Basic genetics and genetic disease (should be in OP4103) Flashcards
what do chromosomes do?
store genetic information in the form of DNA through its unique base sequence
What are diploid cells?
2 sets of chromosomes that are paired and homologous
how many chromosomes do cells normally have?
46 chromosomes which include 22 pairs and 2 sex chromosomes
what are the DNA bases?
adenine - thymine
cytosine -guanine
Give the three steps to how a DNA and its associated protein form a chromosome:
- The DNA double helix wraps around histone proteins forming the nucleosome
- The DNA histone complex coils further and is then wrapped to form the chromosome
- Once the chromosome is visible, the DNA and protein is describes as condensed chromatin
what is the karyotype of a male?
46XY so 46 is the total chromosomes and XY is the male alleles
how many genetic disorders can arise from a single gene mutation?
more than 3000
What does sex linkage mean?
When a gene locus is on the X chromosome
What is autosomal linkage?
When two genes are located on the same chromosome and not on the X and Y chromosome
How does autosomal linkage affect the combination of alleles in gametes?
You can only have both alleles as dominant or both alleles as recessive e.g.
AB and ab
instead of AB Ab aB and ab
What is base substitution?
Where a base is substituted for another and may result in a change of 1 amino acid because the base sequence is changed
What is base deletion or insertion?
Where a base is deleted or inserted causing the number of bases to change
Which type of mutation is more likely to produce a dysfunctional protein?
Base deletion or insertion is more likely to produce a dysfunctional protein than base substitution because it will affect multiple amino acids from the point of mutation causing the amino acid sequence of the polypeptide to be entirely different hence the polypeptide is unlikely to function correct because the sequence of bases in dna is read in triplets
What is chromosome non-disjunction?
When individual nom homologous pairs of chromosomes fail to separate during meiosis
what are the two different types of point mutation?
-missense
-nonsense
-frame shift (base deletion/ substitution
what is a missense point mutation?
when a single base within a codon is swapped so a single amino acid is coded for instead
what is a nonsense base mutation?
where there is a base change that causes the new codon to code for a stop codon and hence terminating the amino acid chain too early
give some single gene mutation disorders and describe how for each one
-marfan syndrome due to a mutation to the structural protein of fibrillin
-familial hypercholesteremia due to a defect in the LDL receptor causing an accumulation of fat in the blood
-phenylketonuria due to defect in it’s enzyme protein phylalanine hydroxylase
-lysosomal storage disease due to a mutation in gene coding for lysosomal hydrolase causing an accumulation in the lysosomes
-neurofibromatosis
-haemophilia
how are mitochondria different to other organelles in terms of dna?
as they have their own genome in the form of circular mtDNA and the genes code for mitochondrial proteins for oxidative phosphorylation
what is mitochondrial disease and how does it come about?
it is a nuclear or mitochondrial mutation and comes about as mtDNA is more prone to mutation than nDNA
what does mitochondrial disease refer to?
disorders caused by reduced atp production
give the occular effects of mitochondrial disease
-drooping eyelids (ptosis)
-inability to move eyes side to side (external ophthalmoplegia)
-blindness (retinitis pigmentosa)
why are mitochondria maternally inherited?
because the mitochondria in the sperm are lost during fertilisation
how many still births are accounted for by chromosomal abnormalities?
45%
Give two reasons for chromosomal disorders arising
-as they may have an abnormal structure
-there may be an abnormal number of chromosomes
what is the basic structure of chromsomes?
the top bit which is the p arm
-the centromere
-the bottom bit which is the q arm
why do structural abnormalities in chromosomes occur?
-due to exchange of genetic material, called translocation when it occurs between non homologous chromosomes
-deletion
-rearrangement
what happens in chromosomal deletion?
theres a loss of genetic material as the chromosome has been shortened
what happens in chromosomal inversion
where there are 2 breaks on a single chromosome and is pericentric is if its on opposite sides of the centromere and paracentric is its on the same arm
what happens in ring formation in chromosomes?
where there are breaks at the telomeric end of the chromosome and acrocentric parts of the chromosome are deleted and the remaining chromosome fuses
what happens in translocation of chromosomes? how is Robertsonian translocation different?
where genetic material is exchanged between non-homologous chromosomes and it can be balanced or unbalanced where chromatids are exchanged or not
in Robertsonian, there is a break near the centromere in 2 acrocentric chromosomes and so the long arms fuse to form a new chromosome made of q arms
What does polyploid mean?
When organisms have three of more sets of chromosomes rather than the usual two causing a condition polyploidy mostly found in plants
When do mutations in the number of individual chromosomes occur and what does this result in?
In chromosome non disjunction because it results in a gamete having either one more or one fewer chromosomes and if fertilised with a gamete that has the normal complement of chromosomes the resultant offspring have more or fewer chromosomes than normal.
What is chromosome non-disjunction?
When individual non homologous pairs of chromosomes fail to separate during the anaphase 2 part of meiosis
what is aneuploidy?
a non exact multiple of haploid set of 23 chromosome pairs
what is monosomy?
a loss of a chromosome
what is trisomy?
an extra copy of a chromosome
name 3 autosomal chromosome disorders and their chromosomal name
-down syndrome = trisomy 21
-edwards syndrome = trisomy 18
-pateau syndrome = trisomy 13
what is turners syndome? what are its affects clinically? how can a patient deal with the effects
where the X gamete in females has structural abnormalities or is not present
-cardiovascular anomalies
-fibrous ovaries which could mean sterile
-short height usually <5ft
growth hormones and oestrogen to lead a normal life
what is teratology?
the study of congenital malformation which are morphological defects present at birth
what are teratogens?
factors that can cause congenital defects:
-viruses e.g. rubella
-irradiation e.g. x-rays, beta, gamma
-chemicals like thalidomide and cytotoxic drugs
what determines susceptibility of a teratogen in teratology?
the developmental stage of the foetus
