Genetics Flashcards
In which direction is DNA always replicated?
5’ to 3’ carbon
How is DNA packaged?
It is wrapped around positively charged histone proteins
Amongst other proteins, DNA is then wound into chromosomes
How many genes are available to be coded in the body?
30,000
What are the 5 phases of the cell cycle?
- G1 - Cell growth
- G0 - Cell functions normally and does not replicate
- S - DNA synthesis and replication
- G2 - DNA replication is checked
- M - Mitosis occurs
Which protein can detect and attempt repair of DNA damage?
p53
Under which circumstances may p53 halt G2?
Low oxygen concentrations
What is Li-Fraumeni syndrome?
A condition characterised by a mutation in the tp53 gene resulting in defective p53 protein
What are the 5 different phases of meiosis I?
- Interphase
- Prophase
- Metaphase
- Anaphase
- Telephase (and cytokinesis)
What are the three differences between RNA and DNA?
- RNA is single stranded
- RNA uses ribose rather than deoxyribose sugar in DNA
- Uracil is used in RNA rather than thymine
After transcription what is produced?
Pre-mRNA
How is mature mRNA obtained?
Splicing of introns to leave only exons which contain coding DNA
In terms of the cell cycle, which stage will the cell remain in most of its life?
G0
Which enzyme is responsible for unzipping DNA?
DNA helicase
Which enzyme copies the 5’-3’ strand?
DNA polymerase
Okazaki fragments are utilised to copy the 3’-5’ strand, these are joined with the aid of which enzyme?
DNA ligase
How is variation obtained in meiosis?
- Crossing over
- Independent assortment
What is a polymorphism?
DNA variant which has a population frequency of greater than 1%
What is a mutation?
A DNA variant which causes or predisposes to a specific disease?
How do polymorphisms and mutations differ?
- Polymorphisms are functioning versions of genes
- Mutations can be harmful
What is a missense mutation?
A wrong base is used in one of the codons
What is karyotyping?
It looks at chromosomes as a whole
Can see deletions of >5 million base pairings
What is a balanced translocation?
There is an even exchange of material between chromosomes
There is no missing or extra genetic information
Usually such chromosomes will still function
What is an unbalanced translocation?
There is an unequal exchange of genetic material between chromosomes
This results in extra or missing information
Usually these chromsomes do not function correctly
What are acrocentric chromosomes?
A chromosome in which the centromere is located very near the end of the chromosome
Two acrocentric chromosomes may stick together is very bad
What is fluorescent in-situ hybridisation?
FISH
Chromosomes can be labelled by fluorescent probes
This can aid in identifying aneuploidy (too many chromosomes in a cell) or translocations etc
What is the risk of a carrier mother passing on a sex-linked genetic condition to her son?
25%
What does the term penetrance mean?
The extent to which a particular gene is expressed in the phenotype of the individual carrying it
In females how is it decided which X chromosome undergoes X inactivation?
It is a random process
What is multifactorial disease?
Disease in which mutations in multiple genes combine with environmental factors to cause disease
Genes involved in multifactorial disease will have what level of penetrance?
Low
What do DNA methylation and acetylation affect about the DNA and histone binding?
They increase the strength of binding
This may slow the rate of transcription when excessive and may cause disease
Describe the meaning of imprinting
Differences in gene expression depending on whether a gene is maternally or paternally inherited
Mitochondrial DNA is inherited from where?
Almost entirely the mother
What is mosaicism?
The presence of two or more populations of cells with different genotypes in one individual
What are the two types of mosaicism?
- Somatic - derived from a post-zygotic mutation
- Gonadal - a person has two populations of cells in the gonads, one with a DNA mutation or chrmosome anomaly
BRCA1/2 mutations are associated with what?
Increased lifetime risk of breast or ovarian cancer
(BRCA1/2 are associated with DNA repair)
What is the normal function of the CFTR gene?
It functions as a channel across the membrane that produces mucus, sweat, saliva, tears and digestive enzymes
It transports cholride ions out of the cell which indirectly controls the water movement allowing for thin free flowing mucus
Mutations in CFTR cause what?
Sodium is not pumped out the cell and into the lumen or digestive or respiratory passages so mucus is thick as water does not enter these areas
