Topic 10: Genetics and Evolution-

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48 Terms

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Temporal speciation

: Occurs as species are only active during specific seasons etc.

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Directional

: Population changes, as one extreme of a range is better adapted.

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Punnett squares

for dihybrid traits: Used to predict the occurrence of a particular geno /phenotype.

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Allele frequency

and evolution: Evolution requires that change with time in populations.

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Polyploidy

has occurred frequently in Allium: Around 50 to 70 % of angiosperms have experienced a(n) .

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Inheritance

: Segregation and independent assortment: Unlinked genes segregate independently as a result of meiosis.

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Chiasmata

formation: Breaks occur in chromosomes and non- sister chromosomes invade a homologous sequence and bind to its region.

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Meiosis I

: Sister chromatids remain associated with each other.

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Disruptive

: Favour extremes over intermediate varieties.

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Stability

is punctuated by periods of rapid evolution.

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Independent assortment

: Occur due to random orientation of pairs of homologous chromosomes in meiosis I.

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New combinations of alleles

: Crossing over produces on the chromosomes of the haploid cells.

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Environmental influence

: Environmental factors blur the differences in phenotype to make them undetectable.

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Results

in a higher frequency of the parental combinations than predicted from Mendelian ratios.

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Gradualism versus

punctuated equilibrium in speciation: Speciation due to divergence of isolated populations can be gradual.

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Polygenic characteristics

: Polygenic characteristics tend to show continuous variation.

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Sympatric speciation

: isolation within the same geographic area; isolation is behavioural.

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O Rapid change

is more common in organisms with short generation times.

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Locus

of a gene: specific position of a gene on one chromosome type.

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● Mitosis

and Meiosis II both separate a replicated chromosome into chromatids.

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Polyploidy

can lead to speciation: ● Can lead to sympatric speciation.

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Exchange of genetic materials

● Crossing over is the exchange of DNA material between non-sister homologous chromatids

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Chiasmata formation

● Breaks occur in chromosomes and non-sister chromosomes invade a homologous sequence and bind to its region

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New combinations of alleles

● Crossing over produces new combinations of alleles on the chromosomes of the haploid cells

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Meiosis I

● Sister chromatids remain associated with each other

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Independent assortment

● Occur due to random orientation of pairs of homologous chromosomes in meiosis I

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● Random movement to poles during anaphase I is caused by independent orientation

direction in which chromosomes face does not affect the direction in which any other chromosomes are facing

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Meiosis II

● Interphase does not reoccur between meiosis I and II

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Punnett squares for dihybrid traits

● Used to predict the occurrence of a particular geno/phenotype

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Linked genes

● Group of genes were all located on the X chromosome of Drosophila

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● Locus of a gene

specific position of a gene on one chromosome type

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● Homologous

two chromosomes with the same sequence of genes

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● Two types of gene linkage

o Autosomal and sex

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Polygenic characteristics

● Polygenic characteristics tend to show continuous variation

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● Number and frequency of variants would be affected by the number of co-dominant alleles for a particular gene

an increasing number of which would bring the distribution close to the normal distribution

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Environmental influence

● Environmental factors blur the differences in phenotype to make them undetectable

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● Gene equilibrium

all members of a population have an equal chance of contributing to the future gene pool

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Allele frequency and evolution

● Evolution requires that allele frequencies change with time in populations

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● Occurs due to

o Mutations

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o Disruptive

Favour extremes over intermediate varieties

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o Directional

Population changes, as one extreme of a range is better adapted

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There are different categories of reproductive isolation

● Reproductive isolation can be temporal behavioural or geographic

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● Allopatric speciation

speciation that occurs due to geographic separation

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● Sympatric speciation

isolation within the same geographic area; isolation is behavioural

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● Temporal speciation

Occurs as species are only active during specific seasons etc

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Gradualism versus punctuated equilibrium in speciation

● Speciation due to divergence of isolated populations can be gradual

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Polyploidy can lead to speciation

● Can lead to sympatric speciation

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Polyploidy has occurred frequently in Allium

● Around 50 to 70% of angiosperms have experienced a polyploidy