LAB 4: Genetics

• Which allele is dominant, the one that results in free earlobes or the one that results in attached earlobes?

  Free earlobes
• How many alleles does a human gamete have for each locus?

  One
• Phenotype: The physical expression of a gene.
• Genotype: The specific alleles that an organism has.
• Dominant: An allele that is fully expressed in a heterozygote.
• Recessive: An allele that is not expressed at all in a heterozygote.
• Homozygous: The two alleles at a particular locus are the same.
• Heterozygous: The two alleles at a particular locus are different.
• Locus: The place on a chromosome where a gene is located. (loci)
• Diploid: Having two alleles at each locus.
• Haploid: Having one allele at each locus.
• Character or Trait: A potentially variable quality or quantity in an organism.
• Hybrid: The offspring of two different varieties.
• Monohybrid Cross: Studying the inheritance of a single character in a hybridization experiment.
• Dihybrid Cross: A hybridization experiment in which the inheritance of two traits is studied.
• Dependent Assortment: The alleles at two loci segregate together into gametes.
• Independent Assortment: The alleles at two loci segregate individually into gametes.
• Evolution: Any change in the frequency of alleles in a population.
• There are two process that can result in evolution:

  • Genetic drift: A change in allele frequency due to chance.
  • Natural selection: Greater average reproductive rate as a result of having a particular trait.
• In humans, the allele for "attached" earlobes is recessive to the allele for "free" earlobes, and the allele for "straight" hairline is recessive to the allele for "widow's peak" hairline. A man who is heterozygous at both loci has a large family with a woman who is homozygous at both loci and has a "straight" hairline and "free" earlobes. Approximately what proportion of their children would we expect to have which phenotypes?


  100% free earlobes, 50% straight hairline, 50% widow's peak
• Define heterozygote in genetic terms.

  A heterozygote has two different alleles at a particular locus.
• If you suffer from an extremely rare genetic disease that is caused by a recessive allele at a single locus, and neither your parents nor your brother have this disease, what is the probability that your brother is a carrier (heterozygous at this locus)?

  2/3 or 66%
• If half the members of a population have the phenotype of the dominant allele, and half have the phenotype of the recessive allele, which allele at this locus is probably more common in the population?

  Recessive
• In ants, males develop from unfertilized eggs (and are therefore haploid) while females (including workers) develop from fertilized eggs (and are therefore diploid). Imagine that ant colour is determined at a single locus, with the allele for dark being dominant and the allele for light being recessive. If the only breeding ants in a colony are a dark male and a light female, what proportion of the male offspring would be dark, and what proportion of the female offspring would be dark?

  100% of males are dark, 0% of females are dark