Each human has how many pairs of chromosomes?
23 pairs in total
22 autosomal pairs, 1 sex-linked pair
G0 phase of the cell cycle
Most cells are resting, carrying out their normal function
G1 phase of the cell cycle
1st growth phase as chromosomes become ready to be replicated
S phase of the cell cycle
DNA replication occurs
G2 phase of the cell cycle
2nd growth phase involving proteins etc.
M phase of the cell cycle
Mitosis - mechanical separation of cell into two daughter cells
Two daughter cells are identical, diploid cells
Variation occurs during meiosis by two main methods, which are?
Independent segregation of homologous chromosomes
In meiosis, one diploid cell becomes…
Four haploid daughter cells
Examples of sequence variations between genes?
Single nucleotide polymorphisms (SNPs)
A polymorphism is…
A change in the genome that does not cause disease in its own right, but can predispose to a common disease
Chromosome 22 looks like a…
A chromosome consists of…
Telomeres at each end
Short arm (p)
Long arm (q)
A chromosome is metacentric if…
Both arms are roughly the same length
A chromosome is acrocentric if…
The p (short) arm is so short it is hard to observe
A chromosome is telocentric if…
The centromere is located at the terminal end of the chromosome
An aneuploidy is…
An abnormal number of chromosomes
Monosomy - missing chromosome from one pair
Trisomy - extra chromosome in a pair
Reciprocal translocations are when…
Segments from two different chromosomes have been exchanged
Robertsonian translocations are when…
A chromosome attaches to another chromosome at the centromere
Only occurs with 13, 14, 15, 21, 22
Monosomy of the sex chromosomes causes…
Trisomy of chromosome 21 causes…
What is FISH?
DNA probes specifically bind to areas of individual chromosomes and apply a fluorescein stain to make the chromosome visible
Useful for detecting aneuploidies
Penetrance is defined as…
The likelihood of having the disease given you have the genetic mutation
Mendelian inheritance encompasses which disorders?
Autosomal dominant disease occurs when…
There is one faulty copy of the gene
Seen in all generations
50% risk of affected child if parent affected
Autosomal recessive disease occurs when…
There are 2 faulty copies of the gene
Often only one generation affected
25% risk of affected child if parents are carriers
Increased likelihood if parents are related
X-linked disease occurs when…
The disease is carried on the X-chromosome only
50% of male children of a female carrier affected
50% of female children of a female carrier affected
All male children of a male carrier normal
All female children of a male carrier will be carriers
Mitochondrial disease occurs when…
Diseased mitochondria passed from mother to child
What is mosaicism?
Occurs when cells within the same person have a different genetic makeup
Epigenetic variation describes…
Functional modifications to the genome that do not involve a change in the nucleotide sequence
Methylation inhibits which process?
What is imprinting?
Variation in gene expression depending on which parent you inherit the gene from
e.g. in Angelman’s syndrome, mother’s UBE3A works fine but father’s is methylated
Heteroplasmy is when…
Different daughter cells contain different proportions of mutant mitochondria (similar to mosaicism)
Where are the 2 checkpoints in the cell cycle where DNA can acquire mutations?
Between G2 and M
Between G1 and S
What is the function of oncogenes?
Promote cell division
What is the function of tumour suppressors?
Inhibit cell division
Only one copy of the tumour suppressor gene is required to be mutated for cancer to occur. True/False?
2 copies required
Cancer is most often inherited as a high penetrance Mendelian disorder. True/False?
More usually multifactorial