Chapter 3 Chromosomes; inheritance and sex
story of the early days of the chromosome theory: A
long and complicated story. Reference: http://zygote.swarthmore.edu/gene1.html
sex chromosomes
XO:Hermann Henking .... Hemiptera, unpaired element the "X body".
1891
XY: Nettie Stevens...Hemiptera, Heteromorphic pair, 1905
named the x-chromosome
major point: determine sex chromosomes by comparison of the chromosomes
of the male and female
major point: sex chromosomes are present in somatic cells
in Drosophila melanogaster..... DrosophilaKaryotype.GIF (Figure
3.1 in your text)
Pairing of X and Y chromosomes during meiosis
homogametic sex (one kind of gamete relative to sex chromosomes)
heterogametic sex (two kinds of gametes relative to sex chromosomes)
In birds and butterflies the male is the homogametic sex, the female
the heterogametic sex.
Important! ....many diagrams show only the sex chromosomes, not the
autosomes. It is important to realize that the autosomes are also present
in the somatic cells and the gametes. That is, we present the partial
genotype and partial array of chromosomes.
8 October 2004
There is a lecture series of the Institute for Science, Engineering
and Public Policy ($40 each). Free student tickets may be available;
check with student government. Information for the series at ...
www.isepp.org Of interest for genetics:
Beyond the Gene by Dr. Evelyn Keller, 21 January 05. The first
one is Dr. Brian Greene on The Fabric of the Cosmos.
Quizzes are returned. 158 out of a class of 201. Many
people are not participating in the recitations; this is ok if they do
not need the recitation periods. Three students did not write their
names clearly on the quizzes; these are not recorded.
Sex chromsomes in plants: Okada, S., T. Sone, et al. (2001). "The Y chromosome
in the liverwort Marchantia polymorpha has accumulated unique repeat sequences
harboring a male-specific gene." Proc Natl Acad Sci U S A 98(16): 9454-9.
picture: ../../Other%20Graphics/Sex%20chromosomes%20plants.tiff
More references on request
PlusLetter system
this is introduced here because
it is necessary for understanding of rest of the course
concept of wild; for model organisms,
wild stock of Drosophila: Oregon R (Roseberg, Oregon 1925 or
earlier.)
situation for humans
We will now introduce another way
of representing genes and chromosomes; there
is a lot of help for learning this: lecture, recitation,
text, workbook
a) To write the genotype
e) Use of the line to separate alleles
Morgan and genes "on" chromosomes
Introduction to Drosophila (Figure 3.1)
Morgan's crosses
Important: the genes go where the chromosomes go. Genes are
located on chromosomesl
Concept of criss-cross inheritance:
white female x wild male gives white males and wild females
Comparison of autosomal and x-linked: AutosXlinked.GIF
Criss cross and non cross cross inheritance to determine x and
autosomal linkage.
Morgan and chromosome theory; non-disjunction
Morgan, Bridges, and L.V. Sampson and non-disjunction
For cross 3, Morgan's student Bridges found some white females
and wild males
illustration from recent paper; nondisjunction.gif...
not on web but reference: McKim,
K. S., J. K. Jang, et al. (2002). "Meiotic recombination and chromosome
segregation in Drosophila females." Annu Rev Genet 36: 205-32.
XO males in Drosophila are sterile; fertility genes on Y in
Drosophila melanogaster
Normal disjunction animation...... Disjunction.GIF
Nondisjunction papers by Bridges www.esp.org
11 October 2004
T. H. Morgan - in normal meiosis the gene for white eye goes with the
X-chromosome
C. Bridges - for rare cases where the X-chromosome is distributed abnormally
the gene for white eye still goes with the X-chromosome
another exception to Morgan by Mrs. Morgan - Lillian Sampson
the gene for white eye is "always" distributed abnormally, again the
gene follows the chromosome
attached-X
chromosome diagram of karyotype ... attachedX.gif
again on Sex determination
in humans...Table 3.2 (not on web)... table2.gif
in Drosophila
Table 3.3 (not on web)... Table.gif
Human sex chromosome syndromes .. Table 3.2
Turner syndrome.. Figure 3.8
Karyotype (not on web): turner.gif
Klinefelter syndrome... Figure 3.9
Two new books - popular reading - of interest
Jones, S. (2003). Y : the descent of
men. Boston, Houghton Mifflin.
Bainbridge, D. (2003). The X
in sex : how the X chromosome controls our lives. Cambridge, Mass.,
Harvard University Press
and just in from the journal Nature 427:199, a review of: Bryan
Sykes 2003 Adam's Curse: A future without Men Bantam
Press
In humans, use of pedigrees (an aside)
Reference: book by Massie, Robert K., Nicholas and Alexandra
in the PSU library: DK258 .M3 1969
Figure 3.12....X-linked dominant....
