Variation and Inheritance

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What is genotype?
The genetic makeup of an organism in respect of that gene.
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What is phenotype?
The observable characteristics of an organism in respect of that gene.
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Give some examples of genetic and environmental contributions to phenotypic variation.
Genetic: Eye colour, Natural hair colour. Environmental: Chlorosis in plants, diet in animals
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What is a dominant allele?
The version of a gene that will always be expressed if present in an organism.
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What is a recessive allele?
The version of a gene that will only be expressed if two copies of the allele are present in an organism.
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What does homozygous mean?
Two identical alleles for a characteristic.
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What does heterozygous mean?
Two different alleles for a characteristic.
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What is continuous variation and how is it caused?
Characteristics that can take any value within a range. Continuous variation is caused by genetic and environmental factors and is polygenic (controlled by a number of genes).
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What is discontinuous variation and how is it caused?
Characteristics that can only appear in discrete values. Discontinuous variation is caused by mostly genetic factors and it is caused by one or two genes.
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How does sexual reproduction lead to genetic variation?
The combination of alleles an organism inherits is determined by sexual reproduction involving meiosis and the random fusion of gametes at fertilisation.
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What is monogenic inheritance?
The inheritance of a single gene.
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How do you carry out a genetic cross for monohybrid inheritance?
1) State the phenotype of both parents. 2) State the genotype of both parents. 3) State the gametes of each parents. 4) Use a Punnett square. 5) State the genotypic proportion of offspring (presented as a ratio). 6) State the corresponding phenotype.
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What is codominance?
When two different alleles for a gene are equally dominant.
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What are multiple alleles?
When genes have more than two versions. Organisms can still only carry two version of the gene. E.g. Blood group
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What are sex linked genes?
The genes carried on the sex chromosomes.
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What is dihybrid inheritance?
A characteristic inherited on two genes.
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With genetic crosses, why can the number of offspring produced differ from the expected ratio of offspring?
1) The fertilisation of gametes is a random process so in a small sample a few chance events may lead to a skewed ratio 2) The genes being studied are both on the same chromosome (linked genes).
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What is autosomal linkage?
When the genes that are linked are found on one of the other pairs of chromosomes.
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What are some features of linked genes?
1) Inherited as one unit- no independednt assortment during meiosis. 2) Cannot undergo random shuffling of alleles during meiosis.
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What are recombinant offspring?
Offspring that have different combinations of alleles than either parent.
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What decreases the likelihood of genes being separated, during crossing over in meiosis, resulting in fewer recombinant offspring being produced?
The closer they are on a chromosome.
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What is the recombination frequency and how is it calculated?
A measure of the amount of crossing over that has happened in meiosis. it is calculated by number of recombinant offspring/total number of offspring.
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What is the chi-squared test used for?
It measures the size of the difference between the observed results and the expected results.
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When is the result of a chi-squared test significant?
When the chi-squared value is less than the critical value.
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What is epistasis?
The interaction of genes at different loci (e.g. gene regulation).
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What is reccessive epistasis?
When a recessive allele results in the lack of an effect (e.g. enzyme production).
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What is dominant epistasis?
When a dominant allele results in a gene having an effect on another gene.
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Card 2

Front

What is phenotype?

Back

The observable characteristics of an organism in respect of that gene.

Card 3

Front

Give some examples of genetic and environmental contributions to phenotypic variation.

Back

Preview of the front of card 3

Card 4

Front

What is a dominant allele?

Back

Preview of the front of card 4

Card 5

Front

What is a recessive allele?

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Preview of the front of card 5
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