Reproduction Flashcards
What happens in sexual reproduction?
The mother and father produce egg and sperm (which are both gametes) by meiosis
What is significant about gametes?
Gametes contain half the number of chromosomes, 23 instead of 46.
What happens in fertilisation? How does this result in variation?
Egg and sperm fuse together to form a cell with the full number of chromosomes. This is why offspring inherit features from both parents. The mixture of genetic information produces variation.
What happens in asexual reproduction?
There is only one parent so the offspring are genetically identical.
How does it happen?
It occurs via mitosis.
What produces asexually?
Some animals and plants, bacteria
What are the advantages of sexual reproduction?
Sexual reproduction results in variation, meaning the population is more likely to withstand environmental changes, diseases or an introduction of a new predator because they can adapt
What are the disadvantages of sexual reproduction?
It requires energy and time to find a partner, it also takes longer
What are the advantages of asexual reproduction?
Asexual reproduction is fast, meaning bacteria can produce colonies quickly in favourable conditions such as abundance of a food source. It uses less energy and there only needs to be one parent.
What are the disadvantages of asexual reproduction?
Asexual reproduction cannot be used for selective breeding as it does not produce variation or a gene pool, therefore we cannot use it to increase food production for example
Which 3 examples of organisms can reproduce asexually and sexually?
Malaria, fungus, plants
Malaria
The parasite reproduces sexually between mosquitos and asexually in a human host
Fungus
It produces spores which become new fungi when in a suitable place, spores can be produced sexually and asexually
Plants
Plants can reproduce asexually and sexually, such as strawberry plants. They produce runners which are horizontal stems along the soil and at various points a new strawberry plant is made (asexual) or seeds (sexual)
Inherited diseases
Some disorders can be inherited from a person’s parents, most of these diseases can be screened for in embryos
Name a genetic disorder caused by a recessive allele
Cystic fibrosis
What is cystic fibrosis?
It is a genetic disorder in the cell membranes which results in the body producing lots of sticky mucus in the air passages, lungs and pancreas.
Recessive meaning
Two copies of the allele are needed in order for it to be expressed
What is a carrier?
A person who only has one copy of the allele
What are the names for a person with two of the same and two different alleles?
Homozygous and heterozygous
An example of a genetic disorder caused by a dominant allele
Polydactyly
What is polydactyly?
A genetic disorder where a baby is born with extra fingers or toes, it usually doesn’t pose any problems
What does dominant mean?
Only one allele is needed for the gene to be expressed
What are the two main types of embryo screening?
During in vitro fertilisation (IVF) or during pregnancy by taking a sample from the placenta
IVF screening
The embryo has a cell removed and its genes analysed before being implanted into the mother, embryos with defects are discarded or used in stem cell research
Embryonic screening in the womb
A cell is taken and its genes analysed, the mother may choose to terminate the pregnancy or keep the child if it has a genetic disorder
Arguments for screening
Helps to stop people suffering, treating disorders costs the government a lot of money, there are laws to stop it going too far (not allowed to choose sex for example)
Arguments against screening
Implies that people with genetic disorders are undesirable which may increase prejudice, it is expensive, may go too far and people may try to choose characteristics
