heredity

• law of segregation

  parent cell Pp yields gametes P and p, homozygous: identical alleles, heterozygous: two different alleles
• law of independent assortment

  during gamete formation, each pair of alleles separates independently
• dihybrid cross

  cross that looks at 2 traits instead of just 1
• rule of multiplication


  determines the chance that 2 or more independent events will occur together in a specific combo
• codominance


  2 alleles affect the visible appearance of an organism in separate, distinguishable ways (heterozygotes express both alleles)
• incomplete dominance


  neither gene is completely dominant; heterozygotes show a distinct intermediate phenotype (traits appear to be combined)
• multiple alleles


  gene that codes for a trait can exist in more than 2 allelic forms

  ex: ABO blood types (3 options of a gene for blood type)
• blood type A

  AA or Ai, Anti-B antibodies
• blood type B


  BB or Bi, Anti-A antibodies
• blood type AB

  AB, no antibodies, universal recipient
• blood type O


  ii, Anti-A and Anti-B, universal donor
• environmental impact


  phenotype depends on genes AND environment, product of a genotype is not a rigidly defined phenotype, but a range of possibilities

  ex: hydrangeas and soil pH
• multifactorial


  many factors, both genetic and environmental, collectively influence phenotype
• polygenic inheritance

  2 or more genes affect a single phenotype characteristic
• quantitative characters

  characters vary along a continuum (in a gradient)
• chromosomal inheritance


  genes located near each other on the same chromosome tend to be inherited together; these are called linked genes
• offspring with a phenotype matching one of the parental phenotypes are called...

  parental types
• chromosomes are passed along as units meaning...

  genes are inherited together
• crossing over


  occasionally breaks the physical connection between specific alleles on the same chromosome
• the farther that genes are...

  the higher probability that a crossing over event will occur = higher recombinant frequency
• map units

  one map unit equals to 1% recombination frequency
• sex linked inheritance


  genes located on either sex-chromosome (mostly X-linked)
• wild type


  most commonly observed phenotype in nature
• X-inactivation in female mammals

  females inherit 2 X chromosomes, but one of them is randomly inactivated in each cell during embryonic development
• Barr body


  inactive X in each cell condenses into a compact object, occur randomly in an embryo, so females have a mosaic of two types of cells

  ex: tortoise shell cats
• on a pedigree, if more males/females are affected, then...

  the trait is sex linked (usually male because they only have one X)