Year 1 Medicine > Genetics and Inherited Diseases > Flashcards

Genetics and Inherited Diseases Flashcards

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1
Q

What is a phenotype?

A

Outward, physical manifestation of organism

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2
Q

What is a genotype?

A

Full hereditary information of organism (even if not expressed)

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3
Q

What are the base pairs involved in the DNA double helix?

A

Adenine to Thymine

Cytosine to Guanine

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4
Q

How many hydrogen bonds are between each C to G base pair?

A

3

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5
Q

How many hydrogen bonds are between each A to T base pair?

A

2

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6
Q

Where does replication of DNA occur?

A

Nucleus

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7
Q

What is a chromosome?

A

Single piece of DNA containing many genes, regulatory elements and other nucleotide sequences.

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8
Q

What is chromatin?

A

The mixture of DNA, proteins and RNA that package DNA within the nucleus.

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9
Q

What is the difference between the 2 forms of chromatin?

A

Heterochromatin (darker stripes) is condensed and contains silenced genes.
Euchromatic is extended and contains active genes.

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10
Q

What is a nucleosome?

A

DNA wrapped around a group of histones

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11
Q

What are the mechanisms for making chromatin more accessible so DNA double helix can be unzipped?

A

Histones can be enzymatically modified

Histones can be displaced by chromatin remodeling complexes

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12
Q

What is meant by DNA replication being semi-conservative and bi-directional?

A

Semi-conservative: one-half of each new molecule of DNA is old; one-half new.
Bi-directional: Replicated in 5’ to 3’ prime direction so one strand is leading and replicated in a single fragment where as the other lagging strand has to be replicated in several fragments as it runs 3’ to 5’.

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13
Q

When are chromosomes most compacted and visible?

A

During metaphase.

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14
Q

What is degeneracy?

A

With the exception of methionine and tryptophan, amino acids are all encoded by more than one codon.

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15
Q

What is the major role of RNA?

A

To be involved in protein synthesis.

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16
Q

What is alternative splicing?

A

Regulated process during gene expression that results in a single gene coding for multiple proteins. In this process, particular exons of a gene may be included within or excluded from the final, processed mRNA produced from that gene. Various combinations of exons.

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17
Q

What is a reading frame?

A

Initiation codon that determines how RNA is read and where reading is started from.

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18
Q

What is the role of tRNA?

A

Translate mRNA sequence into amino acid sequence.

Acts as an adapter molecule between the coded amino acid and the mRNA.

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19
Q

What is rRNA?

A

Component of Ribosomes
Combines with proteins to form ribosomes.
Produced in nucleus.

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20
Q

What is a polysome?

A

Several ribosomes translating a section of mRNA at one time.

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21
Q

What is a telomere?

A

Specific genetic sequence that terminates chromosomes and protects the ends form damage. 5’ - TTAGGG - 3’

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22
Q

Describe the stages of mitosis?

A

Prophase - chromosomes condense
nuclear membrane disappears
spindle fibres form

Metaphase- chromosomes align at equator
fibre at centriole

Anaphase- sister chromatids separate at centromere and move to opposite ends of the cell.

Telophase - new nuclear membranes form
each cell has 46 chromosomes

Cytokinesis - cytoplasm separates
2 new daughter cells.

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23
Q

What are centromeres?

A

Constricted region joining sister chromatids
Repetitive DNA sequences (satellite DNA)
Site of kinetochore - protein complex that binds to microtubules and is required for chromosome separation during cell division.

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24
Q

What is a solenoid?

A

Further wrapping of 6 nucleosomes.

