Introduction Chapter

What is a gene? How is it related to phenotype?

• Gene = factor controlling a trait, located on chromosomes

• Genes can have alternative forms = alleles

• Different alleles → different phenotypes (observable traits)

• Genotype (alleles carried) determines phenotype

How many molecules of DNA make up one chromosome in a nondividing cell? How many molecules of DNA make up one chromosome with two sister chromatids at the start of M phase?

• Nondividing cell: 1 DNA molecule per chromosome

• Chromosome with 2 sister chromatids (start of M phase): 2 DNA molecules (1 in each chromatid)

What is the chromosomal theory of inheritance?

• Proposed by Sutton and Boveri

• Genes are on chromosomes

• Chromosomes and genes both occur in pairs

• They separate during gamete formation → traits passed on

State the 5 subdisciplines of genetics and give an example of each.

• Transmission genetics (classical genetics)
  Example: Mendel’s pea plant experiments

• Molecular genetics
  Example: The discovery of the DNA double helix and the genetic code.

• Population genetics
  Example: Hardy–Weinberg equilibrium or studying sickle-cell allele frequencies in human populations.

• Quantitative genetics
  Example: Height in humans, yield in crops, or milk production in cattle.

• Genomics
  Example: The Human Genome Project.

Define gene. Define genome.

• Gene = factor on chromosomes controlling traits; has alleles

• Genome = complete DNA of an organism (can be studied/edited with CRISPR)

What is the purpose of DNA? What must it be able to do?

• DNA = carrier of genetic information

• Must:

  • Store information

  • Be replicated

  • Be expressed into traits (link genotype → phenotype)

  • Be modifiable (e.g., CRISPR, recombinant DNA)