1. Module 3

1.19. Page 4

Lesson 4

Module 3—The Male and Female Reproductive Systems

Lesson Summary

 

In Lesson 4 you investigated the following focusing questions:

  • How is gender determined at conception?

  • How do the X and Y chromosomes and hormonal influences form gonads and reproductive organs in the female and male embryo and fetus?

Sexual reproduction is necessary to provide variation in a species. The formation of male and female genders in embryos is a complex process that is influenced by chromosome structure and the secretion of sexual hormones. Since all eggs carry the X chromosome, and the sperm carries either an X or a Y chromosome, the male parent determines gender. Typically, for an organism to be male, it must carry the XY sex chromosomes; for an organism to become female, it must carry the XX sex chromosomes. Once the chromosomal structure of the individual is determined, various hormones continue the sexual development of the embryo.

 

For a male embryo to develop the SRY region with the TDF gene, a chain of events begins that leads to the production of testosterone and the eventual outcome of a male fetus. Although the process is not fully understood, the chain of events that leads to the development of a female embryo occurs due to lack of testosterone and other male hormones. Ovaries and the hormones they produce lead to the development of a female fetus.

 

Gender determination begins at conception but continues through to puberty, when the final stages of sex determination are completed. Different genders within a species ensure variation and, ultimately, continuation of a species.

 

Lesson Glossary

 

Consult the glossary in the textbook for other definitions that you may need to complete your work.

 

androgens: male group of steroid hormones; includes testosterone

 

fraternal (dizygotic) twins: twins produced when two different eggs are fertilized by two different sperm; not identical and may be of different genders

 

gender: the sex of an organism

 

gestation: the period of pregnancy

 

puberty: the period when reproductive abilities begin

 

sex characteristics: structures and characteristics that differentiate one gender from the other

 

sex chromosomes: the twenty-third pair of chromosomes that determines gender

 

XX is female, XY is male.

 

testis determining factor (TDF): a protein produced by a gene on the Y chromosome, which results in male primary sex characteristics

 

testosterone: male sex hormone secreted by interstitial cells of the testes; results in male primary and secondary sex characteristics

 

X chromosome: the larger sex chromosome with many more genes than Y

 

Y chromosome: a small sex chromosome that contains the TDF gene; determines maleness of fetus