Presentation on theme: "Mendelian Genetics We know what genotype and phenotype are"— Presentation transcript:
1 Mendelian Genetics We know what genotype and phenotype are We know what genes areWhat do genes do?Genes provide the instructions for an organism’s potential developmentWhy potential ?What affects the phenotype?
2 Mendelian GeneticsPhenotype is affected by genotype, environment chemicals & other genesExample: 1Why is this horse black & white?His genotype is either EE or Ee for black colorWhy the white markings?
3 Mendelian GeneticsRemember the phenotype is affected by other genes as wellThe “other” gene is called the Tobiano gene, which overrides and cancels any color production at all in those locationsWhy the white markings?The gene for black hair production has been turned “off” or overridden at those locations
4 Mendelian Genetics Example: 2 – Your height The genes you received from mom & dad determine your genotypeHowever, environmental factors, diet and hormone involvement affect the phenotypeCan different genotypes result in the same phenotype?Can the same genotypes result in different phenotypes?
5 Mendelian Genetics Gregor Mendel (1822-1884) So someone who is “supposed” to be 6’3” but doesn’t get the nutrition probably won’t reach that heightThe opposite could be true for someone who is “supposed” to be 5’8” and gets too much hormone, they could be tallerGregor Mendel ( )1843 – admitted into Augustinian Monastery1854 – began series of breeding experiments with pea plants- no knowledge of mitosis or meiosis
6 Mendelian Genetics 1865 – reports conclusions of experiments KEY POINTS:- began studying the inheritance of only 1 trait at a time- controlled matings- kept accurate records of outcomesWhy pea plants?Easy to handle, produce lots of offspring, short life cycle, variation existed
7 Mendelian Genetics Mendel allowed the plants he had to Self-pollinate (selfing) – pollen fertilizes an egg from the same flowerFor many generations to attain true-breedersThere were 7 traits he studied in his experiments1. Flower & seed coat color2. Seed color5. Pod shape3. Seed shape6. Stem height4. Pod color7. Flower position
9 Mendelian Genetics Mendel had to be sure these plants didn’t Self-pollinateTo manage this he removed the male parts (anthers) and used them where he desired toCross-pollinate – pollen fertilizes an egg from a different flowerPhenotypes of the resulting seeds (peas) were analyzed and then planted to produce the next gen
10 Mendelian Genetics P-generation P X P = F F1 X F1 = F2 (through self-fertilization)Monohybrid crossesReciprocal crosses – done in both directionsEx. Wrinkled female x smooth male AND Smooth female x wrinkled maleIf the results are the same…If the results are different…
11 Mendelian GeneticsF1 generation always showed traits of one parent, not both (dominant vs recessive)F2 generation showed traits of both parents (3:1) (1:2:1)Mendel reasoned that there were “factors” (genes) that were passed from parent to offspringSince the 2 traits he was examining replaced each other they were assumed to be alternative forms of the same trait (alleles)Homozygous / heterozygousPunnett squares
12 Mendelian Genetics Medel’s principle of segregation - The two members of a gene pair (alleles) segregate from each other during gamete formationThis means that all offspring carry one allele from each parent – the combination of alleles in the offspring is completely randomT1T2 x T3T4T1T3 / T1T4 / T2T3 / T2T4Branch or Fork Diagram
14 Mendelian GeneticsWhat do punnett squares or the branch diagram actually show us?Possible outcomes, not actual – the percentages are for each offspring producedWild-type allele – the allele of a gene that is present in the highest frequency in a wild population*mutations to these genes could produce nonfunctional, partially functional or totally absent proteins
15 Mendelian Genetics*If the function of the protein is lost due to the mutation it is called a loss-of-function mutation (usually recessive)
16 Mendelian GeneticsMendel’s Principle of Independent Assortment – genes on different chromosomes behave independently in gamete productionThis means that the passing of one gene has no correlation with the passing of a second gene (TtGg) – the passing of the ‘T’ has no correlation with the passing of the ‘G’.Complete a punnett square for the cross TtGg x ttGg16
23 Mendelian GeneticsDihybrid cross – cross between 2 individuals that are ‘dihybrid’, meaning they are both hybrid for 2 traits (TtGg x TtGg – 9:3:3:1)If you were to test 2 traits at the same time…P generation: TTGG x ttgg both are ‘true-breeders’ therefore the F1 would be TtGg, completely hybridTrihybrid cross – cross between 2 individuals that are hybrid for 3 traitsP generation: TTGGBB x ttggbb both are ‘true-breeders’ therefore the F1 would be TtGgBb, completely hybrid23
24 Monohybrid cross produces ____ phenotypes Mendelian GeneticsMonohybrid cross produces ____ phenotypes2Dihybrid cross produces ____ phenotypes4Trihybrid cross produces ____ phenotypes8Can you come up with a mathematical formula to be able to determine the number of phenotypes produced in a genetic cross?2nn = number of independently assorting, heterozygous gene pairs24
25 Monohybrid cross produces ____ genotypes Mendelian GeneticsMonohybrid cross produces ____ genotypes3Dihybrid cross produces ____ genotypes9Trihybrid cross produces ____ genotypes27Can you come up with a mathematical formula to be able to determine the number of phenotypes produced in a genetic cross?3nn = number of independently assorting, heterozygous gene pairs25
