Please do the following activities on the student media (Chapter 15):
- MP3 tutor: Chromosomal Basis of Inheritance
- Activity: Polyploid Plants (relate to speciation (sympatric)!!)
CONCEPT 4: APPLYING THE
CHROMOSOMAL BASIS OF INHERITANCE
TO ANALYSIS THE EFFECTS OF
ALTERATIONS IN CHROMOSOME NUMBER
OR STRUCTURE.
Campbell: Chapter 15
Holtzclaw: pg 111
But First…
Linked Genes from last class…
A blue fly with silver spots is mated with a wild type fly (grey, no spots)
and all of the F1 generation are phenotypically wild (grey, no spots).
The F1 fly is mated with a blue fly with silver spots (test cross) with the
following results for the testcross offspring:
1025 wild type
1002 blue with silver spots
352
grey with silver spots
366
blue with no spots
Are the genes for blue and silver spots linked? How do you know? If
so, what is the recombination frequency for the genes for blue and
silver spots?
But First…
Linked Genes from last class…
1025 wild type
PARENTAL TYPE
1002 blue with silver spots PARENTAL TYPE
352
grey with silver spots RECOMBINANT
366
blue with no spots RECOMBINANT
Are the genes for blue and silver spots linked? YES
How do you know? BECAUSE IF IT WAS TRUE INDEPENDENT
ASSORTMENT, THE TEST CROSS OF A DOUBLE HETEROZYGOTE AND
THE DOUBLE HOMOZYGOUS RECESSIVE WOULD HAVE PRODUCED A
1:1:1:1 RATIO
However, the genes are not completely linked… in other words, since
some recombinants exist… the chromosomes must have recombined via
crossing over…
Video Clip
But First…
Linked Genes from last class…
1025 wild type
PARENTAL TYPE
1002 blue with silver spots PARENTAL TYPE
352
grey with silver spots RECOMBINANT
366
blue with no spots RECOMBINANT
If so, what is the recombination frequency for the genes for blue and
silver spots?
Recombination frequency = #recombinants/total # of offspring
= (365+366)/(1025+1002+352+366)
= (731)/(2738)
= 0.266
This means that the genes recombine via crossing over 26.6% of the
time!
Try This!

Genes A, B, and C are located on the same
chromosome. Testcrosses show that the
recombination frequency between A and B is 28%
and between A and C is 12%. A’s in the middle!
Can you determine the linear order of these genes
are their relative distance from each other in map
units?
Try This!

Genes A, B, and C are located on the same
chromosome. Testcrosses show that the
recombination frequency between A and B is 28%
and between A and C is 12%. Can you determine
the linear order of these genes are their relative
distance from each other in map units?
28mu
12mu
40 mu
B
A
C
Learning Intentions
Goal: to analyze mechanisms of chromosomal
inheritance

You must know:
 How
the chromosome theory of inheritance connects the
physical movement of chromosomes in meiosis to
Mendel’s laws of inheritance
 How alteration of chromosome number or structurally
altered chromosomes can cause genetic disorders
Alteration of Chromosome Number

How? Nondisjuction


Occurs when homologous chromosomes do not separate
properly during meiosis II.
Result? Aneuploidy

Incorrect number of a chromosome
Trisomic: three copies of the chromosome
 Monosomic: one copy of the chromosome


OR: Result? Polyploidy

More than two complete sets of chromosomes
What happens next?
What would the haploid gametes look like?
Down’s Syndrome: aneuploidy

Is this
individual
trisomic or
monosomic?
Tetraploid Mammal! Polyploidy
Rearrangement of Chromosome Structure

Portions of a chromosomes may be lost or
rearranged during crossing over
 Deletion
 Fragment
is lost. Missing genes.
 Duplication
 Extra
fragment. Extra genes.
 Inversion
 Backwards
section! May affect genes.
 Translocation
 Moving
a piece to a nonhomologous chromosome
Translocation
Chromosaomal Deletion

Example: Cris du Chat
 Deletion
in chromosome 5 in humans
 Small head, unusual facial features, has a cry that
sounds like mewing of a distressed cat
 Death in infancy or early childhood
 Affects 1 in 20,000 or 50,000 of live births
Try This!
A spermatocyte produces the following four sperm cells:
n+1
n+1
n–1
n–1
1)
These cells are the result of which process?
2)
When would this happen?
Try This!
A spermatocyte produces the following four sperm cells:
n+1
1)
n+1
n–1
These cells are the result of which process?
NONDISJUNCTION
2)
n–1
When would this happen?
DURING MEIOSIS I
Learning Intentions
Goal: to analyze mechanisms of
chromosomal inheritance

You must know:


How the chromosome theory of
inheritance connects the physical
movement of chromosomes in meiosis to
Mendel’s laws of inheritance
How alteration of chromosome number
or structurally altered chromosomes can
cause genetic disorders
Try Worksheet!
 You should be able to answer all questions
on pg 112-114 in Holtzclaw
