2 Gregor MendelModern genetics began in the mid-1800s in an abbey garden, where a monk named Gregor Mendel documented inheritance in peasused good experimental designused mathematical analysiscollected data & counted themexcellent example of scientific methodHe studied at the University of Vienna from 1851 to 1853 where he was influenced by a physicist who encouraged experimentation and the application of mathematics to science and a botanist who aroused Mendel’s interest in the causes of variation in plants. After the university, Mendel taught at the Brunn Modern School and lived in the local monastery.The monks at this monastery had a long tradition of interest in the breeding of plants, including peas. Around 1857, Mendel began breeding garden peas to study inheritance.
3 Mendel’s work Bred pea plants ? cross-pollinate true breeding parents Pollen transferred from white flower to stigma of purple flowerBred pea plantscross-pollinate true breeding parentsraised seed & then observed traitsallowed offspring to self-pollinate & observed next generationall purple flowers resultP = parentsF = filial generationself-pollinate?
5 Looking closer at Mendel’s work true-breedingpurple-flower peastrue-breedingwhite-flower peasXParents100%1stgeneration(hybrids)purple-flower peasIn a typical breeding experiment, Mendel would cross-pollinate (hybridize) two contrasting, true-breeding pea varieties.The true-breeding parents are the P generation and their hybrid offspring are the F1 generation.Mendel would then allow the F1 hybrids to self-pollinate to produce an F2 generation.self-pollinate2ndgeneration3:175%purple-flower peas25%white-flower peas
6 What did Mendel’s findings mean? Some traits mask otherspurple & white flower colors are separate traits that do not blendpurple x white ≠ light purplepurple masked whitedominant allelefunctional proteinaffects characteristicmasks other allelesrecessive alleleno noticeable effectallele makes a non-functioning proteinI’ll speak for both of us!allele producing functional proteinmutant allele malfunctioning proteinhomologous chromosomes
7 Genotype vs. phenotypeDifference between how an organism “looks” & its geneticsphenotypedescription of an organism’s traitgenotypedescription of an organism’s genetic makeupF1PXpurplewhiteall purpleExplain Mendel’s results using…dominant & recessive…phenotype & genotype
8 PP pp Pp x Making crosses Can represent alleles as letters flower color alleles P or ptrue-breeding purple-flower peas PPtrue-breeding white-flower peas ppF1PXpurplewhiteall purplePPxppPp
9 phenotype & genotype can have different ratios Aaaaah,phenotype & genotype can have different ratiosPunnett squaresPp x Pp1stgeneration(hybrids)%genotype%phenotypePpmale / spermPP25%75%Pp50%Ppfemale / eggsPPPpPpPppp25%25%pp1:2:13:1
12 Extending Mendelian genetics Mendel worked with a simple systempeas are genetically simplemost traits are controlled by single geneeach gene has only 2 version1 completely dominant (A)1 recessive (a)But its usually not that simple!
13 Incomplete dominance Hybrids have “in-between” appearance RR WW RW RR = red flowersrr = white flowersRr = pink flowersmake 50% less colorRRWWRWRRRrrr
14 Incomplete dominance P 1st 100% 1:2:1 2nd X true-breeding red flowers white flowers100%100% pink flowers1stgeneration(hybrids)self-pollinate25%white2ndgeneration25%red1:2:150%pink
15 Incomplete dominance RW x RW RR R W RW RR RW R W RW WW RW WW 25% 25% genotype%phenotypeRR25%25%RWmale / sperm50%50%RWRRRWRWfemale / eggsRWWW25%25%RWWW1:2:11:2:1
16 Codominance Equal dominance human ABO blood groups 3 version A, B, iA & B alleles are codominantboth A & B alleles are dominant over i allelethe genes code for different sugars on the surface of red blood cells“name tag” of red blood cell
17 Genetics of Blood type A A A or A i B BB or B i AB O i i pheno-type genotypeantigen on RBCantibodies in blooddonation statusAA A or A itype A antigens on surface of RBCanti-B antibodies__BBB or B itype B antigens on surface of RBCanti-A antibodiesABboth type A & type B antigens on surface of RBCno antibodiesuniversal recipientOi ino antigens on surface of RBCanti-A & anti-B antibodiesuniversal donor
19 One gene: many effectsThe genes that we have covered so far affect only one traitBut most genes are affect many traits1 gene affects more than 1 traitdwarfism (achondroplasia)gigantism (acromegaly)The genes that we have covered so far affect only one phenotypic character, but most genes are pleiotropic
26 Coat color in other animals 2 genes: E,e and B,bcolor (E) or no color (e)how dark color will be: black (B) or brown (b)eebbeeB–E–bbE–B–
27 Environment effect on genes Phenotype is controlled by both environment & genesCoat color in arctic fox influenced by heat sensitive allelesHuman skin color is influenced by both genetics & environmental conditionsThe relative importance of genes & the environment in influencing human characteristics is a very old & hotly contested debatea single tree has leaves that vary in size, shape & color, depending on exposure to wind & sunfor humans, nutrition influences height, exercise alters build, sun-tanning darkens the skin, and experience improves performance on intelligence testseven identical twins — genetic equals — accumulate phenotypic differences as a result of their unique experiencesColor of Hydrangea flowers is influenced by soil pH
28 Genetics of sexWomen & men are very different, but just a few genes create that differenceIn mammals = 2 sex chromosomesX & Y2 X chromosomes = female: XXX & Y chromosome = male: XYXXXY
30 Sex-linked traits Sex chromosomes have other genes on them, too X X X especially the X chromosomehemophilia in humansblood doesn’t clotDuchenne muscular dystrophy in humansloss of muscle controlred-green color blindnesssee green & red as shades of greyXXDuchenne muscular dystrophy affects one in 3,500 males born in the United States.Affected individuals rarely live past their early 20s.This disorder is due to the absence of an X-linked gene for a key muscle protein, called dystrophin.The disease is characterized by a progressive weakening of the muscles and loss of coordination.XY
31 Sex-linked traits HH XHY XHXh Hh x XHY Y XH XH Y XHXH XHXH XHY XHY XH sex-linked recessiveHHXHYXHXhHh2 normal parents,but mother is carrierxXHYYXHXHYmale / spermXHXHXHXHXHYXHYXHXhfemale / eggsXHXhXHXhXHXhXHXhXhYXhY
33 Hemophilia is a sex-linked recessive trait defined by the absence of one or more clotting factors. These proteins normally slow and then stop bleeding.Individuals with hemophilia have prolonged bleeding because a firm clot forms slowly.Bleeding in muscles and joints can be painful and lead to serious damage.Individuals can be treated with intravenous injections of the missing protein.
34 Dominant ≠ most common allele Because an allele is dominant does not mean…it is better, orit is more commonPolydactylydominant allele
35 Polydactyly recessive allele far more common than dominant individuals are born with extra fingers or toesthe allele for >5 fingers/toes is DOMINANT & the allele for 5 digits is recessiverecessive allele far more common than dominant only 1 individual out of 500has more than 5 fingers/toes so 499 out of 500 people are homozygous recessive (aa)