Download HMH 11.1 notes

11.1 Genetic Variation Within Population
KEY CONCEPT
A population shares a common gene pool.
11.1 Genetic Variation Within Population
Genetic variation in a population increases the chance
that some individuals will survive.
• Genetic variation leads to phenotypic variation.
• Phenotype – a collection of all an organism’s physical characteristics. Ex:
height, skin color, hair color etc…
• Phenotypic variation is necessary for natural selection.
• Genetic variation is stored in a population’s gene pool.
– made up of all alleles in a population
– Allele – any of the alternative forms of a gene that occurs at
a specific place on a chromosome.
• allele combinations form when organisms have offspring (organisms get
one allele from each parent).
• Simplified example: Frogs have a gene for skin color (green or brown). G
represents green and g represents brown. G is dominant and g is
recessive.
11.1 Genetic Variation Within Population
• Allele frequencies measure genetic variation. Allele frequency
is the ratio of one allele to the total number of the alleles for
that gene in the gene pool.
– measures how common allele is in population
– can be calculated for each allele in gene pool
Predict: If brown skin color became advantageous, what would likely happen to the
frequencies of alleles G and g in this gene pool?
11.1 Genetic Variation Within Population
Genetic variation comes from several sources.
• 1. Mutation is a random change in the DNA of a gene.
– can form new allele
– can be passed on to
offspring if in
reproductive cells
• 2. Recombination forms new combinations of alleles.
– usually occurs during meiosis
– parents’ alleles
arranged in new
ways in gametes
–egg/sperm cells
11.1 Genetic Variation Within Population
Genetic variation comes from several sources.
• Hybridization is the crossing of two different species.
– occurs when individuals can’t find mate of own
species
– topic of current scientific research as a possible 3rd
source of genetic variation
11.1 Genetic Variation Within Population
Analyze and Infer
• A. What is the relationship between allele frequencies
and a gene pool?
• B. Why aren’t mutations in nonreproductive cells sources
of genetic variation?