Genetic Relationships

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Genetic Relationships

• Similarity among relatives
• Estimation of genetic parameters
• Estimation of Breeding Values
• Optimization of Mating Systems (Inbreeding and
  Cross-breeding)

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IBD- Identical By Descent

• THE BASIS OF GENETIC LIKENESS

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IBD- Identical By Descent

• IDB- Two alleles are IBD if they are copies of a
  single ancestral gene.

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Genetic Relationships

• Coefficient of relationship A measure of
  pedigree relationship. The probable proportion of
  one individuals genes that are IBD to genes of a
  second individual. Correlation between the BV of
  two individuals due to pedigree relationship
  alone.
• Inbreeding Coefficient A measure of the level of
  inbreeding in an animal. The probability that
  both alleles of a gene are IBD.

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Coefficient of relationship - r

• rij ij Coefficient of relationship lt0 1gt
• Expected prop. of alleles in common
• (IBD- Identical By Descent)
• Correlation between breeding values

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R
Path Method
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Coefficient of Relationship
R
of paths/generations separating individuals
through the common ancestor
VALID IF ANCESTOR ISNT INBREED !!
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Additive and Dominance Relationship

• Additive Relationship Measure of the fraction of
  additive gene effects in common between
  relatives.
• gtgtIn a non-inbreed population the additive
  relationship is equal to the coefficient of
  relationship.
• Dominance Relationship Probability that the pair
  of alleles (genotype) between two individuals are
  IBD

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Inbreeding and Coefficient of Relationship

• CA Common ancestor
• K the of common ancestors
• n1 the number of generations separating the
  common ancestor from the sire of X
• n2 the number of generations separating the
  common ancestor from the dam of X
• FCA the inbreeding coefficient of the common
  ancestor

• For Rxy, n1 and n2 and the of generations
  separating the common ancestor from X

F 0 ???
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Step and Rules for Calculating Inbreeding and
Relationship Coefficients Using the Path Method

• Using the Path method to calculate Inbreeding and
  Relationship Coefficients can be a fun exercise!!

• Convert the pedigree to an arrow diagram in each
  individual appears only once.
• Locate common ancestors.
• Calculate F for each CA.
• Fill the Table below
• Sum the last column to compute either Fx or the
  numerator of Rxy
• For Rxy, divide the sum by

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Inbreeding

• Half of parents coefficient of relationship

• Same ancestor on maternal and paternal lines
  inbreed animal

VALID IF ANCESTOR ISNT INBREED !!
rD,E?
Fx ?
Arrow diagram
Pedigree
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Inbreeding

• Half of parents coefficient of relationship

• Same ancestor on maternal and paternal lines
  inbreed animal

VALID IF ANCESTOR ISNT INBREED !!
rD,E?
Fx ?
Arrow diagram
Pedigree
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Example 1

• B
• D
• X A
• E
• C
• CA A, FA 0
• D A E so n1 1, n2 1
• FX ( ½ 111)x(10) 1/8 0.12512.5

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Step and Rules for Calculating Inbreeding and
Relationship Coefficients Using the Path Method

• Each pair of path must start from the common
  ancestor and follow the direction of the arrows
  (no backtracking).
• A pair of paths may not include the same
  individual (except the CA). If the same animal
  appears in both path it should be treated as a
  CA.
• In certain situation an animal is considered its
  own ancestor (separated by 0 generations) to
  avoid double counting. Case of sire daughter
  mating.

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Genetic Relationships

• A
• S
• B
• A
• X
• S
• B
• D
• A
• C
• E

Arrow diagram
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Genetic Relationships

• A
• S
• B
• A
• X
• S
• B
• D
• A
• C
• E

Arrow diagram
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Genetic Relationships

• A
• S
• B
• A
• X
• S
• B
• D
• A
• C
• E

Arrow diagram