ch 2 Flashcards
acrocentric
the terminal location of the centromere (mid region of a chromosome that connects sister chromatids) on chromosomes 13, 14, 15, 21 and 22.
allelic hetergeneity
the situation where multiple alleles at a single locus (the location of a gene on a chromosome) can produce one or more disease phenotypes.
amorphic
pathologic variants that cause a complete loss of function for the gene and yield the same phenotype as a complete gene deletion.
aneuploidy
general term used to denote any unbalanced chromosome complement (when a chromosome rearrangement results in an incorrect amount of genetic material)
antimorphic
pathologic variants that, when present in heterozygous form a non-mutant allele, will result in a phenotype similar to homozygosity for loss of function alleles .
ascertainment bais
the situation in which individuals or families in a genetic study are not representative of the general population because of the the way they are identified.
autosomal
located on chromosome 1-22 rather than x or y.
CpG island
segment of dna that contains a higher density of 5’-cg-3’ dinucleotides ( cytosine and guanine) frequently unmethylated and located close to ubiquitously (constantly encountered) expressed genes
dictyotene
the end of the prophase during femal meiosis I in which fetal oocytes are aressted prior to ovulation
dominant
opposite of recessive alleles …..
dominant negative
mutated allele that overpowers normal allele
dosage compensation
Mechanism by which a difference in gene dosage between two cells is equalized. For XX cells in mammals, decreased expression from one of the two X chromosomes results in a concentration of gene product similar to an XY cell.
End-product deficiency
A pathologic mechanism in which absence or reduction in the product of a particular enzymatic reaction leads to disease.
Epigenetic
Refers to a phenotypic effect that is heritable, through somatic cell division and/or across organismal generations, but that does not depend on variation in DNA sequence. Instead, epigenetic inheritance is associated with alterations in chromatin structure such as DNA methylation or histone modification that can be transmitted during cell division.
Expressivity
The extent to which a variant genotype affects phenotype, including the tissues that are affected, and the severity of those effects.
Fitness
The effect of a variant allele on an individual’s ability to produce offspring.
Founder effect
One of several possible explanations for an unexpectedly high frequency of a deleterious gene in a population. If the population was founded by a small ancestral group, it may have, by chance, contained a large number of carriers for the deleterious gene.
Gamete
The egg or sperm cell that represents a potential reproductive contribution to the next generation. Gametes have undergone
meiosis and so contain half the normal number of chromosomes found in zygotic cells.
Gene dosage
The principle that the amount of product expressed for a particular gene is proportionate to the number of gene copies present per cell.
Genetic
anticipation
A clinical phenomenon in which the phenotype observed in individuals carrying a deleterious gene appears more severe in successive generations. Possible explanations include ascertainment bias or a multistep mutational mechanism such as expansion of triplet repeats.
Haplotype
A set of closely linked DNA sequence variants on a single chromosome.
Hemizygous
A term referring to the presence of only one allele at a locus, either because the other allele is deleted or because it is normally not present; eg, X-linked genes in males.
Heterochromatin
One of two alternative forms of chromosomal material (the other is euchromatin) in which chromosomal DNA is highly condensed and, usually, devoid of genes that are actively transcribed.
Heteroplasmy
The mixture of abnormal and normal mitochondrial DNA molecules in a single cell
