Genetics Exam Revision

Genetics Exam Revision Notes

Cell Biology

  • All living things are made of cells.
  • The nucleus of the cell contains the chromosomes.

DNA Structure

  • DNA consists of two strands joined by nitrogen base pairs, forming a twisted ladder or double helix shape.
  • The correct answer is B. It consists of two strands joined by various nitrogen base pairs, to form a double helix shape.
  • DNA stands for Deoxyribonucleic Acid

Nitrogen Base Pairs

  • The nitrogen base pairs in DNA are complementary.

DNA Discovery

  • James Watson, Francis Crick, and Maurice Wilkins are credited with discovering the double helix structure of DNA.
  • Rosalind Franklin's X-ray work was crucial to their discovery.
  • Rosalind Franklin did not receive a Nobel Prize.

Information Flow

  • The order of information flow in living things is:
    • Organisms contain cells.
    • Cells contain chromosomes.
    • Chromosomes contain DNA.
    • DNA contains genes.
    • Genes code for proteins.

Phenotype

  • The phenotype is the physical appearance or characteristic of an organism.

Heterozygous

  • Heterozygous describes when the pair of alleles for an organism is different.

Allele Pairs

  • Homozygous allele pairs are also called purebred, and heterozygous pairs are called hybrid.

Genotypes

  • Homozygous genotypes are represented by pairs like BB, WW, nn, RR.

Inheritance

  • Blue-eyed child with a blue-eyed father and brown-eyed mother exemplifies dominant/recessive inheritance.
  • Kittens with short tails which parents have long or no tails exemplify intermediate inheritance.
  • Black and white feathered chickens producing mottled chicks is an example of co-dominance inheritance.
  • The genotype of the mottled chicks is BW.

Dominant and Recessive Traits

  • If Aa mates with aa, 50% of offspring will exhibit the recessive trait.

Tom's Handedness

  • If both of Tom's parents are right-handed (R) but Tom is left-handed, the parents' genotypes are Rr x Rr.

DNA Subunits

  • DNA is made of nucleotides.
  • Each nucleotide consists of a nitrogen base, a sugar, and a phosphate group.
  • The four nitrogen bases are Adenine (A), Guanine (G), Thymine (T), and Cytosine (C).

DNA Base Pairing

  • Complementary DNA strand: A T G C C A T becomes T A C G G T A.
  • If 30% of bases are A, then 30% are T.
  • If 20% of bases are C, then 20% are G, leaving 60% for A and T, so 30% are T.

Chromosome Number in Humans

  • Male sperm cell: 23
  • Embryo: 46
  • Heart cell: 46

Chromosome Number in Cats

  • Female cat egg (ova): 19
  • Male cat hair cells: 38
  • Regular cells of a kitten: 38
  • Fertilized egg: 38
  • Male cat sperm cells: 19
  • Sex cells are called gametes.

Sex Chromosomes

  • Male: XY
  • Female: XX
  • The male determines the sex of the child, as he can contribute either an X or a Y chromosome. King Henry VIII was to blame for not having a son because he provides the Y chromosome.

Horse Fur Color

  • Non-grey fur is recessive to grey fur (G).

    • Non-grey fur gene: g
    • Genotypes and phenotypes:
      • GG: Grey fur
      • Gg: Grey fur
      • gg: Non-grey fur
    • Homozygous recessive: gg
    • Homozygous dominant: GG
    • Hybrid: Gg

  • Punnett square: purebred grey (GG) x non-grey (gg)

    • Genotypes: Gg
    • Percentage: 100%
    • Phenotype: Grey
    • Percentage: 100%

Rose Color Breeding

  • Red rose: RR
  • White rose: WW
  • Pink rose: RW
  • Red rose (RR) crossed with pink rose (RW)
    • Genotypes: RR, RW
    • Percentages: 50%, 50%
    • Phenotypes: Red, Pink
    • Percentages: 50%, 50%
  • Crossing red roses with pink roses will not produce white roses. The worker is in trouble because the demand for white roses won't be met.

Roan Cows

  • Brown cow: BB
  • White cow: WW
  • Roan cow: BW
  • Two roan cows crossed (BW x BW)
    • Genotypes: BB, WW, BW
    • Percentages: 25%, 25%, 50%
    • Phenotypes: Brown, White, Roan
    • Percentages: 25%, 25%, 50%