Ch. 6: Linkage and Mapping

pedigree

• used to determine the modes of inheritance in humans since we are not able to do crosses like in other organisms

• requires recognizing patterns associated with different modes of inheritance

proband

• the person for whom the pedigree is initiated

autosomal dominant

• doesn’t skip generations

• affected children will have at least one affected parent

• affects genders equally

• unaffected parents do not pass trait

X-linked dominant traits

• doesn’t skip generations

• affected children will have at least one affected parent

• affected sons might have affected mother

• affected fathers will pass the trait to all of their daughters

• often more women than men affected

autosomal recessive traits

• tends to skip generations

• a affected child does not need to have an affected parent

• affects genders equally

• if both parents are unaffected, they must have an affected allele

• appears more frequently when intermarriage takes place in the family

X-linked recessive traits

• tends to skip generations

• a affected child does not need to have an affected parent

• affects males more than females

• never passed from father to son

• all daughters of affected father’s are carriers

Y-linked

• will affect all sons of affected fathers

• cannot be passed from a mother to a son

• cannot be passed from a father to a daughter

• does not skip generations

mitochondrial

• all children of an affected mother will be affected

• cannot be passed from a father to any of his children

testcross

• test used to check for linkage

• the homozygous recessive parent will always produce parental allele combinations (non-recombinant)

• three possible outcomes

  • unlinked

  • complete linkage

  • linked with some crossing over

unlinked genes

• ½ nonrecombinant progeny and ½ recombinant progeny are produced

complete linkage

• only nonrecombinant progeny are produced

linked genes and some crossing over

• mostly nonrecombinant progeny, only a small proportion recombinant

recombination frequency

• tells you how far apart two loci are on a chromosome

• the father apart two genes are, the more likely a recombination event will occur between them

map units

• (recombinants/ total offspring) x 100 =

order of genes on a chromosome and distance between them

• what recombination can be used to determine

• this is due to recombination frequency being proportional to the distance between genes on a chromosome

50%

• what the recombination frequency is if genes are unlinked, and assort independently