Describe the central dogma
DNA - mRNA - Protein
What are the 2 components of chromosomes?
DNA and his tones (the protein that DNA wraps around)
What is a locus?
The specific position of a specific gene on a chromosome
How is a gene sequence read and transcribed?
Read in 3 letter groups called codons. The ribosome converts codons to amino acids
Define virus.
An intracellular infectious agent
Why do viruses need a host cell?
Need energy from the host cell as the virus cannot carry out its own metabolic pathway
What are the 2 types of virus replication?
- Lytic - impatient. Virus replicates immediately, eventually causing the cell to burst, killing it - then moving on to other host cells to repeat the process
- Lysogenic - dormant (provirus) - waits to replicate. Viral genome becomes a part of the cell genome and continues to replicate as the cell replicates. Something happens, e.g. UV exposure, and the cell’s DNA becomes damaged. The cell then repairs it’s DNA, cutting the virus out of the genome in the process. The virus is then activated, and follows lytic replication cycle.
Describe the components of an operon (3)
- promoter = DNA sequence recognised by RNA polymerase, which initialises transcription
- operator (on/off switch) = regulatory protein binds to a DNA sequence which can interfere with the activity of the polymerase, turning it on or off
- genes for proteins that work together = a sequence of related genes following the promoter and operator
What is chromatin regulation?
Structure of chromatin can be relaxed, making the gene more accessible for transcription
What is transcriptional regulation?
The way in which cells regulate the transcription of DNA to RNA, thereby controlling gene activity
What are the different levels of transcriptional regulation?
- Basal promoter - initiates transcription, located near the 5’ end
- Distal promoter - enhances transcription, only about 10 bp long
What is homeotic genes and what are the results of homeotic mutations?
Homeotic genes are responsible for the anatomical development of an organism. If mutated, one body part could be replaced by another
What is homebox?
A DNA sequence found within homeotic genes
What is the purpose of sexual reproduction?
To create genetic variability
What are the 2 different stages of meiosis?
Meiosis I and meiosis II
- From diploid to haploid - reduction of chromosomes
- Further separation of chromosomes. Create 4 haploid gametes from the original 1 diploid cell
What are the similarities between meiosis 1 and 2?
Both follow the same steps
Prophase - metaphase - anaphase - telophase
Explain 1 of Mendels principles.
- dominance: resultant phenotypes are dependent on dominant and recessive alleles
- segregation: 2 alleles seperate from each other into gametes during meiosis 1
- independent assortment: when gametes are formed, genes segregated independently due to the independent assortment of non-homologous chromosomes
Describe Mendel’s pea experiment
He crossed 2 pure breeding lines. White flower and purple flowered pea plants. The white flower was lost in F1 but reappeared in F2
- saw a 3:1 ratio
Concluded that one trait was dominant. (No co-dominance)
What is hemizygous?
Only get one copy of a gene (e.g. males only get 1 X chromosome and one only copy of each of those genes) therefore, they will always express that allele
Why are recessive alleles recessive?
Difference is at the nucleotide level. Usually the recessive allele has some sort of nucleotide mutation resulting in a non-functional protein (e.g. white flower, pigment)
What is a SNP and how are they used?
SNP= single nucleotide polymorphism
A single base pair
They are used as markers on genes to Mark areas of interest
How is the probability of 2 genes recombining affected by the distance between them?
Larger distance between them, greater chance of recombination
What does it mean if two genes / loci are linked?
They are on the same chromosome
What is 1 cM equivalent to?
1 in 100 times that meiosis happens, the two loci will be recombinant (separated)
E.g. 25 cM = 25% of the time they will be separated and will end up on different chromosomes
