2. I. Human Chromosomes, Genes, and
Human Inheritance
A. Human genome
1. All the DNA of the human species
3. I. Human Chromosomes, Genes, and
Human Inheritance
2. The DNA is divided into thousands of genes on
23 pairs of chromosomes
4. I. Human Chromosomes, Genes, and
Human Inheritance
a. Autosomes are chromosomes that contain genes for
characteristics that are unrelated to sex 22 pairs
b. Sex chromosomes are
the remaining pair of
human chromosomes
consists of the, X and Y
5. I. Human Chromosomes, Genes, and
Human Inheritance
c. Humans have an estimated 20,000 to 22,000 genes
6. I. Human Chromosomes, Genes, and
Human Inheritance
B. Linkage
1. Genes that are located on the
same chromosome
2. Alleles for these genes tend to
segregate together during
meiosis, unless they are
separated by crossing-over
7. I. Human Chromosomes, Genes, and
Human Inheritance
C. Genetic traits
1. Characteristics that are encoded in DNA
2. Autosomal traits are controlled by genes on one
of the 22 human autosomes
3. sex-linked traits are controlled by genes on the
sex chromosomes
8. I. Human Chromosomes, Genes, and
Human Inheritance
D. multiple allele traits are controlled by a
single gene with more than two alleles
9. I. Human Chromosomes, Genes, and
Human Inheritance
E. Polygenic traits are when human traits are
controlled by more than one gene
10. I. Human Chromosomes, Genes, and
Human Inheritance
F. Pleiotropy are when a single gene may affect
more than one trait
11. I. Human Chromosomes, Genes, and
Human Inheritance
G. Epistasis is when one gene affects the
expression of another gene
12. I. Human Chromosomes, Genes, and
Human Inheritance
H. Genetic Disorders
1. Genetic disorders caused by mutations
a. This is mutation is the DNA on a chromosome
b. Few genetic disorders are controlled by dominant
alleles, most are recessive alleles
13. I. Human Chromosomes, Genes, and
Human Inheritance
2. Chromosomal Disorders
a. This is the failure of replicated chromosomes to
separate during meiosis
b. If such gametes are fertilized and form zygotes, they
usually do not survive
c. If they do survive,
the individuals are
likely to have
serious genetic
disorders
14. I. Human Chromosomes, Genes, and
Human Inheritance
I. Treating Genetic Disorders
1. The symptoms of genetic disorders can
sometimes be treated, but cures for genetic
disorders are still in the early stages of
development
2. gene therapy involves inserting normal genes
into cells with mutant genes
