Modes Of Inheritance

Question 1

When is a characteristic dominant?

Answer 1

If it manifests in a heterozygous

Question 2

Why are brown eyes dominant?

Answer 2

Gene responsible for eye colour —> OCA-2

BOCA-2 controls amount of melanin in melanocytes

Question 3

What is a dominant autosomal disorder?

Answer 3

Single gene/allele disease

Disease passed down to offspring —> 1 in 2 chance of being affected

Males and females equally affected and likely to pass on condition

Vertical pedigree pattern

Question 4

What do dominant autosomal disorders tend to be?

Answer 4

Gain-of-function

Dominant negative effect

Insufficient

Question 5

What is gain-of-function?

Answer 5

Gene makes a protein w/ a new function

Question 6

What is dominant negative effect?

Answer 6

Mutated form interferes w/ the activity of proteins it binds —> reduces activity

Question 7

What does insufficient mean in regards to gene mutations?

Answer 7

Mutant in one gene results in 1/2 amount of a protein —> not enough for normal function (rare)

Question 8

What makes Huntington’s disease dominant?

Answer 8

Mutation —> expansion for CAG (glutamine) repeat huntingtin

Result —> abnormal Huntington protein aggregate —> gains pathological function —> toxic to neurons —> cell death

Question 9

What makes Osteogenesis imperfecta (brittle bone) dominant?

Answer 9

Mutations
—> type 1 —> insufficient quantities of collagen

—> type 2, 3 and 4 —> mutation of collagen —> abnormal protein has altered structure —> interferes w/ function of the normal protein

Result —> weakening of connective tissues particularly bone

Question 10

What does recessive mean?

Answer 10

2 copies of the abnormal gene must be present in order for the disease or trait to develop

Question 11

What kind of mutations do autosomal recessive disorders tend to be?

Answer 11

Loss of function

Question 12

What is an autosomal recessive disorder?

Answer 12

Parent and children of affected people are normally unaffected

Each I bling of affected child has 1 in 4 chance of being affected

Males and females equally affected

Flows horizontal pedigree pattern

Question 13

What is a carrier of a recessive disease?

Answer 13

Have low a single copy of a gene but the normal one is sufficient to maintain normal function

Question 14

What increases risk of autosomal recessive diseases?

Answer 14

Consanguineous marriages

Question 15

What makes cystic fibrosis recessive?

Answer 15

Mutation —> various mutations in gene encoding chloride ion channel

Result —> defective chloride ion channel —> loss of function —> work less well, degraded faster or present in inadequate amounts

BUT single channel sufficient to maintain activity

Question 16

How do X-linked recessive disorders affect males and females?

Answer 16

Affects mainly males —> only 1 X chromosome

Females can be carriers

Females have to homozygous

Question 17

If a father has a x-linked recessive disorder…

Answer 17

All daughters will be carriers

All sons will be healthy

Question 18

What is an example of an x-linked recessive disorder?

Answer 18

Haemophilia —> more frequent or severe bleed

Question 19

How do X-linked dominant disorders affect males and females?

Answer 19

Males only affected if mother has disorder

Females can be affected if either mother or father has disorder

Can’t be carrier

Question 20

If a father has an x-linked dominant disorder…

Answer 20

All daughters affected

No sons affected

Question 21

What is an example of an x-linked dominant disorder?

Answer 21

X-linked hypophosphatemia

Question 22

How do Y-linked disorders affect males and females?

Answer 22

Only males affectedc

Vertical pedigree pattern

Question 23

If father has a y-linked disorder…

Answer 23

All sons affected

Question 24

What is an example of a y-linked disorder?

Answer 24

Retinitis Pigmentosa —> cells off retina produce defective protein

Question 25

What is a mitochondrial inherited disorder?

Answer 25

Mutations in mitochondrial DNA

Maternally inherited —> all mitochondria inherited from mother

Vertical pedigree pattern

Question 26

If mopier has a mitochondrial inherited disorder…

Answer 26

All children affected

Question 27

Why does mitochondrial disease have variability?

Answer 27

Mitochondria have multiple copies genome w/ some normal and some mutant —> only express disease effects above a threshold

Replicate by binary fission —> can lose or gain mutated genes

Many mitochondria in each CLL —> random segregation

Question 28

What is an example of mitochondrial disease?

Answer 28

Leber’s hereditary optic neuropathy
—> visual loss in young adulthood —> degeneration of optic nerve and retina