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25 terms

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