Model Answer
0 min readIntroduction
Sex determination, the biological process that determines an individual’s sex, varies across species. Two primary systems are observed: male heterogamety and female heterogamety. These systems differ in which sex possesses dissimilar sex chromosomes. Understanding these differences is crucial for comprehending inheritance patterns and evolutionary biology. Both systems rely on the presence of sex chromosomes, typically X and Y, but their arrangement differs significantly, leading to distinct mechanisms of sex determination.
Male Heterogamety
In male heterogamety, males possess the dissimilar sex chromosomes (XY), while females have two identical sex chromosomes (XX). The male determines the sex of the offspring. If a sperm carrying an X chromosome fertilizes an egg (X), the offspring will be female (XX). If a sperm carrying a Y chromosome fertilizes an egg (X), the offspring will be male (XY). Humans, most mammals, and many insects exhibit this system.
Female Heterogamety
Conversely, in female heterogamety, females have the dissimilar sex chromosomes (XY), while males have two identical sex chromosomes (XX). The female determines the sex of the offspring. If an egg carrying an X chromosome is fertilized by a sperm (X), the offspring will be male (XX). If an egg carrying a Y chromosome is fertilized by a sperm (X), the offspring will be female (XY). Birds, some reptiles (like snakes), and certain fish demonstrate this system.
| Feature | Male Heterogamety | Female Heterogamety |
|---|---|---|
| Sex Chromosomes (Male) | XY | XX |
| Sex Chromosomes (Female) | XX | XY |
| Sex Determination | Male determines sex | Female determines sex |
| Examples | Humans, mammals | Birds, some reptiles |
Key Differences
- The crucial difference lies in which parent carries the sex-determining chromosome (Y).
- The Y chromosome often carries genes responsible for maleness in male heterogamety.
Conclusion
In essence, male and female heterogamety represent alternative strategies for sex determination. Male heterogamety is more common across species, but female heterogamety is prevalent in birds and some reptiles. Understanding these systems is fundamental to comprehending the genetic basis of sex and its evolutionary implications. The differing chromosomal arrangements highlight the diversity of reproductive strategies in the animal kingdom.
Answer Length
This is a comprehensive model answer for learning purposes and may exceed the word limit. In the exam, always adhere to the prescribed word count.