Genetic Foundations of Development
Basic Concepts
Phenotype
- observable characteristics of an individual
Genotype
- genetic makeup of the individual
Chromosomes
- threadlike structures in the cell nucleus that store and
transmit genetic information
Deoxyribonucleic acid (DNA)
- long, double-stranded molecules that make up the chromosomes
Gene
- a segment of a DNA molecule that contains genetic instructions
Mitosis
- process of cell duplication, in which each new cell receives
an exact copy of the original chromosomes
Gametes
- human sperm and ova, which contain half as many chromosomes as
a regular boy cell
Meiosis
- process of cell division through which gametes are formed and
in which the number of chromosomes in each cell is halved
Crossing over
- exchange of genes between chromosomes next to each other
during meiosis
Zygote
- new cell created by union of sperm and ovum at conception
Identical, or monozygotic, twins (MZT)
- twins that result when a zygote, during the early stages of
cell duplication, divides in two. They have the same genetic
makeup
Fraternal, or dizygotic, twins (DZT)
- twins resulting from the release and fertilization of two ova.
They are genetically no more alike than ordinary siblings
Homologous
- pairs of (look alike) chromosomes that a re similar in size,
banding patterns, and genetic makeup
Autosomes
- 22 matching chromosome pairs in each human cell
Sex chromosomes
- 23rd pair of chromosomes, which determines the sex of the
child. In females called XX; in males, called XY
Allele
- each of two, or more, forms of a gene located at the same
place on the autosome
Homozygous
- having two identical alleles at the same place on a pair of
chromosomes
Heterozygous
- having two different alleles at the same place on a pair of
chromosomes
Dominant-recessive inheritance
- pattern of inheritance in which, under heterozygous
conditions, the influence of only one allele is apparent
Carrier
- a heterozygous individual who can pass a recessive gene to his
or her offspring
Polygenic inheritance
- pattern of inheritance involving many genes
