MGSLG. (2020). Module 1 Unit 6

Pedigree diagrams and how they are solved

Pedigree diagrams/genetic lineages

A genetic lineage/pedigree traces the inheritance of characteristics over many generations. Learners should be able to interpret pedigree diagrams.

How to approach answering pedigree diagram questions:

Generation

Analysing the genetic lineage in a pedigree diagram:

Step 1: Mark all the homozygous recessive individuals with blonde hair.  This will be all the white shapes: E, F, G, I, K, N and P as bb on the pedigree chart
Step 2: Work from the generation line 5 up towards the generation line 1 so that you start with the last offspring on the pedigree diagram.  To produce an offspring with bb, BOTH parents must have at least one homozygous recessive gene (b). If the parent is a white shape – then the parent is bb and already marked.  If the parent is a shaded shape and produced a bb offspring, then the parent must be heterozygous Bb.  Mark the Bb parents on the pedigree diagram
Step 3: Parents that are shaded shapes and produce only shaded shape offspring, can be homozygous BB or heterozygous Bb.  Look to the next generation and then work backwards.  Mark the parents on the pedigree diagram
Step 4: Answer the questions that relate to the pedigree diagram.

Try to work out the genotype of A, B, C, D, H, J, L, M and O on your own first.

Let's see if you were right!

  • A and B are Bb because they produce G (bb)
  • If C is BB then D must be Bb or C is Bb then D is BB because H must be Bb to produce K (bb)
  • J is Bb because G is bb and H is Bb (produced sister K - bb)
  • L and M are both Bb because parent J is Bb and I is bb so they cannot be homozygous BB AND L and M produce a son (N) and daughter (P) that are both homozygous bb
  • Offspring O can be either BB or Bb because both parents are heterozygous Bb.


Last modified: Wednesday, 17 March 2021, 1:29 PM