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Rediscovering Biology: Molecular to Global Perspectives

Biology of Sex and Gender

Genes determine whether a human embryo develops as a female or a male. This unit examines new findings and concepts – such as genetic imprinting, intersex conditions, and the effect of the hormones on sex determination – that challenge beliefs about the roles of anatomy, environment, and genetics in the determination of gender.

The online textbook chapters support and extend the content of each video. The Web version can be viewed as a full chapter or as individual sub-sections, and includes links to glossary terms and other related material.

Explore the archive of animations, images and figures from the videos and online textbook. All of the images can be viewed online or downloaded as jpg files.

Read profiles of the expert scientists featured in the video and find the complete transcripts of the interviews conducted for this unit.

Holly A. Ingraham, PhD
David Page, M.D.
Eric Vilain, M.D., PhD

Chapter Contents

Sex and the Y Chromosome
Paternal Inheritance
Evolution of the Y Chromosome
X Inactivation
Genetic Imprinting
Testis-Determining Factor
Ethics of Intersex Treatment
Sex and Disease

Unit Glossary

Genetic imprinting
Differential expression of a gene depending on whether it was maternally or paternally inherited.

Intersex (intersexual)
An organism with external sexual characteristics that have attributes of both sexes. Sometimes used to include individuals whose phenotype cannot be predicted from sex chromosome karyotype.
Mosaic (Mosaicism)
A tissue containing two or more genetically distinct cell types, or an individual composed of such tissues.

Oxidative damage
Free radicals from oxygen damage DNA, RNA and protein in cells, which may explain why oxidative damage is linked to diseases such as cancer, Alzheimer’s disease, and atherosclerosis.
Sex reversal
A difference between chromosomal sex and phenotypic sex
Single nucleotide polymorphism (SNP)
Variations in the DNA sequence that occur when a single nucleotide (A, T, C, or G) in the genome sequence is changed.
X inactivation
Functional inactivation of one copy of the X chromosome in cells of females

Related Resources

Beale, B. 2001. The sexes: New insights into the X and Y chromosomes.
The Scientist 15[15]:18.
Discussion about SRY, DAZ, WNT.

Jegalian, K., and B. T. Lahn. 2001. Why the Y is so weird. Scientific
, February, 56–61.
Evolution of the Y chromosome.

Jobling, M. A., and C. Tyler-Smith. 1995. Fathers and sons: the Y
chromosome and human evolution. Trends in Genetics 11:449–56.

Lewis, R. 2000. Reevaluating sex reassignment. The Scientist 14[14]:6.
Evidence supports nature over nurture in establishing gender identity.

Skorecki, K., S. Selig, S. Blaze, R. Bradman, N. Bradman, P. J. Waburton,
M. Ismajlowicz, and M. F. Hammer. 1997. Y chromosomes of the Jewish priests. Nature 385:32.

The following is a series of articles on sex-based differences in the biology of males and females:

Kreeger, K. Y. 2002. Sex-based differences continue to mount. The Scientist
When it comes to autoimmunity, the sexes respond in their own ways.

Kreeger, K. Y. 2002. X and Y chromosomes concern more than
reproduction. The Scientist 16[3]:25.
Clues lie within about which sex is more predisposed to various diseases.

Kreeger, K. Y. 2002. Yes, biologically speaking, sex does matter. The
Researchers move beyond the basics to better understand the differences between men and women.

Kreeger, K. Y. 2002. Sex-based longevity. The Scientist 16[10]:34.
Societal and lifestyle differences — not biology — appear to have the greatest influences on whether men or women live longer.

Series Directory

Rediscovering Biology: Molecular to Global Perspectives


Produced by Oregon Public Broadcasting. 2003.
  • ISBN: 1-57680-733-9