X-chromosome inactivation
development of the idea
Observations of Barr and Bertram (1949): There is a dimorphism
in normal mammalian individuals; females have a
dark staining body in their somatic interphase nuclei
and males do not have the body. We may call this the
x-chromatin body.
The x-chromosome body: Yohko
Relationship X-chroms and X-chrom bodies ....ChromsXbodies.GIF
Idea of Susumu Ohno(1960): The x-chromatin body represents the
inactive x-chromosome.
Mary Lyon in 1961 put a lot of data together into the Lyon Hypothesis.
The Lyon hypothesis. (1961) During early mammalian development
one of the two x-chromosomes of the normal
XX female becomes inactive. In approximately half of
the somatic cells it is the maternally derived X-chromosome
and in the other half of the somatic cells it is
the paternally derived X-chromosome.
Pictures of calico cats --- too many!!
concept of mosaics, coarse and fine .... ../mosaics.gif
Black / orange genes in the calico cat
Genotype: aa B_ C_ ii L_ mm Oo Ss T_ ww
reference: ..a series of slides on cat coat color
geneticshttp://www.esb.utexas.edu/hampton/zoo325l/Cats/sld017.htm
relative to calico cats and modified ratios see text page 64:
O = orange, X-linked; B = black, autosomal. Cleo is
Oo B_
if the x-chromosome with O is active the B gene is not expressed and the
patch will be orange
if the x-chromosome with o is active the B gene is expressed
and the patch will be black
Timing of X-chromosome inactivation... ../XChromInact.gif
Why x-chromosome inactivation?
Dosage compensation "The presence of heteromorphic sex
chromosomes, i.e. sex chromosomes clearly
distinguishable in form and genetic content, has been
accompanied by the development of mechanisms of dosage
compensation. Dosage compensation ensures that the difference
in copy number of genes on the sex chromosomes in males
and females does not impair embryonic development and adult
viability." from introduction in the reference given below
Mechanism of X-inactivation
See text pages 63 - 64
Proposed mechanism (not on the web, not for exams) ... Xinactivation2.gif
note cis (same chromosome)
and trans (different chromosomes) activities
graphics from: Plath, K., S. Mlynarczyk-Evans, et al. (2002).
"Xist RNA and the mechanism of x
chromosome inactivation."
Annu Rev Genet 36: 233-78. (available PSU computers)
note: blocking factor on one x-chromosome; this becomes active, all
others inactive
ref: Park,
Y. and M. I. Kuroda (2001). "Epigenetic aspects of X-chromosome
dosage compensation." Science 293(5532): 1083-5.
Do human females show the calico cat pattern? See information on
Hypohidrotic Ectodermal Dysplasia (OMIM # 305100)
Other items on X-chromosome inactiation
Escape from X-chromosome inactivation
"Nineteen human
genes have been idntified that are expressed from
both the active and the
inactive X chromosome ...." Annual
Review of Genetics 1997. 31:571-610
Some of these are in the pseudo
autosomal regions.
Late replication of inactive
X-chromosome in S period of cell cycle.
Recent statement about x-chromosome
inactivation. Read if you like.... xinactivation.html .... from: Percec,
I. and M. S. Bartolomei. 2002
Do X chromosomes set boundaries?
Science 295(5553): 287-8.
Y-linkage in humans?
Certainly the male determining gene TDY (SXR, TDF) See OMIM #480000
research involved sex reversal in mice and humans, see text p. 65; XX
males, XY females
review of recent work on Y-chrom in humans; Willard, H. F. (2003).
"Tales of the Y chromosome." Nature 423(6942): 810-1,
813.
Old paper on hairy ears:
Evolution of the Y-chromosome
in humans, recent article: Lahn, B. T. and
D. C. Page. 1999 Four evolutionary strata on the human X
chromosome. Science 286(5441): 964-7.
Recent papers on Y-chromosome
Skaletsky, H., T. Kuroda-Kawaguchi, et al. (2003).
"The male-specific region of the human Y chromosome
is a mosaic of discrete sequence classes." Nature 423(6942):
825-37.
Willard, H. F. (2003). "Tales of the Y chromosome."
Nature 423(6942): 810-1, 813.
chromosomal locations for genes
autosomal
x-linked
y-linked
psuedoautosomal (in pairing portion of X and Y)....XYLinkage.gif
mitochondria
13 October 2004
review of X-chromosome inactivation
**** add revised graphic on life history of inactivation events ..
../XChromInact.gif
And on to chapter 4