Topic 7 - Genetics, populations, evolution and ecosystems

• What is meant by the term genotype?

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

  Expression of genetic constitution and environment
• How do alleles arise?

  By mutation in DNA base sequence
• How many alleles of a gene can be found in diploid organisms?

  2 alleles
• What are dominant alleles?

  Always expressed in the phenotype
• What are recessive alleles?

  Expressed only when homozygous recessive
• What are codominant alleles?

  Both alleles contribute to 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 is the expected phenotype ratio from a cross between two pink-shelled snails?

  Pink-shelled and yellow-shelled snails
• What are the possible blood group phenotypes from a cross between two heterozygous parents with blood groups A and B?

  AB, A, B, O
• How does a pedigree diagram help determine the inheritance pattern of a genetic disorder?

  Shows relationships and phenotypes in a family

  
• What does it mean if a genetic disorder is caused by a recessive allele?

  Both parents must be carriers
• What is the probability of a child being male with a recessive disorder from parents with genotypes hh and Hh?

  ¼ male with disorder
• What is autosomal linkage?

  • Genes on the same autosome
  • Alleles inherited together
  • Less likely to be separated by crossing over

  
• What is the expected phenotype ratio from a dihybrid cross of grey-bodied, normal-winged flies with ebony-bodied, vestigial-winged flies?

  1:1:1:1 ratio
• What is the expected phenotype ratio from a cross between a dwarf pink-flowered plant and a heterozygous tall white-flowered plant?

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

  A gene 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 that a hairless calf is born from a male and female with hair?

  25% probability
• What is the expected phenotype ratio from a cross between a tortoiseshell female and a black male cat?

  1:1:1:1 ratio
• What evidence from a pedigree diagram shows a recessive X-linked phenotype?

  Mother without phenotype has affected child
• How does autosomal linkage affect inheritance?

  Alleles on the same chromosome inherited together
• What results indicate that two genes are linked in fruit flies?

  More offspring with parental phenotypes
• What is the expected outcome of a cross between heterozygous grey-bodied and long-winged flies and black-bodied short-winged flies?

  More grey-bodied long-winged offspring
• What is the expected phenotype ratio from a cross between tomato plants with height and leaf type genes on the same chromosome?

  Ratio depends on linkage and crossing over
• What are the key concepts of inheritance in genetics?

  • Genotype vs. phenotype
  • Alleles: dominant, recessive, codominant
  • Monohybrid and dihybrid crosses
  • Sex-linked and autosomal linkage
• What gametes are produced due to the linkage of the two genes?

  Only GL and gl gametes are produced
• What is the expected phenotype ratio if the genes for height and leaf type were on different chromosomes?

  9:3:3:1 ratio
• What is epistasis?

  Interaction where one gene masks another
• 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?

  Data must be categorical
• Why might observed phenotypic ratios differ from expected ratios in genetic crosses?

  Random fertilization of gametes occurs

  
• How is a chi-squared value calculated?

  O = observed frequencies, E = expected frequencies

  
• How is the chi-squared value analyzed?

  Compare X² value to critical value
• What is the significance of the degrees of freedom in chi-squared tests?

  Degrees of freedom = categories - 1
• What does a significant chi-squared result indicate?

  Reject the null hypothesis