Topic 7

• What is meant by the term genotype?

  Genetic constitution of an organism
• What is meant by the term phenotype?

  The expression of genetic constitution
• How do alleles arise?

  They arise by mutation in DNA sequence
• How many alleles of a gene can be found in diploid organisms?

  2 alleles
• What is a dominant allele?

  Always expressed in the phenotype
• What is a recessive allele?

  Expressed only when homozygous recessive
• What are codominant alleles?

  Both alleles expressed in the phenotype
• What does homozygous mean?

  Same alleles at a specific locus
• What does heterozygous mean?

  Different alleles at a specific locus
• What do monohybrid and dihybrid crosses show?

  • Monohybrid cross: inheritance of one trait
  • Dihybrid cross: inheritance of two traits

  
• What is the expected phenotype ratio in a monohybrid cross between a non-grey female and a heterozygous grey male?

  1:1 ratio of grey to non-grey
• What is the dominant allele for shell colour in the snail species?

  Brown allele (C_B)
• What offspring results from a cross between two pink-shelled snails?

  Pink-shelled and yellow-shelled snails
• What are the possible genotypes and phenotypes from a cross of heterozygous parents for ABO blood groups?

  • Genotypes: I_AI_B, I_AI_O, I_BI_O, I_OI_O
  • Phenotypes: AB, A, B, O
  • Ratio: 1:1:1:1
• What is the probability of a child being male with a recessive disorder from parents with genotypes hh and Hh?

  ¼ male with disorder
• How can you determine if a disorder is caused by a dominant allele using a pedigree diagram?

  Parents with disorder have a child without it

  
• How can you determine if a disorder is caused by a recessive allele using a pedigree diagram?

  Parents without disorder have a child with it

  
• What is independent segregation in dihybrid crosses?

  • Alleles from different genes segregate independently
  • Results in various combinations of alleles in gametes
• What is the expected phenotype ratio from a dihybrid cross of grey-bodied, vestigial-winged flies and ebony-bodied, normal-winged flies?

  1:1:1:1 ratio
• What is a sex-linked gene?

  A gene located on a sex chromosome
• Why are males more likely to express a recessive X-linked allele?

  They have only one X chromosome
• What is the probability of a hairless calf from a male and female with hair?

  25% probability
• What are the expected offspring phenotypes from a tortoiseshell female crossed with a black male?

  • Tortoiseshell female
  • Black female
  • Ginger male
  • Black male
  • Ratio: 1:1:1:1
• What is the expected phenotype ratio from a dihybrid cross involving grey body and red eyes in fruit flies?

  1:1:1:1 ratio
• How does autosomal linkage affect inheritance of alleles?

  • Genes on the same autosome inherited together
  • Crossing over can create new allele combinations

  
• What results from a cross between grey-bodied, long-winged flies and black-bodied, short-winged flies?

  Most offspring have grey bodies and long wings
• What does it mean if two genes are linked?

  They are located on the same chromosome
• What is the result of crossing over between homologous chromosomes?

  It creates new combinations of alleles
• How does the proximity of genes on an autosome affect crossing over?

  Closer genes are less likely to be split

  
• What is autosomal linkage in genetics?

  • Genes located on the same chromosome
  • They tend to be inherited together
  • Less likely to be separated by crossing over

  
• In fruit flies, what is the dominant allele for body colour?

  Grey body colour, G
• What are the phenotypes of the offspring from the cross of grey-bodied long-winged flies and black-bodied short-winged flies?


  Grey body & long wings, black body & short wings
• Why were only GL and gl gametes produced in the fruit fly example?

  Because the genes are linked and no crossing over occurred

  
• What is the dominant allele for height in tomato plants?

  T, for tall plants
• What is the expected phenotype ratio if height and leaf type genes are on different chromosomes?

  9:3:3:1 ratio
• What is epistasis in genetics?

  • Interaction of non-linked genes
  • One gene masks the expression of another
• What are the parental genotypes in the summer squash example?

  aabb and AaBb
• What is the expected ratio of phenotypes in the summer squash example?

  2:1:1 ratio
• When can a chi-squared test be used?

  To compare observed and expected results
• What type of data is required for a chi-squared test?

  Categorical data that can be grouped