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BIOL1010/1011 > Genetics: Lecture 1 > Flashcards

Genetics: Lecture 1 Flashcards

Mitosis, Meiosis, Genetics and Molecular Biology

1
Q

What is Genetics?

A

The study of the inheritance of observable traits from one generation to the next,
and their effect on populations and species. It is a much older field of study compared to molecular biology.
Examples include: blue eyes, huntington’s disease, etc

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2
Q

What is Molecular Biology?

A

The study of the molecular processes
involved in the transfer of genetic information from genotype to phenotype of an organism. It is a fairly new field of study in biology.
Examples include: the study of DNA

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3
Q

Nature vs. Nurture

A

A debate which helps us learn the limits of what can be explained solely by genetics.

Nature: encoded by genetics. Examples include: blood groups (don’t vary from environmental pressure, fully hard-coded by genetics).

Nurture: comes from environmental factors.
Examples: Acidic soil vs Alkaline soil results in different phenotypes (blue and pink flowers on hydrangeas). Temperature impacts the size of a fruit fly’s wings (lower=smaller) and the colours of a rabbit’s paws/tail/ears (lower=black)

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4
Q

What is Determinism?

A

It is the idea of how much of your genes actually determine your phenotype.

Example: some things are completely determined by genetics (blood group) while many might be changed/influenced by environment. Most things are not completely determined by genetics.

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5
Q

Genotype determines __________

A

The range of your phenotype.

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6
Q

What is a phenotype?

A

An organism’s physical and biochemical traits.
Examples include: flower colour, ear
shape, genetic disease, etc.

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7
Q

What is a genotype?

A

An organism’s genetic makeup, the genetic information contained in
genes.

Example: the alleles on a specific locus determine your ear shape or eye colour.

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8
Q

DNA structure?

A

DNA is composed of:

  • sugar-phosphate backbone (consists of deoxyribose sugar and phosphate groups) which makes up the “ribbon”
  • Nitrogenous bases that form the “rungs” of the ladder (A&T and C&G)
  • Hydrogen bonds between nitrogenous bases
  • Antiparallel arrangement (double helix)
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9
Q

DNA size?

A
  • we have roughly 3 billion base pairs.
  • all of our genetic information is encoded in our DNA.
  • DNA is two nm in diameter (one nm in radius).
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10
Q

How is DNA presented?

A
  • DNA is presented as a sequence of nitrogenous bases in a line.
  • Only one is given as we can find the matching counterpart of the base pair.
  • This is different from what we see on television where it is just chromosomes with very limited info.
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11
Q

Structure of a Eukaryotic Chromosome?

A
  • Each chromosome is one long DNA molecule.
  • p (petit) arm and p telomere
  • q arm and q telomere
  • centromere
  • Kinetochore (present at mitosis) interacts with mitotic spindles.
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12
Q

Telomere?

A

A telomere is present at each end of a chromosome, and prevents the DNA from unravelling.

  • The telomere gets shorter with each division. This is associated with aging and is currently being studied.
  • We have about 1 metre of DNA in each cell, so it is important that it is packed well.
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13
Q

Centromere?

A

A constricted region of the chromosome.

  • Kinetochores are present at mitosis and interact with spindles.
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14
Q

Giemsa Stain?

A

The giemsa stain helps us identify concentrated amounts of A-T bonds from concentrated areas of C-G bonds in our chromosomes.

  • The bands are NOT genes, there are thousands of genes on a chromosome
  • Useful for spotting genetic disorders
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15
Q

Significance of Chromosome structure?

A

We need the packaged form of DNA to be able to easily split and move it, therefore it is vital that it is condensed into chromosomes.

  • it is really long when unravelled.
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16
Q

How do chromosomes look most of the time?

A

Most of the time chromosomes look like this in the nucleus, but we like to draw them in the condensed, metaphase form because it easier
to visualize.

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17
Q

What are Homologous Chromosomes?

A

Two chromosomes that are the same size, shape, and contain the same genes. They are NOT identical.

