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24.1 Viewing the Chromosomes
The human karyotype contains 22 pairs of autosomes and one pair of sex chromosomes for a total of 46 chromosomes.

Amniocentesis and chorionic villi sampling provide fetal cells for karyotyping purposes.
1. What are autosomes and sex chromosomes and what are the genotypes of human males and females?

2. What is a syndrome?
Essential Study Partner
Sex Chromosomes
24.2 Changes in Chromosome Number
Inheritance of an abnormal chromosome number is most likely due to nondisjunction.

Down syndrome is due to the inheritance of three copies of chromosome 21.

Several syndromes are the result of inheriting an incorrect number of sex chromosomes.
3. What is the most common cause of an abnormal number of chromosomes?

4. What is a Barr body?
Essential Study Partner
Abnormal Chromosomes

Art Quiz
Nondisjunction and Sex Chromosomes

Exploring Meiosis: Down Syndrome
24.3 Changes in Chromosome Structure
Chromosome mutations include deletions, duplications, translocations, and inversions.

Chromosome mutations are associated with various syndromes.
5. What possible causes are associated with changes in chromosome structure?

6. Why do chromosomal inversions cause problems when the same genetic material is still present?
Essential Study Partner
Abnormal Chromosomes
24.4 Sex-Linked Traits
Certain traits, unrelated to the gender of the individual, are controlled by genes located on the sex chromosomes.

Males who inherit an allele for an X-linked recessive disorder exhibit the disorder because they inherit only one X chromosome.
7. Why are sex-linked disorders, such as red-green colorblindness, much more common in males than in females?
Art Quiz
Barr Bodies
24.5 Linked Genes
Alleles that occur on the same chromosome form a linkage group and tend to be inherited together.
8. How is it possible to easily determine whether two genes are linked on the same chromosome or whether they occur on different chromosomes?

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