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25
What is the purpose of packaging DNA?
Negatively charged DNA neutralised by positive charged histone proteins DNA takes up less space Inactive DNA can be folded into inaccessible locations until required.
26
What does F.I.S.H stand for?
Fluorescent In Situ Hybridisation A technique in which single-stranded nucleic acids (DNA or RNA) are permitted to interact so that complexes, or hybrids, are formed by molecules with sufficiently similar, complementary sequences. Allows specific sequences to be located and highlighted within the genome.
27
Describe the process of meiosis?
Cell division in germ cells Diploid cells (in ovaries and testes) divide to form haploid cells Chromosomes are passed on as re-arranged (recombined) copies Creates genetic diversity
28
Define Oogenesis?
Process of egg formation (only 1 product of meiotic division will produce an egg.)
29
Define Spermatogenesis?
Process of sperm formation
30
What are some key features of fertilisation?
Two haploid cells (egg, sperm) form 1 diploid cell (zygote) – develops into embryo Whether sperm contain an X or Y chromosome determines if embryo is female (XX) or male (XY) Embryo contains an assortment of genes from each original parent – more genetic diversity Mitochondria (and their DNA) come only from mother via the egg – maternal inheritance.
31
What is X-inactivation?
The process of one of a females 2 X chromosomes being switched off to become dormant while the other is permanently expressed. Random act that takes place in early embryonic development.
32
Describe some characteristics of sickle cell disease?
Abnormal HB gene, single gene mutation. Cause red blood cells to become sickle-shaped, and that this can cause pain, tissue damage, infection and even death. Inherited
33
What is the difference in mutations between carriers and the affected?
Carriers only have one mutation that causes a nonfunctional or missing protein. Affected individuals of recessive conditions have mutations in both copies of their gene so they are missing both copies of the key protein.
34
What is the difference in the mutation of a dominant disease compared to a recessive condition?
Dominant conditions only need a single mutation for the condition to be expressed. The mutated protein can be nonfunctional, missing or with a gain of function. Recessive conditions require both copies of the gene to be faulty before it is expressed.
35
What are some characteristics of autosomal dominant diseases?
No skipped generations Each child has a 50% chance of being affected. Male to male transmission Equal chance of males and females being affected. E.g Achondraplasia, Huntington's disease.
36
Describe some characteristics of x-linked inheritance?
Classically only males affected Can skip generations Unaffected females and affected males can transmit the disease No male to male transmission as males only pass on Y chromosome to their son's. E.g Duchenne's muscular dystrophy.
37
What are the 3 types of chromosomal abnormalities?
Numerical Structural Mutational
38
What do numerical chromosomal abnormalities involve?
Wrong number of chromosomes within the karyotype.
39
What do structural chromosomal abnormalities involve?
Large organisational errors or structural rearrangements of chromosomes.
40
What do mutational chromosomal abnormalities involve?
Small number of bases or nucleotides are affected by a mutation.
41
What is trisomy?
An extra chromosome, 47. | E.g Down's syndrome, Edward's syndrome, Patau syndrome.
42
What is monosomy?
One less chromosome, 45. | E.g Turner's syndrome
43
How do numerical chromosomal abnormalities arise?
Problem occurs during chromosomal segregation. Non-disjunction. If problem occurs at meiosis 1 then 2 disomy gametes are produced (extra chromosome) and 2 null gametes are produced. Null gametes do not survive. If problem occurs at meiosis 2 then 2 normal gametes are produced, 1 null and 1 disomy.
44
Why is there more risk when an older women falls pregnant?
Non-disjunction becomes more common with age. Offspring has a higher chance of having a chromosomal abnormality.
45
Describe some numerical chromosomal diseases?
Trisomy 21 (downs) - haracteristic facial dysmorphologies IQ less than 50 Average life expectancy (50-60 years) Alzheimer’s disease in later life ``` Trisomy 13 (patau) - Multiple dysmorphic features and mental retardation About 5% die within first month, very few survive beyond first year ``` Trisomy 18 (Edwards) - Severe developmental problems; most patients die within first year, many within first month ``` Monosomy X (turner's) - Females of short stature and infertile Neck webbing and widely spaced nipples Intelligence and lifespan is normal ```
46
What are some subclassifications of structural chromosomal abnormalities?
``` Balanced Unbalanced Translocations Deletions Insertions Inversions ```
47
What is balanced translocation?
Section of genes from one chromosome is swapped with a section of genes from another. The correct amount of DNA still remains.
48
What is an unbalanced translocation?
Section of genes from a normal chromosome is swapped with a section genes from a balanced translocation chromosome. The amount of DNA is changed as some is now lost.
49
What is an acrocentric chromosome?
A chromosome in which the centromere is located quite near one end of the chromosome.
50
What is the Robertsonian translocation?
A unique form of translocation where 2 acrocentric chromosomes break at their centromeres and fuse together their long arms so one single chromosome is produced. The small arms are lost.
