2. Genetics & The Work of Mendel

3. Gregor Mendel Modern genetics began in the mid- 1800s in an abbey garden, where a monk named Gregor Mendel documented inheritance in peas – used experimental method – used quantitative analysis collected data & counted them – excellent example of scientific method

4. Pollen transferred from white flower to stigma of purple flower anthers removed all purple flowers result Mendel’s work F1F1 P F2F2 self-pollinate Bred pea plants – cross-pollinate true breeding parents (P) P = parental – raised seed & then observed traits (F 1 ) F = filial – allowed offspring to self-pollinate & observed next generation (F 2 )

5. Mendel collected data for 7 pea traits

6. Do Modern Geneticists use Pea Plants? Yeast Bacteria C. elegans Fruit flies These are better because they are easier to maintain in a laboratory. They still have the good qualities of the pea plant: Easily observed traits High reproductive rates

7. Task Design a newspaper ad to attract Mendel or his colleagues to purchase pea plants from your company. – It should convey all the easily observed traits of pea plants. – It should mention reproductive traits.

8. F 2 generation 3:1 75% purple-flower peas 25% white-flower peas Looking closer at Mendel’s work P 100% F 1 generation (hybrids) 100% purple-flower peas X true-breeding purple-flower peas true-breeding white-flower peas self-pollinate Where did the white flowers go? White flowers came back!

9. What did Mendel’s findings mean?  Traits come in alternative versions  purple vs. white flower color  alleles  different alleles vary in the sequence of nucleotides at the specific locus of a gene  some difference in sequence of A, T, C, G purple-flower allele & white-flower allele are two DNA variations at flower-color locus different versions of gene at same location on homologous chromosomes

10. Traits are inherited as discrete units  For each characteristic, an organism inherits 2 alleles, 1 from each parent  diploid organism  inherits 2 sets of chromosomes, 1 from each parent  homologous chromosomes  like having 2 editions of encyclopedia  Encyclopedia Britannica  Encyclopedia Americana What are the advantages of being diploid?

11. What did Mendel’s findings mean?  Some traits mask others  purple & white flower colors are separate traits that do not blend  purple x white ≠ light purple  purple masked white  dominant allele  functional protein  masks other alleles  recessive allele  allele makes a malfunctioning protein homologous chromosomes I’ll speak for both of us! wild type allele producing functional protein mutant allele producing malfunctioning protein

12. Genotype vs. phenotype  Difference between how an organism “looks” & its genetics  phenotype  description of an organism’s trait  the “physical”  genotype  description of an organism’s genetic makeup Explain Mendel’s results using …dominant & recessive …phenotype & genotype F1F1 P X purplewhite all purple

13. Making crosses  Can represent alleles as letters  flower color alleles  P or p  true-breeding purple-flower peas  PP  true-breeding white-flower peas  pp PP x pp PpPp F1F1 P X purplewhite all purple

14. F 2 generation 3:1 75% purple-flower peas 25% white-flower peas ???? Looking closer at Mendel’s work P X true-breeding purple-flower peas true-breeding white-flower peas PPpp 100% F 1 generation (hybrids) 100% purple-flower peas PpPpPpPpPpPpPpPp phenotype genotype self-pollinate

15. Be able to idenitfy and describe the following… Allele Locus Diploid Haploid Dominant allele Recessive allele Phenotype Genotype You may want to make drawings too!

16. Mendel’s 1 st law of heredity Law of segregation – during meiosis, alleles segregate homologous chromosomes separate – each allele for a trait is packaged into a separate gamete PP P P pp p p PpPp P p

17. Monohybrid cross Some of Mendel’s experiments followed the inheritance of single characters – flower color – seed color – monohybrid crosses

18. Dihybrid cross Other of Mendel’s experiments followed the inheritance of 2 different characters – seed color and seed shape – dihybrid crosses Mendel was working out many of the genetic rules!

19. Dihybrid cross true-breeding yellow, round peas true-breeding green, wrinkled peas x YYRRyyrr P 100% F 1 generation (hybrids) yellow, round peas Y = yellow R = round y = green r = wrinkled self-pollinate 9:3:3:1 9/16 yellow round peas 3/16 green round peas 3/16 yellow wrinkled peas 1/16 green wrinkled peas F 2 generation YyRr

20. What’s going on here? If genes are on different chromosomes… – how do they assort in the gametes? – together or independently? YyRr YRyr YyRr YryRYRyr Is it this?Or this? Which system explains the data?

21. Dihybrid cross YyRr YRYryR yr YR Yr yR yr YYRR x YYRrYyRRYyRr YYRrYYrrYyRrYyrr YyRRYyRryyRRyyRr YyRrYyrryyRryyrr 9/16 yellow round 3/16 green round 3/16 yellow wrinkled 1/16 green wrinkled YyRr YryRYR yr YyRr YRyr or BINGO! 

