Chromosomes & Cells

Exam code: 5090

Written by: Ashika|Reviewed by: Caroline Carroll|Updated 2 July 2026

Inheritance is the transmission of genetic information from generation to generation
Chromosomes are located in the nucleus of cells
They are thread-like structures of DNA, carrying genetic information in the form of genes
A gene is a short length of DNA found on a chromosome that codes for a specific protein
This could be a structural protein such as collagen found in skin cells, an enzyme or a hormone
Genes control our characteristics as they code for proteins that play important roles in what our cells do
Think about zooming into the nucleus of a cell, as shown in the diagram below
- On the right is the zoomed-out view
- Which zooms in as we read across the diagram right-to-left

Genes are short lengths of DNA that code for a protein. They are found on chromosomes

Alleles are different versions of a particular gene. The ABO gene for blood group type has three alleles, I^A, I^B and I^O
Alleles give all organisms their characteristics

The nuclei of gametes are haploid
- They contain half the number of chromosomes of a normal body cell
- In humans, this is 23 chromosomes
The nucleus of a zygote is diploid
- It contains the same number of chromosomes as a normal body cell
- In humans, this is 23 pairs of chromosomes
- The zygote continues to stay diploid as it grows into a fetus and embryo during pregnancy

A haploid cell has one copy of each chromosome while a diploid cell has two copies of each chromosome.

Chromosomes