Israeli team develops way to find genetic flaws in fetus at 11 weeks
What Are Sex Chromosomes?
A chromosome is a DNA molecule that contains genetic material. Sex chromosomes are chromosomes that affect your sexual anatomy and reproductive development.
Most of us were raised with the idea that there are two sexes: male and female. We're usually told that people with XY chromosomes are male and people with XX chromosomes are female.
It's a lot more complicated than that.
Typically, there are 46 chromosomes in each human cell. This usually includes a pair of sex chromosomes and 22 pairs of autosomes. Autosomes are all chromosomes that are not sex chromosomes.
Many people are born with variations in sex chromosomes, also called X and Y variations or sex chromosome aneuploidy (SCA).
People with an SCA may have one X chromosome, XXY chromosomes, XXX chromosomes, and so on.
Sex chromosomes typically determine the development of your reproductive organs and your secondary sex characteristics.
For example, your sex chromosomes may determine:
Having certain sex chromosomes may also make you more susceptible to specific health conditions. For example, hemophilia A and B are sex-linked conditions more likely to appear in people with XY chromosomes.
Primary sex determination depends on chromosomes. Secondary sex determination depends mostly on hormones.
Primary sex characteristics include the gonads, which are the glands that produce reproductive hormones in the body.
Secondary sex characteristics are determined by the hormones the gonads secrete. These characteristics include your body's phenotype (how it looks) outside of the reproductive system.
Examples of secondary sex characteristics include:
Many people have a difference in sexual development (DSD), which is also called intersex. "DSD" is a term that describes chromosomes, sex characteristics, and anatomy that can't be defined as exclusively male or female.
As many as 1 in 100 people are born with a DSD.
Not everyone with a DSD has variations in sex chromosomes. Some people with DSDs may have XX or XY chromosomes. But they might also have X and Y variations or SCA.
Variations in sex chromosomes can include:
Different SCAs produce different characteristics.
How many sexes are there?If you look this up, you'll undoubtedly find a variety of opinions on the matter. Some say there are only two sexes, while others say there are an infinite number of sexes.
It depends on your definition of sex: What makes a specific phenotype a "sex"? How do you determine the difference between a sex category and a sex variation? It's hard to say.
Many biologists assert that sex is a spectrum and not a binary, meaning there are many variations in sex and not simply two exclusive categories.
Gender and sex are different things — but gender is also not a binary.
How many people are born intersex?As many as 1 in 100 people are born with a difference in sex development (DSD), which is another term for intersex.
According to the Intersex Society of North America, about 1 in 1,500 to 1 in 2,000 people are determined intersex at birth.
However, some intersex people only find out about their DSD later on in life, like at puberty or as an adult. It's even possible to have intersex traits and never know.
This number depends on how you define "intersex." Many people have variations in sex differences that are not apparent to others. As such, some clinicians might not consider them intersex.
What are karyotypes?Your karyotype is your complete set of chromosomes. A karyotype is used to visualize the appearance of your chromosomes, including the size, number, and shape of the chromosomes.
Sex chromosomes determine the development of your gonads. But sex chromosomes are a lot more complex than most people think.
While we're typically taught that there are only two sex chromosome types — XX and XY — the truth is there are more variations than that.
Sian Ferguson is a freelance health and cannabis writer based in Cape Town, South Africa. She's passionate about empowering readers to take care of their mental and physical health through science-based, empathetically delivered information.
Why The Y Chromosome
Why the Y ChromosomeBack to Build a Family TreeAll men and only men have a Y chromosome. This biological fact allows us to trace back in time a direct, largely unchanged genetic line of inheritance from father to son.
Every person, male or female, has 22 matching pairs of chromosome—one inherited from each parent—but the 23rd pair is different. This unmatched pair, known as the X and Y sex chromosomes, determines whether we are male (XY) or female (XX). A mother always provides a single X chromosome in her egg. Inherit an X from your father and you will be a female, receive a copy of his Y you will be male. And so the Y chromosome travels from father to son with each successive generation of males.
The second thing that makes the Y chromosome unique is that the information carried on Y chromosomes is inherited largely intact over time. Unlike other chromosomes, the genetic material on the Y chromosome is not mixed with each new generation. The reason is that when cells divide in preparation to make sperm and egg, all 23 chromosome pairs line up to exchange random bits and pieces of DNA with their matching partner before separating.
All chromosomes do this exchange of genetic material save the mismatched XY pair. The Y is much shorter, and very little of its genetic information is broken up in an exchange of DNA with the X chromosome. The information carried on the Y chromosome travels from father to son as a nearly exact copy of itself.
Occasionally, during the DNA copying process small changes or mutations occur, and it is these mutational differences that allow us to distinguish the Y chromosome of an individual from his ancestor's. Thus an actual genetic record of the male line going back through time exists—as clear a marker of paternal heritage as a father's family name.
A tangible timekeeper of history, the Y chromosome allows us to trace human evolution, track migration patterns and relatedness in groups of people, and answer paternity questions going back generations. As we pull apart the Y chromosome, we begin to unravel some fascinating stories about our own origins.
Continue: Tracing the CohanimBack to Build a Family Tree
Where are the Ten Lost Tribes?Tudor Parfitt's Remarkable JourneyMystery of Great ZimbabweBuild a Family TreeResourcesTeacher's GuideTranscriptSite MapLost Tribes of Israel Home
Editor's PicksPrevious SitesJoin Us/E-mailTV/Web ScheduleAbout NOVATeachersSite MapShopJobsSearchTo printPBS OnlineNOVA OnlineWGBH©Updated November 2000
X Y Chromosomes
In the imprinted brain theory, everyone's brain is configured somewhere on a spectrum between hypomentalism and hypermentalism. In hypomentalism, the mechanistic, paternal genes are over-expressed, creating a baby with a larger head who demands more from the mother; this child is more likely to have autism. In hypermentalism, the mentalistic, maternal genes are over-expressed; the baby is likely to have a smaller head, demand less from the mother, and develop psychosis. The normal brain falls somewhere between the two extremes, ensuring that the child exhibits neither autism nor psychosis.
Israeli team develops way to find genetic flaws in fetus at 11 weeks
Comments
Post a Comment