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Who was Morgan and what did he do??
http://www.columbia.edu/cu/alumni/Magazine/Legacies/Morgan/
Using fly notation cross a female red eyed fly with a male
white eyed fly! (what do you rememeber?)
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Figure 12.4
Experiment
P
Generation
F1
Generation
Conclusion
P
Generation
X
X
w
w
All offspring
had red eyes.
w
Eggs
Results
F2
Generation
X
Y
F1
Generation
w
Sperm
w
w
w
w
Eggs
F2
Generation
w
w
Sperm
w
w
w
w
w
w
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w
EX. Calico cats (One of the genes for hair color is on X
chromosome)
Two alleles (orange or black)
Why are females patchy??
Each patch has a different X turned on (orange or black)
Orange patch=bunch of cells there with the X with the
orange allele turned on.
Black patch=bunch of cells with the black X on.
Why are males not patchy like females?
Single X and so either the orange or the black hair color
gene on in entire body.
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X = orange
X = black
MALES:
• XY = orange
• XY = black
FEMALES:
• XX = orange
• X X = black
• X X = orange or black patches
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Figure 12.8
X chromosomes
Early embryo:
Two cell
populations
in adult cat:
Allele for
black fur
Cell division and
X chromosome
inactivation
Active X
Inactive
X
Active X
Black fur
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Allele for
orange fur
Orange fur
https://smartsite.ucdavis.edu/access/content/user/000029
50/bis10v/media/ch10/x_inactivation.html
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Anhydrotic dysplasia
X = normal sweat glands
XY….would be?
Normal male
X’Y…would be?
No sweat glands male
X-linked
sweat gland problem
X' = absence of sweat glands.
XX…..
Normal female
X'X' do not have sweat glands
XX' …..
Heterozygous females have patches of skin with sweat glands and
patches of skin without sweat glands. So swaths or populations of
cells that have one X turned on and other patches with a different X
on.
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What do you know about colorblindness?
X linked
Given X inactivation …….should heterozygous
females for colorblindness be able to see color?
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What do you know about colorblindness?
Suppose: X = color vision
X’ = color blind
The retina of a heterozygous (XX’) female will
have some cells with the X inactivated and other
cells with the X’ inactivated.
A heterozygous female has some color blind cells in
her retina.
The non-color blind cells enable her to see color.
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Figure 12.10a
P generation (homozygous)
Wild type
(gray body,
normal wings)
Double mutant
(black body,
vestigial wings)
b vg+
b vg
b vg+
b vg
Term!
Wild-type F1 dihybrid
(gray body,
normal wings)
b vg+
b vg
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Figure 12.10b
F1 dihybrid testcross
Wild-type F1
dihybrid
(gray body,
normal wings)
b vg+
b vg
b vg
Gametes??
Meiosis I
b vg
b vg+
b vg
b vg+
b vg
b vg
b vg
b vg
b vg
Homozygous
recessive
(black body,
vestigial wings)
b vg+
How many different kindsMeiosis
of gametes
I and II from male?
b vg
b vg
How many different
gametes from female?
Meiosis
If IIno
Eggs
b+ vg+
Recombinant
chromosomes
recombination?
b vg
b vg
b+ vg
With recombination?
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b vg+
b vg
Sperm
Figure 12.10c
Recombinant
chromosomes
b vg+
b vg
b vg
944
Blackvestigial
206
Grayvestigial
b vg
Eggs
Testcross
offspring
965
Wild type
(gray-normal)
185
Blacknormal
b vg
b vg
b vg
b vg
b vg
b vg
b vg
b vg
Parental-type offspring
Recombinant offspring
Recombination
391 recombinants  100  17%

frequency
2,300 total offspring
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b vg
Sperm
Figure 12.12
Mutant phenotypes
Short
aristae
0
Long aristae
(appendages
on head)
Black
body
Cinnabar
eyes
48.5 57.5
Gray
body
Red
eyes
Vestigial
wings
67.0
Normal
wings
Wild-type phenotypes
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Brown
eyes
104.5
Red
eyes
1. What kind of sex determination did our ancestors have and
when did the y chrosome evolve?
2. What do they mean SRY evolved from a related gene??
3. The chapter talks about SRY, what does it stand for?
4. Why do you think the Y lost its ability to recombine (other
than at the tips)??
5. Why would the Y lose genes? What kinds of genes would it
be unlikely to lose and why?
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6. Chimps have lost some genes as well but there seems to be
many duplicated genes on the chimp Y, what might these
genes be doing?
7. To review…What is the debate about in the article?
8. What are the “dying gasps of the Y chromosome”?
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Sex Determination patterns
Chromosomal determination
Remember…..we have autosomes as well as sex chromosomes
1.XX/XY -humans and drosophila
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2. ZW –birds
reversed compared to the XY system:
females are heterogametic-females have two different kinds of
chromosomes (ZW)
males have two of the same kind of chromosomes (ZZ)
So they are…….
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3. Haplodiploidy-insect such as ants and bees
Unfertilized eggs develop into haploid individuals, which are the
males.
Diploid individuals are generally female
Males cannot have sons or fathers.
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3. Haplodiploidy-insect such as ants and bees
Unfertilized eggs develop into haploid individuals, which are the
males.
Diploid individuals are generally female
Males cannot have sons or fathers.
Many females can decide the sex of their offspring by storing
received sperm and either releasing it for fertilization or not.
This allows them to create more workers (who are male),
depending on the status of the colony
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Environmental Sex Determination
Temperature at which egg is incubated- alligators, turtles, sex
Sometimes one sex hatches out when it is hot and the other when it
is cool. Males are cool in turtles.
For others, the extreme temperatures are one sex and the middle
temperature is the other. Males hatch out of middle temps in
alligators.
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