Patterns of Inheritance

Question 1

What are multifactorial disorders?

Answer 1

variants in genes causing alterations of function

Question 2

What is autosomal dominant?

Answer 2

A dominant allele (mutation) will determine the phenotype when one copy is present in the gene

Question 3

What are some single gene disorders?

Answer 3

autosomal dominance
autosomal recessive
X-linked

Question 4

What can mutations cause?

Answer 4

loss or gain of a gene function

Question 5

What can mutations affect?

Answer 5

• a single gene (mendelian inheritance)
• chromosomal segment
• several genes acting with environmental influences (multifactorial inheritance)

Question 6

What are some examples of autosomal dominant disorders?

Answer 6

• familial adenomatus polyposis
• achondroplasia (dwarfism)
• marfan syndrome (connective tissue disorder)

Question 7

What are the features autosomal dominant inheritance?

Answer 7

• affected individuals in every generation
• male and female likely to be affected
• inherited from one or other affected parent
• but there can be a new mutation

Question 8

What types of phenotypes can there be in autosomal dominant families?

Answer 8

-wild type
-heterozygous mutant
(homozygous v severe and not usually seen)

Question 9

What is the role of the CF gene?

Answer 9

it encodes a transmembrane protein that transports chloride ions. Mutations disrupt the chloride conductance.

Question 10

What are the features of ataxia telangiectasia?

Answer 10

cerebellum development doesn’t occur correctly so co-ordination issues (e.g walking, eye movement) occur. Mentally, patients are average.

Question 11

List some autosomal recessive disorders

Answer 11

• cystic fibrosis
• sickle cell disease
• ataxia telangiectasia

Question 12

What is a autosomal recessive disorder?

Answer 12

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

Question 13

What are the characteristics of autosomal recessive disorders?

Answer 13

• usually only seen in one generation (unless there is a cousin cousin marriage)
• both parents are normally carriers (unless there is a new mutation)

Question 14

How did recessive mutations originate?

Answer 14

• most mutations will be neutral or inactivating
• default state of mutations is therefore recessive
• in homozygous state there will be no function and consequences will be seen in clinical state
• in the heterozygous state there will be no effect on the allele of the organism

Question 15

For what reason could diploidy evolved?

Answer 15

to protect against recessive mutations

Question 16

Why does dominate of a mutation occur?

Answer 16

• reduced gene dosage (where expression of one allele is not enough for function)
• increased gene dosage (due to 3 copies of a gene)
• altered expression of mRNA (due to loss of regulation of mRNA expression)
• increased or constitutive protein activity (increased half life or loss of normal inhibitory regulation)
• dominant negative effects (in the heterozygous state these mutants antagonise the activity of the normal allele)
• altered structural proteins (mixture of normal and abnormal structure alterations will disrupt the whole structure)
• gain of new protein function (chromosome translocations giving rise to new genes/protein fusion proteins)

Question 17

What are the characteristics of X-linked inheritance?

Answer 17

• incident of the trait is much higher in males than females
• the gene responsible for the condition is transmitted from an affected man through all his daughters
• the gene is never transmitted fro m father to son
• sons always inherit the X chromosome from their mother

Question 18

How does multifactorial inheritance occur?

Answer 18

caused by a combination of small inherited variations in genes, often acting with environmental factors

Question 19

Why do chromosome disorders occur?

Answer 19

caused by excess or deficiency of the genes that are located on the chromosomes or by structural chromosomes

Question 20

Why is the frequency of mitochondrial disorders high?

Answer 20

• MtDNA has a higher proportion of coding DNA
• higher mutation rate in mtDNA (10x higher than in nuclear DNA)
• neuromuscular disease predominates

Question 21

What is the MtDNA bottleneck?

Answer 21

When the number of MtDNA molecules within each oocyte is reduced before being greatly amplified in the mature oocyte