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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