Why can people look like their parents, brothers and sisters but no identical to them?
- A human has 23 PAIRS OF CHROMOSOMES
- A pair of chromosomes carries the same genes in the same place, on each chromosome within the pair.
- However, there are different versions of a gene called ALLELES.
- These alleles may be the same (HOMOZYGOUS) on each pair of chromosome, or different (HETROZYGOUS)
- For example to give blue eyes or brown eyes.
- Sex cells only contain one chromosome from each pair.
- When an egg cell and sperm cell join together, the fertilised egg cell contains 23 pairs of chromosomes.
- One chromosome in each pair comes from the mother, the other from the father.
Reason of variation:
- Do you remember the process of meiosis in I /GCSE Biology?
- Which chromosome we get from each pair is completely random.
- This means different children in the same family will each get a different combination.
- This is why children in the same family look a little like each other and a little like each parent, but are not identical to them.
- The child will share similarities with its parents depending on which characteristics have come from the father and which have come from the mother and which ones are dominant and recessive.
Dominant and Recessive
In I /GCSE Biology, you should know the concept of dominant and recessive alleles!
An allele can be DOMINANT or RECESSIVE
- An individual with one or both DOMINANT alleles (in a pair of alleles) will show the associated DOMINANT characteristic.
- An individual with one RECESSIVE allele (in a pair of alleles) will not show the associated RECESSIVE characteristic.
- An individual with both RECESSIVE alleles (in a pair of alleles) will show the associated RECESSIVE characteristic.
And we're done with this topic! Well Done!
Drafted by Alyssa (Biology)
- "Difference Between Homozygous and Heterozygous", https://cdn1.byjus.com/wp-content/uploads/2018/12/difference-between-homozygous-and-heterozygous.png
- "Fertilisation". Photo from the internet.
- "How is genetic diversity increased by meiosis?", https://qph.fs.quoracdn.net/main-qimg-356d8184477f17ae237adb8986ddaca4.webp
- "recessive. A dominant gene", https://www.genome.gov/sites/default/files/tg/en/illustration/dominant.jpg