Inheritance

• Autosome


  A chromosome that is not an X or Y chromosome
• What is the F1 generation?
• F2 generation


  The second generation of offspring resulting from the cross of two individuals in the F1 generation
• Mendel’s first law of inheritance

  • Law of segregation
  • Alleles separate randomly into gametes
  • Each parent passes one allele to their offspring
• Define monohybrid inheritance.
• What is a sex chromosome?
• What is Mendel’s first law of inheritance?
• Draw an example of a genetic cross diagram.
• F1 generation


  The first generation of offspring resulting from the cross of two individuals in the parental generation
• Mendel’s second law of inheritance

  • Law of independent assortment
  • The alleles of genes assort independently of other genes during gamete formation
• PKU is a recessive condition.
• What is the F2 generation?
• What is Mendel’s second law of inheritance?
• A female who is homozygous recessive for cystic fibrosis (ff) has a child with a heterozygous male (Ff). Draw a Punnett square to illustrate this monohybrid inheritance.
• What is an autosome?
• Sex chromosome


  A chromosome that determines the sex of an organism, e.g. X and Y chromosomes in humans and other mammals
• Monohybrid inheritance


  Where one phenotypic characteristic is controlled by a single gene
• Monohybrid inheritance


  Draw a Punnett square to illustrate the inheritance of a single trait
• Carrying out a test cross

  An individual of unknown genotype is bred with a homozygous recessive individual. Offspring phenotypes are observed to determine the genotype of the unknown individual
• Used to determine whether an individual with a dominant trait is heterozygous or homozygous dominant
• Haemophilia

  An X-linked recessive condition resulting in excessive bleeding and slow clotting of blood
• Mendelian inheritance assumes
• Duchenne muscular dystrophy


  An X-linked recessive condition characterized by muscle degeneration and weakness
• Predicting PKU in offspring

  Two heterozygous parents have a 25% chance of having offspring with PKU
• Sex-linkage


  An allele is located on one of the sex chromosomes. Its expression depends on the sex of the individual
• Purpose of a test cross
• Dihybrid inheritance


  The determination of a trait by the inheritance of two genes
• Phenotypes showing sex-linkage


  • Haemophilia
  • Duchenne muscular dystrophy
• If the chi-squared value is less than the critical value

  The null hypothesis is accepted
• Degrees of freedom are calculated by
• Linkage is
• Haemophilia and Duchenne muscular dystrophy are more common in males because they are X-linked recessive conditions. Males only inherit one X chromosome so are more likely to express the gene in their phenotype
• How a chi-squared test is performed

  1. Make a null hypothesis

  2. Use Mendelian ratios to calculate the expected numbers

  3. Calculate chi-squared value using the chi-squared equation

  4. Calculate the degrees of freedom

  5. Select an appropriate significant level (normally 0.05)

  6. Find the critical value

  7. Compare the chi-squared value with the critical value

  8. Accept or reject the null hypothesis
• If the null hypothesis is rejected, it means
• Duchenne muscular dystrophy is
• The chi-squared test is
• If the chi-squared value is greater than or equal to the critical value

  The null hypothesis is rejected
• Recessive genetic disorder caused by a substitution mutation on chromosome 11. Results in abnormal haemoglobin which distorts red blood cells.
• What does it mean if the null hypothesis is accepted?
• Give an example of condition caused by a gene mutation.