the same time = product of their individual probabilities • Ex: 2 coins both coming up heads = ? • Ex: If DdRr x DdRrwhat is probability of getting DDRR is ?

15. Probability = mathematical chance of an event happening • Rule of multiplication- probability of 2 events occurring at the same time = product of their individual probabilities • Ex. 2 coins both coming up heads = ½ x ½ = ¼ • Ex: If DdRr x DdRr what is probability of getting DDRR is ? chance of DD = ¼, chance of RR = ¼ so ¼ x ¼ = 1/16

16. Rule of addition –p.270, probability that either of two or more mutually exclusive events will occur is calculated by adding the individual probabilities. • What are the chances you will get heads or tails when you flip a coin? • Ex. cross of 2 heterozygotes, what are chances of result being hetero? • Use → trihybridAaBbCc x AaBbCc ? chance of AabbCC?

17. Rule of addition –p.270, probability that either of two or more mutually exclusive events will occur is calculated by adding the individual probabilities. • What are the chances you will get heads or tails when you flip a coin? • ½ + ½ = 1 • Ex. cross of 2 heterozygotes, what are chances of result being hetero? • Chance of recessive egg + dominant sperm = ½ x ½ = ¼ • Chance of dominant egg + recessive sperm = ½ x ½ = ¼ • chance of hetero child is ¼ + ¼ = ½ • Use → trihybridAaBbCc x AaBbCc ? chance of AabbCC?

18. Extensions: • Mendel’s laws were not perfect, in fact, he was lucky (or wise) that he choose peas which have simple inheritance (except pod shape) • Incomplete dominance = 1 allele is not completely dominant over the other thus, there is a 3rd phenotype, intermediate, ex.Carnations/snapdragonsp. 271

19. Codominance = both alleles are expressed • Level of expression varies at different levels • ex: Tay-sachs • at the molecular level – looks codominant – both alleles transcribed • at the biochemical level – looks like incomplete→ a partial level of lipid-metabolizing activity • at the organismal level – heterozygotes are symptom free, homoygote recessives expressdisorder

20. Multiple Alleles = genes that have more than 2 alleles • Ex. blood groups A, B, AB, O (surface carbohydrates) • blood type is the antigen present on the RBC, p. 273 • also contains Rh factor, + or – with standard Mendelian rules

22. Pleiotropy = a single gene has multiple effects • ex: sickle-cell

23. Epistasis = one gene affects the expression of another gene, Ex. pigments in mice

24. Polygenic inheritance = many genes affect the same trait • Ex: skin color, very dark to very light, p. 274

25. Environment plays an important part in gene expression, how much is dependent on the gene, nature vs. nurture argument • Norm of Reaction = The phenotypic range for a genotype, p.275

26. Humans • Pedigree – family tree that shows inheritance over many generations, shows patterns •  = male, O = female, ●= affected, ○= non-affected

27. Recessive human disorders • - usually caused by a defective protein • - heterozygotes are carriers • Why more common than dominant disorders? Examples • Cystic Fibrosis– most common amongst Europeans (4% carry), membrane protein that controls Cl⁻ traffic, causes increase mucus in lungs infections persist • Tay-Sachs – higher in Ashkenazic Jews, can’t break down a type of lipid. How can it be high in a particular pop? • Sickle cell – substitution in one hemoglobin, causes RBC to sickle and clog, carriers are immune to malaria, p. 278 • In which pop. would sickle cell predominate? Consanguinity – mating with relatives, increases expression of recessive disorders. Why?

