Syllabus Edition

First teaching 2023

First exams 2025

|

Homologous Chromosomes (CIE A Level Biology)

Revision Note

Test yourself
Cara Head

Author

Cara Head

Last updated

Homologous Chromosomes

  • In diploid cells there are two complete sets of chromosomes in the nucleus
  • Chromosomes have a characteristic shape
    • They have a fixed length
    • The position of the centromere is in a particular location
  • These characteristic features allow for each chromosome to be identified in a photomicrograph
  • In photomicrographs chromosomes are often grouped into their homologous pairs
  • Homologous chromosomes:
    • Carry the same genes in the same positions (locus)
    • Are the same shape
  • During fertilisation a diploid zygote is formed
    • In a zygote one chromosome of each homologous pair comes from the female gamete and the other comes from the male gamete
  • Having the same genes in the same order helps homologous chromosomes line up alongside each other during meiosis

Homologous Chromosomes Diagram

Human Karyogram showing Homologous pairs, downloadable AS & A Level Biology revision notes

Human Karyogram showing homologous chromosomes

Examiner Tip

Although homologous pairs of chromosomes contain the same genes in the same order they don’t necessarily carry the same alleles (form) of each gene! i.e. We all have the genes to create eyes, some have the allele to create blue eyes and others the allele for brown eyes, for example. 

You've read 0 of your 5 free revision notes this week

Sign up now. It’s free!

Join the 100,000+ Students that ❤️ Save My Exams

the (exam) results speak for themselves:

Did this page help you?

Cara Head

Author: Cara Head

Expertise: Biology

Cara graduated from the University of Exeter in 2005 with a degree in Biological Sciences. She has fifteen years of experience teaching the Sciences at KS3 to KS5, and Psychology at A-Level. Cara has taught in a range of secondary schools across the South West of England before joining the team at SME. Cara is passionate about Biology and creating resources that bring the subject alive and deepen students' understanding