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IB Biology Topic 10 – Genetics HL A3 Revision Sheet © David Faure, InThinking http://www.thinkib.net/biology Meiosis Homologous chromosomes are _____________________________________________ Chiasmata are ____________________________________________ Non-sister chromatids are ____________________________________________ Independent assortment of alleles occurs because of random orientation of ____________ During anaphase spindle fibres are responsible for ______________________________ A difference between meiosis I and meiosis II is _________________________________ Arrange the following chromosomes movements from meiosis in the right order: Double stranded chromosomes line up on the spindle Homologous chromosomes separate as they move to opposite poles of the cell Centromeres split & single stranded chromosomes more to opposite poles of the cell Pairs of homologous chromosomes form tetrads Homologous chromosomes line up on the equator of the spindle Nuclear membrane forms and four haploid cells are produced. Linkage notation Morgan did some crosses with Drosophila flies. He crossed ebony body, scarlet eyed flies (eess) with wild type (genotype EESS) Because both the alleles are on chromosome 3 he used “linkage notation” Complete a punnet square using this notation. Recombinant phenotypes would be ____________________________ and ____________________________ Dihybrid crosses can have 4 x 4 Punnett square. Eg. AaBb x AaBb AB Ab aB Ab AB AABB AABb Ab aB ab If one parent is homozygous then one row is enough. AaBb x AABB AB Ab aB Ab AB AABB AABb AABB only has one possibletype of gamete “AB” Annotate the diagram to explain how crossing over increase variation? In a cross between a brown rabbit with long fur and a white rabbit with short fur there were 4 phenotypes of offspring White short fur Brown short fur White long fur Brown long fur Which are recombinants, explain why.. _____________________________________ ____________________________________ Explain why recombinant phenotypes would be lower in number than normal medelian ratios with linked genes. _____________________________________ _____________________________________ Why is it also likely that these will always be some recombinants, even with linked genes? _____________________________________ Chi-squared test can be used to see if there is a significant difference between observed and expected values. Explain why you have to look up a probability once Χ 2 has been calculated? _____________________________________ ______________________________________ ____________________________________ Dihybrid Inheritance Gene locus (pl. loci) is __________________________________________________________________ Unlinked genes segregate independently because they are found on different ______________________ Discrete variation in a phenotype can be identified because there are few __________________________ Continuous variation is when the phenotype varies _______________ or there are many ______________ Polygenic characteristics have phenotypes which show continuous _________________________ Human height is an example of a Explain how natural selection can be ‘stabilizing’ _____________________________________________________________ ____________________________________________________________ Describe what happens in a gene pool exposed to directional selection _____________________________________________________________ ____________________________________________________________ What is disruptive selection? ______________________________________ Explain how reproductive isolation leads to speciation? _____________________________________ _____________________________________ _____________________________________ _____________________________________ _____________________________________ _____________________________________ Gene pools A “gene pool” is _____________________________ ____________________________ Evolution involves allele frequencies changing in time. Explain why. _____________________________ _____________________________ Compare the 3 methods of reproductive isolation below. Cause of reproductive isolation How it works. Geographical Behavioural Temporal
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Page 1: topic 11 revision sheet - Welcome to IB Biology HL€¦ · IB Biology Topic 10 – Genetics HL A3 Revision Sheet © David Faure, InThinking Meiosis Homologous chromosomes are ...

IB Biology Topic 10 – Genetics HL A3 Revision Sheet

© David Faure, InThinking http://www.thinkib.net/biology

Meiosis

Homologous chromosomes are _____________________________________________

Chiasmata are ____________________________________________

Non-sister chromatids are ____________________________________________

Independent assortment of alleles occurs because of random orientation of ____________

During anaphase spindle fibres are responsible for ______________________________

A difference between meiosis I and meiosis II is _________________________________

Arrange the following chromosomes movements from meiosis in the right order:

Double stranded chromosomes line up on the spindle

Homologous chromosomes separate as they move to opposite poles of the cell

Centromeres split & single stranded chromosomes more to opposite poles of

the cell

Pairs of homologous chromosomes form tetrads

Homologous chromosomes line up on the equator of the spindle

Nuclear membrane forms and four haploid cells are produced.

Linkage notation Morgan did some crosses with Drosophila flies. He crossed ebony body, scarlet eyed flies (eess) with wild type (genotype EESS) Because both the alleles are on chromosome 3 he used “linkage notation” Complete a punnet square using this notation.

