17 Modes of inheritance

Question 1

How many DNA chromosomes to bacteria usually have?

Answer 1

Only 1 (compared to 23 pairs found in humans)

Question 2

How do bacteria divide?

Answer 2

Binary fission (asexual)

Question 3

Roughly how many genes are encoded by bacterial genomes?

Answer 3

4,000-6,000

Question 4

What does each gene encode for?

Answer 4

An mRNA

Question 5

What does each mRNA encode for?

Answer 5

One protein

Question 6

What does homozygous mean?

Answer 6

Two identical copies of an allele for that gene

Question 7

What does heterozygous mean?

Answer 7

Two different alleles for a particular gene

Question 8

What is a locus?

Answer 8

A single position of a gene on the chromosome

Question 9

How many autosomal pairs do humans have?

Answer 9

22

Question 10

How many chromosomes do humans have?

Answer 10

46

Question 11

Roughly how many genes do humans have?

Answer 11

25,000

Question 12

How many different types of single gene disorders are there?

Answer 12

~4,000

Most common ~1/500

Question 13

What is a dominant autosomal characteristic?

Answer 13

A characteristic is dominant if it manifests in a heterozygote

Question 14

Characteristics of dominant autosomal diseases

Answer 14

• Multiple generations affected
• Each affected person normally has one affected parent
• Child of affected person has 1 in 2 chance of being affected

Question 15

What pattern is seen in dominant autosomal disorders?

Answer 15

Vertical pedigree pattern

Question 16

How many people are affected by Huntington’s disease?

Answer 16

1 in 20,000 (UK)

Question 17

What are the symptoms of Huntington’s disease?

Answer 17

• Start at 30-50 years
• Difficulty concentrating
• Depression
• Stumbling
• Involuntary jerking

Question 18

What mutation causes Huntington’s disease?

Answer 18

DNA expansion of a CAG repeat on chromosome 4

Question 19

What does the mutation in Huntington’s cause?

Answer 19

Abnormal intracellular Huntington protein aggregate becomes toxic to neurons resulting in cell death

Question 20

How many people are affected by osteogenesis imperfecta (brittle bone disease)?

Answer 20

1 in 15,000

Question 21

What are some symptoms of osteogenesis imperfecta?

Answer 21

• Bones break easily
• Mild to severe
• Hearing loss
• Breathing problems
• Short height

Question 22

What causes type I osteogenesis imperfecta?

Answer 22

Insufficient quantities of collagen

Question 23

What causes type II, III and IV osteogenesis imeprfecta?

Answer 23

An abnormal protein with an altered structure interferes with the function of the normal protein

Question 24

What do dominant autosomal disorders tend to be?

Answer 24

• Gain-of-function (protein with new function made)
• Dominant negative effect (interference with activity of proteins it binds)
• Insufficient (1/2 amount of a protein produced, not enough for normal function)

Question 25

What is a carrier?

Answer 25

Someone that has lost a single copy of a gene but the normal one is sufficient for normal function

Question 26

What does recessive mean?

Answer 26

Two copies of the abnormal gene need to be present for the disease or trait to develop

Question 27

Recessive disorders tend to be...

Answer 27

Loss of function mutations (deletions)

Question 28

What pattern is seen in recessive autosomal disorders?

Answer 28

Horizontal pedigree pattern

Question 29

How many people are affected by cystic fibrosis?

Answer 29

1 in 3,000 newborns

Question 30

What are some symptoms of cystic fibrosis?

Answer 30

'Failure to thrive' - Prone to respiratory infections - Digestive issues

Question 31

What mutations cause cystic fibrosis?

Answer 31

Various mutations in gene encoding chloride ion channel (CFTR gene on chromosome 7)

Question 32

What does the cystic fibrosis mutation cause?

Answer 32

Defective chloride ion channel | - Loss of function, degraded faster

Question 33

What highly raises the risk of autosomal recessive diseases?

Answer 33

Consanguineous marriages

Question 34

Why are X-linked diseases more impactful on sons?

Answer 34

They only have one copy of the X chromosome

Question 35

Give an example of an X-linked recessive disorder where carriers exhibit subtle signs

Answer 35

Fabry's disease

Question 36

Give an example of an X-linked recessive disorder

Answer 36

Haemophilia (frequent, severe bleeds -> Factors VIII or IX)

Question 37

Main trend in X-linked recessive disorders

Answer 37

All daughters of a man with the disorder will be carriers

Question 38

Main trend in X-linked dominant disorders

Answer 38

All daughters and no sons of an affected father are affected

Question 39

Give an example of an X-linked dominant disorder

Answer 39

X-linked hypophosphatemia

Question 40

What does X-linked hypophosphatemia cause?

Answer 40

- Kidneys can't retain phosphate | - Vitamin D resistant rickets

Question 41

What gene mutation causes X-linked hypophosphatemia ?

Answer 41

XLH gene mutation resulting in inactivity og PHEX protein

Question 42

Main trends in Y-linked disorders

Answer 42

- Only affects males - All sons of affected father - Vertical pedigree pattern

Question 43

Example of Y-linked disorder

Answer 43

Retinitis Pigmentosa

Question 44

What mutation causes retinitis pigmentosa?

Answer 44

Mutation in RPY gene

Question 45

What does the RPY mutation cause?

Answer 45

Cells of retina produce a defective protein

Question 46

Key facts about mitochondria

Answer 46

- Share evolutionary past with bacteria | - Have their own DNA (also use proteins encoded by nuclear genes)

Question 47

Main trend in mitochondrial disorders

Answer 47

Maternally inherited

Question 48

Why is there a variable phenotypic pattern with mitochondrial disorders?

Answer 48

Different cells have different numbers/complements of mitochondria

Question 49

What factors affect the severity of symptoms concerning mitochondrial disorders?

Answer 49

- Amount of WT (wild type) to mutated mtDNA | - Severity of mutation

Question 50

Give an example of a mitochondrial disease

Answer 50

Leber's hereditary optic neuropathy (LHON)

Question 51

What symptoms are common of LHON?

Answer 51

- Visual loss in young adulthood | - Mutations disrupt function of mitochondria (oxidative phosphorylation)