What are chromosomes?
long threads of DNA, found in the nucleus of every cell
How many chromosomes are there in one human body?
23 pairs, 46 chromosomes
What is DNA?
a chemical made out of long molecules with a shape like a twisted ladder
What are genes?
parts of a chromosome that determine a feature of an organism
What are the two gametes in the human body?
egg cell and sperm cell
List as many features of a sperm cell.
- has a nucleus( contains 23 chromosomes)
- has a cell surface membrane
- contains cytoplasm
- has a tail to swim vigorously/to move
- smaller than egg cells
List as many features of an egg cell.
- has a nucleus (contains 23 chromosomes)
- has a cell surface membrane
- contains cytoplasm
- contains food reserves for the zygote
- larger than sperm cells
- cannot move by themselves
What is fertilisation?
the process when an egg cell and a sperm cell fuse together
What is formed after fertilisation?
zygote
What determines the gender of a zygote?
All egg cells contain one X chromosomes. All sperm cells can contain either one X or one Y chromosome. If it is an X chromosome, the zygote will have a XX chromosome and will be a girl.. If it is a Y chromosome, the zygote will have a XY chromosome and will be a boy.
What is inheritance?
the passing of DNA from parent to offspring
What is variation?
differences between individuals that belong to the same species
What 2 factors affect variation?
DNA and enviroment
What is natural selection?
increased chance of survival of individuals that have particular advantageous features; these individuals therefore have a greater chance of survival and passing on their genes to the next generation
