Probability in Genetics

Probability in Genetics

Probability is how we measure things that happen just by luck or chance, like tossing a coin.

Probability is a branch of mathematics that deals with events that are based entirely on chance.

It means we are looking at the possibility of something happening out of all the possible things that could happen.

It is written in numbers starting from 0 up to 1.

Gregor Mendel was the scientist who first used these ideas about chance to explain how parents pass traits to their children.

The two main principles of probability in genetics are:

1. The result of one trial of a random event does not affect the result of later trials of the same event.

2. The probability that two independent events will happen simultaneously is the product of their chances of occurring separately.

When we know how a sickness or a physical look is passed down, we can guess the genes of people in a family just by looking at them.

These guesses help us work out the chance of a particular gene set being passed to children yet to be born.

This information is very helpful for doctors who give advice to parents who are worried about passing a family sickness to their babies.

In genetics, the chance of something happening is always more than zero and can go up to 1.

The formula for working out probability is:

Probability = (Number of times an event occurs) / (Total number of trials)

We usually use two main rules of chance to solve biology problems about genes:

1. The rule of multiplication (product rule).

2. The rule of addition (addition rule).

The Rule of Multiplication

Mendel showed that things like height or hair color in pea plants were passed from parents as separate units.

He found that different traits did not follow each other, so we can study them one by one using chance.

For example, if you cross a plant with green, wrinkled seeds and another with yellow, round seeds, the colors and the shapes follow their own rules separately.

The two traits did not disturb each other.

This rule says if two things happen together, you multiply their separate chances to get the final answer.

The rule of multiplication states that the probability of two independent events occurring together is the product of their individual probabilities.

It means you multiply the chance of the first thing by the chance of the second thing.

Example:

If we cross two pea plants that have both big and small genes for flower color (Pp), what is the chance of getting a baby plant with only small genes (pp)?

The probability that an egg from the heterozygous parent will get a p allele = 1/2.

The probability that sperm from the heterozygous parent will get a p allele = 1/2.

The total chance that the small gene from the egg and the small gene from the sperm will meet is:

1/2 x 1/2 = 1/4.

The Rule of Addition

This rule says if something can happen in more than one way, you add the chances of those different ways together.

The rule of addition states that if an event can happen in two or more independent ways, the total probability is the sum of the probabilities of each way.

It means you calculate the chance for each way it can happen and then plus them together.

Example:

If we cross two pea plants that have both big and small genes (Pp), what is the chance of getting a baby that also has both (Pp)?

There are two different ways to get this result:

The big gene (P) could be in the egg and the small gene (p) in the sperm.

Or the big gene (P) could be in the sperm and the small gene (p) in the egg.

The probability that P is in the egg and p is in the sperm is: 1/2 x 1/2 = 1/4.

The probability that P is in the sperm and p is in the egg is: 1/2 x 1/2 = 1/4.

So, the total chance that a baby with both genes (Pp) will be born is:

1/4 + 1/4 = 1/2.