Download Oral Presentations - Human Reproduction

Oral Presentations
INVITED SESSION
Session 01 – Keynote lectures
Monday 28 June 2004
08:30–09:30
O-001 The Y chomosome - a feministe view
J.A.M. Graves
Research School of Biological Sciences, The Australian National University,
Canberra ACT 2601, Australia
In mammals, sex is determined by an XY male: XX female system in which
a male-dominant gene on the Y (SRY) determines testis, and embryonic testis
determines maleness. Unlike other chromosomes, the Y is a genetic wasteland
– small and full of genetic junk, bearing only 45 genes. Comparisons with
the Y chromosomes of other animals tells us that the human Y chromosome
(and the male determining SRY gene that it bears) evolved relatively recently
and its useful life is already running out.
Sex chromosomes are proposed to have evolved from an ordinary autosome
pair as the Y chromosome was progressively degraded. This must have happened quite recently, since birds and reptiles, from which they diverged 300
million years ago, subscribe to completely non-homologous sex determining
systems. To explore the origin of the human Y chromosome and SRY, we
compared Y chromosomes of the three major mammal groups (eutherians,
marsupials and monotremes). This allowed us to subdivide the human Y into
a tiny ancient region shared by all other mammals, and a recently added
region that is on the Y only in placental mammals. Most of the original human
Y has been lost, and the Y was saved from extinction only by autosomal
addition.
This view of a “wimp Y” is supported by our findings that many or most genes
on the human Y – even those with important functions in male determination
and differentiation – have partners on the X from which they evolved. Even
the sex-determining gene SRY has a partner on the X (the brain-expressed
SOX3), from which it probably derived.
The human Y chromosome is running out of time. In the last 300 million
years, it has lost 1393 of its original 1438 genes, and at this rate it will lose
the last 45 in a mere 10 million years. If you don’t believe this can happen,
ask the mole vole, whose Y has completely disappeared.
But – maybe rescue is at hand. In self-defence, the Y seems to be able to
make more copies of vital genes, and could conceivably correct mutated
genes by complementation within long palindromes. However, I argue that
conversion works both ways, so it is just as likely to wipe out an active gene
as to conserve it. This kind of recombination confers none of the advantages
of exchange between different chromosomes. Conducted in genetic isolation,
it is more like genetic masturbation than real sexual reproduction.
O-002 Noah’s modern ark and the role of ART in conserving
endangered species
D.E. Wildt
Smithsonian’s National Zoological Park, Washington D.C. and the National
Zoo’s Conservation & Research Center, Front Royal VA, USA
Introduction: The ability to reproduce is quintessential to species survival,
thus making the reproductive sciences vital to conserving wildlife species and
indirectly the vitality of entire ecosystems. It has been postulated for decades
that ART (originally artificial insemination, later IVF/embryo transfer, more
recently cloning) can contribute to conserving the earth’s rapidly declining
biodiversity. Part of this excitement is derived from impressive progress
made in combating human infertility and enhancing livestock production
using innovative technologies. However, compared to assisting reproduction
in humans and livestock, the managers and conservators of wildlife face
different challences and logistics. For endangered species in zoos, the aim
is not only to produce more young, but offspring of known provenance and
appropriate genotype that will preserve the integrity of a species, a subspecies
or a population.
Materials and methods: Almost 25 years of studying more than 50 species
have provided the author with an experienced perspective on the value
(and limitations) of reproductive tools and ART for the study and genetic
management of rare wildlife.
Results: It now is clear that the high tech components of the reproductive
sciences, including ART, are not a quick fix for enhanced reproduction in
endangered species. Rather, the primary value of these tools is to characterize the remarkable differences in mechanisms regulating reproductive
success among species (even within the same family) through rigorous and
scholarly study. Data then are useful for management decision-making and
more effective control of reproduction though natural and, when necessary,
’assisted’ means. Examples of using ART successfully will be shared for
the African cheetah, the giant panda (in China) and marine mammals, including the killer whale. These species are benefiting from a combination
of non-invasive endocrine monitoring and artificial insemination with fresh
or thawed spermatozoa. However, for further progress, thousands of species
require fundamental and applied study. Additionally, reproductive physiology and endocrinology studies conducted in a vacuum do not contribute
substantially to conservation. Rather (as will be demonstrated using the giant
panda), integrating reproductive findings with those from other disciplines
is most efficient for tackling problems holistically to conserve species and
heterozygosity.
Conclusion: The foremost value of reproductive science and ART to conserving endangered animals is the discipline’s powerful abilities to understand
fundamental, species-specific reproductive mechanisms. Such scholarly (and
fascinating) information can be applied to improving management by natural,
and occasionally, assisted breeding. Genuine conservation is achieved, however, only when the reproductive knowledge and technologies are integrated
together into multi-dimensional management programs that preserve species
integrity in zoos and in nature.
FREE COMMUNICATION
Session 02 – ART/Clinical/Outcome 1
Monday 28 June 2004
10:00–11:30
O-003 Modes of conception and multiple pregnancy: A national
survey of babies born during one week in 2003 in the U.K.
N. Bardis 1 , M. Deivanayagam 1 , H. Cuckle 2 , A.H. Balen 1
1
Leeds General Infirmary, Reproductive Medicine Unit, Leeds, United
Kingdom; 2 Leeds General Infirmary, Department of Epidemiology, Leeds,
United Kingdom
Introduction: We report what we believe to be the first attempt to study
the mode of conception of all babies born during a specified period of time
related to multiplicity.
Materials and methods: A letter of invitation was sent to each of the 245
maternity units in the United Kingdom. The aim was to collect data on every
baby born during the week of 6th to 12th April, 2003.
Results: Information was collected by 178 maternity units (72.7%). Data
was received on 6,913 deliveries of which 6,812 (98.54%) were singleton,
100 (1.45%) twin and 1 (0.01%) triplet. Thus a total of 7,015 babies were
born. Of the 6,913 pregnancies 6,638 (96%) were conceived spontaneously,
133 (1.9%) were conceived with assistance and information was not provided
for 142 (2.1%). The only triplet pregnancy was conceived spontaneously.
The rate of multiple pregnancy was significantly greater in assisted (18/133,
13.5%) compared with spontaneous (82/6638, 1.2%) conceptions (differ-
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