Pedigree Charts Intro with Y12

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! 

Year 12 Mutation Maltesers Game

Year 12 Bio recently played a game to illustrate how mutations enter the gene pool and change in frequency, and how mutations can be helpful, harmful or neutral (and this can change if the environment changes!)

Equipment needed for this game: 

teaspoons

tablespoons

forks

plastic forks with the middle prongs removed

bowls

shot glasses

maltesers

In this game, students 'live' in different populations at tables around the room. These populations all have a similar niche and are trying to gain access to the same resource - maltesers. These maltesers are found in bowls on a table in the middle of the room.

The game progresses through several rounds or 'generations.'

In the first round, each group has the same adaptation for gathering their resource - plastic forks. Students needed to gather a resource and keep it balanced all the way back to their table, where they could deposit the resource and pass on the fork to the next person. Each group roughly gathered the same amount of maltesers, and they all survived to produce the next generation.

In the next generation one of the populations had a mutation - they lost the middle prongs of their fork! We played another round, and the group missing the middle prongs were unable to gather any maltesers, because the gap in the middle was too big! 

Alas, this was a harmful mutation. It didn't enter the gene pool of the overall population because it failed to help them gain enough resources to survive, and unfortunately that group couldn't pass their genes or alleles onto the next generation. 

(We let the group come back in with a normal fork though, so they could keep playing).

The next generation had another mutation - their adaptation to help them gather was a tablespoon! This turned out to be a helpful mutation, as it was easier to balance and they could gather resources faster than the other groups. 

As they were more successful, in the next generation more groups had tablespoons, as the helpful allele became more frequent in the gene pool.

After a few tablespoon generations another mutation occurred - a teaspoon! I thought this mutation would also be harmful but it turned out to be neutral, as having a smaller spoon didn't seem to affect the ability to balance a malteser in it. 

However!!! Suddenly the environment changed!!

The bowls of maltesers became shot glasses of maltesers. Suddenly having a smaller teaspoon was an advantage in the new environment, as the teaspoon adaptation was too large to get into the bottom of the shot glass. 

The group with the smaller teaspoon SHOULD have had much greater access to maltesers and the next generation should have had a lot greater frequency of alleles for smaller teaspoons. 

However, my class are resourceful and very competitive, and the tablespoon groups quickly worked out that they could use the handle of the tablespoon to scoop out maltesers! So that point was sort of lost, but the rest of the game was good to illustrate how mutations arise and change in frequency in populations over generations, depending on whether they help or harm the organisms' ability to survive or reproduce in their environment.

Mutations in the story:

Fork (at the start)

Fork with prongs missing (harmful, gap too wide for maltesers)

Tablespoon (helpful - easier to balance than fork)

Teaspoon (neutral - turned out to be no different from table spoon)

Change of environment to shot glass (teaspoon advantage now to fit in the glass)