This chapter expands on previous discussions of homolo-

gous chromosomes (19.1).

You’ll gain a better understanding of how meiosis produces

sperm and eggs having new combinations of parent genes

(18.8).

You’ll also learn more about how chromosomes bear genetic

information (19.2), and you’ll see additional examples of how

basic patterns of inheritance operate in humans (19.3).

Key ConCepts

LinKs to earLier ConCepts

Chromosomes and Genes

The two types of chromosomes are

autosomes and sex chromosomes.

All chromosomes carry genes.

Each gene is located at a particular

place on a specific chromosome.

Sections 20.1–20.3

Patterns of Inheritance

Studies of genetic disorders can

reveal how traits in general are

inherited. Some disease traits arise

from dominant or recessive alleles

on an autosome or sex chromo-

some. Sections 20.4–20.6

Changes in Chromosomes

Many genetic disorders arise from

rare changes in the number or

structure of chromosomes. Such

changes can cause harmful or lethal

effects. Sections 20.8–20.9

Cystic fibrosis, or CF, develops when a person

inherits a faulty gene on chromosome 7. The flawed gene doesn’t

provide proper instructions for building the protein that normally

helps chloride and water move into and out of exocrine cells, which

secrete mucus or sweat. In CF, dry, thickened mucus clogs the

airways. Not only is breathing difficult, but the mucus increases

the likelihood of devastating lung infections. CF is most common

in people of European ancestry, including the six young people

pictured here. In most cases of CF the lungs eventually fail. Having

a lung transplant helps some patients, but every day in the United

States at least one person dies of CF, most under age 30.

This chapter discusses the connections between chromosomes,

the genes they carry, and inheritance—including the causes of some

common inherited disorders.

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Top: Science Source; Middle: © Cengage Learning; Bottom:

Lauren Shear/Science Source

Chromosomes and

human GenetiCs

20

From top left: The Cody Dieruf Benefit; Bobby Brooks; Steve Widener; Cynthia Hill; Sheila Fuwell; Randy Herriott

Cody, 23 Jeff, 21

Lindsay, 22 Ben, 23

Savannah, 19 Brandon, 18

Copyright 2016 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s).