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IB bio HL/SL > Unit 10 > Flashcards

Unit 10 Flashcards

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Biology 101 flashcards
1
Q

Chromosomes replicate in phase?

A

Interphase before meiosis

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2
Q

Crossing over

A

The exchange of DNA material between non-sister homologous chromosomes

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3
Q

Product of crossing over…

A

New combination of alleles on the chromosomes of haploid cells

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4
Q

Homologus chromosomes separate in…

A

Meiosis

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5
Q

Independent assortment of genes is due to…

A

Random orientation of pairs of homologous chromosomes in meiosis I

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6
Q

Random orientation in…

A

Meiosis I

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7
Q

Sister chromatids separate in…

A

Meiosis II

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8
Q

The wein ways in which gamete production is able to generate genetic variety in offspring are…

A

• crossing over during prophase l
• Random orientation during metaphase l

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9
Q

Chiasmata

A

Connection points between the non-sister chromatids where they exchange their DNA

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10
Q

Non-sister chromatids

A

Chromatids of two different chromosomes in a pair

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11
Q

The AIM of meiosis

A

Create haploid cells, so that during fertilization, each parent could contribute their own set of genes this promote variation

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12
Q

Duplication occurs

A

Prior to meiotic division

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13
Q

Cell cycle

A

G1 — growth phase
S- synthesis (replication)
G2-growth phase 2
Cell division - mitosis/meiosis, cytokinesis

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14
Q

Prophase l

A

Diploid cell (two chromatids of each chromosome)
DNA supercoils and chromosomes shorten
Nuclear envelope breaks down
Centrioles move to the poles
While the chromosomes are paired sections of chromatid are exchanged in crossing over

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15
Q

Synapsis definition

A

At one stage of prophase I all of the chromatids of two homologous chromosomes become tightly paired up together

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16
Q

Synapsis structure

A

Four chromatids, long and thin, with centromeres

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17
Q

Stages of crossing over

A

1synapsis
2 DNA of one of the chromatids is cut, second cut is made at the same point of the DNA of non-sister chromatid
3 DNA of each chromatid is joined up to the DNA of the non-sister chromatid. In effect we have swapping sections of DNA between the chromatids
4 tight pairing of the homologus chromosomes ends, but the sister chromatids remain tightly connected. Where the cross over a structure called chiasma

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18
Q

Metaphase I

A
  1. Homologus chromosomes pair up at the equator (this means that the two chromosomes of each pair line up on top of each other rather than next to each other)
  2. Each pole’s spindle microtubule attaches to one chromosome from each homologus pair (in mitosis one chromosome would have one of each pole’s spindle microtubules)
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19
Q

Anaphase I

A

1 Each spindle microtubule pulls core whole chromosome of the homologus pair towards its pole causing division of the chromosome pairs across the cell
2.movement due to shortening of the spindle microtubules

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20
Q

Telophase I

A

1 nuclear envelope forms around each set of chromosomes
2. The cell divides into two cells with haploid number of nuclei
3. Chromosomes partly uncoil
4.The cell will proceed with melosis ll

21
Q

Prophase ll

A
  1. chromosomes supercoil again and become shorter
  2. Centrioles again move to the poles of the cell
  3. Nuclear envelopes break down
22
Q

Before meiosis ll

A

There is no duplication of DNA

23
Q

Metaphase ll

A
  1. Chromosomes line up at the metaphase plate, one next to each other across the equator
  2. Therefore, each pole of the cell will receive one DNA copy of each chromosome
24
Q

Telophase Il

A
  1. At this stage each pole of the cell contains half the number of chromosomes compared to the beginning of meiosis I but the same number of chromosomes compared to meiosis II
  2. Can nuclear envelope forms and the cell divides into two cells
  3. we end up with total of four cells each with half the number of chromosomes
25
Q

Distinguish between metaphase one and two

A

Homologus chromosomes separate in meiosis one while sister chromatids separate in meiosis two

26
Q

Explain Mendel‘s second law of independence

A

Independent assortment of genes is due to the random orientation of pairs of homologous chromosomes in meiosis one
Independent assortment only occurs with unlinked gene because linked genes that are present on the same chromosome will be inherited together

27
Q

Distinguish between linked and and linked genes

A

Genes loci Are said to be linked if on the same chromosome
Unlinked genes are on different chromosomes and segregate independently as a result of meiosis

28
Q

Explain the two types of variation and provide specific examples of it

A

Variation can be discrete or continuous example discrete will be flower colour it can only be red or purple or continuous for example human height. The phenotypes of polygenic characteristics tend to show continuous variation. Polygenic traits such as human height may also be influenced by the environmental factors.

29
Q

Application: explain Morgan’s discovery of non-Mendelian ratios in Drosophilia

A

His breeding experiments involving fruit files clearly demonstrated the linked genes were not independently assorted.
Sex linked:
-he discovered a clear sex bias in phenotypic distributions in white eyed mutants
Gene linkage:
-certain phenotypes of combinations occurred in much lower frequencies than was to be expected
-Gene linkage occurred and hence did not independently assort
-Linked alleles could be uncouple via recombination (crossing over) to create alternative phenotypic combinations
These new phenotypes would occur at a much lower frequency
Cross over frequency:
-Genes with a higher crossover frequency are further apart
-Genes with a lower crossover frequency are close together
-developed the first gene linkage maps that show the relative position of genes on a chromosome

