Science Q1 module 3

• Incomplete dominance


  Both alleles are present resulting in an intermediate phenotype
• Incomplete dominance


  • Snapdragon flower - cross between homozygous red and homozygous white produces pink flowers in F1
• Incomplete dominance in Snapdragon

  1. F1 generation: Red (FRFR) x White (FWFW) = Pink (FRFW)

  2. F2 generation: Cross between F1 heterozygotes = 25% red, 50% pink, 25% white
• Codominance


  Heterozygote condition where both traits are present simultaneously
• Codominance


  • Speckled chicken - cross between black and white produces chickens with both black and white feathers
• ABO blood types


  Controlled by a gene with multiple alleles (IA, IB, i)
• ABO blood types


  • A
  • B
  • AB
  • O
• Genotypes for ABO blood types

  IAIA or IAi (Type A)<|>IBIB or IBi (Type B)<|>IAIB (Type AB)<|>ii (Type O)
• Codominance in ABO blood types

  In the heterozygote IAIB, both A and B antigens are expressed
• Multiple alleles
• The ABO blood group system in humans is an example of a gene with multiple alleles
• Phenotype


  Observable physical or biochemical characteristics of an organism
• Human blood types (phenotypes)

  • A
  • B
  • AB
  • O
• Genotype


  Genetic makeup of an organism
• Genotypes for human blood types

  • IAIA or IAi
  • IBIB or IBi
  • IAIB
  • ii
• Blood type A


  • Can receive blood from O, A
  • Can donate blood to AB, A
• Blood type B


  • Can receive blood from O, B
  • Can donate blood to AB, B
• Blood type AB


  • Can receive blood from A, B, AB, and O (universal recipient)
  • Can donate blood to AB
• Blood type O


  • Can receive blood from O
  • Can donate blood to A, B, AB, and O (universal donor)
• In the heterozygote condition, both IA and IB alleles are expressed in the red blood cells that will have the antigens A and B
• Multiple alleles


  A single gene that has more than two alleles
• Alleles in the ABO blood group system


  • A
  • B
  • O
• There are three different alleles for ABO blood types, however, only two are present in an individual at a time
• Allelic combinations for different blood types

  • IAIA or IAi (Type A)
  • IBIB or IBi (Type B)
  • IAIB (Type AB)
  • ii (Type O)
• The IA and IB alleles are dominant over the i allele which is always recessive
• Both IA and IB alleles are expressed equally when inherited together
• Sex chromosomes


  Chromosomes that determine the sex of an organism
• Most humans have an XY sex-determination system
• Males have X and Y chromosomes, while females have two X chromosomes
• A male offspring will be produced when an egg is fertilized by a sperm passing on a Y chromosome, while a female offspring will be produced when an egg is fertilized by a sperm carrying an X chromosome
• There is a fifty-percent probability of having a male and female offspring
• Sex-linked genes


  Genes found either on X or Y chromosomes which are inherited differences among male and female
• Genotypes and phenotypes in humans for X-linked traits

  • XX (Normal female)
  • XXC (Normal female, carrier of the gene)
  • XC XC (Color-blind female)
  • XY (Normal male)
  • XC Y (Color-blind male)
• Sex-limited trait


  Trait limited to only one sex
• Sex-influenced trait


  Autosomal trait expressed in both sexes but more frequently in one than in the other sex
• Traits


  Characteristics that are passed down from parents to offspring
• Levels of trait inheritance

  • No trait has been chosen/ the trait chosen is not an inherited one
  • 1 or two traits are shown/ there are weak genetic links to the traits/ the student has confused the traits and cannot follow them along the family tree
  • All three traits are genetic and can be traced from the maternal or paternal line
  • The students have traced three or more genetic traits/ the traits are inherited in different ways/ the trait can be traced back on both paternal and maternal lines
• Marking on traits do not inherit


  No marking is visible for traits not inherited
• Use of legend


  • No legend is used for clearer descriptions of traits of the family members
  • One legend is used for clearer descriptions of traits of the family members
  • 2 to 3 legends are used for clearer descriptions of traits of the family member
  • Complete legends are used for clearer descriptions of traits of the family members
• Summary of traits


  • No summary of traits has been shown
  • 1 summary of traits is shown
  • Two traits have a summary shown and can be traced from the maternal or paternal line
  • All three traits have summary shown and can be traced from the maternal or paternal line