-A good example is the gene associated with sickle-cell disease, a blood
disease common among African Americans in which red blood cells take on a
-It probably arose as a mutation but became more prevalent in Africa, Central
-This is the principle of natural selectionthe idea that nature selects, or
allows to survive and reproduce, those members of a species whose genes
permit them to adapt to their environment.
-By contrast, genes that reduce the chances th
Genotypes and Phenotypes
-He called some characteristics (for example, smooth seeds) dominant be- cause
they appeared more often in later generations than their opposite traits, which he
-As an illustration of the principles of Mendelian
-Most descriptions of heredity focus on its role in creating differences among
people. Some individuals inherit blue eyes, others brown eyes; some inherit
blood type O; others blood type A or B.
-Virtually all of us also develop in similar ways a
-Indeed, a child who is severely malnourished from the prenatal period onward
may have the genetic potential to be a basketball center but may end up too
short to make the team.
-Environmental influences combine with genetic influences to
-Notice, then, that evolution is not just about genes.
It is about the interaction between genes and environment.
-A particular genetic makeup may enhance survival in one kind of environment
but prove maladaptive in another.
-Which genes are adv
Cell Division and Mitosis
-In this last step, though, a special cell division process occurs in which each
resulting cell receives only 23 chromosomes.
-The end product is one egg (and three nonfunctional cells that play no role in
reproduction) in a fema
DNA and Genetics
-The raw material analyzed was DNA samples from a few humans of diverse
-The drudgery of this monstrous task was done by supercomputers and robots
the size of small cars working along- side human technicians.
-When a trait like multiple genes influence intelligence, many degrees of it are
possible, depending on how many of the genes associated with the trait
-The trait tends to be distributed in the population according to
-The chromosomes of the 23rd pair are the sex chromosomes.
-A male child has one long chromosome called an X chromosome and a short,
stubby companion with far fewer genes called a Y chromosome. Females have
two X chromosomes.
-The photos on th
-Children with Down syndrome have distinctive eyelid folds, short stubby limbs,
and thick tongues.
-Their levels of intellectual functioning vary widely, but they are typically classified
as having some degree of mental retardation and there