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Biosci 202 > Midsem test - topic 1 > Flashcards

Midsem test - topic 1 Flashcards

1
Q

Sources of genetic variation

A
  • independent assortment at metaphase 1
  • crossing over at prophase 1
  • fusion with 2 gametes
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2
Q

Human chromosome number

A

46 - 22 pairs and a pair of sex chroomosomes

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3
Q

Telocentric

A

centromere at one end (<1.7 ratio)

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4
Q

Acrocentric

A

centromere off centre (>1.7 ratio)

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5
Q

Metacentric

A

centromere in middle (>7 ratio)

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6
Q

Telomere role

A

stabilise the chromosomeW

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7
Q

What does nucleoli contain

A

rRna and components of ribosomes

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8
Q

Nucleolar organiser

A
  • secondary constriction
  • located in different positions in different species
  • contains a cluster of genes that code for rRNA
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9
Q

Primary constriction

A

centromere

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10
Q

Why can horse and donkeys form a mule zygote

A

homologous pairs dont interact during mitosis but are similar enough to make zygote

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11
Q

Euchromatin

A
  • loosely packed
  • rich in genes
  • increased recombination frequency
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12
Q

Heterochromatin

A
  • tightly packed
  • less genes
  • decreased recombination frequency
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13
Q

Common chromosome stain

A

Giemsa

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14
Q

Chromatin

A
  • DNA associated with histones
  • not uniformly distributed
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15
Q

Nucleosomes

A

DNA packed around histones

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16
Q

Solenoid

A

nucleosomes organised into coils

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17
Q

Proteinaceous scaffold

A

final arrangement of solenoid coils

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18
Q

Prokaryotic genome size and density

A
  • smaller
  • more dense
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19
Q

Why are eukaryotic genomes less dense

A
  • genes with multiple exons are spliced in multiple different ways
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20
Q

Major components of eukaryotic genome

A
  • 1.5 % exons
  • Unique = introns, non coding DNA, regulatory sequences, exons
  • Repetitive DNA (L1 and Alu) -includes gene families, telomeric repeats, satellite repeats and transposable elements
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21
Q

Dispersed gene families

A
  • DNA sequence of genes within family that have diverged to different functions
  • all proteins coded by family of homologous genes
  • some have become pseudogenes
  • dispersed throughout genome
  • Hemoglobin = alpha and beta globin gene families have multiple different genes at different stages of life
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22
Q

Tandem gene families

A
  • multiple repeats of the same gene (duplication)
  • organised as tandem repeats
  • often share similar functions
  • examples = histones and rRNA gene in nucleolar organiser
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23
Q

Satellite repeats

A
  • highly repeated tandem sequences
  • heterochromatic short AT rich tandem repeats in the centromere
  • can be very abundant
  • short DNA sequence repeats
  • vary between individuals so can be used for DNA fingerprinting and paternity tests
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24
Q

Microsatellites

A

shorter repeated DNA sequence (2-6bp) at a particular locus on the chromosome

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25
Q

Minisatellites

A

longer repeats which doesnt code for proteins (15-100bp)

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26
Q

Transposed sequences

A
  • mobile DNA sequences
  • can insert themselves into many different locations in the genome
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27
Q

Telomeric repeats

A
  • composed of tandem arrays
  • sequence = TTAGGG
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28
Q

How can telomeres be visualised

A

probe chromosome with short sequence of fluorescent ssDNA that binds via complementary base pairing, ssDNA finds homologous chromosomal region during hybridisation

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29
Q

Genes

A

physical and functional unit of heredity

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30
Q

Locus

A

specific place where a gene is located

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31
Q

Alleles

A

different versions of the same gene

32
Q

Homologous

A

paired chromosomes with same gene sequence and loci but may differ in alleles

33
Q

Characteristics of mitosis

A
  • in somatic cells
  • one cell division results in 2 daughter cells
  • chromosome number maintained
  • one S phase per cell division
  • no pairing of homologs
  • no crossover
  • centromeres divide at anaphase
  • conservative
  • can be diploid or haploid
34
Q

