Genetics

• What structures in the cell contain DNA?

  Chromosomes
• What term describes the shape of DNA?

  Double helix
• What type of cell division reduces chromosomes by half?

  Meiosis
• What does the science of genetics explain?

  How characteristics pass from parents to offspring
• What does each gene carry?

  The code for a particular characteristic
• What are alleles?

  Differing forms of a gene
• What are the key genetic terms defined in the study material?

  • Gene: Codes for a characteristic
  • Allele: Form of a gene
  • Homozygous: Same alleles
  • Heterozygous: Different alleles
• What is a monohybrid cross?

  A genetic cross involving one characteristic
• What is the dominant allele for round seeds in peas?

  R
• What is the ratio of phenotypes in the F2 generation?

  3:1
• What do the gametes produced by one parent combine with?

  The gametes of another parent
• When are ratios accurate in genetic crosses?

  With large numbers of offspring
• What does the term 'genotype' refer to?

  Paired symbols showing allele arrangement
• What does the term 'phenotype' refer to?

  Outward appearance of an individual
• What does a dominant allele do in a heterozygous condition?

  Overrides the recessive allele
• What is the phenotype ratio of offspring in a genetic cross?

  3:1 for dominant to recessive
• What is the purpose of a test cross?

  To determine an unknown genotype
• Who is Gregor Mendel?

  The founder of genetics
• What did Mendel deduce about traits in organisms?

  They are determined by factors called genes
• What happens to alleles during gamete formation?

  They separate
• What is the sex chromosome pair for males?

  XY
• What is the sex chromosome pair for females?

  XX
• What is sex linkage?

  Genes on sex chromosomes affecting traits
• What happens to recessive alleles in males?

  They show in the phenotype
• What is the phenotype of offspring from a haemophiliac male and a normal female?

  50% normal carrier females
• What is the phenotype of offspring from a normal male and a carrier female?

  25% haemophiliac males
• What does a Punnett square help with?

  Visualizing genetic crosses
• What are the key points about sex determination in humans?

  • 22 pairs of normal chromosomes
  • 1 pair of sex chromosomes (XX or XY)
  • Equal numbers of boys and girls produced
• What are the exam tips for genetic crosses?

  • Use Punnett squares for easier calculations
  • 3:1 ratio indicates both parents are heterozygous
  • 1:1 ratio indicates one parent is heterozygous
• What are the important findings of Gregor Mendel?


  • Traits are determined by genes
  • Genes can have different forms (alleles)
  • Alleles separate during gamete formation
  • Monohybrid ratios like 3:1 and 1:1
• What is the significance of sex linkage in genetics?


  • Recessive alleles on X chromosome show in males
  • Dominant alleles can mask recessive alleles in females
  • Important for understanding genetic disorders
• What are the characteristics of sex-linked conditions?


  • Carried on sex chromosomes
  • Often affect males more than females
  • Examples include colour blindness and haemophilia
• What are the offspring ratios in genetic crosses?


  • 3:1 ratio for dominant to recessive
  • 1:1 ratio for heterozygous and homozygous recessive
  • Ratios depend on parental genotypes
• What is the role of gametes in genetic crosses?


  • Combine from different parents
  • Determine offspring genotypes and phenotypes
  • Essential for inheritance patterns
• Gene


  A short section of chromosome that codes for a particular characteristic

  Eg. Eye colour
• Allele


  A particular form of a gene
• Example of an Allele 


  Brown eyes and Blue eyes are Different Alleles of the Eye Colour Gene
• Homozygous 


  Describes the situation when both alleles of a gene are the same

  Eg. Both alleles are for brown eyes
• Heterozygous 


  Describes the situation when the Two Alleles of a Gene are Different

  Eg. One Allele is for brown eyes and the other is for Blue Eyes
• How many chromosomes do humans have?

  46 (23 pairs)