2.
58 million base pairs (the building blocks
of DNA)
1% of the total DNA in a male cell
contains 86 genes, which code for only 23
distinct proteins
Acrocentric
Smaller than X
4.
The human Y chromosome is unable to
recombine with the X chromosome, except
for small pieces of pseudoautosomal
regions at the telomeres (which comprise
about 5% of the chromosome's length).
The bulk of the Y chromosome which does
not recombine is called the "NRY" or nonrecombining region of the Y chromosome.
5. Sex chromosome aberrations
47 ,XXY
Klin efelte r sy n dr ome
m ale
tall st atur e
teste s do no t ma tu re
ste ril e
lowe red IQ is co mm on
1/700 m ale bir th s
45 ,X
T u rn er S y nd rom e (X O)
fem ale
sho rt stature
rud im e ntary ova ri es
ste ril e
IQ typ ica ll y nor m al
1/3000 fem ale b irth s
47 ,XYY
Do ubl e-Y sy n dr om e
m ale
above ave rage he igh t, o the rw ise pheno typ ica ll y
no rm al.
A t one time , it wa s claim ed tha t X Y Y m ales are pron e
to v io len t or an ti so c ial behav ior, ba sed on eleva ted
inc idenc e o f 47 ,XYY a m ong inca rce rated m en. N ow
though t to be du e to h igh e r inc idence of m ode rate
m en tal re tarda ti on than for XY m ales .
47 ,XXX
T riso m y -X syn d ro m e
m any pheno typ ica ll y no rm al
the frequency of lowe red IQ is h igher than am ong
XX fe m al es .
6. ◦ These regions are called the pseudoautosomal regions., PAR1 and PAR2.
◦ a crossover in PAR1 is necessary in male meiosis to get proper segregation
of the chromosomes.
7.
8. AZF1 (azoospermia factor 1)
BPY2 (basic protein on the Y chromosome)
DAZ1 (deleted in azoospermia)
DAZ2
PRKY (protein kinase, Y-linked)
RBMY1A1
SRY (sex-determining region)
TSPY (testis-specific protein)
USP9Y
UTY (ubiquitously transcribed TPR gene on Y
chromosome)
◦ ZFY (zinc finger protein)
◦
◦
◦
◦
◦
◦
◦
◦
◦
◦
22. X
SiRNA or Small interference RNA
X
RNA
X
SiRNA
X
X
H
X
X
X
Anti Hemophilia Factor
23. •
Female mammals have an XX genotype.
– Expression of sex-linked genes is similar to autosomal genes in females.
– X chromosome inactivation randomly “turns off” one X chromosome
– ensures that females, like males, have one functional copy of the
X chromosome in each body cell
X
24.
The Y chromosome was identified as a sexdetermining chromosome by Nettie
Stevens at Bryn Mawr College in 1905 during
a study of the mealworm Tenebrio molitor
Hermann Henking
the Y chromosome was the pair of the X
chromosome
. Stevens named the chromosome "Y" simply
to follow on from Henking's "X" alphabetically
That was depond on it shape
28.
Most mammals have only one pair of sex
chromosomes in each cell. Males have one Y
chromosome and one X chromosome, while
females have two X chromosomes. In
mammals, the Y chromosome contains a
gene, SRY, which triggers embryonic
development as a male
Exception of SRY mammals
the platypus(similarity) with the avian Z
chromosome
29.
The X and Y chromosomes are thought to have
evolved from a pair of identical
chromosomes termed autosomes
Until recently, the X and Y chromosomes were
thought to have diverged around 300 million
years ago
However, research published in 2010, and
particularly research published in 2008
documenting the sequencing of the platypus
genome,has suggested that the XY system would
not have been present more than 166 million
years ago
30.
Over time, the Y chromosome changed in
such a way as to inhibit the areas around the
sex determining genes(SRY) from
recombining at all with the X chromosome.
As a result of this process, 95% of the human
Y chromosome is unable to recombine
The tips of the Y chromosome that could
recombine with the X chromosome are
referred to as the pseudoautosomal region.
31.
32.
By one estimate, the human Y chromosome has
lost 1,393 of its1,438 original genes over the
course of its existence, and linear
extrapolation of this 1,393 gene loss over 300
million years gives a rate of genetic loss of 4.6
genes per million years. Continued loss of genes
at the 4.6 genes per million year rate would
result in a Y chromosome with no functional
genes that is the Y chromosome would lose
complete function within the next 10 million
years. Comparative genomic analysis, however,
reveals that many mammalian species
33.
The Y chromosome is passed exclusively
through sperm, which undergo multiple cell
divisions during gametogenesis. Each cellular
division provides further opportunity to
accumulate base pair mutations. Additionally,
sperm are stored in the highly oxidative
environment of the testis, which encourages
further mutation. These two conditions
combined put the Y chromosome at a greater
risk of mutation than the rest of the genome
34.
Without the ability to recombine during meiosis, the Y chromosome is
unable to expose individual alleles to natural selection. Deleterious
alleles are allowed to "hitchhike" with beneficial neighbors, thus
propagating maladapted alleles in to the next generation. Conversely,
advantageous alleles may be selected against if they are surrounded by
harmful alleles (background selection). Due to this inability to sort
through its gene content, the Y chromosome is particularly prone to the
accumulation of "junk" DNA. Massive accumulations of retrotransposable
elements are scattered throughout the Y.[10] The random insertion of
DNA segments often disrupts encoded gene sequences and renders
them nonfunctional. However, the Y chromosome has no way of weeding
out these "jumping genes". Without the ability to isolate alleles, selection
cannot effectively act upon them.
A clear, quantitative indication of this inefficiency is the entropy rate of
the Y chromosome. Whereas all other chromosomes in the human
genome have entropy rates of 1.5–1.9 bits per nucleotide (compared to
the theoretical maximum of exactly 2 for no redundancy), the Y
chromosome's entropy rate is only 0.84.[18] This means the Y
chromosome has a much lower information content relative to its overall
length; it is more redundant.
35.
Even if a well adapted Y chromosome manages to
maintain genetic activity by avoiding mutation
accumulation, there is no guarantee it will be
passed down to the next generation. The
population size of the Y chromosome is
inherently limited to 1/4 that of autosomes:
diploid organisms contain two copies of
autosomal chromosomes while only half the
population contains 1 Y chromosome. Thus,
genetic drift is an exceptionally strong force
acting upon the Y chromosome
