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28 terms

Genetics Terms ch1

• Online Mendelian Inheritance in Man
• Database that lists disease genes
McCandless studies
• Reviewed & categorized children admissions
• 71% had strong genetic component, accounting for 81% of hospital's charges & mean length of stay is 4 days longer
• Tightly wound pieces of DNA
• Houses genes
• Passes on copies of chromosomes to daughter cells
• Analysis of chromosome profile
• Metaphase chromosomes
• Giemsa dye
• Stains heterochromatin in G-bands (A-T rich sequences)
• Can use blood, buccal cells, or amniotic fluid (must culture cells)
• Tightly wound DNA
• Houses genes that are not expressed
• Less tightly wound DNA
• Second chromosome of a pair
• Meiosis I = diploid, chromosomes duplicate (sister chromatids), homologs separate
• Meiosis II = sister chromatids split (haploid)
• Error in meiosis resulting in improper distribution of chromosomes into haploid cells (too many or too few)
• Occurs most during maternal meiosis I
recessive allele
• Mutation → loss-of-function (eliminated/reduced normal activity of mutated gene)
• Phenotype (observed trait) only if second copy is also mutated or absence of second copy
dominant allele
• Mutation → gain-of-function
• Phenotype regardless of second gene
law of segregation
two rules:
• Product rule = probability of independent events occurring together is product of individual probabilities (prob will develop)
• Sum rule = two mutually exclusive events is sum of individual probabilities (prob won't develop)
law of independent assortment
• Any two genes will be inherited as independent units
• Holds true, unless linked genes
linked genes
• Genes that are close to each other on a chromosome
• Can only be separated by recombination
incomplete dominance
• Phenotype depends on gene dosage
• Each allele contributes to the phenotype
• Ex. blood type (O is recessive to both A & B)
incomplete penetrance
• Genotypes does not manifest in phenotype 100% of the time
• Can be due to environment or genetic interactions (modifier loci)
modifier loci
• Alternate genes that can affect phenotype associated with a different gene
• Environmental factors that mimic a genetic condition
• Spontaneous mutation in a gene that leads to clinical condition that may be interpreted as inheritance of a familial germ line mutation (but really something different)
• Many systems affected by a single defect (e.g. 1 gene effects multi. tissues/organs)
complex traits
• Joint actions of a large number of genes
• Ex. genes influencing height govern bone growth & usage of nutritional factors
• Association of DNA & proteins that packs it into higher order chromosomal structure
2 types of chromatin modifications
• Histone modification
• DNA methylation
• *epigenetic
• Mitotically-heritable marks to DNA that do not alter the base sequence itself
(non-sequence modifications effecting gene expression)
histone modifications
• Modification to histone tails → rearrangement of chromatin to open or closed conformation
• Acetylation of lysine = open
• Deacetylation = closed
DNA methylation
• Always on cytosine of CpG dinucleotides (overrepresented in promoter regions)
• If gene promoter is hypermethylated, conserved in cell division via maintenance DNA methylases
• Associated w/ closed chromatin (deacetylated histones ) and GENE SILENCING
• Erased during gametogenesis & replaced at key gamete-specific location of genome (imprinting)
• Methylation specific for the parent of origin
• Imprinted genes will only contribute to phenotype if it is designated as active by the transmitting parent