DNA, chromosomes, genes and alleles
This squirrel has the same gene for fur colour as every grey squirrel. It inherited two copies of a different version of that gene, an allele that cannot make the dark pigment melanin. Four words sit behind this: DNA, chromosome, gene and allele.
By the end of this page you can
- Describe DNA, chromosomes, genes and alleles
- Tell haploid from diploid, with the human numbers
- Put body, cell, nucleus, chromosome and gene in order of size
- Define gene, allele, haploid and diploid
- Answer exam questions on DNA and genes
Goals tick themselves off as you try the activities below.
Photo: pzmyers, CC BY 4.0, via Wikimedia Commons. Resized, JPEG q70.
An albino grey squirrel. Its pink eyes show that it makes no melanin anywhere in its body.
How often it shows up in past papers
Paper 1 counts come from our past-paper bank of CSEC Biology Paper 1s. Paper 2 is not included yet.
From a molecule to a feature
DNA, chromosomes, genes and alleles are four views of the same material. Tap each card.
Six words examiners love
These six words get mixed up in exam answers. Tap each one to see what sets it apart.
What sets it apart?
Tap a word on the list to see its meaning.
At fertilisation a haploid sperm (n) joins a haploid egg (n), so the zygote is diploid (2n) again.
Biggest to smallest
Put these in order of size, from the largest to the smallest. Drag or tap each card into its slot.
What is the largest of these?
Seven terms to know cold
Say what each term means before you flip the card. “Distinguish between” questions need both meanings.
Six quick questions, then a real one
Pick an answer to see why it’s right or wrong.
A gene is
Alleles are
How many chromosomes are in a human sperm cell?
A chromosome is made of
A dog’s body cells have 78 chromosomes. How many are in a dog’s egg cell?
Which list goes from SMALLEST to LARGEST?
exam style · 3 marks
Describe the relationship between DNA, genes and chromosomes.
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Practice questions are written by My V.I.P. Academy. They are not official CXC papers.