Sexual Reproduction and Meiosis Flashcards
What is sexual reproduction?
Where genetic information from two organisms (a father and a mother) is combined to produce offspring which are genetically different to either parent.
In sexual reproduction, what do the father and mother produce?
Gametes (reproductive cells). In animals these are sperm and egg cells.
How many chromosomes do gametes contain?
Half the number of chromosomes of normal cells - they are haploid.
What are the haploid and diploid numbers for humans?
Diploid = 46 Haploid = 23
In fertilisation, what happens first?
A male gamete fuses with a female gamete to produce a fertilised egg, also known as a zygote. The zygote ends up with a full set of chromosomes.
In fertilisation, happens after the male and female gametes fuse?
The zygote undergoes cell division by mitosis, and develops into an embryo.
The embryo inherits characteristics from both parents, as it has received a mixture of chromosomes (and therefore genes) from its father and mother.
In humans, where is the only place meiosis happens?
In the reproductive organs (ovaries and testes).
In meiosis, what happens in the first division?
1) The cell duplicates its DNA so there’s enough for each new cell. One arm of each X-shaped chromosome is an exact copy of the other arm.
2) The chromosomes line up in pairs in the centre of the cell. One chromosome in each pair is from the father and the other is from the mother.
3) The pairs are then pulled apart, so each new cell only has one copy of each chromosome. Some of the father’s chromosomes and some of the mother’s chromosomes go into each new cell.
4) Each new cell will have a mixture of the mother’s and father’s chromosomes. Mixing up genes like this is important as it creates genetic variation in the offspring.
In meiosis, what happens in the second division?
5) In the second division the chromosomes line up again in the centre of the cell. It’s a lot like mitosis. The arms are pulled apart.
6) You get four haploid daughter cells - these are gametes. Each gamete only has a single set of chromosomes. The gametes are all genetically different.
