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Course Outline: 

Course Outline Genetic Data Analysis Probability andamp; Statistics Deviations from Mendelism Epistasis; Unusual Modes of Inheritance Chromosomal Inheritance Chromosomal Abnormalities; Sex Determination Mapping Gene and Genome Mapping Traits Affected by Genes andamp; Environment Quantitative Traits Genes in Populations Genetic Mechanisms of Evolution; Population Genetics of Disease and Disease resistance

Deviations from Mendelian ratios: 

Deviations from Mendelian ratios Lethal Alleles Epistasis Sex linkage Sex influenced inheritance Genetic Anticipation

Mendelian Ratios: 

Mendelian Ratios 3:1 1:2:1 9:3:3:1

Manx Cats: 

Manx Cats

Lethal alleles: 

Lethal alleles F1: Mm x Mm F1: 1 MM 2 Mm 1 mm F2: 1 Lethal: 2 Manx: 1 Normal F2 phenotypic ratio: 2:1 instead of 3:1

Other lethal mutations: 

Other lethal mutations Achondroplasia (humans) Yellow body color (domestic mice) Curly wings (Drosophila)

Epistasis: 

Epistasis Genetic interaction between two (or more) loci. One gene modifies the phenotypic effects of another gene.

Slide8: 

Agouti: wild type

Slide9: 

F2 Phenotype ratio: 9 agouti : 3 black : 4 albino F1: agouti P: agouti albino F2: 9/16 B- C- 3/16 bb C- 3/16 B- cc 1/16 bb cc Simple dominant phenotype? novel phenotype BB CC x bb cc Bb Cc Effect of B locus depends on genotype at C

Slide10: 

Epistasis Normal dihybrid ratio is altered from 9:3:3:1 to 9:3:4 C and B genes have an epistatic interaction

Epistasis: 

Epistasis Locus 1 Locus 2 BB Bb bb CC Cc cc agouti agouti black no effect no effect albino

Biochemical model: 

Biochemical model CC or Cc: tyrosinase is produced (involved in production of melanin) BB or Bb: controls distribution of the pigment

Practice Problem: 

Practice Problem In Labrador retrievers, coat color is controlled by two loci each with two alleles: B,b and E,e respectively. When pure breeding Black labs with genotype BB EE are crossed with pure breeding yellow labs of genotype bb ee the resulting F1 offspring are black. F1 offspring are crossed (Bb Ee x Bb Ee). Puppies appear in the ratio: 9/16 black; 3/16 chocolate; 4/16=1/4 yellow. What genotypes correspond to these three phenotypes?

Practice Problem: 

Practice Problem In the summer squash (Cucurbita pepo) fruit shape is determined by two genes. Two different true-breeding spherical types were crossed. The F1's were all disk, and the F2's segregated 35 disk, 25 spherical and 4 long. Explain these results. What’s the first step? Notice novel phenotypes in F1 and F2: disk, long. What’s the next step? Notice there are three F2 phenotypes. What kind of inheritance will give three F2 phenotypes? Genetic Model? Incomplete, codominance Epistasis Expected F2 ratio? 1:2:1 Variation on 9:3:3:1

Practice Problem, cont.: 

Practice Problem, cont. In the summer squash (Cucurbita pepo) spherical fruit is recessive to disk, True-breeding spherical types from different geographic regions were crossed. The F1's were disk, and the F2's segregated 35 disk, 25 spherical and 4 long. Explain these results. Are the phenotypic ratios closer 1:2:1 or to a variant of 9:3:3:1 ? If phenotypic ratios closer to a variant of 9:3:3:1, then what variant is it? Total # of individuals = 35 + 25 + 4 = 64 64/16 = 4 9*4 = 36 6*4 = 24 1*4 = 4 Phenotypic ratio close to 9:6:1

Practice Problem, cont.: 

Practice Problem, cont. In the summer squash (Cucurbita pepo) spherical fruit is recessive to disk, True-breeding spherical types from different geographic regions were crossed. The F1's were disk, and the F2's segregated 35 disk, 25 spherical and 4 long. Explain these results. If phenotypic ratios are close to 9:6:1, then what are the genotypes associated with each phenotype? 35 disk 25 spherical 4 long What were the genotypes of the original spherical parents? a) AABB, aabb b) AABB, AAbb c) AAbb, aaBB d) Aabb, AaBB e) none of these

Other kinds of epistasis: 

Other kinds of epistasis 1/16 aabb 9/16 A-B- 3/16 A-bb 3/16 aaB- Hint: usually given numbers, not fractions 27 agouti; 12 albino; 9 black

Slide18: 

Yellow Brown X F2 generation F1 generation Parental generation Red 9/16 Yellow 3/16 Brown 3/16 Green 1/16 Red Self-fertilization Practice problem: assign genotypes to P, F1, and F2 phenotypes

