Mendel and HeredityGregor Mendel (1850s) Austrian monk that bred pea plants and from his experiments he formed the basis of GENETICS: study of heredityUsed peas because they had easily distinguishable forms of various traits: flower color, pod shape/color, seed shape/color, plant height and flower placementEasy to grow and matured quicklyTraits are determined by genes received from each parent

Mendels Experimental Design1. Allowed peas to self-pollinate for several generationsPurple flowering plants would produce only purple flowering plants (same for white flowering plants)These were the P or parent generationMendel started his experiments with these2. Cross-pollinated 2 varieties that had contrasting traits (purple flowers X white flowers)pollen from white plant was placed on the stigma of the purple flowerOffspring of this cross would be the F1 generation (filial)--only 1 flower color was present: purple3. Allowed the F1 plants to self-pollinate, planted seeds and the offspring were the F2 generation; rec trait (white) showed up againMendel named the trait that disappeared the recessive trait and the one that showed he called the dominant traitAfter counting all the F2 offspring he found that there was always a 3:1 ratio of purple:whiteMendel found this to be true of ALL the peas identifiable traits

Mendels Theory of HeredityParents pass on genes to offspringnot actual traitsFor each trait, an individual has 2 genes governing that trait: 1 from Mom and 1 from DadIf both genes carry the same info (purple, purple) then the individual is HOMOZYGOUS for that traitIf the genes are different (purple, white) then the individual is HETEROZYGOUS for that traitEach copy of a gene is called an allele; set of alleles that an individual has is called a genotype : PP, Pp or ppshows genes from parents as capital or lower case lettersCapital letters are dominant traits, lower case are recessive traits (ALWAYS use the first letter of the dom trait)Phenotype (purple/white flowers) is the physical appearanceDom allele (capital letter) is expressed, rec allele (lower case letter) is still present but is unexpressed; this rec allele CAN still be passed on to offspring where it might be expressed

Laws of HeredityLaw of Segregation---alleles separate when gametes are formed during meiosis and the chromosomes separateLaw of Independent Assortmentpairs of alleles separate independently of one another during meiosisfor example, if the gamete is heterozygous (Pp) before meiosis, the dom allele (P) goes into 1 new gamete and the rec allele (p) goes into anotherWhat phase of meiosis would this occur?

Legend steps for Genetic Crosses1. Read the word problem and determine WHAT is being crossed2. Determine dom and rec traits from the problem or your text bookALWAYS use the first letter of the dom trait in the problem; capitalize it if dom, lower case if rec3. Using steps 1 & 2 write the parents genotypes4. Draw a punnett square to show the cross--s genotype goes on top of square, s on the side; fill in the boxes with the offsprings possible genotypes5. Write the offsprings possible genotypes in a ratio, always starting with the homozygous dom, then hetero, then homozygous rec6. Write the possible phenotypes in a ratio

Probability Lab or the PENNY LAB!Intro: Mendels crosses can be explained by the rules of probabilitythe likelihood that a specific event will occur, or to put it another way: # of 1 kind of possible outcomesTotal # of all possible outcomesEx : probability that a baby will be a girl? Kind of possible outcomes is 1 and the total # of outcomes is 2 (either boy or girl) so the probability is Purpose: To relate probability to genetic crossesProcedure: Pair up, make a chart, take 2 coins of the same type, toss coins 100 times each, at the same time, record #s in the chart with tally marks, figure % error, place your results in the class chart on the whiteboardConclusion: 1. How does the probability change with the increasing # of tosses?2. What parent genotypes were present?

Other types of crossesWe have been practicing monohybrid crossesthose that deal with only 1 trait (flower color or pod shape, etc)Dihybrid crosses involve 2 different traits; the steps are all the same, except the punnett square has 16 boxes instead of 4! Lets try one!In guinea pigs the allele for short hair (S) is dom over long hair (s) and the allele for black hair (B) is dom over brown hair (b). So if the guinea pig farmer mated a hetero short haired brown male g.p. with a hetero short haired brown female g.p., the steps would look like this:1. hetero short, homo brown X hetero short, homo brown2..S=short, s=long B=black, b=brown3. Ssbb X Ssbb4. Use foil method to determine the parents gametes:Sb Sb sb sbSb SSbb SSbb Ssbb SsbbSb SSbb SSbb Ssbb Ssbbsb Ssbb Ssbb ssbb ssbbsb Ssbb Ssbb ssbb ssbb

5. 4 SSbb : 8 Ssbb : 4 ssbb6. 12 short haired brown: 4 long haired brown

Incomplete Dominance

Complete dom is when the dom trait completely masks the rec trait (Rr = red)Incomplete dom is when you have an intermediary trait in the hetero phenotype (Rr = pink)Common in some flowers like snapdragonsBook uses R and R instead of R and r we will use R (red) and r (white) and you will be told that the problem is Inc domStill supports Mendels Laws of Heredity and the steps are the sameCross a pink snapdragon with a red one

CodominanceWith codominance you have 2 dominant traits that are both expressedBoth the letters are used and both are capitalsRoan coat in horses and cattle is an exampleRed (R) is dom and so is white (W), so when both are present in the genotype (RW) the phenotype is not spotted, but both colors are expressedTry crossing a roan bull with a white cowBlood types are this sort of genetic problemmore about that later..