In humans, gender is determined by a pair of sex chromosomes. Females are XX and males are XY. Of course, things aren't always that simple and a variety of mutations may occur that make someone's gender a bit more ambiguous. Furthermore, having a pair of sex chromosomes is only one way in nature to determine gender - there are certainly others. Use the links below to explore this fascinating topic.
Sex Determination: More Complicated Than You Thought - watch this video to learn about a variety of ways that gender is determined in many different organisms. Be sure to answer the associated 'Think' questions and the 'Dig Deeper' questions after you watch the video.
Gender Testing Athletes - Now that you know what chromosomes are involved, use this link to explore gender determination on the gene level and to see more of what is possible when things go wrong.
Human Genome - after you complete the gender testing activity above, you can go to this site to see the genes on each chromosome. Click the Y-chromosome and read the summary. Then find the SRY gene and click on it to see its location and read a summary. You can feel free to click on the X-chromosome too. Read the summary of the X-chromosome (take particular note of X-inactivation) and then click on the MECP2 gene and read about Rett Syndrome.
Polyploidy - use this link to explore what happens when you have too many or too few sex chromosomes and how a karyotype can be used to diagnose these conditions. Step through each patient's history and complete the karyotyping activities.
Klinefelter's Syndrome - this link gives more specifics about Klinefelter's Syndrome and how many X chromosomes are possible in one individual.