Phenotype ratios

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What does it mean by the term linked genes?
2 or more genes on one chromosome are inherited together, they are linked
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What is autosomal linkage?
Linkage between genes on the first 22 chromosome pairs (not the sex chromosomes)
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What is chiasmata?
The point were 2 non-sister chromatids crossover, exchanging genetic information
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What can prevent the linked genes from being inherited as a single unit?
The alleles being separated by chiasmata
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What are recombinant offspring?
Offspring that have different combinations of alleles than either parent as a result of crossing over
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How do you work out the recombinant frequency?
The number of recombinant offspring/ the total number of offspring
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What is the significance of a recombinant frequency?
If it is 50% or more, it shows there is no gene linkage, if it is less than 50% it shows that there is a gene linkage
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What is the chi-squared test used for?
To determine if there is any significance between the expected and the observed values
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Expected value
Using the expected ratios, turn them into fractions and multiply the fractions by the total number of offspring (expected number of that type of offspring)
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Observed value
The actual number of each type of offspring
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Degrees of freedom
The number of categories minus 1 (e.g. 5 categories so 4 degrees of freedom)
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Critical value
Using the degrees of freedom and the probability of 5% chance (p
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How can you draw a conclusion from the critical value
If the calculated value from the chi-squared formula is greater than the critical value, we reject our null hypothesis, if it is less than critical value we accept the null hypothesis
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What is epistasis?
The effect of one gene on the expression of another
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What is a hypostatic gene?
A gene that is affected by another gene (the epistatic gene)
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What is the effect of an epistatic gene on a hypostatic gene?
The epistatic can 'mask' the effect of the hypostatic, as if will change a process e.g. interrupting a gene sequence and so it affects the overall result
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Give an example of an epistatic gene interrupting a gene sequence
Flower pigment is created by a series of enzyme reactions one after the other with a gene coding for each enzyme, an dominant epistatic gene codes for an enzyme that modifies one of the substrates, altering the whole pathway and changing the colour
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Card 2

Front

What is autosomal linkage?

Back

Linkage between genes on the first 22 chromosome pairs (not the sex chromosomes)

Card 3

Front

What is chiasmata?

Back

Preview of the front of card 3

Card 4

Front

What can prevent the linked genes from being inherited as a single unit?

Back

Preview of the front of card 4

Card 5

Front

What are recombinant offspring?

Back

Preview of the front of card 5
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