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Biology > 3.2 Chromosomes > Flashcards

3.2 Chromosomes Flashcards

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1
Q

Whats the difference in chromosome in prokaryotes and eukaryotes?

A

Prokaryotes have circular chromosomes and eukaryotes have linear chromosomes

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2
Q

What is a genophore?

A

The genetic material of a prokaryote

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3
Q

What does it mean if the DNA of prokaryotic cells is naked?

A

meaning it is not associated with proteins for additional packaging

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4
Q

What are additional circular DNA molecules in prokaryotic cells called?

A

Plasmids

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5
Q

What are plasmids?

A

Plasmids are small, circular DNA molecules that contain only a few genes and are capable of self-replication

  • Plasmids are present in some prokaryotic cells, but are not naturally present in eukaryotic cells
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6
Q

What is bacterial conjugation?

A

Bacterial cells may exchange plasmids via their sex pili.

  • Copies of plasmids to be transferred from one cell to another, allowing spread through a population
    • Allows bacteria to evolve new features within a generation
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7
Q

Why are DNA packaged with histone proteins?

A

= Results in a greatly compacted structure, allowing for more efficient storage

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8
Q

What is the process of Autoradiography?

A
  • Cells are grown in a solution containing radioactive thymidine (tritiated thymidine – 3H-T)
  • The tritiated thymidine is incorporated into the chromosomal DNA of the cell (3H-T is used as thymidine is not present in RNA)
  • The chromosomes are isolated by gently lysing the cells and fixing the chromosomes to a photographic surface
  • The surface is then immersed in a radioactively-sensitive emulsion containing silver bromide (AgBr)
  • The radiation released from the tritiated thymidine converts the Ag+ ions in silver bromide into insoluble metal grains
  • Following a period of exposure, excess silver bromide is washed away, leaving the silver grains to appear as small black dots
  • When the photographic film is developed, the chromosomal DNA can be visualised with an electron microscope
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9
Q

What did John Cairns pioneer?

A
  • a technique for measuring the length of DNA molecules by autoradiography
  • Cairns used autoradiography to visualise the chromosomes whilst uncoiled, allowing for more accurate indications of length
  • By using tritiated uracil (3H-U), regions of active transcription can be identified within the uncoiled chromosome
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10
Q

How did autoradiography help measure the length of DNA molecules?

A
  • Previously, chromosome length could only be measured while condensed during mitosis (very inaccurate due to supercoiling)
  • Now regions of active transcription can be identified within the uncoiled chromosome
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11
Q

What key events were discovered during chromosomal replication by John Cairns and his use of autoradiography?

A
  1. DNA replication involves formation of a replication bubble (and prokaryotic replication involves a single origin of replication)
  2. DNA replication is bi-directional (it occurs independently at both ends of the replication bubble)
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12
Q

What is the constriction point on each chromosome called?

A

Centromere, which divides the chromosomes into two sections (arms)

  • The shorter section is designated the p arm and the longer section is designated the q arm
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13
Q

What is the relationship between the homologous chromosomes and sequence of genes and alleles of those gene?

A

Homologous chromosomes carry the same sequence of genes but not necessarily the

same alleles of those genes

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14
Q

What do homologous chromosomes share with each other?

A
  • The same structural features (e.g. same size, same banding patterns, same centromere positions)
  • The same genes at the same loci positions (while the genes are the same, alleles may be different)
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15
Q

What are homologous chromosomes?

A
  • maternal and paternal chromosome pairs

Sexually reproducing organisms inherit their genetic sequences from both parents = organisms will possess two copies of each chromosome (one of maternal origin ; one of paternal origin)

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16
Q

When are homologous chromosomes seperated?

A

In gametes via meiosis prior to reproduction, in order to prevent chromosome numbers continually doubling with each generation.

Anaphase - spindle fibres contract and pull homologous chromosome to opposite poles

17
Q

What is a diploid?

A

Nuclei possessing pairs of homologous chromosomes (2n)

  • These nuclei will possess two gene copies (alleles) for each trait
  • All somatic (body) cells in the organism will be diploid, with new diploid cells created via mitosis
  • Diploid cells are present in most animals and many plants
18
Q

What is a haploid?

A

Haploid: Half of the number of chromosomes

19
Q

What happens when two haploid gametes fuse?

