Module 3S1 Reproductive Systems

Reflect and Connect

 

From the time a pregnancy is identified, everybody wonders if the developing baby will be a boy or a girl. Normal embryonic sex determination is a complex process requiring that numerous events  take place in the correct order. If all events proceed successfully a “gender-normal” boy or girl will be born.

 

Your understanding of the development of Jane and John’s twins into one female and one male child should be falling into place.    

 

Discuss

 

Choose one, some, or all of the following questions to discuss through the discussion area of your class:

1. What is the advantage of having more than one gender in a species?
2. Historically, women have been held responsible for not producing male children. How has science helped to change this view? Are there places where the historical view is still held?
3. Should gender be tested for at birth? Why or why not?
4. Are there ways to predict whether a pregnancy will result in a boy or girl before the birth?
5. How many sex chromosomes does a platypus have?

Reflect on the Big Picture

 

For Jane and John, having different gendered twins was a great way to start their family. However, during the twins development into one male and one female embryo, an abnormality developed in the female fetus. She was born with only one X chromosome, a condition called Turner’s syndrome. The explanation for and results of this missing chromosome will be discussed in Unit C.

 

Keep track of what is happening with Jane and John by recording the information you learned about their experience in your course folder.

 

Going Beyond

 

You may have noticed that there are often exceptions to the rule in biological studies. This is the case with respect to the X and Y chromosomes that determine gender. It is possible during gamete formation that the TDF gene can be transferred incorrectly or can be missing altogether. Conduct research to find out how individuals can be male with a genotype of XX and female with a genotype of XY.

 

Module 3: Section 1—Lesson 4 Assignment

 

There is no assignment for this lesson.

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 gonad 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 gender in embryos is a complex process that is influenced by chromosome structure and sexual hormones secreted. 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.