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• 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

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