Characteristics of meiosis

A
  • cells in sexual cycle
  • 2 cell divisions resulting in 4 cells
  • chromosome number is halved
  • one S phase for both divisions
  • full interaction of homologs at prophase 1
  • atleast 1 crossover per homolog during prophase 1
  • centromeres divide at anaphase 1
  • promotes variation
  • cells
35
Q

Ratio that occurs when genes are found on different chromosomes

A

9:3:3:1 = independent assortment/unlinked

36
Q

Linked genes

A

found close together so they have a decreased chance of crossover/recombination

37
Q

Test cross

A
  • involves crossing a heterozygous individual with homozygous recssive
38
Q

Trans test cross

A

dominant allele on different homolog, has decreased recombination

39
Q

Cis test cross

A

dominant allele on the same homolog, increased recombination

40
Q

Inter chromosomal recombination

A

genes on different chromosome so recombination occurs via independent assortment during anaphase

41
Q

Intra chromosomal recombination

A

recombination of genes on the same chromosome

42
Q

How does the recombination frequency change the farther apart the genes are

A

it gets closer to 50% but cannot become more than 50% as only 2 sister chromatids are involved

43
Q

Advantages of 3 point test cross

A
  • includes double crossovers
  • allows the order of genes to be determined
  • produces 2 parental and 6 recombinant progeny
44
Q

Interference

A
  • occurs when expected frequency is not equal to the observed
  • one crossover is inhibiting the other crossover
  • when I = 1 there is complete interference
45
Q

Neurospora

A
  • haploid fungi (n=7)
  • asexually and sexually
  • has 2 identical looking mating types which can be regarded as simple sexes
  • one of the first model organisms
46
Q

Neurospora life cycle

A
  • when 2 different mating types come into contact their cell walls and nuclei fuse to form a diploid nuclei
  • perithecia forms which contain asci
  • diploid nuclei undergoes meiosis to produce 8 ascospores in one long asci
  • each meiocyte produces a linear array of 8 ascospores
47
Q

M1 pattern of segregation

A

crossover hasnt occured - 4:4 pattern

48
Q

M2 pattern of segregation

A

crossover between gene and centromere - 2:2:2:2 pattern

49
Q

How do different ascus arrangements occur

A

centromeres attaching to the spindle at random during the 2nd meiotic division

50
Q

To calculate the map distance between a gene and centromere

A

(recombo/total x100) / 2
- HAVE TO DIVIDE BY 2 AS ONLY HALF OF THE PRODUCTS OF ANY MEIOSIS WITH A SINGLE CROSSOVER WILL BE RECOMBINANT

51
Q

physical basis of recombination

A
  • crossing over involves breakage and reunion of non-sister chromatids at the 4 chromatid stage
  • chiasmata = sites of crossing over
52
Q

Physical map of human chromosomes

A
  • shows actual location of genes
  • good resolution and accurate
  • sequence based
  • gene loci determined
  • sources = somatic cell hybrid mapping and genome sequencing
53
Q

Genetic map of human chromosomes

A
  • created from recombination frequency data
  • limited accuracy
  • gene order and relative position determined
  • source = recombination analysis of phenotypic and molecular markers
54
Q

Why is mapping human genes difficult

A

inability to perform a testcross and humans have a small number of progeny

55
Q

X chromosome mapping

A
  • first human chromosome mapped
  • suitable for mapping by recombination analysis because males are hemizygous
56
Q

Techniques to construct human genome maps

A
  • human and mouse somatic cell hybrids = different human chromosomes will be lost in different cell lines
  • FISH = fluorescent hybridisation, tags chromosomes
  • molecular markers = map gene of interest to a molecular marker
57
Q

