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Biology SL > 3.2 Chromosomes > Flashcards

3.2 Chromosomes Flashcards

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1
Q

what do prokaryotes possess instead of a nucleus?

A

nucleoid (genetic material found free in the cytoplasm)

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2
Q

what does the genetic material of a prokaryote consist of? (2)

A
  • single chromosome consisting of a circular DNA molecule (genophore)
  • the DNA of prokaryotic cells is naked (not associated with proteins for additional packaging)
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3
Q

what do prokaryotic cells possess in addition to the genophere?

A

plasmids (circular DNA molecules)

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4
Q

what are plasmids?

A
  • small circular DNA molecules that contain only a few genes and are capable of self-replication
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5
Q

what do bacterial cells do with plasmids?

A
  • exchange plasmids via sex pili in a process called bacterial conjunction
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6
Q

what does the exchange of genetic material allow for bacteria?

A

allows bacteria to evolve new features within a generation (horizontal gene transfer)

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7
Q

why are plasmids ideal vectors for gene manipulation in labs? (2)

A

they can self-replicate and autonomously synthesise proteins

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8
Q

what does the genetic material of eukaryotic cells consist of? (2)

A
  • multiple linear molecules of DNA that are associated with histone proteins
  • the packaging of DNA with histone proteins result in a compact structure for ore efficient storage
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9
Q

what is the organisation of eukaryotic chromosomes? (5)

A
  • DNA is complexed with 8 histone proteins (octamer) to form a nucleosome
  • nucleosomes are linked by an additional histone protein (H1 histone)
  • these coil to form a solenoid structure which is condensed to form a 30nm fibre
  • these fibres then form loops which are compressed and folded around a protein scaffold to form chromatin
  • chromatin will supercoil during cell division to form chromosomes that re visible (stained) under microscope
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10
Q

what is the constriction point of a chromosome called?

A

centromere

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11
Q

why is it significant that sexually reproducing organisms inherit their genetic sequences from both parents?

A

these organism will possess 2 copies of each chromosome

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12
Q

what are maternal and paternal chromosome pairs called?

A

homologous chromosomes

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13
Q

what do homologous chromosomes share?

A
  • the same structural features (eg. same size, banding patterns, centromere positions)
  • same genes at the same loci positions
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14
Q

why must homologous chromosomes be separated in gametes (via meiosis)?

A

to prevent chromosome numbers continually doubling with each generation

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15
Q

why do sexually reproducing organisms have 2 sets of chromosomes (diploid)?

A

receive genetic material from both parents

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16
Q

what must organisms must do to create gametes from the diploid chromosomes?

A
  • they must create gamete with half the number of chromosomes (haploid)
17
Q

what occurs when 2 haploid gametes fuse?

A

it results in a diploid cell (zygote) which grows into new organism

18
Q

what are the characteristics of diploid cells? (4)

A
  • possess pairs of homologous chromosomes(in nuclei)
  • nuclei will possess 2 gene copies (allele) for each trait
  • all somatic (body) cell in the organism will be diploid with new diploid cells created via mitosis
  • diploid cells are present in most animals and many plants
19
Q

what are the characteristics of haploid cells? (4)

A
  • nuclei possessing only 1 set of chromosomes are haploid
  • these nuclei will possess a single gene copy(allele) for each trait
  • all sex cells (gametes) in the organism will be haploid and are derived from diploid cells via meoisis
  • haploid cells are also present in bacteria (asexual) and funji (except when reproducing)
20
Q

how is sex determined in humans?

A

sex chromosomes (pairs of chromosomes)

21
Q

what sex chromosomes do females possess?

A

2 copies of X chromosome (XX)

22
Q

what sex chromosomes do males possess?

A

1 copy of X and 1 copy of Y (shorter)

23
Q

what will the absence of a Y chromosome lead to?

A

female sex organs developing

24
Q

which parent is always responsible for determining the sex of offspring?

A
  • father
  • is male sperm contain X chromosome then girl
  • if sperm contain Y chromosome then boy
25
Q

what are the remaining chromosomes in the body called (the ones which do not determine sex)?

A

autosomes

26
Q

what are karyotypes?

A

the number and types of chromosomes in a eukaryotic cells

27
Q

what is the process which determines karyotypes? (3)

A
  • harvesting cells (from foetus/white blood cells of adults)
  • chemically inducing cell division, then arresting mitosis while chromosomes are condensed
  • stage during which mitosis is halted will determine whether chromosomes appear with sister chromatids or not
28
Q

how do you produce a visual profile?

A

chromosomes are stained and photographed to generate a karyogram

29
Q

What is karyotyping used for? (2)

A
  • to determine the gender of the unborn child (via identification of sex chromosomes)
  • test for chromosomal abnormalities
30
Q

what is down syndrome?

A
  • a condition whereby the individual has three copes of chromosome
31
Q

what is down syndrome caused y? (2)

A
  • by a non-disjunction event in one of the parental gametes
  • the extra genetic material causes mental and physical delays in child development
32
Q

What is the process of autoradiographie? (7)

A
  • cells grown in a solution containing radioactive thymidine
  • triaged thymidine is incorporated into the chromosomal DNA of the cell
  • the chromosomes are isolated by gently losing the cells and fixing the chromosomes to photographic surface
  • the surface is then immersed in a radtioactively-sensitive emulsion containing silver bromide
  • the radiation released from the triaged thymidine converts AG+ ions in silver bro moi de into insoluble metal grains
  • following a period of exposure,excess bromide is washed away, leaving the silver grins to appear as small black dots
  • when the photographic film is developed, the chromosomal DNA can be visualised with an electon microscope
33
Q

How did John Cairns measure autoradiography?

A
  • Used autoradiography to visualise the chromosome whilst uncoiled for more accurate indications of length
  • by using triaged uracil region of active transcription can be identifies within uncoiled chromosome
34
Q

What other discoveries did John Cairns find out by autoradiography? (2)

A
  • DNA replication involves formation of a replication bubble (and prokaryotic replication involves a single origin of replication)
  • DNA replication is bi-directional (it occurs independently at both ends of the replication bubble)
35
Q

What are the general rule for genome size?(3)

A
  • viruses and bacteria tend to have very small genomes
  • prokaryotes typically have smaller genome than eukaryotes
  • sizes of plant gem ones can vary dramatically due to the capacity for plant species to self-fertilise and become polyploid

Biology SL (38 decks)

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