21 terms

Brain Functions - 3

value of study of twins
help separate the contributions of heredity and environment
identical twins
called monozygotic twins; two individuals who share all the same genes/heredity because they develop from the same zygote
fraternal twins
also called dizygotic twins; siblings that share about half of the same genes because they develop from two different zygotes
the proportion of variation among individuals that is due to genetic causes
each DNA segment of a chromosome that determines a trait
structure in the nucleus of cells that contains genes determined by DNA sequences (human cells contain 23 pairs-23 from sperm of father, 23 from egg of mother at fertilization if F contributes a Y sex chromosome baby is male, otherwise female
Turner's syndrome
females with only one X sex chromosome
Kleinfelter's syndrome
males with XXY sex chromosomes
Down syndrome
usually with three copies of chromosome 21 in their cells -chars. incl. rount head, flat nasal bridge, protruding tongue, small round earls, fold in eyelid, poor muscle tone & coordination
genetic make-up of an individual
the expression of the genes
the condition when both genes for a trait are the same
also called hybrid; the condition when the genes for a trait are different
dominant gene
gene expressed when the genes for a trait are different
recessive gene
the gene that is hidden or not expressed when the genes for a trait are different
Tay-Sachs syndrome
recessive trait that produces progressive loss of nervous function and death in a baby
recessive trait that produces a lack of pigment and involves quivering eyes and inability to perceive depth with both eyes
Phenylketonuria (PKU)
recessive trait that results in severe, irreversible brain damage unless baby is fed a special diet low in phenylalanine
Huntington's disease
dominant gene defect that involves degeneration of the nervous system, characterized by tremors, jerky motions, blindness, and death
Sex-linked traits
recessive genes located on the X chromosome with no corresponding gene on the Y chromosome, which result in expression of recessive trait; more frequently in males
color blindness
sex-linked trait with which indivdiual cannot see certain colors, most often red and green