Flashcards · Biology
Reproduction, Meiosis and Variation
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What is a gamete?
A sex cell, such as a sperm or an egg, with half the normal number of chromosomes.
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How many chromosomes are in a human gamete?
23.
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What does haploid mean?
Having one set of chromosomes.
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What does diploid mean?
Having two sets of chromosomes, in pairs.
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Where in the body does meiosis happen?
In the reproductive organs: the ovaries and the testes.
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How many cells does meiosis make from one cell?
Four.
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Are the cells made by meiosis identical?
No. They are genetically different from each other.
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What happens at fertilisation?
A male and a female gamete fuse, to make a diploid zygote.
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How many chromosomes are in a human zygote?
46.
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Why must gametes be haploid?
So that the chromosome number is the same in every generation after fertilisation.
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Which type of division makes two identical cells?
Mitosis.
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Which type of division is used for growth and repair?
Mitosis.
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A cell has 24 chromosomes. How many are in a gamete?
12.
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Why is meiosis important in producing variation?
Chromosomes are shared out randomly, so each gamete has a different mixture of genes.
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Do you need to know the stages of meiosis?
No. You need the main events and the result.
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What is the common mistake about meiosis?
Saying it makes two cells, or that the cells are identical. It makes four different ones.
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How many parents are needed for asexual reproduction?
One.
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Are the offspring of asexual reproduction identical to the parent?
Yes, they are genetically identical clones.
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Which type of cell division is used in asexual reproduction?
Mitosis.
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Give two advantages of asexual reproduction.
No need to find a mate, and a rapid reproductive cycle.
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Give one disadvantage of asexual reproduction.
No variation in the population, so a disease could affect them all.
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How many parents are needed for sexual reproduction?
Two.
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What is the main advantage of sexual reproduction?
It produces variation in the population.
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Give one disadvantage of sexual reproduction.
A mate has to be found, and it is slower.
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Why is variation an advantage if the environment changes?
Some individuals may have features that help them survive.
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Give an example of an organism that reproduces asexually.
Bacteria, strawberry plants (runners), or potatoes (tubers).
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Why was the Irish potato crop affected so badly by blight?
The plants were clones with no variation, so none was resistant.
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Name an organism that uses both types of reproduction.
Strawberry plants, fungi, aphids or malaria parasites.
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Why is asexual reproduction quicker?
There is no need to find a mate or make gametes.
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What is the main problem with a population of clones?
All of them are equally likely to be harmed by the same change or disease.
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Why does sexual reproduction help a species to evolve?
The variation gives natural selection something to act on.
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What mistake do students make about asexual reproduction?
Saying that there are no changes at all. Mutations can still happen, but rarely.
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What is variation?
The differences between individuals of the same species.
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Give two causes of genetic variation.
Mutation and sexual reproduction.
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What is environmental variation?
Differences caused by the environment, such as diet or accidents.
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Are acquired characteristics inherited?
No.
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Give an example of an acquired characteristic.
A scar, a tan, or knowing how to speak French.
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Give an example of a genetic characteristic.
Blood group or eye colour.
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Give an example of a feature caused by both genes and the environment.
Height or body mass.
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Are most features controlled by one gene or many?
Many genes.
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What is continuous variation?
Variation in which a feature can have any value in a range.
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Give an example of continuous variation.
Height, mass or leaf length.
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What is discontinuous variation?
Variation in which a feature falls into separate categories.
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Give an example of discontinuous variation.
Blood group, or sex.
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Which type of graph is used for discontinuous data?
A bar chart, with gaps between the bars.
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Which type of graph is used for continuous data?
A histogram or line graph.
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Why do identical twins help to study the causes of variation?
They have the same genes, so differences between them are due to the environment.
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Why should a sample be random and large?
To avoid bias and make the results more reliable.
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What is a mutation?
A random change in the base sequence of DNA.
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Where do new alleles come from?
Mutations.
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Name two things that increase the rate of mutation.
Ionising radiation (such as X-rays, UV) and certain chemicals.
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When do most mutations occur?
When DNA is copied before cell division.
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Do mutations happen at random?
Yes. They are spontaneous and unpredictable.
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Do most mutations affect the phenotype?
No. Most have no effect.
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Why do many mutations have no effect?
Much DNA is non-coding, and several triplets can code for the same amino acid.
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What size of effect do some mutations have?
A small effect, such as a slightly different protein.
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Can a single mutation have a large effect?
Yes, but rarely.
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Is a mutation in a skin cell passed to children?
No.
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Is a mutation in a gamete passed to children?
Yes.
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Why is there usually a lot of genetic variation in a population?
Mutations have occurred over many generations and produced many alleles.
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Why are mutations important to evolution?
They produce new alleles, which are the variation natural selection acts on.
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Give an example of a beneficial mutation.
A bacterium becoming resistant to an antibiotic.
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Why do bacteria develop mutations in large numbers?
They reproduce rapidly and there are millions in a population.
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What is the mistake in saying "mutations are always harmful"?
Most have no effect, and a few can be beneficial.