Genetic Inheritance of Disease

Question 1

what is a non frameshift deletion

Answer 1

this is when you remove 3,6,9 or a multiple of 3 bases, therefore the reading frame is kept
- this causes a mild change

Question 2

what are the different patterns of inheritance

Answer 2

• Autosomal dominant
• Autosomal recessive
• X linked recessive
• X linked dominant
• Y linked
• Mitochondrial

Question 3

describe autosomal dominant

Answer 3

• Affected individual usually has at least one affected parent
• It affects and is transmitted by either sex
• A child with one affected and one unaffected parent usually has a 50% chance of being affected
• Affects heterozygous individuals
• One allele is mutated

Question 4

what are the diseases associated with autosomal dominant

Answer 4

• Neurofibromatosis
• Marfan syndrome
• Huntington’s disease
• Achondroplasia

Question 5

describe new mutation

Answer 5

sporadic de novo cases – happened early on in development of zygote – happens in autosomal dominant when parents do have the disease, happens in X linked diseases in males

Question 6

describe variable penetrance

Answer 6

genetic background, environment, an affected individual may be asymptomatic, penetrance is how powerful the effect is on the phenotype

Question 7

describe anticipation

Answer 7

disease manifests at a younger age in successive generations for example huntingtons disease, the further down the younger the onset so your children will have the disease earlier on in their lives

Question 8

describe autosomal recessive inheritance

Answer 8

• Parents are usually asymptomatic carriers
• Both parents have to carry it
• Affects either sex
• After the birth of an affected child each subsequent child has a 25% of being affected
• Individuals are homozygous
• Both alleles are mutated in affected individuals

Question 9

describe common Autosomal recessive inheritance conditions

Answer 9

• Cystic fibrosis (1/20 carrier frequency)
• Sicke cell disease
• Thalassaemias

Question 10

describe X linked inheritance

Answer 10

• Affected males born to unaffected parent, mother usually an asymptomatic carrier
• Affects males as they inherit the x from mother, their sons are unaffected and their daughters are carriers
• No male to male transmission
• Carrier females have a 50% chance of having an affected son
• Affect individuals are hemizygous
• One x linked allele is mutated

Question 11

describe common X linked conditions

Answer 11

• Duchenne muscular dystrophy
• Haemophila
• Colour blindness
• Fragile X
• Glucose 6-phosphate dehydrogenase deficiency

Question 12

describe the genetic variation

Answer 12

• Alleles are alternative forms of the same gene
• A genotype refers to the combination of alleles seen in any one person
• Normal or wild type refers to the most common allele in a given population
• If the frequency of the rare allele is greater than 1% these variants are called polymorphic

Question 13

explain the hardy Weinberg destruction

Answer 13

The equilibrium of allele and genotype frequencies in a population 
Can work out frequency of alleles in the population 
Allele C -  frequency P
Allele T – frequenciy Q
Genotype C/C – frequency = p2 
Genotype C/T = frequency = 2pq
Genotype T/T – frequency = q2
P2 + 2pq + q2 = 1

Question 14

what are the expectations of the hardy-weinberg

Answer 14

• Inbreeding
– H-W assumes that a person’s two alleles are picked independently from the gene pool
• Founder effect
– May cause uneven ethnic distribution of recessive disorders
• Heterozygote advantage
– Loss of a deleterious allele compensated for by increased fitness of the heterozygote

Question 15

what is monogenic

Answer 15

rare

Question 16

what is polygenic

Answer 16

common

Question 17

what is the 
- inheritance
- mutations/variants 
- penetrance 
for monogenic

Answer 17

• recessive or dominant
• single
• high

Question 18

what is the 
- inheritance
- mutations/variants 
- penetrance 
for polygenic

Answer 18

• complex familial clusters
• many (10-100s)
• low and variable