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MAT209 > Genetic Variation in Eucaryotes > Flashcards

Genetic Variation in Eucaryotes Flashcards

1
Q

What is the same over both procaryotes and eucaryotes

A
  • Genetic Code
  • Transcription
  • Translation mechanism
  • Basic strategies for DNA replication and repair.
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2
Q

What is the same across species

A

The Genome

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3
Q

Why do individual members of a species look different if their genome is the same
(Phenotypic Variation)

A

Difference in gene sequence.

Differences in regulation of gene expression.

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4
Q

Clonal population

A

Genomes of all members of the species could be the same
Usually procaryotes.
Some examples in eucaryotes e.g. dolly the sheep

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5
Q

In general what are the genomes within a species like

A

They are slightly different

Genetic changes are the drivers of phenotype variations

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6
Q

What are the types of genetic variation

A
  1. Mutations - point mutations, these are usually copying errors during DNA replication
  2. Homologous recombination ( gene duplication. exon shuffling)
  3. Mobile genetic elements ( transposons)
  4. Horizontal gene transfer ( homologous recombination prevalent in procaryotes)
  5. Sexual reproduction is a major source of genetic reassortment
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7
Q

What happens to genes in sexual reproduction

A
  • ## Reshuffling genes appears to help species survive an ever changing and unpredictable environment
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8
Q

Somatic cell

A

These are the cells that make up most of our body

They are only diploid –> They have two sets of chromosomes

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9
Q

Germ Cell

Haploid cells

A

Have a single copy of each gene
These are reproductive cells
Generated by meiosis
Haploid gametes fuse to a diploid cells ( fertilised egg or a zygote

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10
Q

Meiosos

A

Somatic cells / Progenita germ cells where you have a diploid chromasome.
There is cell division but no DNA replication so daughter cells are produced with a single chromasomal copy.
Then two gametes come together to form a deployed organism

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11
Q

Allele

A

Variant of a gene

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12
Q

Homologous recombination

A
  1. Diploid germ cell precursor (germ cell progenita)
  2. One round of DNA replication occurs within this germ cell precursor –> Creating twice the usual number of chromosomes in the cell forming a tetraploid cell.
  3. Next there is pairing of the duplicated homologous chromosomes –> the chromosomes align in parallel with the corresponding genes next to each other (this is called pairing)
  4. Then homologous recombination occurs –> the chromosomes exchange genes
  5. This then splits from a tetraploid cell to a diploid cell and then cell division occurs again before DNA replication
  6. These means in one organism there are 4 different haploid cells within the germ cells –> only one of these will be fertilised

Occasionally mistakes occur during this process e.g. trisomy 21 ( three copies of chromosome 21 handed down from the parents –> causes downs syndrome)

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13
Q

Gene duplication ( a type of homologous recombination)

A

This arrises from a rare combination of events
- Occurs within organisms no just in the sex cells

The mammalian genome contains enormous amounts of non essential DNA –> Introns

e. g Globin protein
- -> Protein in carries oxygen to the different tissues within a mammalian organism
- -> In humans we have 4 differerent genes that code for globin

  • Within the globin gene you have introns and exons –> zoom out for here
  • outside the globin gene you have spacers which contain repetitive sequences of which the exact function we don’t understand
  • During chromasomal pairing, these globin genes are then alligned before homologous recombination can be carried out. This is the pairing stage of miosis
  • Sometimes this pairing is not 100% efficieint –> can have missalighnement during pair formation
  • This causes unequal crossing over and means in one of the chromosomes you have two copies of globin genes in one of the chromosomes and the other has done
  • This unequal cross over leads to gene duplication –> If the gamete that contains twice the gene is fertilised the individual goes on to have two copies of the globin gene which gives rise to phenotypic variation

This has created 4 different types of globin

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14
Q

Exon Shuffling

caused by homolougous duplication

A

Getting close into the gene
Between two exons is the interveining sequence – multiple repeats within them

