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HMB265H1 Study Guide - Final Guide: F1 Hybrid, Ovarian Cancer, Mendelian Inheritance

Human Biology
Course Code
Maria Papaconstantinou
Study Guide

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HMB265H1 Final Exam Notes made by Man Lai Ho
Lecture 2: Mendelian genetics for single gene traits
Discrete: simple genetics (single gene traits)
Continuous: complex inheritance
oQuick and easy to make pure-breeding/inbred lines, genetically homogeneous lines that
show same characteristics, generation after generation
Both parents contribute hereditary material (biparental inheritance)
2 copies of each trait in somatic cell, Gametes contain one copy of the trait
Alleles (different forms of trait) segregate randomly
Inherited traits are dominant (expressed in F1 hybrid) and recessive (silent in F1 hybrid)
oDifference between genotype and phenotype
Law of independent assortment: different traits assort independently
Inheritance is particulate (blending does not happen)
oHereditary factors do not modify each other in a permanent way
Test cross allows distinction between genotype and phenotype
oCross with homozygote recessive
Dihybrid cross: YyRr X YyRr (normal ratios during independent assortment)
oBasics: ¼ YY, ½ Yy, ¼ yy
oY-R-: ¾ X ¾ = 9/16
oY-rr: ¾ X ¼ = 3/16
oyyR-: ¼ X ¾ = 3/16
oyyrr: ¼ X ¼ = 1/16
Lecture 3: Molecular basis of Genetic Polymorphisms
Allelic differences at DNA level can influence mRNA expression and/or protein function, thus the
oDNA->mRNA->protein->organismal traits
oE.g. SNP change in one AA disrupts activity of enzyme
Co-dominance at DNA level (Genotype)
Mutations: source of allelic variation
oPoint mutations
SNPs (Single nucleotide polymorphisms) are alleles
oChanges in repeat number
oChromosomal rearrangements
Gene expression with mutation
oNull: Alters protein
At promoters, exons
oLeaky: somewhat alters protein
Partially on exon
oSilent: usually no alteration
At introns (spliced out)
PKU (Phenylketonuria) (Single gene disorder)
oNormal: phenylalanine->tyrosine
oPKU: phenylalanine->phenylpyruvic acid (malfunction in phehydroxylase)
Buildup of phenylpyruvic acid interfere with nervous system development
oMutations in both exons and introns (interfere with splicing) inactivate gene, cause PKU

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HMB265H1 Final Exam Notes made by Man Lai Ho
BRCA1 gene
oTumour suppressor genes important in repairing DNA damage
oMutations in this gene interfere with DNA repair, lead to cancer risk (particularly breast
and ovarian cancer)
Hundreds of mutations found that increase risk
Haplosufficency: 50% of protein product is sufficient to give wild type phenotype
Haploinsufficiency: 50% of protein product is insufficient to give wild type phenotype
Dominant negative: Mutant allele inhibits other allele from expressing normal amount of protein
Detection of allelic polymorphism at molecular level
oPCR Amplification and DNA sequencing
Most comprehensive
oSNP detection
Of 1-3 more common mutations
Lecture 4: Mendelian Traits in Humans and Human pedigree analysis
Autosomal inheritance
oLocated on non sex chromosomes (1-22)
oAutosomal dominant
Aa (affected) X aa (unaffected)
½ affected, ½ unaffected progeny
AA and Aa exhibit affected phenotype
Males and females equally affected and may transmit trait
Affected phenotype does not skip a generation (trait tend to show up every gen.)
Affected children have at least one affected parent
oAutosomal recessive
Aa (unaffected) X Aa (unaffected)
¼ affected, ¾ unaffected progeny
aa exhibit affected phenotype
can be children of two unaffected carriers
Males and females equally affected and may transmit trait
May skip generations
oIf disease is rare, assume outside individuals to be wild type
Lecture 5: Extension to Mendelian Genetics Part 1
Incomplete dominance
oIntermediate phenotype: F1 hybrid distinct from either homozygous parents
oRR (red), RW (pink), WW (white)
oPhenotypic ratios same as genotypic ratios
oE.g. Familial Hypercholesteraemia
oF1 hybrids express phenotype of both parents equally
oPhenotypic ratios same as genotypic ratios
Genes may have multiple alleles that segregate in populations
oE.g. Blood type

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HMB265H1 Final Exam Notes made by Man Lai Ho
oDominance series
Establish dominance relations between multiple alleles in gene
Perform reciprocal cross between pure-breeding lines of all phenotypes
Pleiotropy: one gene, multiple phenotypes (1:2:lethal)
oUnusual ratios with two phenotypes
1 AA (black), 2 AyA (yellow), AyAy (lethal)
Incomplete penetrance: a given genotype will give certain phenotype only some of the time
oE.g. 75% of homozygous recessive individuals will have disease
Expressivity: phenotypes expressed to different degrees
oE.g. severity of disease can differ with same genotype
Role of environment: Rr flowers
oRed in bright light, cool temperatures
oWhite in Shady conditions, warm temperatures
Sickle-cell syndrome
oMultiple alleles (400+)
Wild type: HbβA; Mutant: HbβS
Pleiotropy: affects more than one trait
Sickling, resistance to malaria, recessive lethality, different dominance
Severe sickling and anemia at high altitudes, resistant to malaria
Lecture 6: Extensions of Mendelian genetics part 2
Complementation: 2+ genes interact, both control a phenotype (9:7)
o2 affected parents can give birth to unaffected progeny if each parent contributes a
different functional gene
oWorks by regulatory and downstream genes
oComplementation test
AAbb X aaBB -> AaBb
Works when phenotype is recessive
Tool to determine complementation groups (how many genes contribute to trait)
oE.g. Ocular-cutaneous albinism
oEffects of allele at one locus mask the effects of another locus
oRecessive epistasis (9:3:4)
Yellow –protein E-> Brown –protein B-> Black
9 B-E- (Black)
3 bbE- (Brown)
4 –ee (Yellow)
E locus epistatic to B locus
oDominant epistasis (12:3:1)
White –inhibitor W-> Green –Protein Y-> Yellow
12 W--- (White)
3 wwY- (Yellow)
1 wwyy (Green)
W is epistatic to Y
Departures from Law of segregation
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