  • Small differences present in homologous chromosomes introduce variation into populations.
  • Variants of genes are called ALLELES.
  • A good analogy is how our textbooks have different editions. Same chapters, same size, same topic/information, different covers and presentation.
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18
Q

What is a Locus?

A

A specific place along the length of a
chromosome where a given gene
is located

Example: Gene for eye colour in fruit flies

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19
Q

What are alleles?

A

Alternative versions of the
same gene.

Example: Each chromosome can have a different version of the eye colour gene - red eye allele or white eye allele

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20
Q

When do homologous chromosomes exist?

A

They exist all the time! They are there in G1 before DNA replication begins.

  • Loci and not changing from one form of DNA to another
  • In the unduplicated and uncondensed form of DNA, loci can still be located in the nucleus.
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21
Q

Homologous chromosomes vs. Sister Chromatids

A

Homologous chromosomes are not identical, not attached by a centromere, and are present in G1

Sister chromatids are two strands of DNA with an identical nucleotide sequence. They are directly copied from one another and joined by a centromere to prepare for mitosis. They are NOT present in G1, and only appear when the cell is preparing to divide. This is called a “mitotic chromosome”

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22
Q

What happens during G1?

A

During G1 the cell is living its life. It eats, grows and sometimes dies. It waits until it is ready to divide, then it makes the decision to go to S phase.

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23
Q

What happens during S phase?

A

During S phase (synthesis), the cell commits to dividing. Then, the cell begins undergoing DNA replication.

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24
Q

What happens during G2?

A

During G2, the cell checks for errors in DNA replication. At that point it makes a decision to continue to M phase. It also grows more and generally gets itself ready for M phase to begin.

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25
Q

What happens during M phase?

A

During M phase, the cell undergoes mitosis. Then, after mitosis, it undergoes cytokinesis.

Cytokinesis is NOT a part of mitosis.

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26
Q

What is G0?

A

Basically a phase where a cell is unable to divide.

Examples include: liver cells, muscle cells, neurons.

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27
Q

Diploid cells?

A

Mammalian somatic cells have two sets of homologous chromosomes. These cells are diploid and referred to as having 2n chromosomes.

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28
Q

Haploid cells?

A

Sex cells (sperm and egg) have just one set of homologous chromosomes. They are haploid and have n chromosomes.

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29
Q

How does a Karyotype work?

A

Mitosis is stopped in metaphase and the pair of duplicated homologous chromosomes are arranged/identified by using colourful stains which specify very specific genes.

  • they are aligned by size
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30
Q

What is a karyotype?

A

A display of condensed chromosomes arranged in pairs.

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31
Q

Application of a karyotype?

A

They can be used to identify chromosomal abnormalities (abnormal arrangement, number)

These abnormalities are associated with certain congenital disorders.

Example: Trisomy 21 is the presence of an extra chromosome 21 and is expressed as Down syndrome.

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32
Q

Eukaryotic Karyotypes?

A

Karyotyping can be done on more than just humans.

  • They can be very similar between different species or they can be very different.

Examples: We have a similar number of chromosomes to mice and chimpanzees. However, some plants have drastically different amounts from one another. This is not a testament to how related they are nor to how complex they are, it only affects the length of each chromosome/how many loci are present per chromosome.

33
Q

Chromosomes consist of…?

A

Proteins and DNA

34
Q

What is DNA complexed with?

A

DNA is complexed with proteins called histones.

35
Q

Chromatin?

A

Chromatin consists of DNA and protein.

  • There are several conformations (levels of packaging/types) of chromatin that exist in the nucleus of living cells.
36
Q

Nucleosomes?

A

Nucleosomes consist of octomers (eight histone proteins) and DNA.

  • DNA double helix is 2nm in diameter
  • They are 10nm in diameter
  • The eight histones are situated tail-out
  • They also have a positive charge to compliment the negative charge of the DNA.
37
Q

Organization of DNA into Chromatin?

A

Consists of nucleosomes and spacer DNA.

