Medical Science, Chapter 16: Human Genetics and the Human Genome

human genetics (p. 347)

the science of inherited variation in humans

human genome (p. 348)

represents the totality of genetic information in human cells

DNA sequencing

researches identify the order of nucleotides in DNA to understand the genetic basis of human similarities and differences

karyotype

an individual’s chromosome composition

pedigree (p. 349)

the transmission of genetic traits within a family over several generations

genome-wide association (GWA) scans (p. 351)

compare the genomes of individuals with a particular disease to healthy individuals without that disease

polyploidy

the presence of multiple sets of chromosomes, common in plants but rare in animals

aneuploidies (p. 352)

abnormalities caused by the presence of a single extra chromosome or absence of a chromosome

disomy

normal state: two of each kind of chromosome in a cell or individual

trisomy

a cell or individual has two copies of each chromosome except for one, which has three copies

monosomy

an individual lacks one member of a pair of chromosomes

nondisjunction

abnormal meiotic division in which chromosomes fail to separate at anaphase

trisomy 21 (p.353)

autosomal trisomy in people with Down syndrome

dosage compensation (p. 354)

mammalian cells compensate for extra X chromosome by rendering all but one X chromosome inactive

Barr body

a region of darkly stained, condensed chromatin next to the nuclear envelope of an interphase nucleus

Klinefelter’s syndrome

Males with an extra X chromosome (XXY); female characteristics, mental/intellectual difficulties, infertile

Turner’s syndrome

“Some” individuals with a single X chromosome (X); female appearance, but some do not mature sexually and can remain infertile, may have mental/intellectual difficulties

inversion (p. 355)

orientation of a chromosome segment is reversed

deletion

breakage causes loss of part of a chromosome, along with the genes on that segment

translocation

a chromosome fragment breaks off and attaches to a nonhomologous chromosome

reciprocal translocation

two nonhomologous chromosomes exchange segments

fragile site (p. 356)

place where part of a chromatid appears to be attached to the rest of the chromosome by a thin thread of DNA

genomic or parental imprinting

the expression of a gene in a given tissue or developmental stage is based on its parental origin - whether it’s inherited from the male or female

epigenetic inheritance

changes in a how a gene is expressed without any change to the coding of the DNA bases

inborn error of metabolism (p. 358)

metabolic disorder caused by the mutation of a gene that codes for an enzyme needed in a biochemical pathway

Phenylketonuria

 a genetic disorder where the body can’t metabolize the amino acid phenylalanine.  The accumulation of excess phenylalanine causes brain damage.

Tay-Sachs Disease (p. 360)

Absence of an enzyme causes a normal membrane lipid in brain cells to fail to break down properly, resulting in accumulation in lysosomes, which swell and cause nerve cells to malfunction

Huntington’s disease

Caused by a rare autosomal dominant allele that affects the central nervous system

Hemophilia A (p. 361)

Caused by an absence of a blood-clotting protein factor VIII; the mode of inheritance is X-linked recessive

gene therapy

aids to compensate for a defective, mutant allele by adding a normal, therapeutic allele (and its expressed protein) to certain cells

amniocentesis (p. 362)

diagnostic technique in which a sample of amniotic fluid surrounding the fetus is obtained

chorionic villus sampling (p. 363)

involves removing and studying cells that will form the fetal contribution to the placenta

preimplantation genetic diagnosis

a relatively new embryo-screening process

in vitro fertilization

gametes are collected, eggs are fertilized in a dish, and the resulting embryo is then implanted in the uterus for development

genetic screening (p. 364)

systematic search through a population for individuals with a genotype or karyotype that might cause a serious genetic disease in themselves or in their offspring

consanguineous matings (p. 365)

matings between genetically related individuals

genetic discrimination

discrimination against an individual or family members due to differences from the “normal” genome in that individual