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How many chromosomes are in human cells?
Human cells have 46 chromosomes.
Which is the longest chromosome in a human cell?
Chromosome 1.
What are chromosomes made up of?
Hundreds of genes.
What does each gene do?
Each gene helps to control a particular characteristic in the organism.
What is the shape of a DNA molecule?
A twisted ladder known as a double helix.
What are gametes?
Sperm and egg cells; life begins when they join.
Why are egg cells larger than sperm cells?
Because they contain food reserves.
What is fertilisation?
The joining of a sperm cell with an egg cell.
What is the new cell formed after fertilisation called?
A zygote.
What chromosomes make a female?
What chromosomes make a female?
What chromosomes make a male?
One X chromosome and one Y chromosome (XY).
Which is smaller: the X chromosome or the Y chromosome?
The Y chromosome.
What is variation?
The differences between individuals of the same species.
What are genes made of?
DNA.
What happens when sperm and egg fuse together?
They produce a new combination of DNA.
What are genetic differences?
Differences in DNA between organisms of the same species.
What else, besides DNA, can cause variation?
The environment.
What can changes in the environment lead to?
Extinction of a population.