  • there is the H1, which is larger than the other nucleosomes and involved in regulating transcription
  • The nucleosomes and spacer DNA are spun into chromatin
38
Q

Euchromatin?

A

Form of chromatin that is readable by machinery that transcribes DNA into mRNA or other types of RNA.

39
Q

Heterochromatin?

A

A more compacted form of chromatin that cannot be read by machinery. Inaccessible to machinery.

40
Q

Chromatid size?

A
  • 30nm chromatin fibres
  • 300nm chromatin fibre loops
  • 700nm sister chromatid
  • 1400nm replicated chromosomes
41
Q

When does DNA become transcriptionally active?

A

When nucleosomes are formed

42
Q

What is the purpose of mitosis?

A

To ensure that an exact copy of the parent cell’s DNA is passed on to the two new daughter cells.

  • Cells split into two daughter cells with equivalent DNA.
  • also a lot more functional and easier to separate and move during mitosis.
43
Q

Mechanisms of mitosis?

A

Mitosis is a continuous processes. We separated those processes into phases as we like to categorize things.

  • Many independent processes are occurring in parallel.
44
Q

How long does mitosis typically take?

A

It typically takes 1-2 hours, but can take more or less time.

45
Q

What is mitosis?

A

The division of genetic material in the nucleus into two daughter cells.

46
Q

G2 of interphase?

A
  • Chromosomes and duplicated and uncondensed.
  • The nuclear membrane is still intact.
47
Q

Prophase?

A
  • Centrosomes (two centrioles) move apart and poles + spindles are formed.
  • Chromosomes condense into sister chromatids.
48
Q

Prometaphase?

A
  • Nuclear envelope disappears
  • Spindles interact with chromosomes
  • Kinetochores attach to each side of the centromere
49
Q

Metaphase?

A
  • Chromosomes align on the metaphase plate
  • there is one centrosome at each spindle pole
  • the cell is put under tension during this stage because of the kinetochores on each sister chromatids.
50
Q

Cohesin?

A

Cohesin is the “glue”between the chromosomes at metaphase and anaphase.

The glue is on both sides, meaning that an equal amount of DNA will end up in each cell.

At the end, the glue will get dissolved.

Spindle microtubules attach to glue on each kinetochore to give tension.

51
Q

What happens when there is too many chromosomes?

A

A cell with an abnormal amount of chromosomes will likely kill itself.

52
Q

Anaphase?

A

Daughter chromosomes move to opposite ends of the cell.

53
Q

Telophase?

A
  • Nuclear envelope reforms
  • Chromosomes decondense
54
Q

Cytokinesis?

A

The cytoplasm divides, creating two new, completely identical daughter cells.

55
Q

Asexual Reproduction?

A

The genetic material is the same in the parents and in the offspring.

  • They are CLONES
56
Q

What is budding?

A

Budding occurs when a bud grows from a parent and drops off, becoming a new organism.

Example: Hydra

57
Q

What is fragmentation?

A

Fragmentation occurs when an organism splits into multiple parts and each new fragment grows into its own new organism.

Examples: plants, some non-vertebrate animals

58
Q

If all the cells in an organism have the same genes, can the nucleus from a differentiated animal cell be used to create a new organism (a clone)?

A

What was done: UV light is used to render the nucleus non-functional (enucleated) by introducing mutations. Then a donor nucleus was transplanted into the cell. Most of these cells developed into tadpoles. Next, they used a completely differentiated intestinal cell as the donor nucleus. Most of the tadpoles failed too develop or stopped developing before the tadpole stage. 2% did actually make it to the tadpole stage!

Conclusion: The potential of a cell nucleus to produce a whole organism decreases as the cell becomes more differentiated, presumably due to changes in the nucleus.

59
Q

Dolly the Sheep?

A
  • In 1997 they used a similar technique to the frog egg experiment.
  • Dolly was one out of hundreds of
    injected nuclei that developed into
    an embryo.
  • Died at 6 years (euthanized) due to a lung condition and arthritis, which occurs in much older sheep.
60
Q

Gametes?