30
Q

Explain how polygenic traits can be influenced by environmental factors

A

Example human height may also be influenced by environmental factors
-The added affect of environmental pressures functions to increase the variation seen for a particular trait
-human height is controlled by multiple genes resulting in a bell shaped spectrum of potential phenotypes
-environmental factors such as diet and health or disease can further influence an individual humans height
Example of human skin colour
-Skin colour is controlled by multiple melanin producing genes but is also affected by factors such as sun exposure

31
Q

Identification of recombinants in crosses involving two linked genes

A

Recombinance final types can be identified by performing a test cross
-Linked genes become separated by a chiasma there will be an exchange of alleles between the nonsister chromatids create new allele combination that are different to those of the parent
-The frequency of recombinant phenotype is within a population will typically be lower than that of non-recombinant phenotypes
-crossing over is a random process and chiasmata do not form at the same locations with every meiotic division
- relative frequency of recombinant phenotypes will be dependent on the distance between linked genes - Greater when the genes are further apart on the chromosome

32
Q

Show how linked genes are represented

A

Alleles are usually shown side-by-side in a dihybrid crosses for example TTBB. In representing crosses involving linkage it is more common to show them as vertical pairs

33
Q

Define gene pool

A

A gene pool consists of all the genes and there are different alleles present in an interbreeding population.
Large Gene pool = high amounts of genetic diversity
Small gene pool = low amounts of genetic diversity
Gene pools can be used to determine allele frequency

34
Q

Explain how evolution occurs with reference to alleles

A

Evolution requires that allele frequencies change with time in populations in ways like:
- mutation
- gene flow: The movement of alleles into or out of a population as a result of immigration or emigration
-Sexual reproduction
-Natural selection

35
Q

What is reproductive isolation

A

Reproductive isolation as whenever your province two populations for interbreeding (keeping their gene pool separate)

36
Q

Temporal isolation (Sympatric)

A

Occurs when two populations differ in their periods of activity or reproductive cycles
-e.g. Leopard frogs and wood frogs reach sexual maturity a different times in the spring

37
Q

Behavioural isolation (sympatric)

A

Occurs when two populations exhibit two different specific courtship patterns
-e.g. Certain populations of crickets may be morphologically identical but only respond to Specific mating songs

38
Q

Geographical isolation (allotropic)

A

Occurs when two populations occupy different habitats or separate niches within a common region
-e.g. lions and tigers occupy different habitats and do not interbreed (usually)

39
Q

List out and explain different pieces of speciation

A

Position due to divergence of isolated populations can be gradual.
-Allopatric and sympataric position results in gradualism
-position is seen as a smooth and continuous process (Big changes results from many cumulative small changes)
-supported by the fossil record of the horse with many intermediate forums connecting the ancestral species to the modern equivalent

Specialisation can occur abruptly
-Punctuated equilibrium suggests that species remain stable for long periods before undergoing abrupt and rapid change

40
Q

Stabilising selection

A

-an intermediate phenotype is favoured at the expense of both phenotypic extremes
-e.g. Human birth weights (too large = birthing complications; too small=risk of infant mortality)

41
Q

Directional selection

A
  • One phenotypic extremist selected at the cost of the other phenotypic extreme
  • e.g. Development of antibiotic resistance in bacterial populations
42
Q

disruptive selection 

A

-both phenotypic extremes are favoured at the expense of the intermediate phenotypic ranges
-e.g. The proliferation of black or white moths in the regions of sharply contrasting colour extremes

43
Q

Explain speciation in the genus allium by polyploidy

A

Polyploidy is an offspring have additional sets of chromosomes
Sympatric Speciation will result if Polyploid offspring are viable and fertile but cannot interbreed with the original parent population
Examples:
Triploid (3n)  = ~ 24 chromosomes (e.g. Allium carinatum- keeld garlic)
Tetraploid (4n) = ~32 chromosomes (e.g. Allium tuberosum - Chinese chives)

44
Q

Allium carinatum Triploid how it leads to speciation

A

Non-disjunction - failure of chromosome Paris to separate during meiosis
Diploid gamete - can lead to polyploidy
Fusion of diploid and haploid gamete produces as triploid cells
Unable to produce Viable Gametes during meiosis

45
Q

State two consequences for chiasmata formation between non-sister chromatids

A

Increased stability of bivalence at chiasmata
Increase genetic variability (if crossing over occurs )

46
Q

Explain how crossing over between linked genes can lead to genetic recombinants

A

The process of crossing over results in the exchange of DNA between the maternal and paternal chromosomes.
Crossing over can decouple Linked Combinations of alleles and therefore lead to independent assortment .
Furthermore crossing over can occur multiple times and between different chromatids within the same, Homologous pair

47
Q

Contest meiosis one with meiosis two

A

In melosis l sister chromatids remain associated with each other the homologues chromosomes behaved in a coordinated fashion in prophase.
- homologus chromosomes exchange DNA leading to genetic recombination and meiosis l is a reduction division in that it reduces the chromosome number by half
-The process that results in the creation of genetic variety of gametes are initiated in meiosis l
-The segregation of homologous chromosomes occurs during anaphase l resulting in two haploid cells each with only one copy of each homologous pair

48
Q

Describe the experiment of Bateson and Punnett that led to results that did not support Mendels law of independent assortment

A

William Bateson and Reginald Punnett conducted crosses with sweet peas
One of the parents cells long pollen(LL) and purple flowers (pp)
The other had round pollen (ll) and red flowers(pp)
The surprising results came in the F (2)generation of a dihybrid cross
Instead of the expected ratio of 9:3:3:1, there was four more of the individuals with the paternal phenotype seen in the P generation
Insert smaller number of the non-paternal phenotypes known as recombinants

IB bio HL/SL (15 decks)

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