Sex Linked Genes:
Sex linked genes help characterize what your child will look like. These genes are carried in the sex chromosomes of each person, which is why they are considered, "sex linked." Men have an X and a Y set of chromosomes, but women have two X's, which is what makes each gender different.
Sex linked genes are considerably easy to figure out. Say a trait is Y-Linked, then, when shown in a pedigree or other chart, it will be evident that the trait is only shown in men because they are the only ones with Y chromosomes. However, both men and women can receive X-Linked traits because both inherit X chromosomes. The only difference is that women have the possibility of being carriers for a certain trait if the trait is X-Linked. This is because women have two X chromosomes and one chromosome may have the trait, but the other might not. This would make the woman be a carrier (if the trait is X-Linked Recessive, because if the gene were X-Linked Dominant, even if only one woman's X chromosome has the trait, the woman would inherit it). Therefore, you can see why men would have a greater chance in inheriting X-Linked Traits because they do not have an option of being a carrier, either they have the trait, or they do not.
Sex linked genes are considerably easy to figure out. Say a trait is Y-Linked, then, when shown in a pedigree or other chart, it will be evident that the trait is only shown in men because they are the only ones with Y chromosomes. However, both men and women can receive X-Linked traits because both inherit X chromosomes. The only difference is that women have the possibility of being carriers for a certain trait if the trait is X-Linked. This is because women have two X chromosomes and one chromosome may have the trait, but the other might not. This would make the woman be a carrier (if the trait is X-Linked Recessive, because if the gene were X-Linked Dominant, even if only one woman's X chromosome has the trait, the woman would inherit it). Therefore, you can see why men would have a greater chance in inheriting X-Linked Traits because they do not have an option of being a carrier, either they have the trait, or they do not.
For example, refer to the picture on the right. You can see that because the trait for colorblindness is found on the X chromosome, the women have a chance of not inheriting the disease but being carriers, whereas the men do not have the chance of being a carrier- either they are colorblind or they are normal.
Aside from X-Linked traits, Y-Linked traits also exist, but there are not as many of these traits that are passed down in the Y chromosome because the Y chromosome only is present in males. Just like when traits are passed down in the X chromosome, men who inherit traits that are Y-Linked must have the trait in his phenotype and there is no way that he is a carrier- either he has the trait or does not. If a particular trait is Y-Linked, women cannot receive this trait because they have two X chromosomes and no Y chromosomes. This makes it impossible for women to receive a trait that is passed through the Y chromosome.
Aside from X-Linked traits, Y-Linked traits also exist, but there are not as many of these traits that are passed down in the Y chromosome because the Y chromosome only is present in males. Just like when traits are passed down in the X chromosome, men who inherit traits that are Y-Linked must have the trait in his phenotype and there is no way that he is a carrier- either he has the trait or does not. If a particular trait is Y-Linked, women cannot receive this trait because they have two X chromosomes and no Y chromosomes. This makes it impossible for women to receive a trait that is passed through the Y chromosome.
Sex Chromosome Abnormalities:
Many of the different chromosomal abnormalities are abnormalities involving the sex chromosomes. Unlike autosomal abnormalities, sex chromosome abnormalities are gender specific. Males are supposed to inherit an X and a Y chromosome and females are supposed to inherit two X chromosomes. Without a Y chromosome, maleness is insufficient and problems may occur. This is the same for femaleness. Without two X's, femaleness cannot happen. Like said previously, sex chromosome abnormalities are gender specific and for females, abnormalities can occur when there is an abnormal change in the number of X chromosomes. Also, male abnormalities can occur due to irregular numbers of either Y or X chromosomes.
Common Sex Chromosome Abnormalities: Females-
Turner Syndrome- this occurs when females oddly inherit one X chromosome, not two. This means that their genotype is X0. Many females who suffer from this syndrome do not survive from birth and if they do, they have severely abnormal growth patterns. Women who survive birth are generally short (averaging to about 4 ft 7 in as adults) and usually have extra folds of skin, small jaws, and high arched palates. They also lack usual womanly characteristics sexually (small and widely spread apart breasts and dysfunctional vagina and ovaries). Typically, sufferers of this syndrome have higher chances of having diabetes, heart defects, thyroid disease, vision and hearing problems, and possibly mental retardation.
Triple-X Syndrome- this syndrome is when women inherit three X chromosomes (ex. XXX, XXXX, or in extremely rare occasions- XXXXX). As these women mature and become adults, these "super females" are usually taller than the average woman. These women have normal development of sexual characteristics (except for the possibility of few ovary abnormalities), but frequently have learning difficulties and are emotionally immature.
Triple-X Syndrome- this syndrome is when women inherit three X chromosomes (ex. XXX, XXXX, or in extremely rare occasions- XXXXX). As these women mature and become adults, these "super females" are usually taller than the average woman. These women have normal development of sexual characteristics (except for the possibility of few ovary abnormalities), but frequently have learning difficulties and are emotionally immature.
Common Sex Chromosome Abnormalities: Males-
Klinefelter Syndrome- this occurs when men inherit extra X chromosomes (ex. XXY, XXXY, or in extremely rare occasions- XY/XXY mosaic). Men who are severely suffering from this syndrome have oddly high-pitched voices, asexual to feminine body contours, breast enlargement, and little body and facial hair. Typically, the men diagnosed with this syndrome have small amounts of testosterone and hormonal imbalance is active. The imbalance can be altered if the Klinefelter men are given testosterone from the age of puberty throughout their lives. Just like women diagnosed with the Triple-X Syndrome, typically the men are taller than other men. Also, these men usually are overweight and have learning difficulties. Even though this is evident, men diagnosed with this seem to be ordinary in appearance and in mentality (more in adulthood) and live in their community without anyone seeing any major differences. Many men who have this syndrome are not even aware of it until they test their fertility. Men who have this syndrome are fertile and can conceive children, but many people who are diagnosed do not produce sufficient amounts of sperm to conceive. There is no scientific evidence that provides proof that men who do have the Klinefelter Syndrome are more likely to be homosexual, but it has been proven that they are less interested in sexual activities. Men with this syndrome are also more likely to develop osteoporosis and diabetes that are more common in women. This is resulted from the low testosterone levels and production. Although the syndromes listed above that concern women are considerably rare, this syndrome is actually quite common.
XYY Syndrome- this occurs when men inherit an extra Y chromosome. Just like women who have the "Triple-X Syndrome," as adults, men who have this syndrome are typically taller than their peers and generally act like any other man. The main difference in these and other men are that they produce higher levels of testosterone than other men and during childhood, they are often very slim, have a lot of acne, and are not very well coordinated. Many men who have this syndrome do not know they have this chromosome abnormality. They go about their lives just as any other man would and are fertile just like any other man. This syndrome is not very common, but is not extremely rare.
XYY Syndrome- this occurs when men inherit an extra Y chromosome. Just like women who have the "Triple-X Syndrome," as adults, men who have this syndrome are typically taller than their peers and generally act like any other man. The main difference in these and other men are that they produce higher levels of testosterone than other men and during childhood, they are often very slim, have a lot of acne, and are not very well coordinated. Many men who have this syndrome do not know they have this chromosome abnormality. They go about their lives just as any other man would and are fertile just like any other man. This syndrome is not very common, but is not extremely rare.
To summarize, the effect of these different Sex Chromosome Abnormalities and Sex Linked Genes in general is the same no matter who you are or who your parents are. The children that have parents who are identical twins will not have any greater risk of inheriting syndromes unless it is evident in a pedigree or other source of chart that these syndromes are common. So, just because your parents are each identical twins- it does not give you a greater risk of having such syndromes.