B4 - Sexual Reproduction And Meiosis Flashcards
Why are offspring genetically different to either parent?
Genetic information from two organisms is combined to produce offspring
What are gametes?
Father and mother produce gametes.
In animals these are sperm and egg.
What do gametes contain?
Half the number of chromosomes of normal cells.
What happens at fertilisation ?
The male gamete fuses with the female gamete to produce a fertilised egg called a zygote.
What is a zygote?
A fertilised egg
How does the zygote end up with the full set of chromosomes?
The chromosomes from the mother pair up with the chromosomes from the father.
How does an embryo develop?
The zygote undergoes cell division by mitosis.
Where does the embryo inherit characteristics from?
From both parents as its received a mixture of chromosomes (and therefore genes) from both parents.
What is meiosis?
A type of cell division.
Where does meiosis occur in humans?
In the reproductive organs (ovaries and testes)
What has to happen before meiosis?
Interphase.
What happens during the interphase?
The cell grows and duplicates it DNA
When the DNA is duplicated what is produced?
X shaped chromosome, each arm is an exact copy of the other arm.
How many cell divisions are there in meiosis?
Two
What happens during the first division in meiosis?
The chromosomes lineup in pairs in the centre of the cell.(one chromosome in each pair comes from each parent)
The pairs are pulled apart.
Describe the chromosomes that each new cells ends up with during the first division of meiosis.
The chromosome number of each new cell is half that of the original cell.
Each new cell has a mixture of the fathers and mothers chromosomes.
Why is it important that the genes are mixed up during meiosis?
It creates genetic variation in offspring, (each offspring will have a different mixture of alleles)
What happens in the second division of meiosis?
The chromosomes line up again in the centre of the cell. The arms of the chromosomes are pulled apart.
How many gametes are produced after meiosis?
Four gametes
After meiosis describe the 4 gametes produced.
Each has a single set of chromosomes.
The gametes are all genetically different.
Why are identical twins genetically identical?
Because they done from a single zygote that splits in two, then develops into two separate embryos.
Explain why gametes need to have half the number of chromosomes of a normal body cell. (2 marks)
During fertilisation, a male gamete fuses with a female gamete to form a zygote/fertilised egg (1 mark)
Gametes need half the chromosome number so that the zygote/fertilised egg ends up with the full number of chromosomes and not twice as many.(1 mark)