Deviations from Mendelism: 

Deviations from Mendelism Sex Linkage

X Linkage: mammals, flies: 

X Linkage: mammals, flies Diploid XAXa XAY Adults Gametes

X Linkage: mammals, flies: 

X Linkage: mammals, flies Diploid XAXa XAY Adults Gametes XAXA XAXa XaY XAY Female Male

Slide22: 


Hairy ears: 

Hairy ears

Slide24: 

Pedigree of Y-linkage A)

Sex Linkage: birds, butterflies: 

Sex Linkage: birds, butterflies Diploid ZBW ZBZb Adults Female Male Gametes ZBZb ZBW ZbW ZBZb Female Male

Slide26: 

Male pattern baldness: what kind of inheritance?

Sex influenced phenotype: 

Sex influenced phenotype Genotype Female Male bb Bald Bald bb’ Not bald Bald b’b’ Not bald Not bald

Slide28: 

Pedigree A) X linkage B) Y linkage C) Sex-Influenced D) Autosomal Dominant E) Autosomal Recessive

Environment-dependent expression of a genotype: 

Environment-dependent expression of a genotype

Siamese or “Himalayan”: 

Siamese or 'Himalayan' Different allele of the C locus that causes albinism. Temperature sensitive.

Phenotypes are not always a direct reflection of genotypes: 

Phenotypes are not always a direct reflection of genotypes Temperature-sensitive alleles: Siamese color pattern Nutritional effects: phenylketonuria Genetic anticipation: several genetic diseases

Phenylketonuria: 

Phenylketonuria Nutritional defect: can’t metabolize phenylalanine. Can lead to severe physical and mental disorders in children, but only if they consume phenylalanine. Disease phenotype can be avoided by eliminating phenylalanine from the diet

Genetic Anticipation: 

Genetic Anticipation Huntington disease Fragile-X syndrome Kennedy disease Myotonic muscular dystrophy

Fragile X syndrome: 

Fragile X syndrome Symptoms: delayed development andamp; mental retardation. More severe in males than females Caused by expansion of triplet repeat (CGG) in a gene on the long arm of the X chromosome Named for breakage of X chromosome in cell preparations.

Fragile X: 

Fragile X Normal range: 7-52 (average=30) 'Pre-mutation': 60-200 repeats Full Mutation: andgt; 230-1000s. DNA becomes abnormally methylated, promoter is inactivated, and gene silenced. Pre-mutation is unstable: maternally-inherited premutation with andgt;100 repeats almost always expands to a full mutation

Genetic Anticipation: Fragile X: 

Genetic Anticipation: Fragile X Most common kind of inherited mental retardation. Named for 'fragile site' Due to expansion of 3-base pair repeat (CGG) in a gene near the tip of the long arm of X chromosome.

Fragile X: 

Fragile X Pre-mutation is unstable: maternally-inherited premutation with andgt;100 repeats almost always expands to a full mutation

Slide38: 

Genetic Anticipation causes subsequent generations in a family to be more severely affected by a disease. It does this by increasing the number of triplet repeats in the fragile area of the X chromosome through the generations. CCG repeats

Huntington Disease: 

Huntington Disease Autosomal dominant lethal (chromosome 4) Progressive neurological deterioration First symptoms appear after reproductive age One of 8 known neurodegenerative diseases caused by expansion of (CAG) repeats All show inverse correlation with age of onset and number of repeats.

Huntington Disease: 

Huntington Disease Autosomal dominant lethal (chromosome 4) Progressive neurological deterioration First symptoms appear after reproductive age One of 8 known neurodegenerative diseases caused by expansion of (CAG) repeats All show inverse correlation with age of onset and number of repeats.

Huntington Disease: 

Huntington Disease Autosomal dominant lethal (chromosome 4) Progressive neurological deterioration First symptoms appear after reproductive age One of 8 known neurodegenerative diseases caused by expansion of (CAG) repeats All show inverse correlation with age of onset and number of repeats.

Which is the pedigree of autosomal dominant (like HD): 

Which is the pedigree of autosomal dominant (like HD)

Organelle inheritance: 

Organelle inheritance Mitochondrial Chloroplast

Mitochondrial inheritance: 

Mitochondrial inheritance Cytoplasmic inheritance: maternal Myoclonic epilepsy and red-fiber disease (MERRF) Muscular uncoordination, deafness, dementia, and epileptic seizures Mutation in a mitochondrial gene interferes with translation of mitochondrial proteins Skeletal muscle cells have blotchy red patches due to excess proliferation of mitochondria

Draw a pedigree of a mitochondrial inherited trait: 

Draw a pedigree of a mitochondrial inherited trait Three generations, beginning with an affected woman

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