Principles of Biology Lecture Notes
Fall, 2006
CHROMOSOMAL INHERITANCE
The Chromosome Theory of Inheritance - The Chromosomal Basis of Mendel’s Laws
 Genes are located on chromosomes
•Mendelian genes have specific loci on chromosomes
•Chromosomes undergo
•And as they do,
•Today's Lecture:
1st Evidence
Sex-Linked Genes
Linkage, Recombination & Mapping
Morgan’s Experimental Evidence: Scientific Inquiry
•Thomas Hunt Morgan: A. first to observe and note genes and chromosomes move together
B. provided convincing evidence Mendel’s heritable factors are on chromosomes
C. worked with fruit flies – Why?
breed at a high rate
new generation every 2 weeks
only 4 pairs of chromosomes
•NOTE:
–Wild
type
–Mutant
Correlating Behavior of a Gene’s Alleles with Behavior of a Chromosome Pair
•1 of Morgan’s crosses:
(mutant)
X
(wild type)
–F1:
CONCLUSION:
F2:
mutant allele must be located on the
Chromosomal Basis of Sex & Sex-Linked Genes
•An organism’s sex
–
Is
–Sex chromosomes have genes for many characters
•SEX-LINKED GENE =
Systems of Sex Determination
Humans & other mammals:
X & Y = sex chromosomes
D:\116106002.doc
other organisms:
2/12/2016
Inheritance of Sex-Linked Genes
•Sex-linked genes follow specific patterns of inheritance
Linked genes
•Inherited together because
•Each chromosome has
How Linkage Affects Inheritance:
•Morgan crossed flies that differed in traits of two different characters
•Morgan determined that
–linked Genes
–Unlinked genes
Genetic Recombination and Linkage
Inheritance of two characters
– some offspring have combinations of traits
– Linked genes
Linkage Mapping: Using Recombination Data:
•A genetic map
–Is
–Can be developed using
•Linkage Map
Is a
Alterations of Chromosome Structure
•Breakage of a chromosome can lead to four types of changes in chromosome structure
•Certain cancers are caused by translocations of chromosomes
D:\116106002.doc
2/12/2016