A

The resulting diploid cell (zygote) can grow and develop into a new organism

20
Q

Why is the father responsible for determining the sex of the offspring?

A
  • Only the absence of a Y chromosome, female sex organs will develop
  • If the male sperm contains an X chromosome, the growing embryo will develop into a girl
  • If the male sperm contains a Y chromosome, the growing embryo will develop into a boy
  • In all cases the female egg will contain an X chromosome (as the mother is XX)
21
Q

What are autosomes and heterosomes?

A

Heterosomes: sex chromosome

Autosomes: The remaining chromosomes in the organism that do not determine sex

22
Q

What are karyotypes?

A

are the number and types of chromosomes in a eukaryotic cell – they are determined via a process that involves:

  • Harvesting cells (usually from a foetus or white blood cells of adults)
  • Chemically inducing cell division, then arresting mitosis while the chromosomes are condensed
  • The stage during which mitosis is halted will determine whether chromosomes appear with sister chromatids or not
23
Q

What is stained in a karyogram and why?

A

Chromosomes to generate a visual profile. They are then arranged into homologous pairs according to size (with sex chromosomes shown last)

24
Q

What is Karyotyping used for?

A
  • Determine the gender of the unborn child (via identification of the sex chromosomes)
  • Test for chromosomal abnormalities (e.g. aneuploidies or translocations)
25
Q

How can Down syndrome be detected through an karyogram? What is Down syndrome caused by?

A

Down syndrome is a condition whereby the individual has three copies of chromosome 21

  • It is caused by a non-disjunction event in one of the parental gametes
  • The extra genetic material causes mental and physical delays in the way the child develops
26
Q

What are organisms with different diploid numbers unable to do? What happens when different species do interbreed?

A

Interbreed

  • In cases where different species do interbreed, offspring are usually infertile (cannot form functional gametes)
    • For instance, a horse (diploid = 64) and a donkey (diploid = 62) may produce an infertile mule (non-diploid = 63)
27
Q

What are the 3 general rules of genome size?

A
  • Viruses and bacteria tend to have very small genomes
  • Prokaryotes typically have smaller genomes than eukaryotes
  • Sizes of plant genomes can vary dramatically due to the capacity for plant species to self-fertilise and become polyploid
28
Q

Why is DNA replicated before meiosis? for what?

A

DNA is replicated before meiosis so that all chromosomes consist of two sister chromatids

29
Q

What are autosomes and heterosomes?

A

Heterosomes: sex chromosome

Autosomes: The remaining chromosomes in the organism that do not determine sex

30
Q

What are karyotypes?

A

are the number and types of chromosomes in a eukaryotic cell – they are determined via a process that involves:

  • Harvesting cells (usually from a foetus or white blood cells of adults)
  • Chemically inducing cell division, then arresting mitosis while the chromosomes are condensed
  • The stage during which mitosis is halted will determine whether chromosomes appear with sister chromatids or not
31
Q

What is stained in a karyogram and why?

A

Chromosomes to generate a visual profile. They are then arranged into homologous pairs according to size (with sex chromosomes shown last)

32
Q

What is Karyotyping used for?

A
  • Determine the gender of the unborn child (via identification of the sex chromosomes)
  • Test for chromosomal abnormalities (e.g. aneuploidies or translocations)
33
Q

How can Down syndrome be detected through an karyogram? What is Down syndrome caused by?

A

Down syndrome is a condition whereby the individual has three copies of chromosome 21

  • It is caused by a non-disjunction event in one of the parental gametes
  • The extra genetic material causes mental and physical delays in the way the child develops
34
Q

What are organisms with different diploid numbers unable to do? What happens when different species do interbreed?

A

Interbreed

  • In cases where different species do interbreed, offspring are usually infertile (cannot form functional gametes)
    • For instance, a horse (diploid = 64) and a donkey (diploid = 62) may produce an infertile mule (non-diploid = 63)
35
Q

What are the 3 general rules of genome size?

A
  • Viruses and bacteria tend to have very small genomes
  • Prokaryotes typically have smaller genomes than eukaryotes
  • Sizes of plant genomes can vary dramatically due to the capacity for plant species to self-fertilise and become polyploid

Biology (57 decks)

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