AQA GCSE Genetics & inheritance Part 2(Biology)

AQA GCSE Genetics & inheritance part 2(Biology)

Genetics & inheritance part 2

What is Genetic Probability?

Probability is used in genetics to predict how likely it is that offspring will inherit certain traits from their parents. By looking at the alleles each parent has, we can calculate the chance of different genetic combinations using tools such as Punnett squares. For example, a probability of 1 in 4 (25%) means that, on average, one out of four offspring is expected to show that trait.

Single gene crosses, where only one gene is involved, are relatively simple to predict because there are only a few possible outcomes. However, most characteristics in real organisms, such as height or eye colour, are controlled by multiple genes working together. This makes their inheritance much more complex and less predictable than single gene traits.

Some characteristics are controlled by a single gene, but most characteristics are controlled by multiple genes (polygenic).

Punnett Squares

Example: Inheriting Height in Plants

Let’s say:

T = tall (dominant allele)
t = short (recessive allele)

Both parents are heterozygous (Tt).

If one parent is homozygous dominant and the other parent is heterozygous.

If an organism is homozygous, this it is also known as pure breeding for that characteristic.

If one parent is homozygous dominant and the other is homozygous recessive.

Both parents here are pure breeding.

In this case one parent is heterozygous and the other is homozygous recessive.

Practice Questions

1.Dimples in humans is controlled by a single gene. Dominant allele D indicates dimples will be present, whilst recessive allele d indicates no dimples.

In each of the following cases draw punnet squares to predict the probablility of offspring with or without dimples.

1a. Two parents that are both homozygous dominant

1b. Two parents that are both homozygous recessive

1c. One parent is homozygous dominant, whilst the other is homozygous recessive

1d. One parent is homozygous dominant, whilst the other is heterozygous

1e. Both parents are heterozygous.