A

Gametes (eggs & sperm) of an organism contain a single basic complement (haploid = n) of chromosomes.

61
Q

Fusion?

A

The fusion of haploid gametes to form a new diploid cell is called FERTILIZATION.

62
Q

What is formed by fusion?

A

A zygote is produced by fusion of egg and sperm (and the adult developed from the zygote) contains, in each cell, two copies of each chromosome (diploid = 2n).

63
Q

Meiosis?

A

The cellular process of reducing the diploid complement of chromosomes to a haploid complement of chromosomes to produce sex cells
(gametes), an essential process for sexual reproduction.

  • Diploid (2N) to Haploid (1N)
64
Q

Key difference between mitosis and meiosis?

A
  • Mitosis: separation of the sister chromatids, creates 2 daughter cells that are diploid.
  • Meiosis I: separation of the homologous chromosomes, creates 4 haploid cells.
65
Q

Meiosis 1?

A

The separation of homologous chromosomes.

Consists of:
- Prophase 1
- Metaphase 1
- Anaphase 1
- Telophase 1 and cytokinesis

66
Q

Crossing over?

A

A pair of homologous chromosomes lay over one another and a few (2-3) chiasma events occur, where genetic materials cross over and exchange with one another.

  • this introduces genetic variation
  • it is extremely important
  • this is why siblings do not look the same
67
Q

Synapsis?

A

The act of two homologous chromosomes coming together and laying on top of one another.

68
Q

Crossing over importance?

A

The number of genes stays the same, and it is simply an exchange of alleles.

  • this limits the amount of harmful mutations in offspring
  • it introduces variation and ensures diversity
69
Q

Prophase 1

A
  • pairs of homologous chromosomes (composed of sister chromatids) undergo chiasmata events where alleles are exchanged between homologs
  • nuclear envelope disappears
  • spindles form and centrosomes begin separation
70
Q

Metaphase 1

A

Same as metaphase except it is homologs paired up rather than sister chromatids.

  • kinetochores attach to microtubule and the homologs line up along the metaphase plate.
71
Q

Anaphase 1

A

Same as anaphase in mitosis other than sister chromatids remain ATTACHED whilst homologous chromosomes separate

72
Q

Telophase 1 and cytokinesis

A

Same as typical telophase in mitosis and two cells are formed with homologous pairs of chromosomes. Then cytokinesis also occurs as normal.

73
Q

Meiosis 2?

A

Meiosis is much more similar to mitosis, but the end product is 4 haploid cells rather than 2 diploid cells.

Consists of:
- Prophase 2
- Metaphase 2
- Anaphase 2
- Telophase 2 and Cytokinesis

74
Q

Chromosome arrangement in Mitosis and Meiosis 1 and 2?

A

Mitosis: sister chromatids
Meiosis 1: homologous chromosomes
Meiosis 2: two sets of sister chromatids

75
Q

What is interkinesis?

A

Interkinesis is the resting period that occurs between meiosis 1 and meiosis 2. There is not a cell cycle between the two stages, this is simply a time where the cell could grow a bit.

Example: the resting period for ovum cells is many years

76
Q

Why sex?

A

Sexual reproduction introduces variation into populations. This limits mutations and also allows for there to be new alleles and new combinations of alleles.

77
Q

What is the purpose of meiosis?

A
  • Divide the number of chromosomes in half: each gamete has one copy of each chromosome. We still want one copy of ALL the genes.
  • Introduce variation: new alleles and/or new combinations of alleles. This happens through crossing over events and the gametes randomly receiving one chromosome from each homologous pair. There is also the random mating (paternal and maternal DNA mixing together).
78
Q

Random assortment?

A

The random assortment of chromosomes that occurs during meiosis gives rise to even more genetic variation.

79
Q

Asexual vs Sexual reproduction?

A

Asexual results in one race being established whilst others are crowded out.
Sexual results in having the best qualities of all four combined into one.

BIOL1010/1011 (22 decks)

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