The Human Genome Flashcards
What is a Barr body?
A cell that has an inactive X chromosome. This occurs in female cells. It is easily identified as a small staining structure in the cell nuclei of female cells.
What is junk DNA?
Genes that are noncoding. They are as a result of evolution. This may include genes that have been implemented into the genome as a result of viral infection in a past generation.
Define pseudogenes and how they can be formed.
Genes that look like genes that code for functional proteins but are non-functional. This may be due to duplication of an ancestral l gene that has diverged and undergone mutation. This could also be as a result of reverse transcription of mRNA which is then integrated into the host. Since it doesn’t have a promoter, it cannot be transcribed. The exact number acts as an inherited allele and so can be used in identification.
Define VNTR
Variable number tandem repeats. . Multiple copies of one gene in a sequence. Often polymerase enzymes can mistake the number of VNTRs and can produce the wrong number of proteins potentially causing disease. e.g. Huntington’s Disease
What is SNPs?
Simple nucleotide polymorphisms. Differences present in 1% of the population. This can have an additive effect to create changes in disease risk.
Give 3 examples of cells without 46 chromosomes
- Erythrocytes lose their nucleus ands so have none
- Megakarocytes (the parent cells of blood platelets) replicate their chromosomes with our dividing and so can be 4n, 8n, 16n ….
- Adult cardiomyocytes are 4n
How many functional chromosomes to women have?
45
What is Synteny?
Where long DNA sequences are present in the same order across species
What is Xist?
A regulatory RNA that switches off a copy of the X chromosome in XX cells.
Why do some organisms have a larger DNA content than others, despite having a similar number of functional genes?
Though the number of functional genes is the same, the number of junk DNA varies. A larger number of non-coding DNA increases the DNA content.
What is the method of retroviruses?
- Attachment to the membrane.
- Entry into the cell.
- Reverse transcriptase. Their mRNA is converted into DNA using the enzyme reverse transcriptase.
- The new piece of DNA is integrated into the DNA of the host cell.
What is the approximate size of the human genome? Bases and genes.
3 x 10^9 nucleotides
20,000 Protein coding genes
The difference is due to the presence of junk DNA
Give the method of Sanger DNA Sequencing.
- The double stranded molecule is heated to break the hydrogen bonds and produce two single strands.
- A primer is annealed to the template strand to allow the addition of new nucleotides.
- 4 reaction mixtures are set up. To each of these the template stand, with the primer is added. This is followed by DNA polymerase and free nucleotides. One of these is radioactive. Each reaction mixture contains a different type of radioactive base. i.e. mixture 1 has radioactive adenine, 2 has radioactive cytosine, 3 has thymine and 4 guanine. Modified nucleotides are also added - only one type is added to each reaction mixture. When this modified nucleotide is added, no more nucleotides can join the chain.
- The DNA is then separated by size using electrophoresis. (DNA is negatively charged. When a current is passed through it, it is attracted to the positive terminal. Shorter chains travel faster than longer chains). This separates polynucleotide chains that differ in length by one nucleotide.
- Each strand is then ordered and the terminating base is recorded. This can be done by identifying the modified base at the end.
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