1095
29
Heredity
The Vocabulary of Genetics
(pp. 1096–1097)
Gene Pairs (Alleles) (pp. 1096–1097)
Genotype and Phenotype (p. 1097)
Sexual Sources of Genetic Variation
(pp. 1097–1099)
Chromosome Segregation and Independent
Assortment (pp. 1097–1098)
Crossover of Homologues and Gene
Recombination (p. 1098)
Random Fertilization (pp. 1098–1099)
Types of Inheritance
(pp. 1099–1101)
Dominant-Recessive Inheritance
(pp. 1099–1100)
Incomplete Dominance (p. 1100)
Multiple-Allele Inheritance (p. 1100)
Sex-Linked Inheritance (pp. 1100–1101)
Polygene Inheritance (p. 1101)
Environmental Factors in Gene
Expression
(p. 1102)
Nontraditional Inheritance
(pp. 1102–1103)
Beyond DNA: Regulation of Gene
Expression (pp. 1102–1103)
Extranuclear (Mitochondrial)
Inheritance (p. 1103)
Genetic Screening, Counseling,
and Therapy
(pp. 1103–1105)
Carrier Recognition (p. 1103)
Fetal Testing (pp. 1103–1104)
Human Gene Therapy (pp. 1104–1105)
T
he wondrous growth and development of a new individual
is guided
by the gene-bearing chromosomes it receives from its parents in egg and sperm.
As we described in Chapter 3, individual
genes
, or DNA segments, contain the
“recipes” or genetic blueprints for proteins. Many of these proteins are enzymes that dic-
tate the synthesis of virtually all the body’s molecules. Consequently, genes are ultimately
expressed in your hair color, sex, blood type, and so on.
Genes, however, do not act as free agents. As you will see, a gene’s ability to prompt the
development of a specific trait is enhanced or inhibited by interactions with other genes,
as well as by environmental factors.
Te science of genetics, which studies the mechanism of heredity (
genes
5
give birth
to), is relatively young, but our understanding of how human genes act and interact has
advanced considerably since Gregor Mendel first proposed the basic principles of heredity
in the mid-1800s. Mendel studied characteristics that vary in an either-or fashion, which
is easier to understand than the more-or-less fashion in which many human traits vary.
previous page 1129 Human Anatomy and Physiology (9th ed ) 2012 read online next page 1131 Human Anatomy and Physiology (9th ed ) 2012 read online Home Toggle text on/off