Biomolecules - Mendelian Genetics + DNA technology

Question 1

Mendelian genetics

Answer 1

Patterns of dominance
- complete: the heterozygous offspring shows the traits of the more dominant alleles
- incomplete: the heterozygous offspring shows a mixture of the alleles
- co-dominance: the heterozygous offspring shows traits from both alleles

Question 2

Hardy Weinberg equation

Answer 2

For determining allele frequency
Assumptions for stable allele frequencies
- no selection
- no mutation
- large population
The sum of the frequency of the dominant allele and recessive allele should add up to 100%

Question 3

Independent assortment

Answer 3

Mendel’s second law
The tendency for traits to be passed independent of each other. This more often occurs between genes on different chromosomes.

Question 4

Gel electrophoresis

Answer 4

-We use it to determine the lengths of DNA in solution
-The DNA migrates from the negative electrode to the positive electrode with the smaller pieces migrating further
-You can use a ladder which has standardised DNA lengths that would show what the length of your DNA fragments are
-Ethydium bromide is an intercalating agent often used to visualise the DNA. You wouldn’t be able to see the band with your bare eyes otherwise
-Each band is a lot of DNA a strands

Question 5

Polymerase Chain Reaction (PCR)

Answer 5

• makes a lot of copies of a specific fraction of DNA
• have a solution of water, salts, nucleotides, primers, taq-polymerase
• Denaturation: DNA is heated up to 96 degrees to separate the strands
• Primer annealing: DNA is cooled down to 55 degrees and primers in the solution bind to ends of the regions you want to copy.
• Primer extension: you heat the DNA back up to 72 degrees. Polymerase in the solution begins to extend the primers across the DNA strand. The polymerase chosen (taq-polymerase) is heat resistant.
  *after once cycle, the original number of DNA molecules is doubled.
  *because all the things you need are in the solution, the process can just keep going on and on
  *primers have high GC content with more hydrogen bonds, leading to more stability

Question 6

Making a DNA a library

Answer 6

DNA library: where you could get the DNA sequences for a protein
In nature, restriction enzymes are found in bacteria as a defence against invading viruses.
-Reverse transcriptase is an enzyme that can work on an mRNA molecule to make a complementary DNA sequence (cDNA). This is single stranded DNA. But DNA polymerase can be added to make double stranded DNA
-inject the cDNA into a cloning vector. Add that cloning vector to a bacteria which will amplify the DNA. Then you can sequence the double stranded DNA and put it in a database.

Question 7

DNA cloning

Answer 7

• cut out the gene you want to clone with restriction enzymes
• the gene is pasted into a plasmid using DNA ligase to connect the backbones as well as a gene for antibiotic resistance
• this plasmid is then inserted into a bacterium by introducing it into a solution of bacteria and induced heat shock to make the bacteria take in the plasmid
• you try to grow that bacteria on a plate with antibiotics so that only the bacteria that have taken in your plasmid will survive. The bacteria that survives can then express those genes

Question 8

Southern blot

Answer 8

1. Cleave DNA
2. Gel electrophoresis on DNA fragments
3. Transfer gel onto a filter - allows us to visualise (nitrocellulose paper for example)
4. Expose to radio labelled DNA
5. Expose filter to x-ray film to visualise radio labelled probe

Northern blots study RNA

Question 9

Gene expression

Answer 9

• knock out: if you’re trying to figure out what gene does something in particular, you can knock out the gene you suspect and see if the cell is still able to perform that function.
• reverse genetics: you sequence a gene and then look for other gene sequences in the genome that are similar and look for homologous sequences. If you know what homologous sequences might do, you might know what the new gene does.