Chapter 15
The Chromosomal
Basis of
Inheritance
Timeline
Sutton
Morgan
Fruit Fly
Reasons
Genetic Symbols
Examples
Recessive
mutation:
w = white eyes
w+ = red eyes
Dominant Mutation
Cy
= Curly wings
Cy+ = Normal wings
Morgan Observed:
Morgan crossed
The F1 offspring:
All
had red eyes.
This suggests that white eyes
is a genetic _________?
F1 X F1 = F2
Morgan discovered:
Fruit Fly Chromosomes
Morgan Discovered
Linked Genes
Body Color
and Wing type
Example
b+b vg+vg X bb vgvg
(b+ linked to vg+)
(b linked to vg)
If unlinked: 1:1:1:1 ratio.
If linked: ratio will be altered.
Crossing-Over
If Genes are Linked:
Linkage Strength
Genetic Maps
Comment
- only good for genes
that are within 50 map units of
each other. Why?
Genetic Maps
Sex Linkage in Biology
Chromosomal Basis of
Sex in Humans
Human Chromosome
Sex
SRY
Sex Linkage
Males
X-linked Disorders
Samples of X-linked
patterns:
X-linked Patterns
Comment
Watch
how questions with
sex linkage are phrased:
Chance of children?
Chance of males?
Can Females be
color-blind?
Y-linkage
Sex Limited Traits
Sex Influenced Traits
Baldness
Barr Body
Lyon Hypothesis
Examples
Calico Cats
XB
= black fur
XO = orange fur
Calico is heterozygous, XB XO.
Question?
Why
don’t you find many
calico males?
Chromosomal
Alterations
Number Alterations
Aneuploidy
Comment
Types of Aneuoploidy
Turner Syndrome
Characteristics
Other Sex
Chromosome changes
Kleinfelter Syndrome
George Washington
May
have been a Kleinfelter
Syndrome individual.
Much taller than average.
Produced no children.
Meta female
Super male
Trisomy events
Question?
Why
is trisomy more
common than monosomy?
Question?
Why
is trisomy 21 more
common in older mothers?
Polyploid
Question?
In
plants, even # polyploids
are often fertile, why odd #
polyploids are sterile. Why?
Structure Alterations
Result
Translocations
Cri Du Chat Syndrome
Philadelphia
Chromosome
Parental Imprinting
of Genes
Example:
Cause:
Result
Why have parental
imprinting?
Method
to detect that TWO
different sets of
chromosomes are in the
zygote.
Experiment
Can
fuse nuclei into mouse eggs.
If male/male = normal placenta,
abnormal fetus
If female/female = abnormal
placenta, normal fetus
If male/female = normal placenta
and normal fetus
Extranuclear
Inheritance
Result
Mitochondria
Chloroplasts
Variegated Examples
Variegation in
African Violets
Comment
Cells
can have a mixture of
normal and abnormal
organelles.
Result - degree of expression
of the maternal inherited trait
can vary widely.
Summary
Know
about linkage and
crossing-over.
Sex chromosomes and their
pattern of inheritance.
Variations of chromosomes
and inheritance patterns.
Summary
Be
able to work genetics
problems for this chapter.