Chapter 3: Forming a New Life Flashcards
Union of sperm and ovum to produce a zygote; also called conception .
fertilization
One-celled organism resulting from
fertilization.
zygote
Twins conceived by the union of two
diff erent ova (or a single ovum that has
split) with two diff erent sperm cells; also
called fraternal twins ; they are no more
alike genetically than any other siblings.
dizygotic twins
Twins resulting from the division of a single zygote after fertilization; also called identical twins ; they are genetically similar.
monozygotic twins
The genetic transmission of heritable characteristics from parents to offspring
heredity
Sequence of bases within the DNA molecule; governs the formation of proteins that determine the structure and functions of living cells.
genetic code
Chemical that carries inherited instruc-
tions for the development of all cellular
forms of life.
deoxyribonucleic acid (DNA)
Coils of DNA that consist of genes.
chromosomes
Small segments of DNA located in definite positions on particular chromosomes; functional units of heredity.
genes
Complete sequence of genes in the
human body.
human genome
A process by which the non–sex cells divide in half over and over again, the DNA
replicates itself, so that each newly
formed cell has the same DNA structure as all the others.
mitosis
Permanent alterations in genes or
chromosomes that may produce
harmful characteristics.
mutation
In humans, the 22 pairs of chromo-
somes not related to sexual expression.
autosomes
Pair of chromosomes that determines
sex: XX in the normal human female,
XY in the normal human male.
sex chromosomes
Two or more alternative forms of a gene
that occupy the same position on
paired chromosomes and aff ect the
same trait.
alleles
Possessing two identical alleles for a trait.
homozygous
Possessing diff ering alleles for a trait.
heterozygous
Pattern of inheritance in which a child
receives identical recessive alleles,
resulting in expression of a nondominant
trait.
recessive inheritance
Pattern of inheritance in which, when a
child receives diff erent alleles, only the
dominant one is expressed.
dominant inheritance
Pattern of inheritance in which multiple
genes at diff erent sites on chromo-
somes aff ect a complex trait
polygenic inheritance
Observable characteristics of a person.
phenotype
Genetic makeup of a person, containing
both expressed and unexpressed
characteristics.
genotype
Combination of genetic and
environmental factors to produce
certain complex traits.
multifactorial transmission
Mechanism that turns genes on or off
and determines functions of body cells.
epigenesis
Pattern of inheritance in which a child
receives two diff erent alleles, resulting
in partial expression of a trait.
incomplete dominance