26 Pedigree AnalysisGenetic evaluation of human inheritance is difficult because it is not ethically possible to control the matingsTherefore we often rely on pedigree analysis to determine patterns of inheritance (how it is passed from gen to gen)How do we know if genes are passed? We rely strictly on phenotypes over several generationsProband – affected individual in which the pedigree is discovered
27 Pedigree SymbolsMaleAffected / UnaffectedFemaleCarrier / HeterozygousMatingCarrier of sex-linkedParents with 1 boy and 1 girl (birth order)StillbirthTwinsMarriage of blood relatives
28 Pedigree AnalysisGenerations – numbered with Roman numerals (II)Individuals – numbered with Arabic numerals (2)Refer to a particular person as II - 2*If affected individual is born to unaffected parents:probably caused by recessive trait*If affected individual is born to affected parents:May be caused by dominant or recessive traitRecessive TraitsRequire homozygosityMay have originated from a mutation
32 Recessive TraitsEx. albinismIn U.S. – 1 in 17,000 of the white population1 in 28,000 of the African American pop1 in 10,000 of the Irish populationOf those affected by rare recessive traits…1. Most have “normal” parents (heterozygous)2. Matings between heterozygous individuals should produce a 3:1 ratio of “normal” progeny3. When both parents are affected, homozygous, their offspring will usually exhibit the trait
33 Dominant TraitsExpressed when heterozygous or homozygousDominant mutant alleles produce phenotypes due to gain-of-function mutations they produce new genes with new functionsEx. Woolly hair, Achondroplasi,Brachydactyly, Marfan syndromeBecause mutant dominant alleles are rare it is rare to find an individual homozygous for the mutant dominant allele
34 Dominant TraitsCharacteristics of dominant inheritance1. An affected individual must have an affected parent2. Usually does not skip generations3. Heterozygous individual will transmit the mutant gene to half their progeny
35 Mendelian GeneticsHow can one determine the genotype of an individual exhibiting the dominant phenotype?Test cross – cross of an individual of unknown genotype, usually dominant, with a homozygous recessive individual to determine the unknownData resulting from genetic crosses rarely match the “expected” ratiosIt is the job of the geneticist to do statistical analysis to understand the significance of the deviation from the predicted results35
36 Questions1. A purple-flowered pea plant is crossed with a white-flowered pea plant. All the F1 plants produce purple flowers. When the F1 plants are allowed to self-pollinate, 401 of the F2 have purple flowers and 131 have white flowers. What are the genotypes of the parental and F1 generation plants?ANSWER: P – PP x ppF1 – Pp x PpF2 – probably deduce a 1:2:1ratio
37 Questions2. Consider 3 gene pairs Aa, Bb, and Cc, each of which affects a different character. In each case the uppercase latter signifies the dominant allele and the lowercase letter the recessive allele. These 3 gene pairs assort independently of each other. Calculate the probability of obtaining a the following:a. an AaBBCc zygote from a cross of individuals that are AaBbCc x AaBbCc
38 Questionsb. an AaBBcc zygote from a cross of individuals that are aaBBcc x AAbbCCc. an A_B_C_ phenotype from a cross of individuals that are AaBbCC x AaBbccd. an aabbcc phenotype from a cross of individuals that are AaBbCc x aaBbcc
39 Questions3. In chickens, the white plumage of the leghorn breed is dominant over colored plumage, feathered shanks are dominant over clean shanks, and pea comb is dominant over single comb. Each of the gene pairs segregates independently. If a homozygous white, feathered, pea-combed chicken is crossed with a homozygous colored, clean, single-combed chicken and the F1 are allowed to interbreed, what proportion of the birds in F2 the will produce only white, feathered, pea-combed progeny if mated to a colored, clean-shanked, single combed birds?
41 Questions4. In tomatoes, red fruit color is dominant to yellow. Suppose a tomato plant homozygous for red is crossed with one homozygous for yellow. Determine the appearance of:a. the F1 tomatoesb. the F2 tomatoesc. the offspring of a cross of the F1 tomatoes back to the red parentd. the offspring of a cross of the F1 tomatoes back to the yellow parent
42 Questions5. In maize, a dominant allele A is necessary for seed color, as opposed to colorless (a). Another gene has a recessive allele wx that results in waxy starch, as opposed to normal starch (Wx). The two genes segregate independently. An AaWxWx plant is testcrossed. What are the phenotypes and relative frequencies of offspring?
43 Questions6. In guinea pigs, rough coat (R) is dominant over smooth coat (r). A rough-coated guinea pig is bred to a smooth one, giving eight rough and seven smooth progeny in the F1 generation.a. What are the genotypes of the parents and their offspring?b. If one of the rough F animals is mated to its rough parent, what progeny would you expect?
44 Questions7. In cattle, the polled (hornless) condition (P) is dominant over the horned (p) phenotype. A particular polled bull is bred to three cows. Cow A, which is horned, produces a horned calf; polled cow B produces a horned calf; and horned cow C produces a polled calf. What are the genotypes of the bull and the three cows, and what phenotypic ratios do you expect in the offspring of these three matings?
45 a. What is the genotype of the mother? Questions8. Consider the following pedigree, in which the allele responsible for the trait (a) is recessive to the normal allele (A):a. What is the genotype of the mother?b. What is the genotype of the father?c. What are the genotypes of the children?d. Given the mechanism of inheritance involved, does the ratio of children with the trait to those without match what would be expected?