Topic 10: Genetics and Evolution-

Temporal speciation

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

Directional

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

Punnett squares

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

Allele frequency

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

Polyploidy

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

Inheritance

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

Chiasmata

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

Meiosis I

________: Sister chromatids remain associated with each other.

Disruptive

________: Favour extremes over intermediate varieties.

Stability

________ is punctuated by periods of rapid evolution.

Independent assortment

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

New combinations of alleles

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

Environmental influence

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

Results

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

Gradualism versus

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

Polygenic characteristics

________: Polygenic characteristics tend to show continuous variation.

Sympatric speciation

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

O Rapid change

________ is more common in organisms with short generation times.

Locus

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

● Mitosis

________ and Meiosis II both separate a replicated chromosome into chromatids.

Polyploidy

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

Exchange of genetic materials

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

Chiasmata formation

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

New combinations of alleles

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

Meiosis I

● Sister chromatids remain associated with each other

Independent assortment

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

● 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

Meiosis II

● Interphase does not reoccur between meiosis I and II

Punnett squares for dihybrid traits

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

Linked genes

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

● Locus of a gene

specific position of a gene on one chromosome type

● Homologous

two chromosomes with the same sequence of genes

● Two types of gene linkage

o Autosomal and sex

Polygenic characteristics

● Polygenic characteristics tend to show continuous variation

● 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

Environmental influence

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

● Gene equilibrium

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

Allele frequency and evolution

● Evolution requires that allele frequencies change with time in populations

● Occurs due to

o Mutations

o Disruptive

Favour extremes over intermediate varieties

o Directional

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

There are different categories of reproductive isolation

● Reproductive isolation can be temporal behavioural or geographic

● Allopatric speciation

speciation that occurs due to geographic separation

● Sympatric speciation

isolation within the same geographic area; isolation is behavioural

● Temporal speciation

Occurs as species are only active during specific seasons etc

Gradualism versus punctuated equilibrium in speciation

● Speciation due to divergence of isolated populations can be gradual

Polyploidy can lead to speciation

● Can lead to sympatric speciation

Polyploidy has occurred frequently in Allium

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