Pedigree Charts

A Pedigree Chart is simply a family tree, where we are focusing on one particular inherited characteristic. We can use it to make predictions and inferences about the genotypes of individuals based on their phenotypes, parents' phenotypes, and/or offsprings' phenotypes.

Test Crosses

Whenever we have a dominant allele, we express the dominant phenotype. This means we cannot be certain of our genotype. We may be heterozygous, or homozygous dominant. If the allele is represented by the letter A (or a), we could be Aa or AA.

How do we find out the genotype of an individual expressing the dominant phenotype? In humans, it is a bit unethical, so we would struggle to do so without mapping their genes - time consuming and costly at the moment!! In plants and some animals, we do a test cross, breeding it with an individual expressing the recessive phenotype.

Punnett Squares

Punnett Squares are a convenient way to predict and explain inheritance. They only work if there are only two options for a gene (two possible alleles), and if the characteristic is controlled by only one gene (set of alleles).

By completing a Punnett Square, we can predict the probability of an offspring (child) having a certain characteristic (phenotype) and having a certain genotype (homozygous dominant, heterozygous, or homozygous recessive).

If you would prefer my explanation, here it is (although I think the Amoeba Sisters do a much better job of it!!)

Predicting Inheritance - Overview

Over the next couple of weeks, we will explore how to use our knowledge of DNA, alleles, genes, chromosomes, cell division and sexual reproduction to predict and explain the inheritance of characteristics/traits. Sounds like a lot!!

This video is a really good overview of the majority of what we are going to learn, and how to apply our knowledge to predicting and explaining inheritance.