Genetic diagrams

L.O  To learn how to interpret genetic diagrams and learn how genes are passed on and how they present themselves.

Genetic diagrams can be used to show the several possibilities that may occur within the genes of the offspring.

The initial pioneer of genetic experiments was a scientist called Gregor Mendel who performed experiments on pea plants in the 19th century.

He investigated the height of pea plants. The first experiment included tall pea plants and dwarfed pea plants. He crossed the two types and observed the offspring. He found that all the offspring were tall pea plants.

This is illustrated in the genetic diagram below

A capital T highlights the tall pea plant and a lower case t highlights a dwarfed pea plant

Genetic diagrams

When looking at the genetic diagrams and when answering exam questions it is important to know the correct terminology when describing the offspring genetic information.
Allele is a term used to describe different versions of the same genes. For example for the eye colour gene, different colours would be alleles as they all determine the same characteristic.
If an organism has two alleles, which are the same, then it is known as homozygous, if there are different then it is heterozygous
When considering the diagram, if the dominant allele is present once, then it is heterozygous dominant, it is present twice, it is called homozygous dominant. This is also true of the recessive allele.

recessive allele

Genetic diagrams are particularly useful in determining the possibility of the child getting a disease from the parent. The parent can either be infected by the disease or can be a carrier.

A carrier is someone who is heterozygous, meaning they have both alleles; lucky for them the one that causes the disease is a recessive one so they are not affected.

1 in 4 chance


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