M2.2 - Medical Genetics
Dizygotic twins share an average of ____ of the same alleles
50%
______________: -Absence or partial deficiency of melanin in the skin, eyes, and hair -It can also occur in a wide variety of animals
Albinism
What is the inheritance pattern for a trait that occurs with equal frequency in both sexes and will be inherited, on average, by 50% of the offspring of an affected individual who had only one affected parent?
Autosomal dominant
What is the inheritance pattern when the trait occurs with the same frequency in both sexes and two unaffected heterozygotes have, on average, 25% affected children?
Autosomal recessive
Vitamin __-resistant __________ is a disorder involving softening and weakening of the bones (of children primarily caused by lack of vitamin D
D, rickets
Which type of mutation causes a dominant genetic disorder through the production of an altered protein that works against the action of the normal protein?
Dominant-negative
_____________: the degree to which a penetrant gene is phenotypically expressed
Expressivity
What is syndactyly?
Fused fingers
______________________ is the phenomenon in which a person has only a single functional copy of a gene, and that single functional copy does not produce a normal phenotype.
Haploinsufficiency
There are three common explanation for autosomal dominant disorders... 1) ______________________ -The heterozygote has 50% of the normal protein -This is not sufficient for a normal phenotype 2) ________-____-__________ mutations -Mutation changes protein so it gains a new function 3) ___________ ___________ mutations -The altered gene product acts antagonistically to the normal product (so one copy in a negative state is enough to mask/block the normal gene product)
Haploinsufficiency, gain-of-function, dominant negative
Which disease has also been called "royal disease" because it has affected many members of European royal families?
Hemophilia
_________________: -The major symptom of the disease is that the blood cannot clot properly when a wound occurs -Common accidental injuries pose a treat of severe internal or external bleeding
Hemophilia
________________ disease: -The major symptom of the disease is the degeneration of certain types of neurons in the brain -This leads to personality changes, dementia, and early death
Huntington
__________ ________________ refers to the phenomenon that a disease can be caused by mutations in two or more different genes For example: _____________ -Blood clotting involves a cellular cascade that involves several different proteins -Thus, a defect in any of these proteins can cause the disease --Hemophilia A = defect in clotting factor VIII --Hemophilia B = defect in clotting factor IX --Hemophilia C = defect in clotting factor XI
Locus heterogeneity, hemophilia
X-Linked Dominant Traits _________ are often more severely affected
Males
What is true of X-linked dominant disorders such as Rett syndrome and Aicardi syndrome?
Males die at an early stage of development
Which of the following characteristics of inheritance for hemophilia can be observed in the pedigree for the family of Queen Victoria and Prince Albert? -________ are more likely to be affected than females -Mothers of affected males often have __________ with the disease
Males, brothers
______________ ________ share 100% of the same alleles
Monozygotic twins
________________: the proportion of individuals with a specific genotype who manifest the corresponding phenotype
Penetrance
______________: An organism whose phenotype has been modified to resemble the phenotype of a different mutant organism
Phenocopy
_________________: suppression of limb development -Caused by a _____________ allele with variable expressivity
Phocomelia, dominant
What is brachydactyly?
Shortened-fingers
_______________ disease: -Affected individuals appear healthy at birth, but then develop neurodegenerative symptoms at 4 to 6 months --Cerebral degeneration, blindness and loss of motor function -These patients typically die at 3 or 4 years of age
Tay-sachs
__________________: -Sedative -Between 1959-1962 children with shortened limbs were born to mothers who took the drug early in their pregnancy
Thalidomide
Approximately how many human diseases have a genetic basis?
Thousands
Autosomal Dominant Traits T/F: Members of both sexes are affected equally
True
True or false: Genetic diseases often show a specific age of onset
True
True or false: Identical twins share a genetic disease more often than fraternal twins
True
The following human diseases: 1) Vitamin-D resistant rickets 2) Rett syndrome 3) Incontinentia pigmenti are inherited in an ________________ _____________ manner
X-linked dominant
Vitamin D-resistant rickets is an _______________ ________________ disorder
X-linked dominant
The following human diseases: 1) Androgen insensitivity syndrome 2) Duchenne muscular dystrophy 3) Hemophilia A are inherited in an ________________ _____________ fashion
X-linked recessive
What is the inheritance pattern for a trait that more commonly affects males than females and can be observed in brothers or fathers of a woman who has affected sons?
X-linked recessive
What is the inheritance pattern for a trait that more commonly affects males than females and which will occur in about 50% of the sons born to the unaffected daughter of an affected male?
