Autosomal Recessive And X Linked

Question 1

_______make up the largest category of Mendelian disorders.

They occur when both alleles at a given gene locus are mutated.

Answer 1

Autosomal recessive traits

Question 2

Autosomal recessive

These disorders are characterized by the following features:

(1) The trait does not usually affect the parents of the affected individual, but______ may show the disease;

(2) siblings have (ratio) of having the trait (i.e., the recurrence risk is 25% for each birth); and

(3) if the mutant gene occurs with a low frequency in the population, there is a strong likelihood that the affected individual (proband) is the product of a_______ marriage.

Answer 2

siblings

one chance in four

consanguineous

Question 3

Autosomal Recessive

• The expression of the defect tends to be more_____ than in autosomal dominant disorders.
•_______ is common.
• Onset is frequently____ in life.
• Although new mutations associated with recessive disorders do occur, they are rarely detected clinically. Since the individual with a new mutation is an asymptomatic heterozygote, several generations may pass before the descendants of such a person mate with other heterozy-gotes and produce affected offspring.
• Many of the mutated genes encode enzymes. In hetero-zygotes, equal amounts of normal and defective enzyme are synthesized. Usually the natural “margin of safety” ensures that cells with half the usual complement of the enzyme function normally.

Answer 3

uniform

Complete penetrance

early

Question 4

Autosomal recessive disorders include almost all inborn errors of_____.

Answer 4

metabolism

Question 5

Nervous Disorder in ADD

Answer 5

Huntington disease
Neurofibromatosis
Myotonic dystrophy
Tuberous sclerosis

Question 6

Urinary ADD

Answer 6

Polycystic kidney disease

Question 7

GUT ADD

Answer 7

Familial polyposis coli

Question 8

Hematopoietic ADD

Answer 8

Hereditary spherocytosis von Willebrand disease

Question 9

Skeletal ADD

Answer 9

Marfan syndrome*
Ehlers-Danlos syndrome (some variants)*
Osteogenesis imperfecta
Achondroplasia

Question 10

Metabolic ADD

Answer 10

Familial hypercholesterolemia*
Acute intermittent porphyria

Question 11

Metabolic Disorder ARD

Answer 11

Cystic fibrosis
Phenylketonuria
Galactosemia
Homocystinuria
Lysosomal storage diseases*
Antitrypsin deficiency
Wilson disease
Hemochromatosis
Glycogen storage diseases*

Question 12

Hematopoietic ARD

Answer 12

Sickle cell anemia
Thalassemias

Question 13

Endocrine ARD

Answer 13

Congenital adrenal hyperplasia

Question 14

Skeletal ARD

Answer 14

Ehlers-Danlos syndrome (some variants)*
Alkaptonuria*

Question 15

Nervous ARD

Answer 15

Neurogenic muscular atrophies
Friedreich ataxia
Spinal muscular atrophy

Question 16

All sex-linked disorders are X-linked, and almost all are_______.

Answer 16

recessive

Question 17

In X linked Disorders

Several genes are located in the “male-specific region of Y”; all of these are related to______

Males with mutations affecting the Y-linked genes are usually_____, and hence there is no Y-linked inheritance.

Answer 17

spermatogenesis

infertile

Question 18

X-linked recessive inheritance accounts for a small number of well-defined clinical conditions.

The Y chromosome, for the most part, is not homologous to the X, and so mutant genes on the X do not have corresponding alleles on the Y.

Thus, the male is said to be_____ for X-linked mutant genes, so these disorders are expressed in the male.

Answer 18

hemizygous

Question 19

X linked

• An affected male does not transmit the disorder to his____, but all____ are carriers.

____of heterozygous women have, of course, one chance in two of receiving the mutant gene.

Answer 19

sons

daughters

Sons

Question 20

X linked

The heterozygous____ usually does not express the full phenotypic change because of the paired normal allele.

Answer 20

female

Question 21

There are only a few X-linked ______ conditions.

They are caused by _____ disease-associated alleles on the X chromosome.

Answer 21

dominant

Question 22

These disorders are transmitted by an affected heterozygous female to half her sons and half her daughters and by an affected male parent to all his daughters but none of his sons, if the female parent is unaffected.

Vitamin D-resistant rickets is an example of this type of inheritance.

Answer 22

XLDD

Question 23

X-Linked Recessive Disorders

Answer 23

Duchenne muscular dystrophy
Hemophilia A and B
Chronic granulomatous disease
Glucose-6-phosphate dehydrogenase deficiency
Agammaglobulinemia
Wiskott-Aldrich syndrome
Diabetes insipidus
Lesch-Nyhan syndrome
Fragile X syndrome*

Question 24

are characterized by expression in heterozygous state; they affect males and females equally, and both sexes can transmit the disorder.

Answer 24

Autosomal dominant disorders

Question 25

Enzyme proteins are not affected in autosomal dominant disorders; instead, (2) are involved

Answer 25

receptors and structural proteins are involved.

Question 26

occur when both copies of a gene are mutated; enzyme proteins are frequently involved.

Males and females are affected equally.

Answer 26

Autosomal recessive diseases

Question 27

are transmitted by heterozygous females to their sons, who manifest the disease.

Female carriers usually are protected because of random inactivation of one X chromosome.

Answer 27

X-linked disorders