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Zoology Semester 1 > APS125 Genes - Hindle > Flashcards

APS125 Genes - Hindle Flashcards

1
Q

What is population genetics?

A

The study of genetic variation in populations

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2
Q

Why is population genetics studied?

A 
Understand how natural selection operates
Understand genetic disease
Understand human origins and evolution
Help conservation biology
Forensic science
Agricultural improvement
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3
Q

What are mutations?

A

Failure to store genetic information faithfully.
The source of all genetic variation.
Necessary for natural selection and evolution

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4
Q

What can mutations be induced by?

A

Radiation, UV, X rays

Mutagen = any agent that increases the mutation rate

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5
Q

What is a mutagen?

A

Any agent that increases the mutation rate - increases chemical reactivity in the cells

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6
Q

Are gametic cells diploid or haploid?

A

Haploid

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7
Q

What is polyploidy?

A

Greater than two paired sets of chromosomes

  • always lethal in humans (1-3% of conceptions)
  • common in higher plants - related species often vary in ploidy
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8
Q

Are bacteria polyploid?

A

No they have one set of chromosomes so are monoploid

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9
Q

What is aneuploidy?

A

When a chromosome is missing or an extra chromosome is present

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10
Q

Give examples of aneuploidy in autosomes

A

Nullisomy - both members of a pair missing - lethal

Monosomy - one member of a pair missing - lethal

Trimsomy - one extra chromosome - usually lethal
- trisomy 21 - Down’s syndrome (longevity 40 yrs)

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11
Q

Give examples of aneuploidy is sex chromosomes

A

Lacking a chromosome:

  • 45X = turner’s syndrome. Infertile
  • 45Y - inviable

Extra chromosomes - minor effects

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12
Q

What are translocation mutations?

A

When parts are exchanged between non-homologous chromosomes
e.g. centromeric fusion (robertsonian translocation)
Carriers are normal, but offspring can have the wrong number of copies of each chromosome - usually lethal

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13
Q

What are deletion chromosome mutations?

A

When part of a chromosome is missing - patient only has one copy of each gene in that region - the severity depends on the size of the missing region

Chromosome 5 - Cri-du-Chat syndrome

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14
Q

What are inversion chromosome mutations?

A

When parts are broken out of chromosomes and repaired facing the wrong direction

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15
Q

What are the types of inversions?

A

Paracentric - centromere excluded - often no effect on phenotype

Pericentric - includes centromere - possible problems in meiosis

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16
Q

How big is the human genome?

A

3 x 10^9 (3 billion) base pairs

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17
Q

How is the genetic code degenerate?

A

An amino acid can be encoded by more than one codon

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18
Q

What is the start codon in DNA?

A

ATG

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19
Q

What are the types of DNA coding region mutations?

A

Substitutions
Insertions
Deletions

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20
Q

What are the types of DNA non-coding region mutation

A

Repeat length variation

Useful genetic markers

21
Q

If a single point mutation leads to different codon that codes for the same amino acid what is it?

A

Silent (or synonymous)

22
Q

What are microsatellites?

A

Simple tandem repeats of non-coding DNA - nearly always harmless
- a set of short repeated DNA sequences at a particular locus on a chromosome, which vary in number in different individuals and so can be used for genetic fingerprinting.

Widely used in: finding disease genes, conservation genetics, evolutionary genetics, agricultural improvement

23
Q

What are the differences between somatic and gametic mutations?

A

Gametic are heritable, can be severe and affect all cells

Somatic are not heritable, are usually mild and do not affect all cells

24
Q

Where was Mendel born?
When were his experiments published?
When was work rediscovered?

A

1822
1866
1900

25
Q

Why is the garden pea useful for genetic studies?

A

Comes in a wide variety of phenotypes - many features controlled by single genes
Readily available, short generation time, large number of progeny
Usually breeds by self-pollination
Easy to manipulate (cross)

26
Q

How are peas crossed?

