Inheritance Patterns

Question 1

What is aneuploidy?

Answer 1

Having an abnormal number of chromosomes in a haploid set

Question 2

What is Chromosome 22q11 Deletion syndrome?

Answer 2

• Also called DiGeorge syndrome
• Prevalent 1 in 4-6,000 cases
• characteristic facial features

Question 3

What can go wrong with mitochondrial inheritance?

Answer 3

• All the mitochondria is inherited from the mother

Question 4

what is imprinting?

Answer 4

One allele active, the other is inactive

Question 5

What is mosaicism?

Answer 5

Somatic mosaicism= genetic fault present in only some tissues in the body (in one cell, allele normal functioning, in another may have mutation)

Question 6

What is Mendel’s Law?

Answer 6

He deduced that genes come in pairs and are inherited as distinct units, one from each parent

Question 7

How does Mendel’s Law apply to segregation?

Answer 7

Allele pairs separate/segregate randomly from each other during meiosis - each reproductive cell has a single allele for each trait

Question 8

What is independent assortment?

Answer 8

traits are transmitted to offspring independently of one another

Question 9

What is allelic heterogeneity?

Answer 9

• Different mutations within the same gene result in the same clinical condition e.g. cystic fibrosis
• Thus an individual with an autosomal recessive may be a compound heterozygote for two different mutations

Question 10

What does autosomal recessive look like?

Answer 10

• Homozygous state
• requires 2 defected genes
• Males/females equally affected
• Affected individuals are only in the single generation
  E.g. cystic fibrosis

Question 11

What are the outcomes/chances with autosomal recessive?

Answer 11

• Chance of having = 25%
• Chance of being a carrier = 50%
• Chance of affected child’s sibling being a carrier = 66.6%

Question 12

What is Consanguinity?

Answer 12

Reproductive union between two relatives

Question 13

What is autozygosity?

Answer 13

Homozygosity by descent e.g. inheritance of the same altered allele through 2 branches of the same family

Question 14

What does autosomal dominant inheritance look like?

Answer 14

• Disease manifests in heterozygous state
• Males/females affected equally
• Affects multiple generations
• Transmission from both sexes to both sexes
• Both parents can sometimes be unaffected E.g.
  Gonadal mosaicism (don’t have genes for it)
• Mother has reduced penetrance
• Mother has variable expression

Question 15

What is the chance of an offspring affected in autosomal dominant inheritance?

Answer 15

Only one defected gene needed = 50% chance offspring affected
E.g. Huntington’s Disease

Question 16

What is penetrance?

Answer 16

Percentage of individuals with a specific genotype showing the expected phenotype

Question 17

What is expressivity?

Answer 17

Refers to the range of phenotypes expressed by a specific genotype

Question 18

What is anticipation?

Answer 18

When a nucleotide is passed on through generations, it can get bigger and so more chance of a genetic disorder

Question 19

What does X-Linked inheritance look like/ caused by?

Answer 19

• Caused by mutation on the X chromosome
• Never male to male – sons always get X chromosome from mother
• All daughters from affected males are carriers
• Transmitted usually through unaffected female
• Can be recessive ( Duchenne’s muscular dystrophy) or dominant (Alport’s Syndrome)

Question 20

What are some genetic causes of disease?

Answer 20

Individually rare, but cumulatively enough to have regional genetic services
Eg: Down syndrome, Cystic Fibrosis, Huntington’s, Haemophilia

Question 21

What are some multifactorial causes of disease?

Answer 21

Combination of genetic and environmental. Main cause of disease in developed countries
Eg: Spina bifida, Cleft palate, Diabetes, Schizophrenia

Question 22

What are some environmental causes of disease?

Answer 22

Main causes of disease in third world and A & E (genetics play small role)
Eg: Poor diet, Infection, Drugs, Accident