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22 Cards in this Set

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Types of single gene (mendelian)
Autosomal dominant
Autosomal recessive
X-Linked dominant
X-link recessive
Locus
Specific location of a gene on a chromosome. (ex. 15q21.1) P = petite side, Q = larger side.
Alleles
Alternative forms of a gene at a given locus.
Compound Heterozygous
2 different abnormal alleles at one locus in one individual.
Geneotype and phenotype
Genotype = genetic makeup
Phenotype = observed characteristics
Characteristics of autosomal dominant inheritance
1) Only one copy of mutant allele is necessary for expression of trait.
2) Heterozygote has a 50% chance to pass on mutant allele.
3) Homozygous offspring are at no risk
Characteristics of autosomal dominant pedigree
1) Transmission is from generation to generation.
2) boys and girls equally affected
3) Male to male transmission is possible
4) Unaffected individuals (usually) have unaffected children
Penetrance
% of individuals with the mutation who have signs of the disease. Can be complete of incomplete
Obligate Heterozygote
Someone who has affected mother and children but no symptoms himself. Probably because of incomplete penetrance.
Pleiotropy
Multiple phenotypic effects in different tissues an organs from a single gene mutation
De novo mutation
Unaffected parents have a child with a dominant disorder.
What causes an increase in risk of autosomal dominant de novo mutations?
Age of father because sperm stem cells replicating throughout life, have increase chance for a mutation.
Germline mosaicism
When a mutation occurs in some of the gonadal tissue but not the somatic tissue. Causes unaffected parents to have affected child. If present, phenotypically normal parents have higher chance of having multiple affected children.
Causes for variable expression
1) Enviromental factors
2) Modifying background genes
3) Genetic Heterogeneity (allelic or locus)
Allelic heterogeneity
Different types of mutations at the same locus can result in variable expression of the genes.
Locus Heterogeneity
When a disease phenotype is caused by a mutation of genes in different loci.
Anticipation
Tendency for a certain disease to show progressivly earlier onset and increasing severity in successive generations. Caused by increase in trineucleotide repeats.
Characteristics of autosomal recessive inheritance
1) Two copies of mutant allele are necessary
2) Heterozygotes are completely normal.
3) 2 carrier parents have a 25% chance of having affected child regardless of gender.
4) Unaffected offspring have 67% chance of being carriers.
5) All offspring of affected individual will be carriers.
Characteristics of autosomal recessive pedigree
1) Disorders rarely present in parents but may be in siblings
2) Number of affected males and females equal
3) Consanguinity is more likely to be present.
Consanguinity
Relationship with relative. More common in people who have rare autosomal recessive disorders.
Clinical characteristics of autosomal recessive disorders
1) Cluster in ethnic groups with geographic or religious isolation.
2) Penetrance is usually complete and there is less phenotypic variability than dominant.
3) Most AR are enzyme abnormalities.
4) Can have genetic heterogeneity
Why are there rarely individuals with 2 dominant mutant alleles?
Usually it is not compatible with life.