  • Missalignment can occur between introns –> caused by chromosomal crossover
  • Two of the same exons can then end up in one of the gametes (meaning it have three exons overall) –> This causes changes in normal protein function if the gamete becomes a human
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15
Q

Why does misalignments happen

A

Because these repeated sequences exists and sometimes the two chromosomal copies can be shifted slightly

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16
Q

What caused the diversity of proteins in humans

A

It is thought that present day proteins arose from a handful of original exons

Present day proteins contain a patchwork of many different protein domains

17
Q

What is the percentage makeup of DNA

A

70% is exon, intron and RNA coding
30% is repeated sequences of DNA
1/3rd of this 30% consists of satellite DNA
2/3rds of this 30% consists of more complex repeated sequences

10% of human DNA consists of 2 families of transposons

  1. Alu sequences
  2. L1 ( Line 1)
18
Q

What is the function of satellite DNA

A

This has no known function and is found at centromeres and telomeres

19
Q

Transposons

A

Mobile genetic elements
Sections of DNA that can randomly move within a chromosome
Encode for a particular protein called transposase –>This allows this section of DNA to cut itself out of the Genome where it is placed and randomly go and integrate itself into another position in the chromosome –> help by the enzyme integrase

It is thought that these were originally viral particles that lost their ability to leave the human genome –> retain their ability to move to different sections of the human chromosome

20
Q

Transposons

A

Mobile genetic elements
Sections of DNA that can randomly move within a chromosome
Encode for a particular protein called transposase –>This allows this section of DNA to cut itself out of the Genome where it is placed and randomly go and integrate itself into another position in the chromosome –> help by the enzyme integrase

It is thought that these were originally viral particles that lost their ability to leave the human genome –> retain their ability to move to different sections of the human chromosome

21
Q

Two examples of transposons

A 
Alu sequence 
Line 1 (L1) genes
22
Q

What happens during the random movement of transposons in the human genome

A

Sometimes separate the regulatory regions of the genes from the protein coding regions

–> This leads to inactivation of certain genes within the genome

Integrate at the junction between control elements and protein coding sequences
Can also integrate themselves into introns or exons –> If exon that particular protein domain no longer exists for that genome–> the protein looses function.

No complimentory sequence –> seemingly random integration

23
Q

What is the makeup of a transposon

A

Can be DNA sequences

Can be RNA sequences

24
Q

How do retrotransposons move

A

Via an RNA intermediate

25
Q

What can mediate exon shuffling

A

Transposons

26
Q

What does factor 8 mutation lead to

A

One of the proteins that helps blood clot so when there is a mutation it leads to haemophilia

27
Q

Viruses

A
  • Highly mobile pieces of DNA/RNA that can escape from cells
  • They were first identified as causing disease
  • Consist of genes that code for a protein coat
  • Often lethal to host cells
  • Can be made of DNA or RNA that can be single or double stranded
  • The amount of protein that can fit into the protein coat is limited
  • Can only reproduce inside a living cell by using the cells biochemical machinery
  • Simple RNA viruses must contain genes that encode RNA replicases inside the cell
  • The simplest viruses have 3 genes (minimum) –> Can have several hundred
28
Q

retroviruses

A

Viruses that have RNA as their core genetic componenet

  • Retro refers to the unnatural process where we have RNA as a component for producing DNA. The reverse transfer of information from RNA –> DNA
  • Retroviruses can only infect eucaryotic cells
  • They are a single stranded RNA virus
  • Uses reverse transcriptase to synthesise DNA from an RNA template
  • They encode and contain the enzyme
  • Makes a DNA/RNA hybrid and then a double stranded DNA
  • Integrase inserts DNA into the host genome
  • Transcripts are made using the host RNA polymerase
  • Proteins are translated using the host ribosomes which forms a new virus
  • Often used in drug development–> For HIV drugs is uses reverse transcriptase as a biomarker–> Stops the conversion of RNA into DNA in turn stropping integration into the human genome
29
Q

What else can this genetic change cause

A

Not only pheonotipic variation but also sometimes cause diseases such as cancer

Viruses than cause cancer are called tumour viruses

MAT209 (15 decks)

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