Patterns of Inheritance

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What is continuous variation?
When the individuals in a population vary within a range and there are no distinct categories (e.g. normal distribution curve, height).
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What is discontinuous variation?
When there are 2 or more distinct categories and no intermediates (e.g. blood type)
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What is phenotypic variation?
The variation in an organisms phenotype (e.g. displayed characteristics).
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How does genotypic variation affect phenotypic variation?
Alleles vary between organisms of the same species so genotype varies. Sexual reproduction, meiosis, crossing over and independent assortment also cause genotypes to differ.
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What are polygenic and monogenic characteristics?
Polygenic - inherited characteristics that show continuous variation are influenced by many genes. Monogenic - inherited characteristics that show discontinuous variation are influenced by only one gene.
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How does the environment affect phenotypic variation?
Variation can be caused by differences in the environment e.g. food, climate, lifestyle. Genotype influences characteristics an organism is born with but environmental factors can affect development of these characteristics.
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What is a gene?
A sequence of bases on a DNA molecule that codes for a polypeptide which results in a characteristic.
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What is an allele?
An alternative version of the same gene (the order of bases is slightly different as alleles code for different versions of the same characteristic).
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What is a locus?
The position on a chromosome where a particular allele is found.
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What is genotype?
The alleles an organism has.
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What is phenotype?
The characteristics of an organism produced by its alleles.
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What are codominant alleles?
Both alleles are expressed in the phenotype as neither is recessive.
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What is monogenic inheritance?
The inheritance of a characteristic controlled by a single gene
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Phenotypic ratios for dihybrid crosses.
1. Cross of 2 homozygous for both alleles -> all offspring heterozygous. 2. 2 heterozygous -> 9:3:3:1 ratio. 3. Heterozygous + homozygous recessive -> 1:1:1:1.
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What is sex linkage?
When the allele that codes for the characteristic is located on a sex chromosome (X or Y)
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What are the sex chromosomes for males and females?
Males: XY, Females: **
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What is an autosome?
Any chromosome that is not a sex chromosome.
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What is autosomal linkage?
Genes on the same autosome are linked as they aren't split up during independent assortment and alleles will be passed on together. They can only split up during crossing over so the closer together they are, the less likely they will be split up.
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What is epistasis?
When an allele of one gene masks/blocks the expression of the alleles on other genes.
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What effect do dominant epistatic alleles have?
If the epistatic allele is dominant, having at least one copy will result in masking of other genes.
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What effect do recessive epistatic alleles have?
If the epistatic allele is recessive, having 2 copies will mask the expression of other genes.
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Phenotypic ratios for epistatic genes.
Recessive epistatic alleles: homozygous r + homozygous d -> 9:3:4. Dominant epistatic alleles: homozygous r + homozygous d -> 12:3:1.
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What is the Chi-Squared test?
A statistical test used to see if the results of an experiment support a theory.
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What is a null hypothesis?
The hypothesis should be that there is no significant difference between the observed and expected values.
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What is the Chi-Squared formula?
X^2=∑(O-E)^2/2
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How is the critical value used?
Degrees of freedom = no. of classes - 1. Find the critical value that corresponds to the degrees of freedom calculated (to 0.05 or 5%)
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How can you reject/accept the null hypothesis?
If X^2 > critical value, reject null hypothesis. If X^2 < critical value, fail to reject null hypothesis.
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Card 2

Front

What is discontinuous variation?

Back

When there are 2 or more distinct categories and no intermediates (e.g. blood type)

Card 3

Front

What is phenotypic variation?

Back

Preview of the front of card 3

Card 4

Front

How does genotypic variation affect phenotypic variation?

Back

Preview of the front of card 4

Card 5

Front

What are polygenic and monogenic characteristics?

Back

Preview of the front of card 5
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