– Sexual inheritance in birds.

As we saw the other day, humans have sexual inheritance. But there are two types of sexual inheritance, and most birds have a different type of sexual inheritance to develope the sex of their offspring.

In the type of sexual inheritance humans have, the male is heterozygous (XY) and the female is homozygous (XX) for a sex factor This type takes place in lots of living beings, and it is called Drosophilia.

On the other hand, there is another type of sexual inheritance, called the Abraxas type, in which the male is homozygous (ZZ) for a sex factor and the female is heterozygous (WZ). Most birds, incluiding chickens, ducks and canaries, have this type of sexual inheritance.

Anyway, the results of this two types are approximately the same, both meaning a 50% possibilities for both genders.

– Sexual inheritance in bees.

Bees have a very particular way of determining the gender of the new larvae. Recient experiments have prooved that the queen can decide to lay fertilized or unfertilized eggs. Unfertilized eggs will produce drones, while fertilized ones will produce females, workers and queens. This experiments have prooved that que queen deliverately mantains a balance between the two genders, changing the normal rate of fertilized eggs when we force or change the conditions.

The gene that determines the gender in bees is called the csd (complementary sex determination) gene.

In humans, sex is determined by the combination of sex-determining chromosomes one has. In females, both sex-determining chromosomes are the same – XX; for males the two chromosomes are different – XY. Bees do things a bit differently. Specific combinations of the csd gene regulate the gender and social roles of each bee.

If the bee has two different alleles, the csd gene will be female (it has two alleles because it was fertilized). If it has only a single version of the gene, it will become a normal, fertile male. Finally, if the bee has two identical csd types it will become a diploid male, which is infertile.

– Women with only one X.

The X chromosome carries a couple thousand genes, but few, if any, of these have anything to do directly with sex determination. Early in embryonic development in females, one of the two X chromosomes is randomly and permanently inactivated in nearly all somatic cells (cells other than egg and sperm cells). This phenomenon is called x-inactivation or lyonization, and creates a Barr-body.

Therefore, a Barr body is the inactive X chromosome in a female cell.

X-inactivation ensures that females, like males, have one functional copy of the X chromosome in each body cell. It was previously assumed that only one copy is actively used. However, recent research suggests that the Barr-body may be more biologically active than was previously supposed.

But, there are women that only have one X chromosome.

This condition is normally produced by the Turner syndrome, and it is called monosomy X.  The Turner syndrome is a problem that appears approximately in one of every 2500 women.

There are characteristic physical abnormalities, such as short stature, swelling, broad chest, low hairline, low set ears, and webbed necks. Girls with Turner syndrome typically experience gonadal dysfunction (non-working ovaries), which results in amenorrhea (absence of menstrual cycle) and sterility. Concurrent health concerns are also frequently present, including congenital heart disease, hypothyroidism (reduced hormone secretion by the thyroid), diabetes, vision problems, hearing concerns, and many autoimmune diseases. Finally, a specific pattern of cognitive deficits is often observed, with particular difficulties in visuospatial, mathematical, and memory areas.

– People with XXY.

¿Why some people have this strange genotype for their gender? The main reason, is a particular syndrome, called the Klinefelter’s syndrome.

Klinefelter’s syndrome is, therefore, a condition in which males have an extra X sex chromosome. While females have an XX chromosomal makeup, and males an XY, affected individuals have at least two X chromosomes and at least one Y chromosome. It is the most common sex chromosome disorder. The principal effects are development of small testicles and reduced fertility. A variety of other physical and behavioral differences and problems are common, though severity varies and many boys and men with the condition have few detectable symptoms.

That’s all folks;

Rubén Laplaza