Today Year 12 learned about pedigree charts. To start with they each picked a cat and colored in the nose either pink or brown, and gave their cats a name. As they finished I put them up in a pedigree chart, to show the relationships between each of their cats.
I thought this might be a good way to introduce pedigree charts. We did a 'mini whiteboard quiz' where I asked who the parents of Ziggy were, who the two grandparents of Nala and Mufasa were, etc.
On the side of the board I also drew the squares and circles used in pedigree charts to represent male and females. Then I colored in the symbols depending on whether the cats had a pink or red nose.
The questions in the whiteboard quiz became harder; which trait is most likely recessive? (Brown, because Churry and King have pink noses but their offspring Jerry has a brown nose. Meanwhile, Lilo and Junior both have brown noses, and only produced brown-nosed Ziggy and Simba). What are the genotypes of Brown and Cat? Etc.
Once we started to try and work out genotypes based off relationships and offspring/parents, students became a little more confused. We moved on to some activities on my genetics website and I moved around, trying to help.
I thought I would try to show my thought process while working out genotypes based on phenotypes in pedigree charts:
IF pink noses were recessive, Churry and King would both be homozygous recessive; nn. How, then, could they have produced brown-nosed Jerry, when neither of them has a dominant allele to pass on? They couldn't!
Therefore, brown noses must be recessive.
That means Jerry must be nn, because Jerry has a brown nose.
Where did Jerry get his two recessive nn alleles from? Both of his parents must carry at least one recessive allele. They must be ?n,
What is their other allele?
Jerry's parents Churry and King both have pink noses, the dominant colour. They must have at least one dominant allele, to have pink noses. That means their other allele must be N.
Therefore both Churry and King are heterozygous; Nn. Both parents are showing the dominant phenotype, but must also carry a recessive allele each to produce children with both pink and brown noses:
To produce both phenotypes, both parents must be heterozygous. If they were both NN, then 100% of their children would also have the dominant trait of pink noses.
As you can see, Churry and King produced offspring with both pink and brown noses. The offspring with pink noses (Bestfriend Stealer and Tom) could be NN or Nn - we will have to see what their genotypes are based on their own offspring!
Hopefully this blog post helped people learn how pedigree charts can reveal genotypes, as well as relationships between individuals. Maybe you can even work out Bestfriend Stealer's genotype, based off her offspring Nala and Mufasa's phenotypes!