OUTLINE
I. Relating Mendelism to Chromosomes
A Mendelian inheritance has its physical
basis in the behavior of chromosomes during sexual life cycles
B Morgan traced a gene to a specific
chromosome
C Linked genes tend to be inherited
together because they are located on the same chromosome
D. Independent assortment of chromosomes
and crossing over produce genetic recombinants
E. Geneticists can use recombination
data to map a chromosome’s genetic loci
II. Sex Chromosomes
A. The chromosomal basis of sex varies
with the organism
B. Sex-linked genes have unique patterns
of inheritance
III. Errors and Exceptions to Chromosomal Inheritance
A. Alterations of chromosome number
or structure cause some genetic disorders
B. The phenotypic effects of some
genes depend on whether they were inherited from the mother or father
C. Extranuclear genes exhibit a non-Mendelian
pattern of inheritance
OBJECTIVES
After reading this chapter and attending lecture, the
student should be able to:
1. Explain how the observations of cytologists and geneticists
provided the basis for the chromosome theory of inheritance.
2. Describe the contributions that Thomas Hunt Morgan,
Walter Sutton, and A.H. Sturtevant made to current understanding of chromosomat
inheritance.
3. Explain why Drosophila melanogaster is a good
experimental organism.
4. Define linkage and explain why linkage interferes
with independent assortment.
5. Distinguish between parental and recombinant
phenotypes.
6. Explain how crossing over can unlink genes.
7. Map a linear sequence of genes on a chromosome using
given recombination frequencies from experimental crosses.
8. Explain what additional information cytological maps
provide over crossover maps.
9. Distinguish between a heterogametic sex and a homogamettc
sex.
10. Describe sex determination in humans.
11. Describe the inheritance of a sex-linked gene such
as color-blindness.
12. Explain why a recessive sex-linked gene is always
expressed in human males.
13. Explain how an organism compensates for the fact
that some individuals have a double dosage of sex-linked genes while others
have only one.
14. Distinguish among nondisjunction, aneuploidy, and
polyploidy; explain how these major chromosomal changes occur and describe
the consequences.
15. Distinguish between trisomy and triploidy.
16. Distinguish among deletions, duplications, translocations,
and inversions.
17. Describe the effects of alterations in chromosome
structure, and explain the role of position effects in altering the phenotype.
18. Describe the type of chromosomal alterations implicated
in the following human disorders: Down syndrome, Klinefelter syndrome,
extra Y (Jacobs Syndrome), triple-X (Triplo-X) syndrome , Turner
syndrome, cri du chat syndrome, and chronic myelogenous leukemia.
19. Define genomic imprinting and provide evidence to
support this model.
20. Explain how the complex expression of a human genetic
disorder, such as fragile-X syndrome, can be influenced by triplet repeats
and genomic imprinting.
21. Give some exceptions to the chromosome theory of
inheritance, and explain why cytoplasmic genes are not inherited in a Mendelian
fashion.
KEY TERMS
| chromosome theory of inheritance | linkage map | polyploidy |
| wild type | cytological map | deletion |
| mutant phenotype | Duchenne muscular dystrophy | duplication |
| sex-linked genes | hemophilia | Inversion |
| linked genes | Barr body | translocation |
| genetic recombination | nondisjunction | Down syndrome |
| parental type | aneuploidy | fragile X syndrome |
| recombinants | trisomic | monosomic |