Sex Determination-In Humans, Birds, Honey bee

Introduction

The establishment of sex in an organism or progeny through differential development is known as sex determination. It decides whether the baby will be male or female. For this objective, different animals employ a variety of tactics. Some organisms, such as turtles, rely only on environmental conditions to determine their sex, such as temperature. While human sex, as well as that of insects such as grasshoppers, fireflies and Drosophila is determined genetically.

Types Of Chromosomal Basis of Sex Determination

Here’s the sex determination in humans, birds, honey bee classification.

1) XO type (XX-XO type): It can be found in various insects, including grasshoppers. Male and female individuals have differing numbers of chromosomes. All eggs (ova) include an additional X-chromosome in addition to the autosomes. However, only 50% of sperms have X-chromosomes. In grasshoppers, eggs fertilised with (A+X) type sperm develop into females, whereas eggs fertilised with (A+O) type sperm develop into males. As a result, sperm decides the offspring’s gender. The X-chromosome was identified as the sex chromosome because of its role in determining sex.

2) XY type (XX-XY) type: Males in a variety of insects, including Drosophila and mammals, including humans, have two types of sex chromosomes (X and Y), while females have two types of sex chromosomes (X and Y) (XX). The number of chromosomes in both males and females is the same. The Y-chromosome in males is frequently shorter than the X-chromosome.

3) ZW type (zz-zw) type- sex chromosomes in birds are designated Z and W, and the male is the homomorphic sex (ZZ) and the female heteromorphic (ZW). In most avian species the Z chromosome is a large chromosome

Sex Determination in Humans, Birds & Honey Bee

• Humans

The male-specific Y chromosome is important for determining sex in humans and contains genes necessary for spermatogenesis in humans. However, not all of the genes required to form a testis or germ cells must be found on the Y chromosome; several are known to be found on the X chromosome or the autosome. Males have a single X and a single Y chromosome(XY), while females have two X chromosomes (XX) .

Apart from the autosome, 50% of the total sperm generated have the X-chromosome, and the other 50% have the Y-chromosome. Fertilisation of the ovum (22+X) with sperm carrying either the X or y chromosome has an equal chance. The zygote develops into a female (44+ XX) if it fertilises the ovum (22+ X) type sperm.

As a result, the sex of the kid is determined by the genetic makeup of the sperm. It is also obvious that each pregnancy has a 50% or 1/2 chance of producing either a male or female child.

• Birds

In birds, the sex chromosomes are labelled Z and W, with the male being homomorphic (ZZ) and the female being heteromorphic (ZW). The Z chromosome is large in most bird species, usually the fourth or fifth largest and it contains almost all of the known sex-linked genes. The W chromosome is a significantly smaller micro chromosome with a large amount of repetitive sequence DNA. 

• Honey Bee

In honey bees, sex determination is based on the number of chromosomes an individual receives. By parthenogenesis, an offspring created by the combination of a sperm and an egg develops as a female (queen or worker), while an unfertilised egg develops as a male (drone).

Parthenogenesis is of the following types:

>Thelytoky: This type of parthenogenesis produces females solely. Rotifers are an example.

>Arrhenotoky: Parthenogenesis is used to create men in this type. For example honey bees.

>Amphitoky: The parthenogenetic egg can form any sex in this case. For example  Aphis.

This indicates that males have half the number of chromosomes as females. Males are haploid, with 16 chromosomes, whereas females are diploid, with 32 chromosomes. This is known as the haplodiploid sex-determination system, and it has unique characteristics such as men producing sperm through mitosis, the lack of a father and therefore the inability to have sons, but the presence of a grandfather and the ability to have grandsons.

Males in Arrhenotoky are haploid (as they are formed from parthenogenesis). The females have a diploid chromosome. Male gametes (haploid) will go through mitosis and develop into male sex cells (sperms are also haploid). Meiosis will occur in the diploid eggs, resulting in haploid daughter cells or eggs.

The result of a haploid egg combining with haploid sperm is a diploid female. They will generate haploid males again if the haploid eggs do not unite with the sperm.

Features of a Haploid Male Honey Bee

• A haploid male honey bee contains a single pair of chromosomes

• Sperm cells are created through mitosis

• A male bee’s genetic makeup is entirely acquired from its mother

• When a queen bee mates, her genetic material is recombined for an inheritance, but the daughter’s offspring inherits the drone’s chromosomes

• A drone has no father and no sons, but it has a grandpa and can have grandsons
• One advantage of haploid male honey bees is that lethal mutations are cleared out early and hence they cannot pass on the mutation to their offspring

Note: Three different varieties of bees may be seen in the beehive, these are the male or drone bees, queen bees and worker bees. Also, note that queen and worker bees are females, making them diploid, whereas drones are males, making them haploid.

Conclusion

We’ve learned about sex determination in humans, birds and honey bees, their definition, their classification and more. It is fair to state that the subject is huge, and understanding it in depth would take time and effort. Hope the content helped you clear some basics of sex determination.