51
What is a deletion?
A deletion is when a chromosome breaks at 2 points and the section of genetic material in between is deleted.
52
What is an inversion?
A section of genetic material is turned around during a DNA repair event.
53
Describe some characteristics of genetic mutations?
Can be germline or somatic Can cause gene disruption and disease association. Polymorphism Can be non-coding or coding
54
What are the different types of coding genetic mutations?
Silent - no change in amino acid sequence even though the base pairing was altered. Missense - A single amino acid is altered within the sequence. Protein can be produced but is faulty. Nonsense- An amino acid is changed for a stop codon. Protein suddenly stops, not produced. Frameshift - deletion or insertion of a base.
55
How can genetic mutations be detected?
Polymerase chain reaction (PCR)- amplifies DNA Gel electrophoresis- separates DNA fragments by size Restriction fragment length polymorphism (RFLP) analysis Amplification refractory mutation system (ARMS)- looks for a known mutation DNA sequencing- chain termination method
56
What is fitness?
The relative ability of organisms to survive (long enough) to pass on their genes.
57
What are some factors that can effect fitness?
Deleterious alleles cause a decrease in fitness. Advantageous alleles occasionally cause an increase in fitness. Role of family/society in food sourcing, defence against invaders, keeping them out of harm, education.
58
What are some common recessive diseases?
Sickle cell anaemia Thalassaemia Cystic fibrosis
59
Where are de novo mutations most common?
In dominant and x-linked mutations, especially where disease reduces reproductive fitness. Unlikely to cause disease if they occur in recessive genes.
60
What does non-random mating lead to?
Leads to increased mutant alleles, thereby increasing proportion of affected homozygotes.
61
What is assortative mating?
Choosing a meting partner based on shared characteristics. E.g more common in people with deaf and blindness.
62
What is consanguinity?
The marriage between close blood relatives. E.g cultural pressures to marry within clan.
63
What is natural selection?
A gradual process by which biological traits become either more or less common in a population.
64
What is the outcome of negative selection?
- Reduces reproductive fitness. - decreases the prevalence of traits. - leads to gradual reduction of mutant allele.
65
What is the outcome of positive selection?
- Increases reproductive fitness. - Increases the prevalence of adaptive traits. - Heterozygote advantage.
66
Give some examples of recessive diseases that provide a heterozygous advantage?
Sickle cell anaemia - resistance to malaria in tropical Africa. Cystic fibrosis - resistance to cholera and typhoid in Western Europe. Congential adrenal hyperplasia - resistance to influenza B.
67
What is genetic drift?
Random fluctuation of one allele transmitted to high proportion of offspring by chance. Mutations are widespread and neutral.
68
What is the founder effect?
The reduction in genetic variation that results when a small subset of a large population is used to establish a new colony. e.g CF in Faroe Islands.
69
What are some mechanisms for non-mendelian inheritance?
Incomplete penetrance - environmental factors and genetic modifiers. Genomic imprinting - variants from parents. Extranucelar mutations - mitochondrial mutations. Anticipation - triplet repeat expansion.
70
What is penetrance?
The frequency with which a trait is manifested by individuals carrying the gene.
71
What are genetic modifiers?
Genes that have small quantitative effects on the level of expression of another gene. May involve polymorphism.
72
What are some environmental factors that effect penetrance?
Lifestyle, diet, smoking, alcohol consumption, drugs, stress, pollution, chemicals, infection
73
What is genetic imprinting?
Genes are expressed from only one chromosome. | Parent-of-origin dependent.
74
What are epigenetic modifications?
Heritable changes in gene function that cannot be explained by changes in DNA sequences.
75
What is uniparental disomy?
Inheritance of a chromosome pair from one parental origin.
76
What is gynogenic uniparental diploidy?
2 maternal genomes - results in Mass of embryonal Ovarian teratoma.
77
What is androgenic uniparental diploidy?
2 paternal genomes - results in Mass of placenta and Hydatidiform mole.
78
What are some human models from imprinting disorders?
Angelman syndrome - epilepsy, mental retardation, awkward gait, inappropriate laughter. Deletion of maternal copy. Prader-Willi syndrome - hypotonia (low muscle tone), mental retardation, short stature, marked obesity. Loss of paternal copy.
79
Describe the mitochondrial genome?
Circular All received from maternal genes. 37 genes 13 coding genes.
80
Why does mitochondrial genome have a higher mutation rate than in nucleus?
Lack of efficient DNA repair system. Lack of protective proteins, such as histones. Damaged by reactive oxygen species (ROS), such as free radicals.
81
What is heteroplasmy?
2 or more mutated mitochondrial DNA.
82
What is anticipation?
Disease presents at earlier age and/or increasing severity in succeeding generations.
83
What are some examples of diseases with anticipation?
Triplet repeat diseases: - Huntington’s disease - Myotonic dystrophy - Fragile X syndrome
84
What is complex inheritance?
Combination of multiple genetic and environmental factors only some of which might be known. Encoded by multiple loci. Common in disease.

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