Predicting Inheritance Lesson 7

Students will be able to use Punnet Squares to predict the likelyhood of a trait being passed to an offspring and be able to read pedigree diagrams.

Success Criteria

Students will understand that punnet squares are a tactic used by scientists to predict inheritance of specific traits and be able to read how pedigree diagrams work.

Learning Intention

​Recap: Terminology

We learnt that Allele's is a version of a gene. We also learnt that some alleles can be dominant and some can be reccessive.

For an Allele to be dominant, one version of the gene must be present. We represent dominant genes with a capital letter.

For an Allele to be recessive, two version of the gene must be present. We represent recessive genes with a lower case letter.

​Recap: Punnet Squares

We also covered the basics of punnet squares. Punnet squares look like a table, scientists use this to calculate the inheritance of a particular gene.

​Recap: Punnet Squares continued

Punnet squares are filled out as follows:
Lets say we are calculating the likely hood of a person inherting blue coloured eyes. Both Parents have brown eyes but have a reccesive variant of the gene. (Bb)

We place the parents alleles into the first row and coloum.

We then fill out the table by placing the letters down and across.

​Recap: Punnet Squares continued

In the following table we can see the possible genotypes being
BB = Brown eyes
Bb = Brown eyes
Bb = Brown eyes
bb = Blue eyes

Therefore the odds of the child having blue eyes = 25%

​Punnet Square Excercise

The gene for a pumpkin skin colour has 2 Alleles: Orange and Green. Orange skin is dominant, Green skin is recessive.

In the example below an Orange pumpkin (GG) is crossed with a green pumpkin with allele's (gg). The following punnet square will be drawn.

​All possible outcomes have a dominant allele, so there is a 100% chance that the offspring will be orange.

Learning the terminology

Reminder: Remember the term Hetrozygous and Homozygous. Remember these has they are the common terms used in the field!

Homozygous: The same variant of the gene, for example GG and gg

Hetrozygoys: Different variants of the gene, for example Gg and gG

​Pedigree Diagrams

Are used by scientists to look at a families genetic history.
It can be used to show:
Relationships between individuals
How many offspring each individuals have

and most importantly:  Indicates which individuals have certain genetic pathogenic variants, traits, and diseases within a family as well as vital status.

They can vary in look and take many different forms.

Lets look at some examples

The following diagram shows how hemophilia is inherited within a particular family tree.

Example 2

A more generalised example

​Investigating a condition

For this next exercise, we will flex our information-finding skills by investigating one of the following 5 genetically inherited conditions.

Firstly choose a genetic condition you want to research a bit about:
1. Huntington's disease
2. Cystic Fibrosis
3. Marfan's Syndrome
4. Haemophilia
5. Muscular Dystrophy

What to investigate

Answer the following questions about your selected condition

1. What is the condition?
2. What are its symptoms?
3. Are there any treatments?
4. Something you find interesting about the condition

Key points

In your notebook, type the following key points:

Pedigree Diagrams: A family tree that Indicates what individuals have certain genetic pathogenic variants, traits, and diseases within a family as well as vital status.

Homozygous: The same variant of the gene, for example GG and gg

Heterozygous: Different variants of the gene, for example Gg and gG