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HMB265H1 Study Guide - Final Guide: Amine, Viral Vector, Xyy Syndrome

Human Biology
Course Code
Maria Papaconstantinou
Study Guide

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HMB265H1 Lecture Notes Condensed
Maria Papaconstantinou’s Section 1: Lectures 1-11
Lecture 2: Mendelian Genetics
Qualities of a good model organism:
o Short generation time, can be self-fertilized (inbred), simple reproductive biology, many progeny
Law of Segregation: two members of gene pair segregate from each other into gametes
o One half of gamete carry one member of pair, so does other: Aa A and a
o Alleles unite at random at fertilization one from each parent
Law of Independent Assortment: segregation of alleles are not affected by other loci results in
predictable phenotypes in the F2, creates equal chance for all four gamete combinations
o So an individual with Yy Rr will segregate into these gametes: YR, Yr, yR,yr
Test crosses can be done with fully recessive individual to uncover traits of the target
o This will reveal any recessive alleles that are hidden
o Monohybrid (3:1) or dihybrid (9:3:3:1) will work with this method
Laws of Probability for Multiple Genes
  
Sum Rule: Calculates the probability that A or B will occur mutually exclusive events
o Add each of the probabilities together, as shown below left
Product Rule: Calculates the probability that A and B will occur independent events
o Multiply each of the individual probabilities together, as shown below right
Lecture 3: Molecular Basis of Genetic Polymorphisms and
Their Detection
Wildtype = allele whose freq >= 1%
Mutant = allele whose freq < 1%
Monomorphic: gene with only one wt; polymorphic: gene
with > 1 wt

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Lecture 4: Mendelian Traits in Humans and Pedigree Analysis
Autosomal Inheritance: Affects non-sex chromosomes so everyone has same chance of getting
Dominant: Homozygous and heterozygotes individuals have same phenotype
o Affected phenotype does not skip a generation vertical pattern of inheritance
o Affected children always have at least one affected parent
o Two affected parents produce unaffected children if parents are heterozygous
o Most deleterious traits are not passed on
o Those who marry into the family are assumed to be homozygous dom unless said otherwise
Recessive: only homozygous recessive exhibit affected phenotype
o May skip generations horizontal pattern of inheritance
o Affected can be children of two unaffected carriers (heterozygotes)
Esp seen in consanguineous matings often uncovers recessive traits
o All children of two affected should be affected
o Rare recessive traits show a horizontal pattern not seen in earlier generations
o May show vertical pattern if trait is very common in the population
Probability and Pedigrees
Product law for independent events: parents are Bb and want a child that is BB
o Sperm with B allele = ½ ; Ovum with B allele = ½
o BB child = P(sperm B) x P(ovum B) = ½ x ½ = ¼ chance
Sum law for dependent events: both parents Aa, and want child Aa
o P(sperm A) = P(sperm a) = P(ovum A) = P(ovum a) = ½
o This is different than first example bc there’s multiple scenarios to get desired result
o Aa child = P(sperm A) x P(ovum a) + P(sperm a) x P(ovum A) = ¼ + ¼ = ½
Pedigree Key
Lecture 5: Extensions of Mendelian Genetics I

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Codominant Alleles
Blood can have more than two alternatives: IA, IB, i
o 6 genotypes ensue, but 4 phenotypes as there is a dominance series of: IA = IB > i
o Both alleles are expressed in heterozygotes ABO codes for cell surface protein, making antigen
o A and B antigens can be present
Establishing Dominance Relations: perform
reciprocal crosses between pure-breeding lines
Look at phenotype of heterozygote to
determine dominance relationships
Pleiotropy: Single gene determines more than one distinct, unrelated
characteristics some are lethal
One gene has many symptoms or controls several functions Ex.
porphyria variegata (auto dom)
o Mutation here leads to non-func enzyme, leading to porphyrin
accumulation = toxic
o Decrease in hemoglobin, leading to symptoms like mad behaviour
Lethality: one allele of the agouti mice results in yellow fur or death
o Yellow mice can’t breed true as two copies of the yellow genes
results in death in utero
o Results in a 2:1 genotypic:phenotypic ratio, shows danger of
consanguineous mating
Other Notes
Variable expressivity: phenotype that varies in intensity diff levels of symptoms for cystic fibrosis
Incomplete penetrance: phenotype not always expressed with genotype 80% have polydactyly
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