Genes, DNA and Inheritance
- Biology
- Ages 11–14 · Grades 6–8
What you’ll find out
- DNA in chromosomes carries coded instructions; a gene is a section of DNA that codes for a protein.
- Chromosomes come in pairs, one of each pair from each parent, and genes influence traits through proteins.
- Mutations change DNA; most have no effect, some harm and a few help, and they are the source of variation.
No sign-up and no real names. In the lesson you check your understanding as you read, and practise until it sticks.
Instructions in DNA
Inside the nucleus of almost every cell is DNA, a very long molecule shaped like a twisted ladder, called a double helix. DNA carries the instructions for building and running a living thing. It is coiled tightly into structures called chromosomes; most human cells contain 46 of them, arranged in 23 pairs. A gene is a section of DNA that holds the instructions for making one protein. Proteins do most of the work in cells, and they help determine traits such as eye colour. You inherited your genes from your parents.
Mutations and variation
Occasionally, the DNA code changes. Such a change is called a mutation. Mutations can happen when a cell copies its DNA before dividing and makes a small error, or when DNA is damaged by radiation or certain chemicals. Most mutations have no noticeable effect, some are harmful, and a few turn out to be helpful. A mutation in an egg or sperm cell can be passed on to offspring. Together with the mixing of genes from two parents, mutations create the variation we see among living things.
Curriculum links: NGSS MS-LS3-1 · NGSS MS-LS3-2 · England KS3: Genetics and evolution · Cambridge Lower Secondary Stages 7–9: Biology · NCERT Science, Classes 6–8