Chapter 11

Genetic traitswhich do you have?Widows peak vs. straight hairlineFree earlobes vs. attached earlobesDimples vs. no dimplesCleft chin vs. no cleft chinStraight thumb vs. curved thumbMid-digit hair vs. no mid-digit hairLonger 2nd toe vs. shorter 2nd toe (compared to big toe)Can roll tongue vs. cant roll tongue

Chapter 11Introduction to Genetics

11-1 the work of gregor mendelHeredity: transmitting genetic information from parent to offspringGenetics: the study of heredityGene: a piece of DNA that codes for a traitAlleles: a different form of a geneTrait: specific characteristic that varies between individualsGametes: specialized cells involved in sexual reproduction (eggs and sperm)Mendel and his peasA priest with a gardenStudied pea plantsMale part = stamenFemale part = pistilFertilization: joining of male and female partsForm a new cell (seed)

Pea plants = true breedingTrue-breeding: pass on ALL genetic traits to offspringSelf-pollinating- use male and female parts from same plantBreed offspring identical to parent

Cross-breedingUsing male and female parts from different plantsMendel attempted this with pea plantsAka: cross pollination

So what did mendel do?Identified 7 traitseach with 2 contrasting characteristicsCrossed those characteristicsResulted in hybrid plantsP generation (parents)F1 generation (offspring)

What did he find?Offspring only showed the traits of one parent2 conclusions:1. Inheritance is determined by factors passed from parent to offspring (genes and alleles)2. Principle of dominancesome alleles are dominant others recessive

Where did the recessive trait go?Next, Mendel allowed self pollination to occur againResults of F2 generation (offsprings offspring) of the plants = showed dominant trait of plants = showed recessive traitThe recessive trait was still therejust hiding

segregationSeparation of alleles during gamete formationOccurs so gametes only carry one type of alleleWhy we saw only one type of the trait

IIIIIIMomDadgametes11-2 probability and punnett squaresMendel repeated experiments, got same resultsProbability: likelihood that an event will occurEx: coin flip (1 in 2 odds)Each turn is independent of any previous or future turnsPrinciples of probability can be used to predict outcomes of genetic crosses

Punnett squaresUsed to predict/compare the genetic variations that will result from a crossAlleles:capital letter = dominantlowercase letter = recessive

Punnett squares(Tt)(Tt)Parents allelesThe boxes in the square contains every possible combination of alleles

Punnett squaresTT or tt = homozygous (2 identical alleles)Tt = heterozygous (2 different alleles)

TT or Tt = dominant allele will showtt = recessive allele will show

= dominant allele shown = recessive allele shown*3:1 ratio for dominant trait

Genotype vs. phenotypeGenotype: genetic makeupWhat the alleles are (TT, Tt or tt)Phenotype: physical characteristicsWhat you see (tall or short)

TT or TtttProbability and predictionsREMEMBER: probability only predicts averagesNOT precise outcomesLarger numbers of trials means outcomes closer to the probability

Punnett square example questionsIn seals, whisker length is determined by two alleles. W codes for long whiskers and is dominant over w which codes for short whiskers. Draw a Punnett square to show a cross between a homozygous long whiskered dad and a heterozygous long whiskered mom.What percentage of their offspring would have long whiskers? Short whiskers?What percentage of their offspring would be homozygous? What percentage would be heterozygous?Punnett square example answersWhat percentage of their offspring would have long whiskers?100%What percentage would have short whiskers?0%What percentage of their offspring would be homozygous?50%What percentage would be heterozygous?50%

11-3 exploring meNdelian geneticsMendels next question: do alleles separate independently?Tried crossing 2 traits at onceFound that round (R) peas and yellow (Y) peas were dominant traitsWould they stay together or separate?

Law of independent assortmentGenes for different traits will segregate independently of each other during gamete formation

Accounts for all genetic variation!

Summary of mendels principles Inheritance of traits is determined by genes (alleles) passed from parent to offspring

When 2 or more alleles exist, some will be dominant and some will be recessive

In sexually reproducing organisms, each adult has 2 copies of each gene which separate when gametes are formed

Alleles for different traits usually separate independentlyExceptions to the rulesGenetics is very complicatedSome alleles are not simply dominant/recessiveSome traits controlled by multiple genes

Incomplete dominanceOne allele is not completely dominant over anotherA mixing occursEx: Mirabilis plant- crossing red flowers with white flowers gives you pink flowers

Xcodominance2 dominant alleles (both will contribute to the phenotype)Both alleles are present and can be seenEx: erminette chicken- has both black and white feathers

Multiple alleles3 or more alleles availableGives more options for the combination of allelesEx: blood types

Polygenic traitsTraits controlled by 2 or more genesEx: skin colorLOTS of variation

Applying mendels principlesThomas Hunt MorganUsed fruit fliesAll principles held true

Genetics and the environmentGenes act as the blue print plan for living thingsEnvironment will influence how the plan worksEx: sunflowerHeight and color determined by genesInfluenced by water, light, temperature, soil, etc.)

11-4 MeiosisMendels principles require 2 things:1. Organisms inherit single copy of genes from each parent2. Therefore, when gametes are formed, those copies must separate

Buthow?

chromosomesRemember: genes are found on chromosomesHalf come from mom and half come from dadEach chromosome has a corresponding chromosome(1 from mom and 1 from dad)Known as homologous chromosomes

ChromosomesDiploid- cells that contain both sets of homologous chromosomesHaploid- cells that contain only a single set of homologous chromosomesGametes!

mEIosisMeiosis: the process where chromosome # is cut in half by separating homologous chromosomes in diploid cells (makes gametes)

Turns 1 diploid cell into 4 haploid cellsInvolves meiosis I and meiosis II

Meiosis IMust go thru interphase first to replicate chromosomesProphase I- chromosomes pair with homologous chromosomes (these are called tetrads)Crossing over- exchange parts of chromatidsVery important for genetic variationGet new allele combinations

Meiosis 1 (continued)Metaphase I- line up across middle, attach to spindleAnaphase I- spindle pulls homologous chromosomes apartTelophase I- two new nuclear membranes formCytokinesis- two new diploid cells are formed

Important!After Meiosis 1, the 2 new diploid cells have shuffled sets of chromosomesFrom crossing overDifferent from each otherDifferent from original cellGenetic variation

Meiosis IIProphase II- sister chromatids condenseMetaphase II- sister chromatids line upAnaphase II- sister chromatids separateTelophase II and cytokinesis = 4 new haploid cells

Gamete formationMales = spermFemales = eggsusually, only 1 of the 4 produced are used in reproduction (actually become an egg)

Mitosis vs. meiosisMitosisEnd with 2 genetically identical diploid cellsRole: growth and replacement of cellsAsexual reproductionMeiosisEnd with 4 genetically different haploid cellsRole: make gametes

11-5 linkage and gene mapsLinkage: if genes are close to each other on a chromosome, they may be inherited linked togetherchromosomes follow the Law of Independent AssortmentNOT individual genes

Gene mapsGene maps: shows the relative locations of genes on a chromosomeHow can we tell this?The closer together genes are, the more likely they are to be linkedHuman Genome Project

Annemarie parisiWill you go to prom with me?

-EJ