Answer
See Solution
Work Step by Step
The Trait : Dimple in the Checks
- if present - dominant ( DD or Dd ).
if absent - recessive ( dd ).
- Brian ( male ) has dimple and his 3 brothers have
dimples.
- Brian's mother has no dimple ( phenotype ) -
so genotype is dd ( recessive , homozygous )
Brian s maternal mother - has no dimple - dd
- Brian's father has dimple and all grandparents of
father have dimple - so, no appearance of the
recessive trait ( dd ) -no carrier ( Dd ) in father
family - they are genotype ( DD ) and Brian s
father is genotype ( DD ).
- so, Brian and his 3 brothers has dimple ( phenotype)
and are Dd genotype ( carrriers ).
The Pedigree
- in it
1- female is symbolized by circle and male by
square.
2- the symbols of parents are joined by a horizontal
marriage line.
3- vertical line shows offsprings of mating.
4- affected individuals are represented by colored
square or circle.
5- the generations are numbered with Roman
numbers ( I, II, III ..... etc ).
How to do the Pedigree
- by working from the bottom and applying the rules of
Dominant - Recessive inheritance you can deduce
the genotype of parents
Brian and his 3 brothers have dimple
mother of brian has no dimple- mother is dd
( recessive trait, homozygous )
father of Brian has dimple - so, father is DD
( because Brian and his brothers all have dimple,
100% dimpled ).
then, father is DD and mother is dd- Brian and
his brothers are genotype ( Dd , Carriers ).
- Grandparents of the father - all have dimple -
-no appearance of the Recessive trait in any
generation of the father family - they are
genotype DD , father and mother of Brians father
are DD.