A

Anthers removed before they shed pollen
Transfer pollen from one plant to another
Cross-pollination

(discard anthers, brush pollen onto stigmas)

27
Q

What 4 conclusions did mendel draw from his data that all F2 progeny had around a 3:1 ratio?

A
  1. Alternative versions of a gene (alleles) cause variation
  2. An organism inherits two alleles, one from each parent
  3. Alleles may be dominant or recessive
  4. Alleles segregate during gamete production
28
Q

What is Mendel’s first law?

A

The principle of segregation:
The 2 members of a gene pair segregate from each other during the formation of gametes. Half the gametes carry one member of the pair, the other half carry the other member.

29
Q

What is mendel’s second law?

A

The principle of independent assortment:
The alleles of different genes segregate independently of each other
- exceptions when 2 genes are physically proximate on the same chromosome - the closer they are, the greater the variation in the law

30
Q

What is the Mendel-Fisher controversy?

A

Mendel’s ratios were always very close to the theoretical expectations - very low probability - “too good to be true?” - did Mendel fabricate the data? - fisher attributed to an unknown assistant

31
Q

What would blending inheritance lead to?

A

All individuals becoming the same

e.g. white + red = pink, pink + pink = pink

32
Q

If one gene is involved in the inheritance of a disease what is the disease known as?

A

Mendelian or monogenic disease

33
Q

If many genes are involved in the inheritance of a disease what is it known as?

A

Multifactorial disease

34
Q

What does a dot in a pedigree symbol indicate?
2 lines?
1 line?

A

A carrier of the disease
Inbreeding
Marriage

35
Q

What is cystic fibrosis caused by?

A

2 copies of ∆508 mutation in CFTR gene, resulting in a 3bp deletion and nonfunctional chloride channel protein

36
Q

What are some examples of x-linked recessive disorders?

A

Duchenne muscular dystrophy
Red-green colour blindness
Haemophilia

37
Q

Females are XX and males are XY. How is this inequality compensated for?

A

X-inactivation (lyonisation) - in each cell of females one X is randomly inactivated

38
Q

How many Drosophila species are there?

A

at least 144

39
Q

Why are drosophila used for genetic studies?

A

Easy to rear
Rapid generation time
Model organism since early 1900
Genome was sequenced before humans

40
Q

When was it suggested that ‘factors’ (genes) lie on chromosomes?

A

1903

proven in 1909-10 from the fly room - white eye mutants

41
Q

In drosophila is the gene for red eyes dominant or recessive?
Where are these genes found?

A

Dominant
(white is recessive)
On X chromosomes (so females have 2 copies, males have 1)

42
Q

How many pairs of chromosomes do drosophila have, and how many genes do they have?

A

4 chromosomes

~14,000 genes (20,000 in humans)

43
Q

When morgan crossed drosophila and found that the genes for purple vs red eyes and for vestigial vs normal wings, which were expected to give equal frequencies for each outcome, did not assort independently, what does this mean?

A

The genes are linked (on the same chromosome)

Some genotypes occur in smaller frequencies due to recombination

44
Q

How does recombination occur?

A

An enzyme nicks one strand of DNA at a homologous sequence.
A recombination enzyme inserts the cut strand into the second DNA molecule, which is nicked in the process.
Ligase anneals the nicked ends in new combinations.
The molecules then resolve into recombinants.

45
Q

What does the variation in the proportion of recombinants for different genes indicate?

A

Different distances between genes on chromosomes

46
Q

What is the recombination fraction and what does it measure?

A 
Recombinant frequency (e.g. of fly genotypes)/total number of (flies) studied
Measures the distance between genes
47
Q

How do you account for double recombination when detecting recombinants?

A

Square the additive map distance, and minus this from the additive map distance.

48
Q

If two genes are not linked what do we expect the recombination factor to be?

A

~0.5

if much lower than this then genes are linked

49
Q

Do asexual organisms recombine?

A

No

Zoology Semester 1 (16 decks)

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