X-linked recessive Since the daughter is unaffected, the trait must be inherited as an X-linked recessive
Short-limed dwarfism is termed ________________________
achondroplasia
X-Linked Recessive Traits Affected FEMALES come from ___________ fathers and ____________ or ____________ mothers
affected, affected, carrier
X-Linked Recessive Traits Affected MALES result from ____________ mothers or mothers who are ___________
affected, carriers
Autosomal Recessive Traits Members of both sexes [are/are not] affected equally
are
Autosomal dominant compelling helio-ophthalmic outburst syndrome (aka achoo) is an ______________ _____________ disorder
autosomal dominant
Huntington Disease (HD) is an _________________ _______________ disorder
autosomal dominant
Penetrance and expressivity are used most often with _____________ ______________ traits
autosomal dominant
The following human diseases: 1) Huntington disease 2) Marfan syndrome 3) Aniridia are inherited in an ________________ _____________ fashion
autosomal dominant
Albinism is an ________________ _______________ disorder
autosomal recessive
Cystic fibrosis an an ____________ ______________ disorder
autosomal recessive
Phenylketonuria is an ______________ ______________ disorder -The defect is in the gene that encodes phenylalanine hydroxylase
autosomal recessive
Sickle cell disease is an ______________ ____________ disorder
autosomal recessive
Tay-Sachs disease is an ____________ ______________ disorder
autosomal recessive
The following human diseases: 1) Sickle cell disease 2) Phenylketonuria 3) Cystic fibrosis are inherited in an ________________ _____________ fashion
autosomal recessive
Autosomal Dominant Traits Two affected parents [can/cannot] product unaffected offspring Example: dad can be "Hh" and mom can be "Hh", offspring could be "hh" which is unaffected
can
Autosomal Recessive Traits Unaffected parents [can/cannot] have an affected child For example: If dad is "Rr" and mom is "Rr" - parents are unaffected but offspring could be "rr" --> affected
can
Autosomal Recessive Traits Two affected parents [can/cannot] have an unaffected child
cannot
Autosomal Recessive Traits Traits are more likely to occur in ________________________ marriages
consanguineous
What is the most common lethal genetic disease among caucasians?
cystic fibrosis
Siamese cats have a __________ fur at their extremities due to temperature
darker
X-Linked Dominant Traits Affected males have no normal _______________ and no affected _________
daughters, sons
X-Linked Dominant Traits Trait [does/does not] skip generations
does not
Autosomal Recessive Traits Healthy = ________________ Disorder = ___________________
dominant, recessive
Suppose a disease-causing allele shows autosomal recessive inheritance. How could a carrier of this disease-causing allele be identified? Carriers often show reduced activity for the _____________ encoded by the allele
enzyme
Disorders that involve defective ______________ typically have an autosomal recessive mode of inheritance
enzymes
X-Linked Recessive Traits Trait can NEVER be transmitted directly from __________ to _____
father, son
Y-Linked Traits Affected males get it from their ____________ and give it to their ______
fathers, sons
What are two reasons for incomplete penetrance and variable expressivity? 1) ________ interactions 2) ____________________ effects
gene, environmental
X-linked recessive inheritance poses a special problem for males -Males have only a single copy of most X-linked genes (XY) --They are termed _______________ -Therefore, a female heterozygous for an X-linked recessive gene will pass this trait to ______ her sons
hemizygous, half
X-Linked Dominant Traits Affected ___________________ females transmit the trait to approximately half of their children of either sex
heterozygous
Autosomal Dominant Traits The ___________________ for the disease-causing allele is generally more severely affected than the heterozygote
homozygote
X-Linked Dominant Traits Affected _____________________ females transmit the trait to all their children
homozygous
Autosomal Dominant Traits Trait [is/is not] usually present in every generation
is
A ______________ can be used to identify changes in chromosome number and structure associated with a disease condition
karyotype
Chromosomal abnormalities related to genetic diseases can be detected by producing a ____________________
karyotype
A situation where a disease may be caused by mutations in two or more different genes is called ____________ ____________________
locus heterogeneity
X-Linked Recessive Traits Most affected individuals are _________
male
Y-Linked Traits Trait only affects __________
males
X-Linked Dominant Traits Affected males must come from affected ______________
mothers
X-Linked Dominant Traits Affected females come from affected....
mothers or fathers
Autosomal Dominant Traits Sufferers must inherit only _____ allele to have the disorder
one
When a human disease is caused by a mutation in a single gene, scientists follow the pattern of inheritance by analyzing charts called human ______________
pedigrees
Chances are, if it's an enzymatic disorder, it's an autosomal _________________ disorder
recessive
Autosomal Dominant Traits Healthy = ________________ Disorder = ___________________
recessive, dominant
Autosomal Recessive Traits Trait tends to ______ generations
skip
X-Linked Recessive Traits Trait may _______ generations
skip
X-Linked Recessive Traits Affected females WILL have affected _______
sons
Autosomal Recessive Traits Sufferers must inherit _____ alleles in order to have this disorder For example: the offspring must inherit an "r" from the mom and an "r" from the dad in order for offspring to have to autosomal recessive disorder
two
Autosomal Dominant Traits Unaffected parents produce [affected/unaffected] offspring Example: dad is "hh" and mom is "hh", offspring will be "hh" --> unaffected, healthy
unaffected
Autosomal Dominant Traits On average, half the children of an affected parent [will/will not] be affected
will
Hemophilia is an ________________ _____________ disorder
x-linked recessive