LIFESCI 7B Lecture Notes - Lecture 4: Allele Frequency, Population Genetics, Allele
10 Jun 2018
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21.1: Genetic Variation
● Let’s ignore environmental effects on phenotype for a sec and just focus on genetic effect
Population genetics is the study of patterns of genetic variation.
● despite high degree of phenotypic variation, humans rank low in terms of overall genetic variation
compared with other species.
○ Adelie penguins have 2-3x more genetic variation than we do (and they all look the same????)
● species A group of individuals that can exchange genetic material through interbreeding to produce
fertile offspring.
○ gene pool All the alleles present in all individuals in a population or species.
■ Individuals of a species represent different allele combos possible
■ More variety in gene pool=more genetic variation/diversity in species
● Population genetics is the study of genetic variation in natural populations
○ population All the individuals of a given species that live and reproduce in a particular place;
one of several interbreeding groups of organisms of the same species living in the same
geographical area.
Mutation and recombination/segregation are the two sources of genetic variation
● Also following recombination: segregation of homologous chromosomes during meiotic cell division
which shuffles mutations to create new combinations
● MUTATIONS:
○ Focusing on germ-line (inheritable) mutations for the sake of evolution
○ neutral mutations Genetic changes that have no effect or negligible effects on the organism and
its survivability/reproductivity
○ deleterious mutations Genetic changes that are harmful to an organism.
○ advantageous mutations Genetic changes that are beneficial and improve their carriers’
chances of survival or reproduction.
■ can increase in frequency in a population as adaptations until eventually they are carried
by every member of a species
● RECOMBINATION among heterozygous alleles can give rise to new alleles
● MUTATIONS is the ultimate source of of genetic variation, and recombination shuffles mutations into
new combinations!!!!! (recombination wouldn’t do anything if there were no mutations)
21.2: Measuring Genetic Variation
● allele frequency Among all the alleles of a gene in a population, the proportion that are of a specified
allele.
To understand patterns of genetic variation, we require information about allele frequencies.
● allele frequency of an allele=number of x’s present in the population/ total number of alleles
○ fixed Describes a population that exhibits only one allele at a particular gene.
■ Allele frequency=100%
Early population geneticists relied on observable traits and gel electrophoresis to measure variation.
● Studying genetic variation in a population based on observable traits is difficult because multiple genes
can contribute to a phenotype and phenotype is influenced by genotype AND environment
● Early geneticists focused on study of single-gene traits (like blood type)
● Use of protein gel electrophoresis to measure genetic variation
DNA sequencing is the gold standard for measuring genetic variation.
● Protein gel electrophoresis is limited: what about noncoding genome?
● DNA sequencing covers both, coding and noncoding
○ differences in DNA sequence studied, such as a T rather than a G at a specified nucleotide
position in a particular gene.
○ Used to measure allele frequency rather than proteins
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Let"s ignore environmental effects on phenotype for a sec and just focus on genetic effect. Population genetics is the study of patterns of genetic variation. Despite high degree of phenotypic variation, humans rank low in terms of overall genetic variation compared with other species. Adelie penguins have 2-3x more genetic variation than we do (and they all look the same????) Species a group of individuals that can exchange genetic material through interbreeding to produce fertile offspring. Gene pool all the alleles present in all individuals in a population or species. Individuals of a species represent different allele combos possible. More variety in gene pool=more genetic variation/diversity in species. Population genetics is the study of genetic variation in natural populations. Population all the individuals of a given species that live and reproduce in a particular place; one of several interbreeding groups of organisms of the same species living in the same geographical area.
