Genetics&The Work of Mendel
Modern 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 methodGregor Mendel
Pollen transferred from white flower to stigma of purple flower all purple flowers resultMendels work?self-pollinateBred pea plantscross-pollinate true breeding parentsraised seed & then observed traitsallowed offspring to self-pollinate & observed next generation
Mendel collected data for 7 pea traits
Looking closer at Mendels workParentsXself-pollinate
What did Mendels findings mean?Some traits mask others purple & white flower colors are separate traits that do not blend purple x white light purplepurple masked whitedominant allele functional proteinaffects characteristicmasks other alleles recessive allele no noticeable effectallele makes a non-functioning proteinhomologous chromosomesIll speak for both of us! allele producing functional proteinmutant allele malfunctioning protein
Genotype vs. phenotypeDifference between how an organism looks & its geneticsphenotype description of an organisms traitgenotype description of an organisms genetic makeupExplain Mendels results usingdominant & recessive phenotype & genotype
Making crossesCan represent alleles as lettersflower color alleles P or ptrue-breeding purple-flower peas PPtrue-breeding white-flower peas ppPp
Punnett squaresPp x Pp3:11:2:1%genotype%phenotypePPPpPppp1stgeneration(hybrids)Aaaaah,phenotype & genotype can have different ratios
2007-2008Beyond Mendels Laws of Inheritance
Extending Mendelian geneticsMendel 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!
Incomplete dominanceHybrids have in-between appearanceRR = red flowersrr = white flowersRr = pink flowersmake 50% less colorRRRrrrRRWWRW
Incomplete dominancetrue-breedingred flowerstrue-breeding white flowersXPself-pollinate
Incomplete dominanceRRRWWWRW1:2:11:2:1%genotype%phenotypeRW x RW
CodominanceEqual dominancehuman ABO blood groups3 versionsA, 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 cellsname tag of red blood cell
One gene: many effectsThe genes that we have covered so far affect only one traitBut most genes are affect many traits 1 gene affects more than 1 traitdwarfism (achondroplasia)gigantism (acromegaly)
Acromegaly: Andr the Giant
Aa x aaInheritance pattern of AchondroplasiaaaAaAaAaAa x AaAaaaaaAa50% dwarf:50% normal or 1:1AAaaAa67% dwarf:33% normal or 2:1Aa
Many genes: one traitPolygenic inheritanceadditive effects of many geneshumansskin colorheightweighteye colorintelligencebehaviors
Human skin colorAaBbCc x AaBbCc can produce a wide range of shadesmost children = intermediate skin color some can be very light & very dark
AlbinismJohnny & Edgar Wintermelanin = universal brown color
Coat color in other animals2 genes: E,e and B,bcolor (E) or no color (e)how dark color will be: black (B) or brown (b)EBEbbeeBeebb
Phenotype is controlled by both environment & genesColor of Hydrangea flowers is influenced by soil pH Human skin color is influenced by both genetics & environmental conditionsEnvironment effect on genesCoat color in arctic fox influenced by heat sensitive alleles
Genetics of sexWomen & men are very different, but just a few genes create that differenceIn mammals = 2 sex chromosomes X & Y2 X chromosomes = female: XXX & Y chromosome = male: XYXYXX
Sex-linked traitsSex chromosomes have other genes on them, tooespecially the X chromosomehemophilia in humansblood doesnt clotDuchenne muscular dystrophy in humansloss of muscle controlred-green color blindnesssee green & red as shades of greyXYXX
Dominant most common allelePolydactylydominant alleleBecause an allele is dominant does not meanit is better, orit is more common
Polydactyly recessive allele far more common than dominant only 1 individual out of 500 has more than 5 fingers/toes so 499 out of 500 people are homozygous recessive (aa)the allele for >5 fingers/toes is DOMINANT & the allele for 5 digits is recessive individuals are born with extra fingers or toes
Hound Dog Taylor
****He 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 Mendels 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.
**P = parentsF = filial generation****In 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.
**************************The genes that we have covered so far affect only one phenotypic character, but most genes are pleiotropic****************The relative importance of genes & the environment in influencing human characteristics is a very old & hotly contested debate
a 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 experiences
******Duchenne 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.
****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.