Recombinant phenotypes would be ____________________________ and ____________________________

Dihybrid crosses can have 4 x 4 Punnett square. Eg. AaBb x AaBb

AB Ab aB Ab

AB AABB AABb

Ab

aB

ab

If one parent is homozygous then one row is enough. AaBb x AABB

AB Ab aB Ab

AB AABB AABb

AABB only has one possibletype of gamete “AB”

Annotate the diagram to explain how crossing over increase variation?

In a cross between a brown rabbit with long fur and a white rabbit with short fur there were 4 phenotypes of offspring

White short fur

Brown short fur

White long fur

Brown long fur Which are recombinants, explain why..

_____________________________________

____________________________________

Explain why recombinant phenotypes would be lower in number than normal medelian ratios with linked genes.

_____________________________________

_____________________________________

Why is it also likely that these will always be some recombinants, even with linked genes? _____________________________________

Chi-squared test can be used to see if there is

a significant difference between observed and

expected values. Explain why you have to look

up a probability once Χ2 has been calculated?

_____________________________________

______________________________________

____________________________________

Dihybrid Inheritance Gene locus (pl. loci) is __________________________________________________________________

Unlinked genes segregate independently because they are found on different ______________________

Discrete variation in a phenotype can be identified because there are few __________________________

Continuous variation is when the phenotype varies _______________ or there are many ______________

Polygenic characteristics have phenotypes which show continuous _________________________

Human height is an example of a

Explain how natural selection can be ‘stabilizing’

_____________________________________________________________

____________________________________________________________

Describe what happens in a gene pool exposed to directional selection

_____________________________________________________________

____________________________________________________________

What is disruptive selection? ______________________________________

Explain how reproductive isolation leads

to speciation? _____________________________________

_____________________________________

_____________________________________

_____________________________________

_____________________________________

_____________________________________

Gene pools

A “gene pool” is

_____________________________

____________________________

Evolution involves allele frequencies changing in time. Explain why. __________________________________________________________

Compare the 3 methods of reproductive isolation below.

Cause of reproductive isolation

How it works.

Geographical

Behavioural

Temporal

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chromosomes which share the same genes, size and shape
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crossing over points which occur during prophase I of meiosis
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the single chromatid strands of different chromosomes in a homologous pair
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chromosomes
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pulling chromosomes / chromatids to opposite poles
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Meiosis I reduces chromosome number, butmeiosis II splits chromatids, the overall numberdoesn't change.
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#1
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#2
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#3
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#4
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#5
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#6
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Parts of each chromosomeare exchangedThis promotes recombinationof genes in dihybrid crosses Some of the red DNA becomespart of the blue chromosome
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The position on a specific chromosome where the gene is always found in a species
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chromosomes
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phenotypes
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gradually
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Phenotypes
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variation
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polygenic characteristic, which shows continuous variation.
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Brown short fur and White long fur are recombinantsThis is because the mix of phenotypes is different from parents
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AABb
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AAbb
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AaBB
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AaBb
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AaBb
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Aabb
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AaBB
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AaBb
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AAbb
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AaBb
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Aabb
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aaBb
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aabb
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aaBb
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AaBB
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AaBb
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--- ab
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---- ab
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There is a tendency for the two linked alleles to be inherited together, reducing the # of recombinants
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Crossing over will usually create some recombinants
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all the alleles for a gene in the wholepopulation
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As natural selection occurs - the allelesfrom individuals which don't reproduceget lost from the gene pool
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populations of a species can't reporducebecause they are separated by a river/mountain
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populations don't reproduce because theitcourtship rituals don't attract the other sex
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populations don't reproduce because they are separated in time, (day/night or seasons)
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wildtype body with scarlet eyes
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ebony body with wild type eyes
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the Chisquared statistic gives a measure of the cumulative difference between observed and expectedThe probability of getting this difference depends onthe number of values in the sample - so a lookup table is used.
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If the middle value of a feature is the most successful (fittest) and the values different fromthe mean are selected against, then stabilizing selection occurs. e.g. birth weight of babies
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In directional selection one allele is selected against and this allele reduces in frequency.Over time there are more of the 'fittest' allele, but the other allele is unlikely to disappear.
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When the middle value is selected against, forming twoforms of a feature, but not the middle value,even though the feature varies continuously.
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If two population of a species are isolatedthen their alleles/genes don't mix any more.Over time, many generations, there is a gradualaccumulation of small genetic differences between the two populations.Eventually the genetic makeup of the two populationsis too different to produce fertile offspring.New species form
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