While genes determine most of our physical characteristics, the exact combination of genes we inherit, and thus our physical traits, is in part due to a process our chromosomes undergo, known as genetic recombination.
Meiosis, the form of cell division unique to egg and sperm production, sets the stage for sex determination by creating sperm that carry either an X or a Y sex chromosome. But what is it about the X or Y that determines sex? Before a meiotic cell divides, its two sets of chromosomes come together and cross over, or swap, segments. The first animation shows normal crossing over, where the X and Y chromosomes exchange pieces only at their tips. The second animation shows a rare mistake in which the Y chromosome transfers a gene called SRY to the X chromosome, resulting in sex-reversed babies. Studies of sex-reversed individuals led researchers to identify the master switch for sex determination, the SRY gene, which tells a fetus to become a boy.
Meiosis, the form of cell division unique to egg and sperm production, sets the stage for sex determination by creating sperm that carry either an X or a Y sex chromosome. But what is it about the X or Y that determines sex? Before a meiotic cell divides, its two sets of chromosomes come together and cross over, or swap, segments. The first animation shows normal crossing over, where the X and Y chromosomes exchange pieces only at their tips. The second animation shows a rare mistake in which the Y chromosome transfers a gene called SRY to the X chromosome, resulting in sex-reversed babies. Studies of sex-reversed individuals led researchers to identify the master switch for sex determination, the SRY gene, which tells a fetus to become a boy.
Four talks focus on sex determination-the molecular and genetic mechanisms that determine whether an organism will be male, female or a hermaphrodite.
Meisosis animation 49:00-53:00
53:21 SRY animation Y to X crossing over
53:30 SRY transfer 54:45
In this "clicker case," students learn about sex determination, meiosis, and chromosomal "crossing over" through the story of Santhi Soundararajan, an athlete from Kathakkurichi, India, who was stripped of a medal at the 2006 Asian Games after failing to pass a sex test. The case is called a clicker case because it combines the use of student personal response systems (clickers) with case teaching methods and formats. The case itself is a PowerPoint presentation (~2 MB) shown in class that is punctuated by questions students respond to using their clickers. It can be adapted for use without these technologies. Developed for an introductory biology class for both majors and non-majors, the case could also be used in an anatomy and physiology course or an endocrinology course.
In this "clicker case," students learn about sex determination, meiosis, and chromosomal "crossing over" through the story of Santhi Soundararajan, an athlete from Kathakkurichi, India, who was stripped of a medal at the 2006 Asian Games after failing to pass a sex test. The case is called a clicker case because it combines the use of student personal response systems (clickers) with case teaching methods and formats. The case itself is a PowerPoint presentation (~2 MB) shown in class that is punctuated by questions students respond to using their clickers. It can be adapted for use without these technologies. Developed for an introductory biology class for both majors and non-majors, the case could also be used in an anatomy and physiology course or an endocrinology course.
The Y chromosome is only one-third the size of the X. Although the Y has a partner in X, only the tips of these chromosomes are able to recombine. Thus, most of the Y chromosome is inherited from father to son in a pattern resembling asexual, not sexual, reproduction. No recombination means no reassortment, so deleterious mutations have no opportunity to be independently selected against. The Y chromosome therefore tends to accumulate changes and deletions faster than the X. Degradation doesn't occur in X chromosomes because during female meiosis, the X has the other X as a full partner in recombination.
Interactive exploration that challenges you to determine whether an athlete is qualified to compete as a female. Along the way you may gain some understanding of the biology of sex and in particular how sex is determined in humans.
nteractive exploration that challenges you to determine whether an athlete is qualified to compete as a female. Along the way you may gain some understanding of the biology of sex and in particular how sex is determined in humans.
Simulators which display cummulative generation graphs for variables. Very cool data rich resource! Includes Carbon cycle, demographis (human populations), Disease transmission, ecology, and energy simulations.
The online textbook provides a background to understand and discuss the natural functioning of the different Earth systems; it introduces humans as part of the overall ecosystem and explores what is needed to sustain human life; and it looks at the effects that human actions have on different natural systems. The online textbook also includes full-color images of related figures, glossary terms, and a bibliography for further reading.
Data rich simulation where students adjust parameters and run simulator for 100 iterations and see how 1) two plant species compete for a niche or 2) how composition of a food web changes over time
Links to online textbook, videos, visuals, scientists.
DNA is an interactive Web site where students can learn about DNA and its structure and function, the scientific history of its discovery and its development into a powerful tool in biology, technology, and medicine, and about the Human Genome Project, genetic engineering, and some of the implications and ethical issues surrounding genetic technology.
With its famous opening scene at a Harvard graduation, this classic of education research brings into sharp focus the dilemma facing all educators: Why don't even the brightest students truly grasp basic science concepts? This award-winning program traces the problem through interviews with Harvard graduates and their professors, as well as with a bright ninth-grader who has some confused ideas about the orbits of the planets.
Socrative is a smart student response system that empowers teachers to engage their classrooms through a series of educational exercises and games via smartphones, laptops, and tablets.
This is a website for high school science students. You'll find a variety of interactive quizzes, games and puzzles to practice what you're learning in Grade 9 Science, Grade 10 Science, Grade 11 Biology and Grade 12 Biology. There are also some specific student resources, such as worksheets and slideshows, for each course.