INHERITANCE

• What is the branch of science that studies how characteristics are passed from one generation to the next?

  Genetics
• Why have humans selected and crossed plants and animals for over 200 years?

  To produce improved varieties through the mixing of genetic material
• What significant discovery was made in 1953 that advanced gene technology?

  The structure of DNA was discovered
• What is monohybrid inheritance?

  The inheritance of a single characteristic
• How do genes exist in relation to chromosomes?

  Genes exist in pairs on homologous chromosomes
• What are alleles?

  Different forms of a gene controlling a particular characteristic
• What is the genotype for an individual with albinism?

  nn
• What does the dominant allele N do in relation to melanin production?

  It stimulates melanin production
• What is the phenotype of an individual with genotype nn?

  Albino with very pale skin, hair, and eyes
• What is the difference between homozygous and heterozygous individuals?

  Homozygous individuals have identical alleles, while heterozygous individuals have different alleles
• What are the possible combinations of alleles controlling melanin production?

  • NN: Homozygous dominant (normal pigmentation)
  • Nn: Heterozygous (carrier, normal pigmentation)
  • nn: Homozygous recessive (albino)
• What do gametes produced in meiosis contain?

  Only one allele from each homologous pair
• What happens during fertilization in terms of alleles?

  Chromosomes and the alleles they carry recombine to form pairs in the zygote
• What are the results of a cross between a homozygous dominant and a homozygous recessive parent?

  • All offspring have normal pigmentation (genotype Nn)
  • Phenotype: Normal pigmentation
• What are the results of a cross between a heterozygous parent and a homozygous recessive parent?

  • 50% of offspring have normal pigmentation (genotype Nn)
  • 50% of offspring have albinism (genotype nn)
• What are the results of a cross between two heterozygous parents?

  • 75% of offspring have normal pigmentation (genotypes NN or Nn)
  • 25% of offspring have albinism (genotype nn)
• What is co-dominance in genetics?

  When neither allele dominates, and both influences are visible in the heterozygous individual
• What is sickle cell anaemia caused by?

  An abnormal allele that produces abnormal haemoglobin S
• What are the possible combinations of alleles controlling haemoglobin production in sickle cell anaemia?

  • HbA HbA: 100% haemoglobin A
  • HbA HbS: 55–65% haemoglobin A, 35–45% haemoglobin S
  • HbS HbS: 100% haemoglobin S
• What are the symptoms of sickle cell anaemia?

  Painful crises, anaemia, increased vulnerability to infections, and jaundice
• What are the results of a cross between two parents with sickle cell trait?

  • 25% of offspring are normal (genotype HbAHbA)
  • 50% of offspring have sickle cell trait (genotype HbAHbS)
  • 25% of offspring have sickle cell anaemia (genotype HbSHbS)
• What are the ABO blood groups controlled by?

  Three alleles: IA, IB, and IO
• What are the dominance relationships among the ABO blood group alleles?

  • IA and IB are both dominant to IO
  • IA and IB are co-dominant to each other
• What are the results of a cross between a heterozygous parent with blood group A and a heterozygous parent with blood group B?

  • 25% of offspring have blood group AB
  • 25% of offspring have blood group A
  • 25% of offspring have blood group B
  • 25% of offspring have blood group O
• What determines the sex of an individual in humans?

  The sex chromosomes, X and Y
• Which parent determines the sex of the offspring?

  The father, as he can pass on the Y chromosome
• What is the genotype for a female in terms of sex chromosomes?

  XX
• What is the genotype for a male in terms of sex chromosomes?

  XY
• What are sex-linked characteristics?

  Characteristics determined by genes carried on the sex chromosomes
• Why are males more likely to express sex-linked conditions?

  Because they have only one X chromosome
• What is haemophilia?

  A sex-linked condition where blood fails to clot
• What are the possible combinations of alleles controlling blood clotting in haemophilia?

  • XH XH: Female, normal blood clotting
  • XH Xh: Female, normal blood clotting (carrier)
  • Xh Xh: Female, haemophiliac
  • XH Y: Male, normal blood clotting
  • Xh Y: Male, haemophiliac
• What are the results of a cross between a female carrier of haemophilia and a male with normal blood clotting?

  • All female offspring have normal blood clotting
  • 50% of male offspring have normal blood clotting
  • 50% of male offspring have haemophilia
• What is colour blindness?

  A sex-linked condition where the sufferer cannot distinguish certain colours
• What is the dominant allele for normal vision in colour blindness?

  R
• What is the recessive allele that causes colour blindness?


  r
• What is the genotype of a male with haemophilia?

  XhY
• What is the genotype of a female carrier for normal blood clotting?

  XHXh
• What are the parental phenotypes in the cross described?

  Female with normal clotting and male with normal clotting
• What are the gametes produced by the female and male in the cross?

  • Female gametes: XH, Xh
  • Male gametes: XH, Y