genetics Flashcards
what is sexual reproduction
where genetic information from 2 organisms is combined to produce offspring which are genetically different to either parent
what is a gamete
reproductive cells
examples of reproductive cells
sperm
egg
what is a haploid cell
half the number of chromosomes in the normal cell
examples of diploid cells
gametes (sperm and eggs)
what happens during fertilisation
a male gamete fuse with a female gamete to produce a fertilised egg, also known as a zigote. The zygote sperm ends up with the full set of chromosomes (so it is diploid).
The embryo inherits characteristics from both parents, as it has received a mixture of chromosomes (and therefore genes) from its mum and its dad.
what is a zygote
female gamete which produces a fertilised egg
how are gametes produced
meiosis which only happens in reproductive organs
what happens during meiosis
DIVISION 1:
1) Before the cell starts to divide, it 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) In the first division in meiosis (there are two divisions) the chromosomes line up in pairs in the centre of the cell. One chromosome in each pair came from the organism’s mother and one came from its father.
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 the genes like this is really important it creates genetic variation in the offspring.
DIVISION 2:
5) In the second division the chromosomes line up again in the centre of the cell. It’s a lot like mitosis. The arms of the chromosomes are pulled apart.
6)You get four haploid daughter cells - these are the gametes. Each gamete only has a sinole set of
chromosomes. The gametes are all genetically different.
what is asexual reproduction
divide by mitosis, results in two diploid daughter cells, which are genetically identical to each other and to the parent cell
what is sexual reproduction
involves meiosis and the production of genetically different haploid gametes, which fuse together to form a diploid cell
asexual reproduction advantages
- produce lots of offspring quickly as it’s independent
e.g. bacteria E. coke can divide every half an hour - only one parent is needed, can happen whenever without waiting
asexual reproduction disadvantages
- no genetic variation
- if environment changes and conditions become unfavourable, the whole population may be affected
sexual reproduction advantages
- creates genetic variation
- if environment changes, more chance some will survive
- can lead to natural selection and evolution
sexual reproduction disadvantages
- takes more time and energy
- two parents are needed, can be a problem if one is isolated
what is DNA made up of
polymers made up of lots of repeating units called nucleotides
what is a nucleotides
one sugar molecule, one phosphate molecule and one base
what are the 4 bases called
adenine
thymine
cytosine
guanine
what bases pair together
A,T
G,C
how is DNA stored
chromosomes which contain genes