Genetics Definitions

  • Genes: portion of the DNA molecule that codes for a particular protein.
  • Loci: location in the DNA molecule of the gene
  • Alleles: forms of a gene
  • Homozygous: paired alleles are identical
  • Heterozygous: paired alleles are different
  • Genotype: set of all alleles (i.e. genetic expression)
  • Phenotype: all observable traits (i.e. physical expression)
  • Genome: The complete set of chromosomes for an organism.

Genetic Variation

  • Species that possess a greater number of genes have the potential for increased genetic diversity
  • Similarly, the greater the number of different alleles for these genes, the greater the extent of genetic variation there will be within a species and from individual to individual
  • Genetic diversity within a population increases enormously through sexual reproduction, as the various alleles from two parents recombine in each offspring

Hardy-Weinberg Principle

  • Gene pool: The total number of all alleles within a population.
  • Allele frequency: Within a species, the proportion of gene copies in a given allele.
  • Population geneticists developed a method to quantify a gene pool by measuring allele frequency.

Hardy-Weinberg Formula


The Hardy Weinburg Principle

  • Allele frequency will not change from generation to generation as long as:
  • The population remains large.
  • Mating opportunities are equal.
  • No mutations occur.
  • No migration occurs.
  • No natural selection occurs. ie. All individuals have an equal chance at reproducing.

Sample Questions

  • 1) A population has only two alleles, R and r, for a particular gene. The allele frequency of R is 30%. What are the frequencies of RR, Rr, and rr in the population?
  • 2) A population has only two alleles, A and a, for a particular gene. The allele frequency of a is 25%. How many would have the genotypes of AA, Aa, and aa in a population of 150?

  • 1) 0.09 RR, 0.42 Rr, 0.49 rr
  • 2) 84.375 AA, 56.25 Aa, 9.375 aa

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