Mendelian Inheritance Flashcards
gamete?
how many chromosomes?
sex cells (ova and sperm cells). one copy of each chromosome, 1-22 plus x or y. (23)
somatic cell?
how many chromosomes?
any cell which is not a gamete.
2 copies of chromosomes 1-22, plus xx or xy. (46)
autosome?
any chromosome not considered a sex chromosome (1-22)
Allosome
Sex chromosome
Gonosome
Sex chromosome
Haploid
ex?
Having one copy of each chromosome.
gamete.
Diploid
ex?
Having two copies of each chromosome.
somatic cell, secondary spermatocyte/oocyte.
gene
a sequence of DNA that encodes a specific protein or RNA
Allele
one of several alternative forms of a gene sequence at a locus
An autosomal gene has how many alleles?
2; maternal and paternal
Polymorphism
When a locus has multiple alleles present in a population (with at least 1% incidence)
Locus
A specific location on a chromosome
Wild-type
The allele that is present in the majority of the population. (Not deleterious)
Mutant
The allele that differs from wild-type due to mutation
Genotype
Set of alleles an individual possesses.
Phenotype
expression of the alleles (clinical manifestations)
Homozygous
two alleles at a particular locus are identical
Heterozygous
two alleles at a particular locus are different
Hemizygous
refers to X-linked genes in males, who only have one x-chromosome
pleiotropism
a single mutant gene may result in many phenotypic variants
recurrance risk
probability that an offspring will express a genetic disease
pedigree analysis
information obtained from a family tree tracing a certain trait
Dominant allele
Allele that is always expressed, even if another allele is present
Incompletely dominant
ex?
expression of two different alleles results in intermediate phenotype
(red flower plus white flower equals pink flower)
Codominant
ex?
each allele results in observable phenotype
blood type: AA, BB, AB all different phenotypes
Recessive
requires presence of 2 identical alleles to express phenotype
Loss-of-function
reduced production of a gene product or inactive protein
Gain of function
gene product gains new function (most often toxic properties)
Autosomal dominant
most often affects enzymes, receptors, feedback inhibitors and structural proteins
typical mating pattern of autosomal recessive
heterozygous affected with homozygous nml
skipped generations are unlikely
Dominant negative
mutant allele negatively affects nml allele
Haploinsufficiency
Nml physiology requires more than half of the fully functional gene product
Penetrance
frequency in which the allele expresses itself phenotypically
Incomplete penetrance
the allele is NOT expressed phenotypically
Autosomal recessive (mating patterns)
parents not usually affected, can skip a generation
Autosomal recessive (penetrance, mutation source)
Usually completely penetrant, not usually a new mutation, onset usually early in life
X-linked dominant
cannot be passed father to son; heterozygotic females affected
Dosage compensation
x-linked recc hetero females usually don’t express full phenotypic change (affected and nml alleles randomly shut off in somatic cells, leading to variable expression)
In X-linked recessive, males….
Will all be affected
Cosanguinuity
Mating between related individuals; more likely to result in recessive disorderes being expressed
Y-linked disorders
Generally affect fertility, so not considered a means of inheritance
X-inactivation
inactivates 1 copy of X-chromosome in all somatic cells in females
when/how does x-inactivation occur?
During blostocyst formation, gene regions are methylated and condensed into heterochromatin. (Random: 50/50 maternal/paternal)
Barr Body
highly condensed chromosome visible in nuclei of cells in interphase
Genetic Mosaicism
condition in which cells with different genotypes or chromosome constitutions are present in the same individual (stems from inactivations). Once fixed, all decendents will have same deletion
Incomplete x-inactivation
some regions not inactivated; manifesting heterozygotes; some females will express x-linked recessive mutation due to x-inactivation
locus heterogeneity
single disorder caused by mutations at different chromosome loci
consequences of enzyme defects
accumulation of substrate, decreased end product, failure to inactivate a damaging substrate
Expressivity
severity of expression of the phenotype among individuals with genotype
variable expression
variability in degree of phenotypc expression
allelic heterogeneity
different mutations can be responsible for more or less severe expression (usually not within a family)
pleiotropy
a single disease-causing mutation affects multiple organ systems
proband
first studied in a pedigree
