2Gregor MendelIn the 1800s the popular inheritance theory was “blending”--offspring were a mixture of their parentsthis suggests that organisms will become uniform over time (we know this isn’t true)Mendel had a “particulate” theory (genes)this was observed through his observations of pea plants
3Mendel’s Peas.He carefully planned all his breeding experiments, taking careful notes on the results.his experiments started with true-breeding varietiesthen followed the offspring for 2 generations.(P, F1, and F2)
4dominant and recessive alleles Through thousands of crosses, Mendel’s observations led to 2 fundamental principles of heredity.Law of Segregationtwo alleles separate during gamete formation (meiosis) and end up in different gametesdominant and recessive allelestwo heterozygous parents crossed always have a phenotypic ratio of 3:1 (Punnett Squares)Law of Independent Assortmenteach pair of alleles segregates independently of each other pair of alleles during meiosisthe chance of inheriting one trait from either parent is separate from all other traitsfor typical Medelian inheritance only
6Non-Mendelian Inheritance Certain patterns of inheritance are more complex than those discovered by Mendel (either controlled by one gene or 2+ genes)When trait is controlled by a single gene...Complete Dominance--classic Mendelian patterns (strictly dominant or recessive)Incomplete dominance--neither allele is completely dominant (blending in heterozygous phenotype)flower colorCodominance--two alleles shown independently in heterozygous phenotypeanimal coloration
8multiple alleles-when a gene for a specific trait has more than two alleles. Results in multiple phenotypes.This usually works in combination with incomplete or codominanceHuman ABO blood groupsRabbit Fur Color
9pleiotropy--when a gene has multiple phenotypic effects. Single gene affects multiple things in an organism.Most genetic diseases present this wayCystic fibrosis and Sickle Cell anemia
10Lethal Genes: a gene that leads to the death of the organism when inherited in homozygous genotype (either dominant or recessive)Dwarfism in humans (dominant allele)Manx cats (recessive)Yellow coat color in mice (dominant)
11When a trait is determined by two or more genes... epistasis-the phenotype at one locus alters the gene at a second locusInteraction of two genes to control a single phenotype, does not have an additive effectMight mask another gene, or cause a completely new phenotypeLabrador Retrievers and coat color2 genes: E (pigment) e (no pigment) ; B (black), b (brown)
12polygenic inheritance--an additive effect of two or more genes on a single phenotypic character Many genes working together to determine a particular traitskin color, height, weight, hair color, eye color in humans
13When inheritance depends on chromosomes... sex-linked traits--specific traits are carried on the X or Y chromosome.results in some traits affecting boys more often than girlsX-linked traits: carriedon X chromosomefemales carriers;males have trait or not
14Sex-linked traits…Colorblindness, baldness, sickle-cell anemia, hemophilia, Duchenne muscular dystrophy all are examples of sex-linked traits.If a normal-sighted woman whose father was colorblind marries a colorblind man, what percentage of their sons will be colorblind? Daughters?
15Disorders Resulting from Altered Chromosomes Chromosome NumberDuring meiosis chromosomes can fail to split evenly (nondisjunction)AneuploidyResults in severe phenotypic changes in an individualDiagnosed via karyotypeDown Syndrome (trisomy 21)Klinefelters Sydrome (XXY)Turner Syndrome (X)
16Chromosome StructureSometimes parts of chromosomes are altered during cell division or altered due to environmentDeletion: missing pieceDuplication: extra pieceInversion: attach upside down in homologous pair, or within chromosmeTranslocation: piece joins non-homologous chromosomeCri du chat: deletion chromosome 5Leukemia: translocation (chromosome 9 attaches to 22) “Philadelphia Chromosome”Fragile X: duplication (repeat at end of X)
17Good Morning AP Bio!Today we are going to discuss our last type of inheritance pattern (linked genes)…then practice solving some of those problems.Reminder: Test corrections are due tomorrow!You will have time tomorrow to work through and finish your genetics practice problems packet (due Monday)
18Crossing Over… Revisited Remember: crossing over occurs during meiosis, when chromosomes trade allelesProduces “recombinant chromosomes”Some genes are located very closely on a chromosome, and are usually inherited together.They are called “linked genes”
19linked genes: genes located near each other on the same chromosome are often inherited together genes do not assort independently, so ratio of offspring varies depending on location of genesresult in genetic recombination (offspring with traits different from parents)This lack of independent assortment indicates the genes are on the same chromosome.
20http://www.bozemanscience.com/genetic- recombination-gene-mapping/ Thomas Morgan and his grad student first discovered linked genes in drosophila (fruit flies).When crossing a heterozygous wild-type fly (b+b vg+vg) to a black body, vestigial wings (b vg) he discovered allele frequencies that didn’t match the prediction83% parental types, 17% recombinant typesIdentified that crossing over had occurred.recombination-gene-mapping/
21Mapping a ChromosomeThe recombination frequency (%) is the same as the map units (distance) between genes on a chromosomeLess than 50% recombination = same chromosomeWe can use this information to map genesSmaller number = closer togetherGreater than 50% recombination = different chromosomeNot able to map
22Practice ProblemThe crossover frequency (recombination) between genes E and F is 6%, between E and G is 10% and between F and G is 4%.Determine the sequence of genes on the chromosome.
23When inheritance relies on other things… Environmental InfluenceNature vs. nurtureExpression of traits determined by environmental influences
24Nonnuclear Inheritance (mitochondria and chloroplasts) These organelles have their own DNA that replicates separately from nuclear DNAFollows non-mendelian inheritanceAll your mitochondrial DNA (mDNA) is from your mom!“mitochondrial diseases”—result from mutations in mDNA
25Genomic ImprintingPhenotype depends on if allele is inherited from mom or dad (autosomal)Allele from either parent is “silenced” by the presence of other alleleExample of epigeneticsAffects very few genes, not common
26Chimera Single organism composed of genetically distinct traits Two genomes, one organism!Results from multiple fertilized eggs fusing during development
27PedigreesUsed to visually trace traits within human families (helps identify inheritance patterns)Circle= femaleSquare = male