genetic bases of disease Flashcards
(35 cards)
1
Q
What are alleles
A
different variations of the same gene that impart the same characteristic
2
Q
What is Mendel’s Law of Segregation (4)
A
- characteristics can have alternate versions - alleles
- each characteristic has 2 alleles
- dominant allele is expressed
- 2 alleles for each characteristic segregate during gamete production
3
Q
What is the centromere and telomere
A
Centromere – the constriction point in the chromosome
Telomere – tips of chromosome
4
Q
What are the types of chromosomes (4)
A
- Metacentric - centromere in centre
- submetacentric - centromere near the middle
- acrocentric - centromere near the end of chromosome
- telocentric - centromere at the end of the chromosome
5
Q
What is the difference between haploid and diploid (4)
A
- Haploid = 1 copy of each chromosome
- Diploid = 2 copies of each chromosome
- Somatic cells = diploid
- Gametes = haploid
6
Q
What happens during mitosis (4)
A
- Generating diploid cells
- Prophase - duplicated chromosomes (two sister chromatids)
- Metaphase - chromosomes align at the metaphase plate
- anaphase telophase - sister chromatids separate during anaphase
7
Q
What happens during meiosis (7)
A
- Generating haploid sex cells
- Parent cell chromosome duplicates
- prophase - Tetrad formed by synapsis of homologous chromosomes
- metaphase - tetrads align at the metaphase plate
- anaphase telophase - homologous chromosomes separate; sister chromatids remain together
- anaphase ii - no further duplication; sister chromatids separate
- Results in genetic variation
8
Q
What is the importance of meiosis (4)
A
- Germ-line cells (diploid) produce gametes (haploid)
- Produces genetic variation among offspring (evolutionary adaptation) via:
- Independent segregation of homologous chromosomes
- Recombination of homologous chromosomes by crossing over
9
Q
What are types of point mutations (3)
A
- Substitution - base replaced with another
- Insertions - information added to genome
- Deletions - information removed from the genome
10
Q
What are outcomes of point mutations (4)
A
- No change in sequence
- Missense sequence - amino acid changed, non-functional protein
- Nonsense sequence - no protein
- Rearranged sequence - non-functional protein
11
Q
What are single nucleotide polymorphisms (SNPs) (3)
A
- difference in a single nucleotide
- most common type of genetic variation among people (DNA polymorphism)
- most SNPs have no effect on health or development but are useful
12
Q
What can single nucleotide polymorphisms be used for (3)
A
- predict an individual’s response to certain drugs
- track the inheritance of disease genes within families
- associated with complex diseases such as heart disease, diabetes, and cancer
13
Q
What are the main types of genetic disorders (4)
A
- Single gene (Mendelian/monogenic)
- Multiple gene (complex/polygenic)
- Chromosomal
- Mitochondrial
14
Q
What are classifications of single gene disorders (5)
A
- Autosomal dominant - Huntington’s
- Autosomal recessive - Cystic fibrosis, sickle cell anaemia
- X-linked dominant
- X-linked recessive - haemophilia, G6PD deficiency
- Y-linked - male infertility
15
Q
What causes Huntington’s disease (3)
A
- A triplet repeat expansion (CAG = glutamine)
- in the Huntingtin gene (chromosome 4)
- Severity related to size of expansion
16
Q
What causes Cystic fibrosis
A
Mutation in the CFTR (Cystic Fibrosis Transmembrane Regulator) gene
17
Q
How do X-linked dominant gene disorders work (2)
A
- Affected females will have a 50-100% chance that their child will inherit the disorder
- Affected males will have normal sons and affected daughters
18
Q
How do X-linked recessive gene disorders work (2)
A
- Affected males will have normal sons and carrier daughters
- Affected females will have a 50% chance that their child inherits the disorder (sons only) or is a carrier (daughter)
19
Q
What are Y-linked gene disorders (4)
A
- Only affects males
- Usually results in infertility, so rarely passed on
- The Y chromosome is relatively small and contains very few genes
- there are relatively few Y‐linked disorders
20
Q
What are multiple gene disorders (4)
A
- Changes/mutations in multiple genes
- probably associated by varying environmental factors
- Hard to establish a clear-cut inheritance pattern
- e.g. heart disease, Alzheimer’s, arthritis, cancers, obesity, autism, hypertension, cleft palate…
21
Q
What are chromosomal disorders (3)
A
- Changes that affect the entire chromosome.
- Can be structural alterations or changes in number of the chromosomes
- These changes are usually not inherited but occur during the formation of reproductive cells
22
Q
What are the types of chromosomal disorders (2)
A
- Sex chromosomal disorders
- Autosomal chromosomal disorders
23
Q
What are the types of sex chromosomal disorders (4)
A
- Turners syndrome (XO, monosomy X) - female, minor, infertile
- Triple-X syndrome (XXX) - female, infertile, reduced mental acuity
- Klinefelter’s syndrome (XXY, XXXY) - male, low testosterone, female features, sterile
- Jacob’s syndrome (XYY) - male, acne, v tall, aggressive
24
Q
What are autosomal chromosomal disorders (3)
A
- Down’s syndrome
- Edward’s syndrome
- Patou syndrome
25
What happens in Down's syndrome (3)
1. Extra chromosome 21.
2. mental retardation
3. characteristic physical appearance
26
What happens in Edward's syndrome (3)
1. Trisomy of chromosome 18.
2. More severe than Down’s
3. most foetuses don’t survive
27
What happens in Patou syndrome (4)
1. Extra chromosome 13.
2. Very severe
3. mental disorder
4. physical defects resulting in death as babies.
28
What are mitochondrial genetic disorders (2)
1. Heteroplasmy – cells contain varying numbers of mtDNA (some may have mutations others don’t)
2. Leber's Hereditary Optic Neuropathy (LHON)
Results in loss of vision due to degradation of optic nerve
29
What is gene therapy (6)
1. Treatment of a disease, that is caused by an absent or abnormal gene
2. Gene(s) can be replaced, altered or supplemented.
3. Genetic disease can be caused by single or multiple genetic components
4. Human Genome Project – sequenced the entire human genetic makeup
5. Pharmacogenetics/pharmacogenomics – study of the genetic bases of variation in patients responses to drugs
6. Personalised medicines
30
How are genes used as drugs ex vivo (4)
1. A therapeutic gene is inserted into a specifically engineered virus
2. cells from the target tissue are removed from the patient
3. the cells are grown in large numbers in tissue culture plates. The cultured cells are then mixed with the virus.
4. the cells are then returned to the patient to replace the function lost due to the inheritance of mutant gene(s).
31
What must be considered when using genes as drugs (5)
1. Identify the genetic component of the disease
2. Therapeutic gene's desired effect
3. Local/systemic treatment?
4. Duration of therapeutic gene expression
5. Route of administration
32
What is somatic gene therapy (2)
1. Insertion of genetic material into diploid cells where the therapeutic gene is not passed on to offspring
2. No change in the genetic profile is passed on
33
What is germ-line gene therapy (4)
1. treatment of unborn ‘patients’.
2. Manipulation of genes in gamete cells.
3. Permanent cures to hereditary disorders
4. Ethical issues raised
34
What are the main categories of gene delivery vectors (2)
1. Viral vectors
2. Non-viral systems
35
What diseases are targeted with gene therapy (2)
1. Single gene disorders - Cystic F, ADA, SCID, familial hypercholesterolemia
2. multifactorial genetic disorders - cancer, atherosclerosis, diabetes mellitus
