Identifying Linkage

• What is the focus of section 6.2.6?

  Predicting inheritance and identifying linkage
• What is autosomal linkage?

  Genes on the same chromosome assort together
• How does linkage affect inheritance?

  It alters how parental alleles are passed on
• How can linked genotypes be represented?

  Using brackets around linked alleles
• What does the dominant allele T produce?

  A normal length tail
• What does the recessive allele t produce?

  A shorter length tail
• What does the dominant allele G produce?

  Green scales
• What does the recessive allele g produce?

  White scales
• What are the parental phenotypes in the newt cross?

  Normal tail, green scales x short tail, white scales
• What are the parental genotypes in the newt cross?

  TtGg x ttgg
• What are the parental gametes for the newt cross?

  TG, Tg, tG, tg
• What is the predicted ratio of phenotypes without linkage?

  1:1:1:1 ratio of phenotypes
• What is the predicted ratio of genotypes without linkage?

  1 TtGg : 1 Ttgg : 1 ttGg : 1 ttgg
• What is the predicted phenotypic ratio with linkage?

  1 normal tail, green scales : 1 short tail, white scales
• Why does the phenotypic ratio change with linkage?

  Because genes are located on the same chromosome
• How does sex linkage affect inheritance?

  It affects which alleles are passed on
• How can sex linkage be identified?

  Using pedigree diagrams and Punnett squares

  
• What happens when a gene is sex-linked?

  Phenotypes are not evenly spread across sexes
• Why are males more likely to show sex-linked recessive conditions?

  They have only one X chromosome
• What is a carrier female?

  Has one recessive allele masked by a dominant
• What are the three phenotypes for females with X-linked genes?

  Normal, carrier, and has the disease
• What are the two phenotypes for males with X-linked genes?

  Normal or has the disease
• What is the predicted ratio of phenotypes from a cross between a normal male and a carrier female?

  1 normal female : 1 carrier female : 1 male with haemophilia : 1 normal male
• What is the predicted ratio of genotypes from the same cross?

  1 XX : 1 XX : 1 XY : 1 XY
• What is haemophilia?

  A sex-linked disease affecting blood clotting
• What is the role of factor VIII?

  It is needed for normal blood clotting
• What happens when a person has only the recessive allele f?

  They don’t produce factor VIII
• What is the significance of crossing over during meiosis?

  It breaks linkage and recombines characteristics

  
• What are recombinant offspring?

  Offspring with different characteristics than parents
• Why are recombinant offspring present?

  Due to crossing over during meiosis