Haplodiploid Sex Determination

Summary

This script delves into the fascinating world of sex determination across various species, highlighting the XY system in humans and the diverse mechanisms in others like spiders, butterflies, birds, and honeybees. It explores the discovery of honeybee genetics by Johannes Json, the haplodiploidy system, and the role of the CSD gene. The narrative also touches on the importance of population genetics, the maintenance of sex allele diversity, and the evolutionary implications of polyandry in honeybee queens.

Takeaways

• 🧬 Human sex determination is based on the combination of X and Y chromosomes: XX for females and XY for males.
• 🕷 Spiders have an XO system where males lack a Y chromosome, and XX indicates females.
• 🦋 In butterflies, males are ZZ and females can be ZW or have missing sex chromosomes, unlike the human XY system.
• 🐦 Birds have a ZW system where males are homogametic and females are heterogametic.
• 🐢 Turtles exhibit temperature-dependent sex determination, where the environment dictates the sex of the offspring.
• 🐝 Honeybees have a haplodiploid sex determination system where males develop from unfertilized eggs and are haploid, while females are diploid.
• 🏆 Johannes Json proposed that male honeybees develop without fathers, a discovery that led to the understanding of honeybee sex determination.
• 🧬 Honeybee sex is determined by a single gene, the CSD gene, which has multiple alleles that can combine to form either viable females or diploid males.
• 🐝 Diploid male honeybees are not viable and are consumed by nurse bees shortly after hatching.
• 🧬 The honeybee population maintains a balance of different sex alleles through natural selection, favoring rare alleles to prevent frequent production of diploid males.
• 🐝 Queens mate with multiple males to increase brood viability and reduce the chances of producing diploid males, supporting the evolution of polyandry.

Q & A

How do humans determine sex?

In humans, females have two X chromosomes (XX), while males have one X and one Y chromosome (XY). A person inherits an X chromosome from both parents; if both are X chromosomes, the individual is female, and if one is a Y chromosome, the individual is male.

What is the term 'gametes' in the context of sex determination?

Gametes are the reproductive cells (sperm and eggs) that participate in sexual reproduction. Females produce larger, stationary gametes (eggs), while males produce smaller, motile gametes (sperm).

How does the sex determination system differ in spiders compared to humans?

In spiders, the sex determination system is XO for males (missing a Y chromosome) and XX for females. This is different from humans, who have XY for males and XX for females.

What are the different sex chromosome combinations in butterflies?

In butterflies, males can be ZZ (two of the same chromosomes), while females can be either ZW (two different sex chromosomes) or ZO (missing one chromosome).

How does the environment influence sex determination in clownfish?

In clownfish, sex can change based on environmental conditions and sexual competition. They can transition from female to male or male to female depending on these factors.

What external factor determines the sex of turtles?

In turtles, sex is determined by the temperature of the soil in which the eggs are incubated, which is an external signal that dictates whether they develop into males or females.

What did Johannes Json discover about honeybee sex determination?

Johannes Json discovered that honeybee males have no fathers. He conducted experiments with unmated queen bees that still produced males, suggesting that males develop from unfertilized eggs.

What is the term 'haploidy' in relation to honeybee sex determination?

Haploidy refers to having a single set of chromosomes. In honeybees, males (drones) develop from unfertilized eggs and thus have only one set of chromosomes, making them haploid.

What did PW Whiting propose about sex determination in parasitic wasps?

PW Whiting proposed that a single gene is responsible for sex determination in parasitic wasps. He observed diploid males, which led him to conclude that there must be a gene that determines sex, with different alleles leading to either male or female development.

What did Otto Mackensen discover about honeybee sex determination?

Otto Mackensen proposed that honeybees have a similar sex determination system to parasitic wasps, with a gene series that determines sex. He suggested that matings between a queen and a drone with matching sex alleles would produce lethal diploid males.

What did Jaroslaw Cebra discover about diploid honeybee males?

Jaroslaw Cebra discovered that diploid honeybee males are not lethal but are consumed by nurse bees shortly after hatching. He demonstrated this by grafting drone larvae into queen cells and then transferring them back to drone combs, where they developed into diploid males.

What is the significance of the CSD gene in honeybee sex determination?

The CSD gene is the single gene responsible for determining the sex and gender of honeybees. It has multiple alleles, and different combinations of these alleles result in either diploid females or diploid males, with the latter typically being consumed by the colony.