Inheritance Patterns Flashcards
What are the 3 principles of genetics?
Segregation
Dominance
Independent assortment
What is meant by independent assortment?
Every gene has 2 alleles that code for a trait.
In heterozygotes, one allele is dominant meaning it will always show, one is recessive and is masked by the dominant allele
What is meant by segregation?
Allele pairs separate/segregate randomly from each other during meiosis each cell has a single allele for each trait
What is meant by independent assortment?
Traits are transmitted to offspring independently of one another
What is Mendelian inheritance?
Autosomal and sex-linked
Dominant and recessive
What is non-mendelian inheritance?
Imprinting
Mitochondrial inheritance
Multifactorial
(Mosaicism)
What are the categories of genetic disorders?
Chromosome abnormalities
Single gene disorders
Multi-factorial and polygenic disorders e.g. spina bifida, cleft lip and palate
What is a autosome?
Any chromosome, other than the sex chromosomes (X or Y), that occurs in pairs in diploid cells
What is meant by recessive?
Manifest only in homozygotes
What is an allele?
One or more alternative forms of a gene at a given location (locus)
What is meant by homozygous?
Presence of identical alleles at a given locus
Homozygotes are affected
What is meant by heterozygous?
Presence of two different alleles at a given locus
Heterozygotes are unaffected and are usually referred to as carriers
What is meant by allelic heterogeneity?
The situation where different mutations within the same gene result in the same clinical condition e.g. cystic fibrosis. Thus an individual with an autosomal recessive condition may be a compound heterozygote for two different mutations
What are features of autosomal recessive inheritance?
Typical features:
•Male and females affected in equal proportions
•Affected individuals only in a single generation
•Parents can be related, i.e. consanguineous
What is cysticfibrosis?
Chronic condition affecting mainly lungs and gut, variable presentation, can affect other systems
What is meant by consanguinity?
Reproductive union between two relatives
What is meant by autozygosity?
Homozygosity by descent, i.e. inheritance of the same altered allele through two branches of the same family.
What are features of autosomal dominant inheritance?
Typical features:
•Male and females affected in equal proportions
•Affected individuals in multiple generations
•Transmission by individuals of both sexes, to both sexes
•But don’t forget penetrance & variability!
What is meant by peretrance?
The percentage of individuals with a specific genotype showing the expected phenotype
What is meant by expression?
Refers to the range of phenotypes expressed by a specific genotype
What is meant by recurrence rich?
50% for transmission of mutation
•BUT will the person be affected?
•Depends on penetrance and expression
What is meant by anticipation?
Whereby genetic disorder affects successive generations earlier or more severely, usually due to expansion of unstable triplet repeat sequences
Example – Myotonic Dystrophy
What is somatic mosaicism?
Genetic fault present in only some tissues in body.
What is gonadal mosaicism?
Genetic fault present in gonadal tissue.
