Chapter 7 Flashcards
Define sexual differentiation
A fetus following a unique developmental path according to its sex.
When does sexual differentiation begin?
Around the 5th week of gestation
What to fetus begin developing into before differentiating?
Female. The presence of the Y-chromosome overrides the “default setting”.
What is Turner Syndrome?
People with only 1 X-chromosome
Define the pseudoautosomal region
The ends of the sex chromosome. They are homologous with each other, allowing for alignment between the X & Y chromosomes during meiosis.
What is the SRY gene?
Sex-determining region of the Y-chromosome. Produces the testes determining factor
Define the testes determining factor
A transcription factor that causes testes development and male development.
Define a transcription factor
Induces transcription/activation of many other genes
How many genes does the Y-chromosome have?
~150 poorly-understood genes. Previously thought as a wasteland of junk DNA (this is not true!)
What happens to people who lose their Y chromosome after development?
Higher risk of cancer and addition, impaired immunity against sicknesses.
How many genes are on the X-chromosome?
~1000 genes
What genes are on the X chromosome?
Diverse biological processes including sexual development, immunity, and cognitive development
Why must one of the X chromosomes in females be inactivated?
2 active copies of the X is harmful to health, so 1 X chromosome must be inactivated in each cell.
Each cell randomly inactivates a different X.
Define X inactivation
AKA dosage compensation. When one X chromosome is inactivated in each female cell.
How does X-inactivation occur?
One X-Chromosome produces an RNA molecule called Xist. Xist RNAs coat the other X chromosome, causing it to condense and ecome nonfunctional.
Define Barr Body
A condensed X-chromosome that has no gene expression.
Define sex ratio
Ratio of males : females in a population
Define primary sex ratio
Amount of males:females at CONCEPTION
Define secondary sex ratio
Amount of males:females at BIRTH
What are the primary and secondary sex ratios?
1.05male:1female
Why are these ratios slightly skewed?
Males have a higher mortality rate. Since they take on more societal roles and are more risk-taking/reckless, a slight amount more of men are born.
How is a fetus’ sexual development influenced?
By the environment of their mother
How can the mother’s environment influence sexual development?
- Slight alteration of the primary/secondary sex ratio
-Impair male masculinity or female femininity.
How can a mother’s environment alter primary/secondary sex ratios?
Due to the Willard-Trivers Hypothesis. Causes an asymmetric breeding by gender, as all females have a chance to reproduce but not all males reproduce (some DONT reproduce, some reproduce a lot)
Define the Willard-Trivers Hypothesis (4points)
- A stressful environment creates a low-quality child
-A low quality female is more fertile than a low-quality male
-A high quality male is more fertile than a low-quality female
-To maximize fecundity, there is a bias of offspring gender towards female in a stressful envrionment, and towards male in a non-stressful/good environment.
How can a mother’s environmnt influence masculinity/femininity?
Maternal stress results in high cortisol, which can cause many health problems in the fetus.
What does high cortisol do to a fetus?
Impairs testosterone surge in male fetus, hindering normal male sexual development and altering behavior.
Female fetus’ are generally more resilient to cortisol leels.
What 2 main environmental factors can influence masculinity/femininity?
- Maternal psychological stress
- Endocrine-disrupting chemicals
Since infertility rates are rising….
Society is dying
Define heterogametic
Sex has 2 different chromosomes in a species (ex. male in humans are XY)
Define homogametic
Sex has 2 of the same chromosomes (ex. females in humans are XX)
Define hermaphrodites
Species tht have both testes and ovaries
What is an example of a hermaphrodite?
Nematodes (C. elegans).
Males can impregnate hermaphrodites, and hermaphrodites can also impregnate themselves.
Define temperature-dependent sex determination
Higher or lower temperature in the environment results in an alteration of the sex while a species is in fetus/egg.
