Microevolution (Population Genetics)

Question 1

What is Microevolution (population genetics)?

Answer 1

• It is the study of the distribution of alleles within population and the mechanism that can cause allele frequencies to change over time
• A population (not individuals) evolve through changes in its gene pool, therefore population genetics is also the study of evolution

Question 2

What does a population geneticist study?

Answer 2

• Population geneticists usually focus their attention on Mendelian populations, which is a group of interbreeding, sexually reproducing individuals that have a common set of genes (gene pool)
• Population geneticists study the variation in alleles within and between groups and the evolutionary forces responsible for shaping the patterns of genetic variation found in nature

Question 3

What is a gene and what is a locus?

Answer 3

• Gene:
  • Basic unit of heredity
  • The physical entity transmitted from parent to offspring during reproduction that influences hereditary traits.
• Locus:
  • Specific position on a chromosome where a gene is located.

Question 4

What is a genotype and a phenotype?

Answer 4

• Genotype:
  • The genetic constitution (code) of an individual
• Phenotype:
  • The physical expression of the genetic code (genotype)

Question 5

What are Diploid/Haploid Genotypes?

Answer 5

• Diploid/Haploid Genotypes:
  • Many animals and plants have two copies of a gene (diploid)
  • Some organisms (e.g. bacteria) have only one copy (haploid)
  • Some plants have more than two copies (polyploid)

Question 6

What is an Allele

Answer 6

• Allele:
  • Alternative form of a gene e.g. “A” and “a” allele for a genotype Aa
• Classical Allele Terms:
  • Dominate allele of a gene (uppercase letter) is the form of a gene that is expressed in the phenotype (physical form)
  • Recessive allele of a gene (lowercase letter) is the form of a gene that is not expressed in the phenotype (physical form)
  • Example Aa - “A” is the dominant allele, “a” is the recessive allele

Question 7

What does Heterozygous and Homozygous mean?

Answer 7

• Heterozygous (diploid):
  • The two alleles at a locus are not identical (different DNA sequence). - For example, Aa (or aA)
• Homozygous (diploid):
  • The two alleles of a gene are identical (same DNA sequence). - For example, AA or aa

Question 8

What are Allele Frequencies?

Answer 8

• Allele frequencies (diploid):
  • Refers to the frequency of an allele (e.g. “A” or “a”)
  • Symbols p and q are usually used for the two alleles.
  • p + q = 1

Question 9

What are Genotype Frequencies?

Answer 9

• Genotype frequencies (diploid):
  • If A and a are at the frequency of p and q respectively
  o the frequency of the AA genotype is p × p or p^2
  o the frequency of the aa genotype is q × q or q^2
  o and the frequency of the heterozygote genotypes (e.g. Aa) is 2pq