Biology - Genetics Chapter 6

• Incomplete Dominance


  neither allele for a gene completely conceals presence of another

  heterozygote expresses a phenotype in between

  red + white parent generation = pink F1

  use superscripts for incomplete dominance
• Codominance


  both alleles for a trait is equally expressed in a heterozygote
• Sickle Cell Anemia

  codominance - Hb^s = sickle cell

  caused by form of gene that directs creation of hemoglobin

  sickle cells do not transport oxygen effectively b/c it cant pass through small blood vessels --> blockage and damage

  Heterozygous SIckle Cell (Hb^a + Hb^s) is resistant to malaria
• Multiple Alleles


  traits b/c of the interaction of two alleles

  individual has two alleles per trait but population can have multiple types

  C> Cch> Ch> c <-- order of dominance
• HUman Blood Type


  multiple allele AND codominance

  3 types: IA IB i

  4 phenotypes: A, B, AB, O

  receiving wrong blood type is dangerous
• A blood type

  IA + i or IA IA
• B blood type


  IB i or IB IB
• AB blood type

  IA + IB

  universal recipient b/c it can receive any blood type
• O blood type


  ii

  universal donor of blood
• ABO antibodies


  form in serum when it encounters "missing" ABO antigens in foods or micro-organisims
• Rh factor


  inherited protein found on surface of red blood cells

  inherited independent of blood types

  Rh+ = dominant and has protein

  Rh - = recessive and doesn't have protein
• Rh Incompatability

  develop in pregnant Rh- mothers with a Rh + infant

  placenta ensures mothers blood does not mix with infant

  if mixed blood occurs the body develops anitbodies which affect the SECOND child

  antibodies cross the placenta and affect the 2nd child
• Polygenic Inheritance


  some traits exhibit continuous variation --> phenotypes vary like skin color

  controlled by polygenic traits
• Polygenes / polygenic traits


  group of genes contributing to same trait

  each dominant allele contribute to trait

  eg. the more dominant alleles the darker your skin
• Environmental Effects


  can determine whether a gene is turned on or off

  eg. dark himalayan rabbits - due to a gene that is active below certain temperatures
• Walter Sutton's findings

  did research and found out that alleles on the same chromosome do not assort independently
• Linked Genes

  genes that do not assort independently or are inherited together

  study in 1905 by William Bateson and Reginald Punnet found that gametes produced by parental generation assort together (dominant with dominant)
• How are there four phenotypes then?

  alleles segregate from each other ONLY during crossing over in porhase 1

  fewer gametes with recombined alleles in F2 b/c crossing over is random and occurs infrequently
• Recombined Alleles

  alleles who's homologous chromosomes underwent crossing over
• Chromosome Mapping


  determining the relative location of genes on a chromosome

  crossing over occurs more frequently when alleles are farther apart on the same chromosome
• Sex Linked Inheritance

  Thomas Hunt Morgan chose to study fruit flies

  he discovered F2 females with red eyes but F2 males with white and red eyes

  determined the gene for eye color is linked to gender
• Sex Linked Traits

  traits controlled by genes on either sex chromosome

  X has 2000 genes while Y has less than 100
• X Linked Genes

  found on x chromosomes --> females have two copies
• Y-linked genes


  few are known because Y chromosome has less than 100 genes
• Sex linked traits in humans

  normally a genetic disorder

  If its X-linked dominant - affected males will affect their daughters

  If its X-linked recessive - males need 1 allele to be affected and females need two alleles to be affected
• Hairy Ears


  Y - linked
• Hemophilia 


  x linked recessive
• Familial Hypercholesterolemia

  incomplete dominance genetic disorder

  on allele of mutated gene is required to show symptoms of disorder

  if allele for normal gene is present symptoms are not as severe