table 29.3: selected hereditary traits in humans

normal skin pigmentation

albinism

near or farsightedness

normal vision

PTC taster/ ability to taste phenylthiocarbamide

PTC nontaster

polydactyly (extra digits), brachydactyly (short digits), syndactylism (webbed digits)

normal digits

diabetes insipidus

normal urine excretion

Huntington disease

normal nervous system

widow’s peak

straight hairline

curved (hyperextended) thumb

straight thumb

normal Cl- transport

cystic fibrosis

hypercholesterolemia (familial)

normal cholesterol level

most patterns of inheritance don’t conform to

the simple dominant-recessive inheritance pattern

incomplete dominance

a situation where neither member of the pair of alleles is dominant over the other

example of incomplete dominance is

inheritance of sickle cell anemia

multiple-allele inheritance occurs when genes have

more than two alternative forms

example of multiple-allele inheritance

inheritance of ABO blood group

within multiple-allele inheritance pattern

there is also codominance

in the case of codominance

two genes (type A and type B blood) are expressed equally

polygenic inheritance is seen when a trait is

controlled by the combined effects of two or more genes

complex inheritance is seen when a trait occurs due to the

combined effects of many genes and environmental factors

examples of complex traits

skin color

hair color

eye color

height

metabolic rate

body build

the 46 human chromosomes are identified by

thei size, shape, and staining pattern

karyotype

an entire set of chromosomes arranged in decreasing size order and according to position of centromere

the 23 pairs of human chromosomes include

22 pairs of autosomes and one pair of sex chromosomes (x and y)

males have an x and a y chromosome

females have two x chromosomes (one is automatically inactivated)

whether the sperm that fertilizes an egg carries an x or y chromosome

determines gender of zygote

sex-linked traits are non-sexual traits that

are inherited on the x chromosome

an example of a sex-linked trait

red-green color blindness

disorders

male infertility

female infertility

congenital defects

down syndrome