Define the terms ‘phenotype’ and ‘genotype’.
Phenotype = all the traits an individual has Genotype = the sequence of DNA bases (transmitted to offspring)
Where is the genotype found?
The genotype is encoded in DNA found in the nucleus of cells where it encodes information.
DNA is organised into chromosomes (humans have 23 pairs).
What are the four different bases of DNA? What happens when there is a change in the sequence of bases and what do proteins determine?
The base pairs are A-T and C-G. When there is a 1 letter change in the sequence, it changes which protein is put in the chain. Protein determine the phenotype.
Describe the process of transcription and translation.
- 2 strands of DNA are pulled apart due to weak bonds
- Bases are now exposed so a molecule called Messenger RNA comes in
- Messenger RNA reads off the exposed bases and forms a transcript of the genetic sequence
- Transcript is carried out into ribosome and rest of cell
- Amino acids are made and put into chain in an order dictated by Messenger RNA. This reflects the DNA sequence in the nucleus.
Describe the process of transcription and translation.
- 2 strands of DNA are pulled apart due to weak bonds
- Bases are now exposed to a molecule called Messenger RNA (mRNA) comes in
- mRNA reads off the exposed bases and forms a transcript of the genetic sequence
- Transcript is carried out into ribosome and rest of cell
- Amino acids are made and put into a chain in an order dictated by mRNA. This reflects the DNA sequence in the nucleus.
What is a ‘codon’ and what is the genetic code?
A codon is a triplet of bases that stands for each amino acid. The genetic code is the mapping of the codons in the mRNA to the amino acids in the assembled proteins.
Describe two redundancies in the genetic code.
Synonymous substitutions - errors in reading of 3rd base of codon will often make no difference to amino acid produced.
Codons that differ in the 1st base will produce chemically similar amino acids.
What are introns and exons?
Introns = non-coding sequences Exons = stretches of codons translate into proteins
Identify and define two types of non-coding DNA?
Transposable elements - the same sequence hundreds of base pairs long which can change its position within a genome.
Pseudogenes - remains of sequences that were once used.
How do gametes form?
Gametes form through meiosis - paired chromosomes in the progenitor cell line up nect to each other and may exchange DNA
Describe independent segregation and linkage.
The physically closer 2 genes are on a chromosome, the greater the genetic linkage between them. The probability of recombination tearing them apart is linked to the distance between them.
Describe single-base substitutions.
This is when a base will get substituted whilst copying CAGT.
Transitions = changes between chemically similar base pairs (C+T, G+A)
Transversions = changes between chemically dissimilar base pairs (C+G, C+A).
