Autosomal linkage

• What is a dominant allele?

  An allele that is always expressed
• What are recessive alleles?

  Alleles expressed only without a dominant allele
• What does genotype refer to?


  The genetic composition of an organism
• What is phenotype?

  The characteristic due to genotype and environment
• What is a gene?

  A small section of DNA coding for a polypeptide
• What are alleles?

  Alternative forms of one gene
• What is dihybrid inheritance?

  • Inheritance of two genes
  • Analyzed using a Punnett square
  • Example: shape and color of peas
• What does the round allele represent in the pea shape gene?

  It is the dominant allele
• What does the wrinkled allele represent in the pea shape gene?

  It is the recessive allele
• How is the yellow allele represented in the color gene?

  With a capital Y
• How is the green allele represented in the color gene?

  With a lowercase y
• What is the genotype of a homozygous dominant round yellow pea?

  Homozygous dominant for both genes
• What is the genotype of a homozygous recessive wrinkled green pea?

  Homozygous recessive for both genes
• What gametes can a homozygous dominant round yellow pea produce?

  Capital R and capital Y
• What gametes can a homozygous recessive wrinkled green pea produce?


  Lowercase r and lowercase y
• What is the expected phenotype ratio from a dihybrid cross of two heterozygous parents?

  9:3:3:1 ratio
• What is the significance of the F1 generation?

  • First generation of offspring
  • Result from crossing two parent genotypes
  • All offspring are heterozygous
• What happens when two heterozygous parents are crossed?

  They produce a variety of offspring genotypes
• What is the impact of crossing over in meiosis?

  It creates new combinations of alleles
• What is autosomal linkage?

  Two genes located on the same chromosome
• What chromosomes are considered autosomal?

  Chromosomes 1 to 22
• How does autosomal linkage affect inheritance?

  Alleles are inherited together on the same chromosome
• What happens to the expected gametes in autosomal linkage?

  Only specific combinations are produced
• What is the phenotype ratio when genes are linked?

  3:1 ratio
• What is the effect of crossing over on phenotype ratios?

  • Can create new phenotypes
  • Alters expected ratios
  • Results in more genetic variation
• Why are some phenotypes less common in linked genes?

  Crossing over is a rare event
• How can crossing over lead to unexpected phenotypes?

  It creates new allele combinations
• What is the summary of dihybrid inheritance and autosomal linkage?

  • Dihybrid inheritance involves two genes
  • Expected ratio is 9:3:3:1
  • Autosomal linkage means genes are on the same chromosome
  • Crossing over can change expected ratios