Structural chromosomal changes

A
  • deletion
  • duplication
  • inversion
  • translocaion
58
Q

Deletions

A
  • usually requires 2 chromosomal breaks
  • results in the absence of a centromere
  • terminal = at end
  • interstitial = within chromosome arm
  • intragenic = small deletion within a gene that inactivates the gene
  • multigenic = involve several genes, creates dosage problem
  • in meiosis chromosomes with deletion will form a loop to account for the loss
59
Q

Duplications

A
  • tandem = adjacent, inserted next to duplicate
  • insertional = located elsewhere in genome
  • a diploid cell with a duplication with have 3 copies which causes a dosage issue
  • effective for increasing the number of copies and size
  • to detect a duplication look at banding patterns and presence of loops at meisosi
60
Q

Inversions

A
  • involve 2 chromosome breaks in same chromosome, region is flipped then reinserted
  • paracentric = centromere is outside the inversion
  • pericentric = centromere is inside the inversion
  • dont change the amount of genetic material
  • has to have 1 centromere and 2 telomeres to survive
  • acentric chromosome = lacks a centromere so it will not segregate in anaphase
  • inversion loop forms during meiosis to pair with homolog
61
Q

Translocations

A
  • involves movement of genetical material between non-homologous chromosomes or within the same chromosome
  • reciprocal = part of one chromosome is exchanged with one another
  • non reciprocal = part of one chromosome moves to another without exchange
  • can result in hybrid genes
  • chimps have more chromosomes due to translocation and loss of chromosome
62
Q

chimp and human chromosome difference - translocation

A
  • human chromosome 2 is metacentric with G-banding patterns that match 2 acrocentric chromosomes in chimps
  • human chromosome 2 has end to end fusion of 2 chromosomes
63
Q

Numerical chromosomal changes

A
  • euploidy
  • aneuploidy
64
Q

Euploidy

A
  • change in number of sets
  • common in plants = polyploidy
  • major mechanism by which new plant species have evolved
  • increased chromosome number = increased cell size
  • autopolyploid = sets from one species
  • allopolyploid = sets from 2 or more species that are closely related and partly homologous
65
Q

Aneuploidy

A
  • change in number of individual chromosomes
  • can arise in chromosome is lost if centromere is deleted, small chromosomes generated by translocations are lost, gametes arise from nondisjunction due to failure of seperation
66
Q

Meiotic nondisjunction

A
  • happens in humans but most die in utero
  • monosomy = 2n-1, non viable except turners chromosomes
  • trisomy = 2n + 1, viable in 21 (down syndrome),13,18 and sex chromosomes
67
Q

Mosaic

A

genetically distinct cells within an organism that are derived from a single zygote
- at birth = nondisjunction
- later in life = alterations

68
Q

Chimera

A

genetically distinct cells within an organism that are derived from multiple zygotes
- birth = fusion of 2 zygotes
- later in life = transfusion of donor cells

69
Q

Types of sex determination

A
  • chromosomal = sex determined by genes located on the sex chromosomes
  • genes
  • environment
70
Q

Gene dosage

A

number of copies in a gene present in a genome

71
Q

Turners syndrome

A
  • XO = sterile female
  • aneuploidy
72
Q

Klinefelters syndrome

A

XXY = sterile male
- anueploidy

73
Q

SRY gene

A
  • responsible for maleness
  • encodes for a transcription factor
  • protein binds to DNA and stimulates transcription of other genes which promotes development of testes
  • turns on SOX 9
  • SOX 9 cooperates with other genes to activate expression of AMH
  • determined genetically and hormones
74
Q

Androgen insensitivity syndrome

A

mutation on gene for androgen receptor on the X chromosome, embryo develops as female

75
Q

Barr body

A
  • inactivated X chromosome
  • stable through mitosis but reactivated for meiosis in those that give rise to ova
  • inactivation involves modification of DNA and histones
  • multiple copies of RNA product of XIST attach and inactivate X
  • females arent that affected by X linked diseases due to the 2 copies of X
76
Q

Tortoiseshell cats

A
  • mosaic of 2 type of cells = active X derived from male and active X derived from female
  • occurs early in development

Biosci 202 (4 decks)

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