Terms Flashcards
(67 cards)
Genetic Drift
Isolated population will change with time, due to pressures and random events
Gene Flow
Intermixing of populations, from small numbers or large migrations adds new alleles, brings in mutations
Founder Effect
very few founders, may mean gene frequencies do not reflect larger popluation
Segregation
Two copies of each gene are in the parent but the offspring will receive one. There is an equal probability to inherit either one of those copies
Independent Assortment
Each gene is inherited independently of the other genes. Genes affecting the same function are not not inherited as a group.
The exception occurs in cross-linking
Multiplication rule
Probablility of multiple events occurring together. Multiply the risks of each event to get overall risk
Addition rule
Probability of either one or another of multiple events occurring. Add risks of each to get overall risk. All add up to one.
Example, Probability of having three kids and of those three having at least on boy and one girl. 1/8 all girls and 1/8 having all boys = 3/4 chance of that not occurring.
Autosomal Dominant
Single copy of the gene can cause the phenotype.
Usually half of children will be affected (50% recurrence risk). Father-Son transmission rules out x-linked.
No-skipped generations (a positive phenotype has to be present to pass down trait)
Autosomal Recessive
Disorders are rare individually generally as two parents have to be carriers (Aa x Aa). Recurrence risk is 25% with two carrier parents.
Possible to skip a generation. Males and females are equally as likely which rules out sex-linked pattern
New Mutation
Occurs when the inheritance pattern shows no other affected individuals when they would be likely as in autosomal dominant or x-linked
Parentage of child is confirmed
and Neither parent has evidence of carrying the mutation.
Germline Mosiacism
Mutations occur in one of many cells that produce many or few germ cells. As a result Autosomal dominants or X-linked disorders appear in very unlikely pedigress or odd proportions.
Reduced Penetrance
Phenotype mild to non-existing in some individuals due to modifying genes. May affect children more severely.
Age-dependent Penetrance
Combination of delayed age of onset and reduced
Variable expression
Severity of disorder depends on expression. One child may have 3 out of the 5 different anomalies associated while another child may have all five.
Pleiotrophy
Multiple effects from one mutation. The single mutated gene can affect multiple tissues.
DNA transcription factors and extracellular matrix proteins.
Alellic heterogeneity
Multiple mutant forms causing different effects of the same gene. Example is the gene that codes for hemoglobin. Mutation causes hemoglobin disorders, sickle cell and B-thalassemias.
Locus Heterogeneity
Multiple genes affect one pathway and a similar disorder can be produce but different genes may be affects. Urea cycle defects all cause mental retardation
Anticipation
Some disorders are more severe in later generations (such as myotonic dystrophy) or they may occur earlier (E.g Huntington’s disease).
Repeat expansions
Short sequence of direct repeats in gene. Some are repeated codons (E.g. CAGs in Huntington’s disease).
In Meiosis repeats get longer
Proband
A particular subject being studied or reported on. Denoted with an arrow on a pedigree.
Consanguinity
Marrying and having children with a blood relative (someone of the same kinship).
Coefficient of Relationship
The porbability of sharing a common gene from an ancestor.
X-linked Recessive
Passed through the female line, appear mostly as affected males if they do not reproduce. Affected females will have all affected boys.
No father-son transmission. Passage through females can give “skipped generations”
X-Linked Dominant
More females will be affected. In all generations. No father son transmission. All Daughters of affected males are affected.
