Genes and Chromosomes
Genes sit on chromosomes and code for proteins.
About this topic
A gene is a section of DNA coding for a specific protein, or functional RNA. DNA is packaged with histone proteins into chromosomes; humans have 46 (23 pairs) in most cells, with one of each pair from each parent. Different versions of a gene are alleles.
The 22 pairs of autosomes plus sex chromosomes (XX female, XY male) make up the karyotype. The human genome contains around 20,000 protein-coding genes. A gene's position on a chromosome is its locus.
Humans have around 20,000 genes spread over 23 pairs of chromosomes, with chromosome 1 being the largest. A karyotype is a picture of all chromosomes lined up in pairs, used to detect conditions such as Down syndrome, which involves an extra copy of chromosome 21. Alleles are different versions of the same gene, found at the same position on homologous chromosomes.
Most of the DNA is not genes: much of it is regulatory sequences or has unknown functions. Different species have different numbers of chromosomes, such as 8 in fruit flies and 78 in dogs, so number is unrelated to complexity. A common confusion is gene versus allele: eye colour is controlled by genes; blue and brown versions are alleles.
Key ideas
- Humans have 46 chromosomes
- Alleles are gene versions
- Genome is all DNA
Quick check
Use cases: where Genes and Chromosomes helps
- Homework: review the key idea behind Genes and Chromosomes before you start a problem set.
- Exam revision: use the quick check to test whether you can recall Genes and Chromosomes without notes.
- Visual learning: play with the interactive lab to see how Genes and Chromosomes changes when you adjust its inputs.
- Teaching a friend: explain Genes and Chromosomes in your own words, then compare your version with the key ideas.
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Frequently asked questions
What is Genes and Chromosomes?
Genes sit on chromosomes and code for proteins.
What will I learn in Genes and Chromosomes?
Humans have 46 chromosomes. Alleles are gene versions. Genome is all DNA.
Is Genes and Chromosomes part of Biology?
Yes. It is one of 150 Biology topics on LearnViz HighSchoolEdu, with 3 key ideas, a live animation and a quick check.
Does the Genes and Chromosomes lab work on a phone or tablet?
Yes. The animation resizes to fit your screen and supports touch, so you can drag, tap and slide with your finger.
How should I study Genes and Chromosomes?
Read the summary and key ideas first, play with the interactive lab to see the idea in motion, then answer the quick check. If you get a question wrong, go back to the key idea it tests.
Do I need an account, and is my progress saved?
No account is needed. Marking a topic as learned is saved in your own browser, so it stays on that device and is not sent to a server.