2 copyright cmassengale Mendelian Genetics4/20/2017Gregor Johann MendelBetween 1856 and 1863, Mendel cultivated and tested some 28,000 pea plantsHe found that the plants' offspring retained traits of the parentsCalled the “Father of Genetics"copyright cmassengale
4 Chromosomes and Genetics Genes are short regions of this DNA that hold the information needed to build and maintain the bodyHeredity- the passing of characters from parents to offspringGenetics- the branch of science that deals with heredity.
8 Ratios: Mendel’s Results When Mendel allowed the F1 plants to self-fertilize, the F2 generation included both purple-flowered and white-flowered plants.The white trait, absent in the F1, reappeared in the F2.Based on a large sample size, Mendel recorded 705 purple-flowered F2 plants and 224 white-flowered F2 plants from the original cross.
9 Mendel’s 4 HypothesesAlternative versions of genes account for variations in inherited characters, which are now called allelesconcept of alleles (P=purple, p=white)For each character an organism inherits two alleles, one from each parent. This set of alleles is called its genotype.If the two alleles at a locus differ, the dominant allele is fully expressed in the organism’s appearance (phenotype).The law of segregation - the two alleles for a heritable character separate (segregate) during gamete formation and end up in different gametesAllele for purple flowersLocus for flower-color geneHomologouspair ofchromosomesAllele for white flowers
10 Homozygous- when the two alleles of a particular gene present in an individual are the same Heterozygous-when the alleles of a particular gene present are different.
11 Mendel’s law of Segregation The two alleles for a character segregate (separate) when gametes are formed.
12 Mendel’s Law of Independent Assortment ~The alleles of different genes separate independently of one another during gamete formation.
13 Vocabulary Character –heritable feature Trait – each variant for a characterTrue-breeding – plants that self-pollinate all offspring are the same varietyMonohybrid cross – a cross that tracks the inheritance of a single characterP generation – (parental) true-breedingF1- (first filial) offspring of P generationF2 – (second filial) offspring from F1 cross
15 Punnett Squares: Probability Probability – predict likelihood of an event or outcomePunnett square – grid for organizing genetic informationCan be used to make predictions about a cross between two organsimsMonohybrid Cross – cross between two parents and one trait
16 Rules to the Punnett Square 1. Figure out the genotypes of the parents.TT & ttMomDad
17 Rules to the Punnett Square 2. Figure out what kinds of gametes the parents can produce.TT & ttMomDadtT
18 Rules to the Punnett Square 3. Set up a Punnett Square for your mating.MomT TtTtTtDadTtTt
19 Rules to the Punnett Square Genotype- genetic make-up (the alleles an organism has.) Phenotype – Physical Features or characteristics.
23 Autosomal traits vs. Sex-linked traits Autosomes – body chromosomes – first 22 pairSame in both male and femaleSex Chromosomes – 1 pair, last pairXX – FemaleXY - Male
24 Sex Linked TraitsTraits controlled by recessive genes located on sex chromosomes (normally associated with the X chromosome)Hemophilia – blood clotting enzymeis absentQueen Victoria’s family affected
25 Sex Linked TraitsRed – Green Colorblindness – individuals cannot distinguish between these two colors
27 Pedigree Charts Males = Females = Generations = Roman Numerals Individuals = Numbered sequentiallyTrait Expressed = Filled inNon Carriers = EmptyCarrier (not ill) = Half filledIndividual who carries a recessive allele that is not expressed
28 Pedigree ChartsChart which shows how a trait and the genes that control it are inherited within a familyIdentifies the presence or absence of particular trait in members of each generation
29 Today... Pedigree analysis In humans, pedigree analysis is an important tool for studying inherited diseasesPedigree analysis uses family trees and information about affected individuals to:figure out the genetic basis of a disease or trait from its inheritance patternpredict the risk of disease in future offspring in a family (genetic counseling)
30 Today... Pedigree analysis How to read pedigreesBasic patterns of inheritanceautosomal, recessiveautosomal, dominantX-linked, recessiveX-linked, dominant (very rare)Applying pedigree analysis - practice
31 Autosomal recessive traits Trait is rare in pedigreeTrait often skips generations (hidden in heterozygous carriers)Trait affects males and females equallyMost common onesCystic fibrosisSickle cell anemia
32 ex. achondroplasia (a sketelal disorder causing dwarfism) Autosomal dominant traitsThere are few autosomal dominant human diseases (why?), but some rare traits have this inheritance patternOnly need to get the trait from one parent to be affected.ex. achondroplasia (a sketelal disorder causing dwarfism)
33 X-linked recessive pedigrees Trait is rare in pedigreeTrait skips generationsMales are more often affected than femalesAffected fathers DO NOT pass to their sons,
34 ex. Hemophilia in European royalty X-linked recessive traitsex. Hemophilia in European royalty
35 X-linked dominant pedigrees Trait is common in pedigreeAffected fathers pass to ALL of their daughtersMales and females are equally likely to be affected
36 Beyond Mendelian Genetics: Incomplete Dominance Mendel was lucky!Traits he chose in thepea plant showed upvery clearly…One allele was dominant over another, so phenotypes were easy to recognize.But sometimes phenotypes are not very obvious…
37 Polygenic TraitsWhen a character (physical feature) is influenced by several different genes, the character is Polygenic.Examples: Height, weight, color of skin, hair, and eyesCause slight and often variable range of differences throughout population
38 Incomplete Dominance Snapdragon flowers come in many colors. If you cross a red snapdragon (RR) with a white snapdragon (rr)You get PINK flowers (Rr)!R Rr rGenes show incomplete dominance when the heterozygous phenotype is intermediate.R r
39 Incomplete dominance R r R r When F1 generation (all pink flowers) is selfpollinated, the F2 generation is 1:2:1red, pink, whiteR rR RR rr rRr
40 CodominanceTwo alleles affect the phenotype in separate and distinguishable ways.Neither allele can mask the other and both are expressed in the offspring and not in an “intermediate” form.
41 Multiple Alleles Blood Type Genes with 3 or more alleles are said to have Multiple alleles.Blood type is determined by three alleles, IA, IB, and i.The IA and IB alleles are both dominant over i, but neither IA, IB is dominant over the other (Codominance)
42 Environmental Impact on Phenotype pH of the soil will change the color of hydrangea flowers from blue to pink
44 Genetic Disorders Sickle Cell Anemia Cystic fibrosis Hemophilia A hereditary mutation is a mistake that is present in the DNA of virtually all body cellsGenetic Disorders arise from mutationsSickle Cell AnemiaCystic fibrosisHemophiliaHuntington's DiseaseHypercholesterolemia