28. Dominant inherited disorders • – rarer than recessive. Why? Examples • Achondroplasia – type of dwarfism • Huntington's – late acting degeneration of nervous system, due to single allele on tip of chromosme #4 • Knowledge of this makes disease detectable. many different factors affect onset, but genetic predisposure present • ex. Heart disease, diabetes, cancer Multifactorial disorders

29. Genetic testing and counseling • 1) carrier recognition - help make decisions about whether or not to reproduce • Can test for Tay-Sachs, sickle-cell, and cystic fibrosis, etc. • 2) fetal tests • amniocentesis – take amniotic fluid from around fetus, do karyotype • chorionic villus sampling (CVS) – take villi, do karyoptype, fast, earlier, more risk, p. 280 • ultrasound – imagery using sound waves, look for physical problems • fetoscopy – fiber optics • Culturing escaped fetal blood cells in mother’s blood • 3) Newborn screening – ex. PKU

31. Big Picture of Inheritance… • must be looked in integrated light…i.e. it is a product of genes working collectively and is influenced by environmental cues • Must view emergent properties of organism as a whole, not a reductionist view of single genes acting in isolation

33. So, why is Gregor Mendel theGREATEST BIOLOGIST EVER?Even though he wasn’t really a biologist

34. Ch 15 Chromosomes and Inheritance

35. Chromosome theory of inheritance: genes are located on chromosomes, they segregate and independently assort

36. T.H.Morgan • rediscovered Mendel’s work 1900’s, specific genes on specific chromosomes? • work on fruit fly, why? • fast repro., easy to handle, 4 pairs of chromosomes (1 pair are sex chromosomes) • gene symbol is based on the mutant or recessive ex. curly is recessive = Cy, if normal then Cy+ • wild type is the type seen in nature = +

37. Experiment- p 289 • white eyed male (♂)→ crossed with a red eyed female (♀)→ in F2 only males had white eyes ? • how is no independent assortment possible?

38. Experiment- p 289 • white eyed male (♂)→ crossed with a red eyed female (♀)→ in F2 only males had white eyes ? → eye color and sex are linked • Linked genes = when genes are on the same chromosome, so they are inherited together

39. Sex linked traits = located on a sex chromosome, p. 290, ex. Hemophilia • few genes on the Y, thus most sex-linked diseases are seen in males b/c on the X (not masked), females often carriers, p. 290 • X-inactivation = females inactivate one of their X’s (see cat diagram) • inactive X becomes a Barr body • Typically both chromosomes genes are expressed

40. Examining 2 genes: How could you determine if a two genes were “linked”?How could you tell distance between two genes?

41. Examining 2 genes: How could you determine if a two genes were “linked”?How could you tell distance between two genes?

42. Recombination = offspring with different combinations of traits than the parents, caused by crossing over or mutations • Parental types – same phenotype as a parent • Recombinants – differ from parents, *p. 293-294 • What is % of recombination of the peas?

43. Recombination = offspring with different combinations of traits than the parents, caused by crossing over or mutations • Parental types – same phenotype as a parent • Recombinants – differ from parents, *p. 293-294 • What is % of recombination of the peas? 50% - one-half of the offspring are expected to inherit either of the two phenotypes

44. Recombination • What would a recombination of 25% tell you about the chromosomal location of two given genes?

45. Recombination • What would a recombination of 25% tell you about the chromosomal location of two given genes? • The genes’ loci are on the same chromosome • Why is the recombination % not 0? • What would a recombination of 0.5% tell you about their respective locations?

46. Recombination • What would a recombination of 25% tell you about the chromosomal location of two given genes? • The genes’ loci are on the same chromosome • Why is the recombination % not 0? • Crossing-over separates them • What would a recombination of 0.5% tell you about their respective locations? • That their respective loci are in close proximity on the same chromosome

47. Sturtevant and gene mapping • use recombination frequency to determine distance of genes • The farther apart two genes are, the higher the probability that crossover will occur between them and ∴ the higher the recombination frequency • made chromosome maps • find relative distance between farthest genes, find distance of an end and a middle, fill in other genes • double crossovers can occur too, throw # off a little • Made distance unit: 1 map unit = 1% recombination

49. Final product: a genetic (linkage) map

50. HUMAN GENETIC DISORDERS