22. Can you think of an exception to this? Mendel’s 2 nd law of heredity round wrinkled Law of independent assortment – different loci (genes) separate into gametes independently non-homologous chromosomes align independently classes of gametes produced in equal amounts – YR = Yr = yR = yr only true for genes on separate chromosomes or on same chromosome but so far apart that crossing over happens frequently yellow green :11:1:1 Yr yR YR yr YyRr

23. What to know… Content: Difference between a chromosome, gene, allele, and locus Genotype vs phenotype Dominant vs recessive alleles Homozygous vs heterozygous Mendel’s Laws of heredity (1 st and 2 nd ) Why the Pea Plant was a good model organism Current model organisms Incomplete dominance Co-dominance

24. What to know… Skills: use a Punnett square to predict genotypes and phenotypes of offspring. (monohybrid and dihybrid) Interpret data from Punnett squares (genotypic and phenotypic ratios) Analyze Pedigrees to determine dominant or recessive inherited traits.

25. 2006-2007 Beyond Mendel’s Laws of Inheritance

26. Extending Mendelian genetics Mendel worked with a simple system – peas are genetically simple – most traits are controlled by a single gene – each gene has only 2 alleles, 1 of which is completely dominant to the other The relationship between genotype & phenotype is rarely that simple

27. Incomplete dominance Heterozygote shows an intermediate, blended phenotype – example: RR = red flowers rr = white flowers Rr = pink flowers – make 50% less color RR  RR  WW  RW WWRW

28. Incomplete dominance true-breeding red flowers true-breeding white flowers X P 100% 100% pink flowers F 1 generation (hybrids) self-pollinate 25% white F 2 generation 25% red 1:2:1 50% pink

29. Co-dominance The two alleles are equally, but separately expressed: – Ex: Roan horses &cattle, B = brown hair, b = white

30. Co-dominance 2 alleles affect the phenotype equally & separately – not blended phenotype – human ABO blood groups – 3 alleles I A, I B, i I A & I B alleles are co-dominant – glycoprotein antigens on RBC – I A I B = both antigens are produced i allele recessive to both

31. Genetics of Blood type pheno- type genotype antigen on RBC antibodies in blood donation status AI A I A or I A i type A antigens on surface of RBC anti-B antibodies __ BI B I B or I B i type B antigens on surface of RBC anti-A antibodies __ ABI A I B both type A & type B antigens on surface of RBC no antibodies universal recipient Oi ii i no antigens on surface of RBC anti-A & anti-B antibodies universal donor

32. Pleiotropy Most genes are pleiotropic – one gene affects more than one phenotypic character 1 gene affects more than 1 trait dwarfism (achondroplasia) gigantism (acromegaly)

33. Acromegaly: André the Giant

34. Sex linked traits Genes are on sex chromosomes – as opposed to autosomal chromosomes – first discovered by T.H. Morgan at Columbia U. – Drosophila breeding good genetic subject – prolific – 2 week generations – 4 pairs of chromosomes – XX=female, XY=male 1910 | 1933

35. autosomal chromosomes sex chromosomes Classes of chromosomes

36. Huh! Sex matters?! F 2 generation 100% red-eye female 50% red-eye male 50% white eye male Discovery of sex linkage P X F 1 generation (hybrids) 100% red eye offspring true-breeding white-eye male true-breeding red-eye female

37. Genes on sex chromosomes Y chromosome – few genes other than SRY sex-determining region master regulator for maleness turns on genes for production of male hormones – many effects = pleiotropy! X chromosome – other genes/traits beyond sex determination mutations: – hemophilia – Duchenne muscular dystrophy – color-blindness

38. Sex-linked – usually means “X-linked” – more than 60 diseases traced to genes on X chromosome Human X chromosome

39. Map of Human Y chromosome? < 30 genes on Y chromosome Sex-determining Region Y ( SRY ) linked Channel Flipping ( FLP ) Catching & Throwing ( BLZ-1) Self confidence ( BLZ-2) note: not linked to ability gene Devotion to sports ( BUD-E) Addiction to death & destruction movies ( SAW-2) Scratching ( ITCH-E) Spitting ( P2E) Inability to express affection over phone ( ME-2) Selective hearing loss ( HUH) Total lack of recall for dates ( OOPS) Air guitar ( RIF)

41. Hemophilia Hh x HH XHYXHY XHXhXHXh XHXhXHXh XHXH XhXh XHYXHY Y XHXH sex-linked recessive XHXH Y male / sperm XHXH XhXh female / eggs XHXHXHXH XHXhXHXh XHYXHYXhYXhY XHXHXHXH XHYXHY XHXhXHXh XhYXhY carrierdisease

42. Pedigree analysis Pedigree analysis reveals Mendelian patterns in human inheritance – data mapped on a family tree = male= female= male w/ trait = female w/ trait

43. Simple pedigree analysis 12 3456 12 3456 What’s the likely inheritance pattern?