•
•
•
•
•
•
Chapter 15: Chromosomal Basis of Inheritance
A century ago the relationship between genes and chromosomes was not obvious
Today we can show that genes are located on chromosomes (______________)
The location of a particular gene can
be seen by tagging isolated
chromosomes with a fluorescent dye
that highlights the gene
Several researchers proposed in the
early 1900s that genes are located on
chromosomes
The behavior of chromosomes
during _____________ was said to
account for Mendel’s laws of
___________________ and
_______________________________
The chromosome theory of
inheritance states that:
•
•
Morgan’s Experimental Evidence:
Scientific Inquiry
• The first solid evidence associating a
specific gene with a specific
chromosome came from
_______________________________,
an embryologist
• Morgan’s experiments with fruit
flies provided convincing evidence
that chromosomes are the location of
Mendel’s heritable factors
• Characteristics that make fruit flies a
convenient organism for genetic studies:
• They breed at a high rate
• A generation can be bred every two
weeks
• They have only ________ pairs of
chromosomes
• Morgan noted _________________, or
normal, phenotypes that were common in the fly populations
• Traits alternative to the wild type are called _________________ phenotypes
Correlating Behavior of a Gene’s Alleles with Behavior of a Chromosome Pair
• In one experiment, Morgan mated male flies with white eyes (mutant) with female flies with red
eyes (wild type)
– The F1 generation ___________________________
– The F2 generation showed the _____ red:white eye ratio, but only ______ had white eyes
• Morgan determined that the white-eye mutant allele must be located on the __ chromosome
• Morgan’s finding supported the chromosome theory of inheritance
Try a basic Punnett Square to prove this is an Xlinked trait:







Each chromosome has hundreds or thousands of
genes.
Genes located on the _______________________
that tend to be inherited ______________ are called
______________________________.
Morgan did other experiments with fruit flies to see
how linkage affects inheritance of two characters
Morgan crossed flies that differed in traits of ____________________ and ____________________
From the results, Morgan reasoned that body color
and wing size are usually inherited together in
specific combinations (parental phenotypes)
because the genes are on the
_________________________________
However, ______________________________
were also produced
Understanding this result involves exploring genetic
___________________________, production of
offspring with combinations of traits differing from
either parent
Genetic Recombination and Linkage
 The genetic findings of Mendel and Morgan relate to the chromosomal basis of ___________________
 Mendel observed that combinations of traits in some offspring differ from either parent
 Offspring with a phenotype matching one of the parental phenotypes are called ___________________
 Offspring with nonparental phenotypes (new combinations of traits) are called ____________________
types, or recombinants
 A _______ frequency of recombination is observed for any two
Gametes from yellow-round
genes on different chromosomes
heterozygous parent (YyRr)
 Morgan discovered that genes
can be linked, but the linkage
was ___________________, as
evident from recombinant
phenotypes
Gametes from green Morgan proposed that some
wrinkled homozygous
process must sometimes
recessive parent (yyrr)
_________ the physical
connection between genes
on the same chromosome
 That mechanism was the
_____________________ of
homologous chromosomes