genetic variation

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39 Terms

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Meiosis

A reduction division that produces haploid gametes with half the number of chromosomes of normal body (somatic) cells.

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Mutation

The source of genetic variation.

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Crossing over

The exchange of sections of DNA between homologous chromosomes.

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Independent assortment

Describes the different possible combinations of maternal and paternal chromosomes.

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Random fertilization

Introduces variation because the combination of gametes that fuses to form the zygote is random.

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Allele

An alternative form of a gene.

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Phenotype

Observable characteristics of an organism.

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Genotype

The alleles present within cells of an organism.

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Dominant

An allele that is always expressed in the phenotype, even if only one copy of the allele is present.

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Recessive

An allele that is only expressed in the phenotype if two copies of the allele are present, i.e., homozygous recessive.

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Homozygous

Two identical alleles of a gene (a homozygous organism is called a homozygote).

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Heterozygous

Two different alleles of a gene (a heterozygous organism is called a heterozygote).

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Codominance

Both alleles contribute to the phenotype without mixing, e.g., blood type.

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Multiple Alleles

More than two possible versions of an allele.

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Chi-Squared Test

A statistical test used to establish whether the difference between observed and expected results is significant.

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Sample size for Chi-Squared Test

Must be sufficiently large (>20) and can only be used for discontinuous variation data.

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Null hypothesis

The assumption that there is no significant difference between observed and expected results.

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Critical value

The value obtained from the chi-squared test is compared to this to determine if the null hypothesis is accepted or rejected.

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Significance in Chi-Squared Test

If the x² value is greater than the critical value, the null hypothesis is rejected, indicating a significant difference.

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Autosomal gene linkage

Implied if the null hypothesis is rejected, e.g., color and wing length in Drosophila.

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Linked Genes

Genes that are inherited together due to their proximity on the same chromosome.

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Sex-linked Genes

Genes that appear on the X chromosome, often leading to disorders more common in men.

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Haemophilia

A genetic disorder characterized by the absence of clotting factor VIII, resulting in improper blood clotting.

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Red-green Colourblindness

A genetic condition affecting the ability to distinguish between red and green colors, often linked to the X chromosome.

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Natural Selection

The process through which allele frequencies change over time due to selection pressures acting on the gene pool.

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Stabilising Selection

A type of natural selection that reduces variation in a population by selecting against extreme phenotypes.

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Disruptive Selection

A type of natural selection that increases diversity in a population by selecting for extreme phenotypes in diverse conditions.

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Directional Selection

A type of natural selection that shows a change from one phenotype to another that is more advantageous to the environment.

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Population Bottleneck

The effect of a catastrophic event that dramatically reduces population size by at least 50%, causing a severe decrease in genetic diversity.

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Founder Effect

The loss of genetic variation that occurs when a small number of individuals form a new population with allele frequencies not representative of the original population.

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Genetic Drift

Random changes in the gene pool of a population that occur by chance, not due to any selective advantage or disadvantage.

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Hardy-Weinberg Equation

A mathematical formula used to estimate the frequency of alleles in a population, represented as p + q = 1.0.

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p

The frequency of the dominant allele (represented by A) in a population.

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q

The frequency of the recessive allele (represented by a) in a population.

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p^2

The frequency of homozygous dominant individuals (AA) in a population.

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2pq

The frequency of heterozygous individuals (Aa) in a population.

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q^2

The frequency of homozygous recessive individuals (aa) in a population.

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Genetic Equilibrium

A state in which allele frequencies in a population remain constant over generations.

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Conditions for Hardy-Weinberg Equilibrium

No mutations, random mating, large population, no migration, and no selection pressure.