Genetics - Reproduction 157-162 Flashcards
what is sexual reproduction
where genetic information from two organisms is combined to produce offspring which are genetically different to either parent
what happens in sexual reproduction
4 points
1) the mother and father produce gametes by meiosis
2) in humans each gamete contains 23 chromosomes and the egg and sperm cell then fuse together (fertilisation)
3) this forms a cell with the full number of chromosomes
4) the mixture of genetic information produces variation in the offspring
what happens in asexual reproduction
3 points
1) there’s only one parent so the offspring are genetically identical to the parent
2) it happens by mitosis
3) the new cell has exactly the same genetic information as the parent and is called a clone
what happens in meiosis
5 points
1) before the cell divides it duplicates its genetic information forming two armed chromosomes
2) after replication the chromosomes arrange themselves into pair then line up in the centre of the cell
3) the pairs are pulled apart so each new cell only has one copy of each chromosome, some of the father’s and mother’s chromosomes go into each cell
4) in the second division the chromosomes line up again in the centre and the arms of the chromosomes are pulled apart
5) you get four gametes each with only a single set of chromosomes, each of them are genetically different because the chromosomes get shuffled up
what happens after gamete fusion
1) the gametes (in humans sperm and egg cells) fuse together in fertilisation
2) the new cell divides by mitosis to make a copy of itself
3) mitosis repeats many times to produce lots of new cells in an embryo
4) as the embryo develops the cells then differentiate into different types of specialised cells that make up the whole organism
what are the advantages of sexual reproduction
4 points
1) the offspring have a mixture of two sets of chromosomes which means there’s variation in the offspring
2) variation increases the chance of a species surviving a change in the environment
3) because the individuals with the characteristics that make them better for the environment survive more, they are more likely to breed successfully and pass on there genes (natural selection)
4) we can use selective breeding to speed up natural selection, this means we can increase food production
what are the advantages to asexual reproduction
4 points
1) there only needs to be one parent
2) uses less energy as organisms don’t have to find a mate
3) faster
4) many identical offspring can be produced in favourable conditions
how do malarial parasites reproduce
3 points
1) malaria is caused by parasites spread by mosquitoes
2) when a mosquito bites a human the parasite is transferred to the human
3) the parasite reproduces sexually when it’s in the mosquito and asexually when it’s in the human host
how do fungi reproduce
5 points
1) many species of fungi can reproduce asexually and sexually
2) these species release spores which can become new fungi when they land in suitable places
3) spores can be produced sexually and asexually
4) asexually produced spores form fungi identical to parent fungus
5) sexually produced spores introduce variation and are produced in response to an unfavourable change in the environment increasing the chance the population will survive
how do plant reproduce
5 points
1) lots of species of plant produce seeds sexually and can also reproduce asexually
2) for example strawberry plants produce ‘runners’ which are stems that grow horizontally on the surface of the soil away from the plant
3) at various points along the runner a new strawberry plant forms identical to the original plant
4) another example is plants that grow from bulbs, new bulbs can form from the main bulb and divide off
5) each new bulb can grow a new identical plant
how do chromosomes decide your sex
3 points
1) their are 23 pairs of chromosomes in every human body cell, of these are 22 that control you characteristics
2) the 23rd pair are XX or XY and decide you sex
3) females have XX chromosome and males have XY chromosome
how do sperm and egg cells get X or Y chromosomes
3 points
1) when making sperm X and Y chromosomes are drawn apart in the first division of meiosis
2) there’s a 50/50 chance each sperm cell gets an X/Y chromosome
3) when making eggs, the original cell has two X chromosomes so all the eggs have one X chromosome
