FORS-2106EL Lecture Notes - Lecture 14: Product Rule, Genotype Frequency, Gregor Mendel
27 Jun 2018
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Forensic Biology - Day 14 2017.11.09.
Population Genetics
Genetcs: the study of patterns of inheritance of specific traits between parents and offspring
Populatons: groups of individuals, often classified by grouping together those sharing a common
ancestry
Populaton: a collection of interbreeding organisms living in a geographic area
-population genetics: amount and distribution of genetic variation within and among
populations
-Genetic diversity within a species is characterized by allele frequencies
-genetic variability is measured by the amount of gene heterozygosity
-changes in allele and genotype frequencies occur over time!
Gregor Mendel
-Studied pea plants in order to view their order of inheritance that gets passed on from
one generation to the next, like the seed colour, flower colour, pod colour, height, etc.
Laws of Mendelian Genetics
-Law of segregation: states that the two members of a
gene pair separate from each other during sex-cell
formation (meiosis), so that one half of the sex cell
carry one member of the pair and the other one half
of the sex cells carry the other member of the gene
pair. In other words, chromosome pairs separate
during meiosis so that the sex cells (gametes)
become haploid and possess only a single copy of a
chromosome
-Law of Independent Assortment: states that different
segregating gene pairs behave independently due to
recombination where genetic material is shuffled
between generation
Genotypes
-total number of possible genotypes in a population =
k(k+1) /2
-where k is the # of alleles at a locus
-k = expected # of homozygous genotypes
find more resources at oneclass.com
find more resources at oneclass.com
-k(k-1)/2 = expected # of heterozygote genotypes
-We can compare expected to observed genotypes and the number of individuals with
each genotypes
Hardy-Weinberg Equilibrium
-Frequency of A = p
-Frequency of B = 1
-p+q=1
-p2 + 2pq + q2 = 1
-Both independently discovered (in 1908) the mathematics
for independent assortment that is now associated with
their names as the principle
-HWE proportions of genotype frequencies can be
reached in a single generation of random mating
-HWE is a simple way to relate allele frequencies to
genotype frequencies
-Will predict how genotype frequencies will be inherited
from generation to generation
-Allele frequencies remain the same from one generation
to the next, following all assumption
-assumptions made:
-large, randomly mating population
-no mutation
-no gene migration (in or out)
-no selection
-no genetic drift
Example
population =n=150
genotypes
AA =54
Aa =72
aa =24
total −#−of −alleles =2 *150 =300
genotype −frequencies
AA =54 /150 =0.36
Aa =72 /150 =0.48
aa =24 /150 =0.16
Allele −Frequencies
freq(A)=p=2(54) +72
300
=0.6
freq(a)=p=2(24) +72
300
=0.4
Next −generation
A=p=0.6 a=q=0.4
A=p=0.6 AA =p2=3.6 Aa =2pq =0.48
a=q=0.4 Aa =2pq =0.48 aa =q2=0.16
What −if :
genotypes
AA =60 /150
Aa =60 /150
aa =30 /150
genotype −frequencies
AA =60 /150 =0.4
Aa =60 /150 =0.4
aa =30 /150 =0.2
Allele −Frequencies
freq(A)=p=2(60) +60
300
=0.6
freq(a)=p=2(30) +60
300
=0.4
find more resources at oneclass.com
find more resources at oneclass.com
