Mendelian Inheritance and mitcohcondrial genetics Flashcards

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1
Q

What contributions lead to human disease?

A

Genetic and environmental

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2
Q

What are the classification of genetic disorders?

A
Single gene 
Multifactorial
Chromosome
Mitochondrial
Somatic
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3
Q

How can gain or loss of gene function come about?

A

But mutations in DNA

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4
Q

What is a genotype?

A

A pair of alleles at a locus

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5
Q

What are some single gene disorders?

A

Autosomal Dominant
Autosomal Recessive
X-linked

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6
Q

What is autosomal dominance?

A

A dominant allele (mutation) will determine a
phenotype when only one copy is present
in the genome.

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7
Q

What are some autosomal dominant disoders?

A

FAP - Familial Adenomatous polyposis

Achondroplasia - Dwarfism

Marfan Syndrome

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8
Q

What are the features of autosomal dominant inheritance?

A

Affected individuals in every generation

Male and female equally likely to be affected

Inherited from one OR other affected parent

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9
Q

What phenotypes are generally encountered in autosomal dominant families?

A

Wild type and heterozygous mutant

Homozygous are usually very severe and often not seen

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10
Q

What type of disorder is cystic fibrosis?

A

Autosomal recessive

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11
Q

What are the features of cystic fibrosis?

A
Problems with:
Lungs
Pancreas
Sweat glands
Sometimes other organs

Encodes a transmembrane protein that transports chloride ions, Mutations disrupt this chloride conductance

Affects 1/2500 people

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12
Q

What are some other autosomal recessive disorders?

A
Primary Haemochromatosis
Cystic fibrosis
Sickle cell disease
Phenylketonuria
Ataxia Telangiectasia
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13
Q

What causes Ataxia Telangiectasia?

A

Biallelic mutation of ATM gene

Mutation can occur at any point in the gene and produces the same effect

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14
Q

What are autosomal recessive disorders?

A

A recessive allele has no effect on the organism’s
phenotype if only one copy of the allele is present
in the genome.

You could be carrying a mutation in a gene and be
totally unaware of this- case for carriers of recessive
Diseases

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15
Q

What are the features of autosomal recessive disorders?

A

Only seen in one generation

Both parents are normally carriers

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16
Q

What is the origin of recessive mutations?

A

Most random mutations will either be neutral
or inactivating.

Default state of mutations is therefore recessive.

In the homozygous state there will be no function
and consequences will be seen in clinical state.

In the heterozygous state there will be no effect
of the allele on the organism.

17
Q

How does dominance of a mutation occur?

A
Dominant disorders outnumber recessive.
Occur via molecular basis:
Reduced gene dosage (haploinsufficiency)
 Increased gene dosage 
 Altered expression of mRNA
 Increased protein activity
 Dominant negative effects 
 Altered structural proteins
 Gain of new function
18
Q

What are the features of X-linked inheritance?

A
  1. Incidence of the trait is much higher in males than females
  2. The gene responsible for the condition is transmitted from an affected man through all his daughters.
  3. The gene is never transmitted from father to son.
  4. Sons always inherit their X chromosome from their mother.
19
Q

Give an example of a disease that is X-linked inherited?

A

Haemophilia

Duchenne Muscular Dystrophy

20
Q

What is multifactorial inheritance?

A

Multifactorial inheritance disorders are caused by a combination of small inherited variations in genes, often acting together with environmental factors.

Heart disease, diabetes, and most cancers are examples of such disorders.

Behaviors are also multifactorial, involving multiple genes that are affected by a variety of other factors.

Genetic contribution to behavioral disorders such as alcoholism, obesity, mental illness and Alzheimer’s disease.

21
Q

How are chromosome disorders caused?

A

Chromosome disorders are caused by an excess or deficiency
of the genes that are located on chromosomes, or by structural changes within
chromosomes. Down syndrome, for example, is caused by an
extra copy of chromosome 21 (trisomy 21), although no
Individual gene on the chromosome is abnormal.

22
Q

Why is the frequency of mitochondrial disorders high?

A

MtDNA has a much higher proportion of
coding DNA (93%) compared with about 3% in nuclear
DNA. Remember, however there is still about 100Mb
nuclear DNA.

Higher mutation rate in mtDNA. Rate at which
mutations are fixed in mtDNA is about 10x higher than/.
in nuclear DNA.

23
Q

How are mitochondrial mutations fixed?

A

the mitochondrial molecule has to replace all other molecules to return to homoplasmy.

24
Q

What are mitochondria deficient in?

A

Recombination

25
Q

What is Lebers optic atrophy?

A

The relationship between the genotype (mutation) and phenotype (clinical picture) can be complex

i. Homoplasmy may be tissue specific. Tissue examined may not be the critical tissue in the pathogenesis.
ii. MtDNA is more variable than nuclear DNA. May need the mutation together with some polymorphism
iii. Some mitochondrial diseases seem to have a quantitative nature. Need a threshold deficit to develop symptoms.
iv. Many mitochondrial functions are encoded by nuclear genes. So these may modify the mitochondrial phenotype.

26
Q

How is mitochondrial DNA inherited?

A

MtDNA is inherited from the maternal oocyte

27
Q

What diseases predominantly arise from mitochondrial mutations?

A

Neuromuscular diseases

28
Q

What is heteroplasmy?

A

Presence of two DNA populations such as nuclear and mitochondrial