MBG 1: Human Mendelian Genetics

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What is a change in the normal base pair sequence of DNA called

Mutation

What are the four possible single gene (Mendelian) disorders

Autosomal dominant
Autosomal recessive
X-linked dominant
X-linked recessive

What is the specific physical location of a gene on a chromosome called

Locus

What are the alternate forms of genes at a given locus called

Alleles

What is it called when a single mutant allele causes disease regardless of the form of the other allele

Dominant Condition

What is it called when two mutant alleles must be present in order for a disease to occur

Recessive Condition

What is it called when the alleles are the same at a given locus

Homozygous

What is it called when the alleles are different are a given locus

Heterozygous

What is it called when there are two different abnormal alleles at one locus in one individual

Compound Heterozygotes

What is the genetic composition of an individual called. It refers to the alleles at a specific locus

Genotype

What are the observed clinical or physiological characteristics of an individual called

Phenotype
*In some genetic disorders, the phenotype is produced by the interaction of a person's genotype and environment (PKU)

What type of inheritance has the following characteristics:
1) Only one copy of a mutant allele is necessary for expression of a trait
2) Offspring have a 50% chance of being affected
3) Homozygous normal offspring are not at risk for disorder

Autosomal Dominant Inheritance

What are the four noticed pedigree characteristics of autosomal dominant inheritance

Transmission is vertical
Male to male transmission is observed
Number of males and females affected is equal
Unaffected individuals have unaffected children

What is it called when different individuals can express the same mutant allele in different ways and with varying degrees of severity. What are two examples

Variable expression: Treacher-Collins syndrome and Neurofibromatosis I

What is the term for the proportion of individuals who have a disease causing mutation and show observable signs or symptoms of the disease

Penetrance
*Complete penetrance: 100% of individuals who have a mutant allele express the disease to some degree (NF1) vs. Incomplete penetrance (post axial polydactyly)
*Penetrance is often age dependent

What is the term for an individual who is heterozygous for a gene mutation but shows no features of the disorder

Non-penetrance

What is the term for when there are multiple phenotypic effects in different tissues and organs produced by a single gene mutation

Pleiotropy

What is it called when an unaffected parent has a child with a dominant disorder. What is an example

De novo (new) mutation
Ex. Achondroplasia
*mutation rates increase with increase parental age

What is the term used when there is a mutation in the gonadal tissue of an unaffected parent of a child with an apparently new mutation. What is an example

Germline (gonadal) mosaicism
Ex. OI II

What is the term for different mutations (alleles) at the same locus resulting in variable expression of a disease

Allelic heterogeneity

What is the term for a particular disease phenotype due to mutations at different loci

Locus heterogeneity

What is the term for the tendency for certain disease to show progressively earlier onset and increasing severity in successive generations. Whats an example

Anticipation
Ex. Myotonic dystrophy

What type of inheritance are these characteristics of
1) Two carrier parents have a 1/4 chance of having a homozygous, affected child with each pregnancy regardless of gender
2) Unaffected offspring have a 2/3 chance of being heterozygous
3) all children of an affected individual will be carriers

Autosomal recessive inheritance

What is the term for relationship by descent from a common ancestor

consanguinity

What type of inheritance has the following characteristics
1) Cluster in ethnic groups with geographic or religious isolation
2) Penetrance is usually complete and there is less phenotypic variability

Autosomal recessive inheritance

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