sex determination- lecture 10 Flashcards
what is sry
sex determining region on the y chromosome
function of sry
sry is a transcription factor that is necessary for an individual to become biologically
male and is sufficient for male development. When an SRY transgene is
inserted into an XX embryo, even without the other Y chromosome genes, it
results in the embryo developing the male phenotype, including functional
male internal and external genitalia and gametes. This shows that SRY can
serve as a “switch” to initiate the typical male development pathway during
embryogenesis
give one reason: disconnect in karyotype and actual sex of individual can be caused by
mutated or missing sry gene
give another reason: disconnect in karyoype and actual sex of individual can be caused by
androgen insensitivity
pseudo autosomal region
turner syndrome
Turner syndrome, a condition that affects only females, results when one of the X chromosomes (sex chromosomes) is missing or partially missing. Turner syndrome can cause a variety of medical and developmental problems, including short height, failure of the ovaries to develop and heart defects
Their sex
chromosome genotype is denoted as “XO” to indicate that they have only
one X chromosome instead of 2 as a biological female should have
This indicates that at least one X chromosome is required for human
development, and two for fertility in females
Klinefelter syndrome
Klinefelter syndrome (sometimes called Klinefelter’s, KS or XXY) is where boys and men are born with an extra X chromosome. Chromosomes are packages of genes found in every cell in the body. There are 2 types of chromosome, called the sex chromosomes, that determine the genetic sex of a baby.
This is the most common male sex chromosome disorder, and is characterized by traits such as small testes, reduced facial hair, and sterility.
Nonetheless, these individuals have many male sexual characteristics,
providing further support for the idea that a single Y chromosome, even with multiple X chromosomes, is sufficient for development of the male phenotype
have genotype XXY, XXXY, or XXYY
poly x syndrome
is a genetic disorder caused by the presence of an extra X
chromosome in females
genotype XXX or XXXX
Poly-X syndrome does not lead to any particular physical features. Some individuals with the disorder are sterile, but this is not true of all Poly-X individuals. While little effect is
observed for physical features, the probability that a poly-X female will
exhibit intellectual disabilities increases with increasing number of X
chromosomes, underscoring the importance of gene dosage. Gene
expression and protein levels are finely tuned, so the more extra X’s an
individual has, the more negative consequences are observed, likely
because X-inactivation is not complete
poly y syndrome
XYY syndrome, also known as Jacobs syndrome, is an aneuploid genetic condition in which a male has an extra Y chromosome. There are usually few symptoms (often
goes undiagnosed, because individuals who have it rarely exhibit any
significant observable anomalies)
These may include being taller than average, acne, and an increased risk of learning disabilities
sex determination in other organisms
sexual dimorphism
Sexual dimorphism is the systematic difference in form between individuals of different sex in the same species. For example, in some species, including many mammals, the male is larger than the female. In others, such as some spiders, the female is larger than the male.
gynandromorph
Gynandromorphs are individuals that contains both male and female characteristics.
Gynandromorphs contain cells that possess different combinations of sex
chromosomes - some cells have sex chromosomes that make them female,
while others have sex chromosomes that make them male. This makes the
organism itself partially male and partially female. The mechanism by which
this occurs is best understood in butterflies, where it can be (though not
always) caused by spontaneous mitotic nondisjunction of sex chromosomes
during development
mitotic nondisjunction
mitotic nondisjunction of sex chromosomes
mosaic gynandromorph
predominantly display the phenotype associated
with one sex, with patches of cells having characteristics of the other. The
difference between bilateral and mosaic phenotypes is due to differences in
the timing of sex chromosome nondisjunction (with very early non-disjunction
leading to bilateral gynandromorphs)
When this nondisjunction happens later in development, a mosaic gynandromorph can be produced. If we start with an initial ZW individual,
most of the cells would develop the female phenotype, but if the W chromosome is “lost” by a cell later in development, it (and its descendent
cells) will display the male phenotype instead. The earlier nondisjunction
happens, the more cells will be affected and the greater the extent of the
mosaicism.
types of sex determination
chromosomal, genic, environmental
sex chromosome evolution
dosage compensation
Barr body
A Barr body or X-chromatin is an inactive X chromosome