Autosomal Recessive Inheritance Flashcards
____ is an example of an autosomal recessive trait
Sickle cell disease
In sickle cell disease, the distorted red cells have a reduced survival time and this results in a severe ____ with a need for repeated blood transfusions.
chronic haemolytic anaemia
T/F. In sickle cell disease, distorted red cells may also occlude vessels causing recurrent infarctions, especially of the lungs, bones and spleen.
True.
The predominant haemoglobin in normal adults is ____ w/c has two ____ and two ____ polypeptide chains in each molecule.
haemoglobin A (HbA); α - globin; two β – globin
Sickle - cell disease is caused by a point mutation in each ____ gene on chromosome ____ at the codon for the ____ amino acid.
β - globin; 11; sixth
The resulting ____ has a substitution of ____ in place of _____. This difference causes distortion of red cells, especially at reduced oxygen tension (the basis of the ____) and also alters the electrophoretic mobility of the protein
haemoglobin S (HbS); valine; glutamic acid; ‘ sickling test’
T/F. Patients with sickle cell disease have two mutant HbS gene copies (HbS/HbS), one having been inherited from each parent.
True. Autosomal recessive pattern
Relatives ’ carrier status for sickle cell amenia can be determined by ____.
haemoglobin electrophoresis
In marriages between two persons who are heterozygous to a autosomal recessive trait, what is the genotypic ratio for that trait?
one quarter homozygous normal, one quarter homozygous affected, and one half heterozygous normal
T/F. If by chance a person with sickle - cell disease marries a heterozygote, then there will be a 1 in 2 chance on average that each child will be affected.
True.
T/F. If both parents have sickle - cell disease, then only children with sickle - cell disease can be produced.
True.
T/F. The majority of parents of children with sickle - cell disease are not blood relatives (consanguineous), but if they are there is an increased risk for this and other autosomal recessive disorders.
True.
Family members at risk can be screened by the ____ or ____ and, where a pregnancy is at risk of homozygous sickle - cell disease, ____ may be offered.
sickling test; haemoglobin electrophoresis; prenatal diagnosis by DNA analysis
In highly inbred populations, the affected person has a substantial risk of mating with a carrier, and this may result in a pedigree with apparent vertical transmission of an autosomal recessive trait a phenomenon called _____.
pseudodominant inheritance
T/F. Hence, parental consanguinity, while not a prerequisite, is an important clue that a condition affecting their child is an autosomal recessive trait.
True.
Sickle - cell disease affects up to ____ black Africans, who have a carrier frequency of up to about ____.
1 in 40; 1 in 3
T/F. This high frequency of sickle cell carrier in black africans is believed to be due to the selective advantage of these carriers w/ regard to malarial infection.
True. Heterozygote advantage
Ethnic associations may also arise from the ____ in genetically isolated populations (Table 8.3 ). Hence, the ethnic origin of a patient may be an important clue in the diagnosis of an autosomal recessive disorder.
founder effect
At least ____ autosomal recessive traits are known in humans.
1730
T/F. Autosomal recessive traits is associated with enzyme defect.
True. In about 15% of autosomal recessive traits, an enzyme defect has already been demonstrated and is to be expected in many of the remainder.
For autosomal recessive traits, not just one but multiple different mutant alleles may occur at the locus. This is called _____.
multiple allelism or allelic heterogeneity
T/F. In multiple allelism, some, but not all, of these alleles result in sufficient reduction of enzyme activity to produce disease in the homozygous state.
True. Hence, the recessive inheritance pattern
Many conditions that were believed to be single genetic entities are now known to be genetically ____ i.e. to have several different genetic causes.
heterogeneous
An individual who has two different mutant alleles at a locus is termed a _____.
compound heterozygote or genetic compound.
T/F. Genetic heterogeneity should not be suspected if different modes of inheritance are apparent in different families or if offspring of parents who are autosomal recessive homozygotes are not invariably affected.
False.
In ____, cell lines from two affected individuals are fused in vitro to determine whether heterogeneous cross - correction of the phenotype can be demonstrated.
complementation studies
The similar term ____ refers specifically to the related situation in w/c a single genetic phenotype is known to result from mutations in different genes.
locus heterogeneity
These diseases are known to result from a mutation in either of a number of autosomal genes (locus heterogeneous).
Tuberous sclerosis; polycystic kidney disease
_____ refers to the converse correlation, where different mutations at one locus can result in different clinical conditions.
clinical heterogeneity. For example, different types of mutations in the same androgen receptor gene can result in either androgen insensitivity or spinal and bulbar muscular atrophy
