Chapter 3: Biological Foundations, Prenatal Development, and Birth Flashcards
phenotype
directly observable characteristics that result from one’s genotype
genotype
the complex blend of genetic information that determines our species and influences all our unique characteristics
chromosomes
rodlike structures which store and transmit genetic information
DNA (deoxyribonucleic acid)
structures that compose chromosomes; a long double-stranded molecule that looks like a twisted ladder. Each rung of the ladder consists of a pair of chemical substances called bases.
gene
a segment of DNA along the length of the chromosome
mitosis
The process of cell duplication, in which each new cell receives an exact copy of the original chromosomes
gametes
Sex cells, or sperm and ova, which contain half as many chromosomes as regular body cells.
meiosis
The process of cell division through which gametes are formed and in which the number of chromosomes in each cell is halved.
zygote
The newly fertilized cell formed by the union of sperm and ovum at conception.
crossing over
During meiosis, the exchange of genes between chromosomes next to each other.
autosomes
The 22 matching chromosome pairs in each human cell.
sex chromosomes
The twenty-third pair of chromosomes, called XX in females and XY in males, which determines the sex of the child.
identical (monozygotic) twins
Twins that result when a zygote, during early cell duplication, separates into two clusters of cells with the same genetic makeup. Distinguished from fraternal, or dizygotic, twins.
fraternal (dizygotic) twins
Twins resulting from the release and fertilization
of two ova. Genetically, they are no more alike than ordinary siblings. Distinguished from identical, or monozygotic, twins.
allele
each of two or more of the same gene located at the same place on the chromosomes
homozygous
Having two identical alleles at the same place on a pair of chromosomes. Distinguished from heterozygous.
heterozygous
Having two different alleles at the same place on a pair of chromosomes. Distinguished from homozygous.
dominant–recessive inheritance
A pattern of inheritance in which, under heterozygous conditions, the influence of only one allele is apparent.
carriers
A heterozygous individual who can pass a recessive trait to his or her offspring.
modifier genes
Genes that enhance or dilute the effects of other genes.
incomplete dominance
A pattern of inheritance in which both alleles are expressed in the phenotype, resulting in a combined trait, or one that is intermediate between the two.
x-linked inheritance
A pattern of inheritance in which a recessive gene is carried on the X chromosome, so that males are more likely than females to be affected.