Q.Explain sex determination in human beings.

An organism showing a mixture of male and female characters (male with female features) is a gynandromorph.

A gynandromorph is an individual whose body contains both male and female characteristics — some regions/tissues develop as male and others as female. It commonly arises from abnormal distribution of sex chromosomes during early cleavage and is well known in insects (e.g. bilateral gynandromorph fruit flies and butterflies).

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(a) Pigeon, Parrot, Sparrow.

ZW-ZZ sex determination is characteristic of birds; pigeon, parrot and sparrow are all birds, unlike bats or cats which are mammals with XX-XY determination.

In the ZW-ZZ type of sex determination, found in birds (and some reptiles/insects), the female is the heterogametic sex (ZW) and the male is homogametic (ZZ) - the reverse of the mammalian XX-XY system. Pigeon, Parrot and Sparrow are all avian species and therefore all show ZW- …

In the ZW-ZZ system taught in the syllabus, females are heterogametic (ZW) and males are homogametic (ZZ), a pattern characteristic of birds.

Sex determination mechanisms vary across taxa. In the ZW-ZZ system, the female carries two different sex chromosomes (ZW) and is therefore the heterogametic sex, while the male carries two identical Z chromosomes (ZZ) and is homogametic — the reverse of the mammalian XY system. This is the pattern taught for birds (e.g., poultry). Option (a) Reptiles as a group are more commonly associated with temperature-dependent sex determination (in many turtles and crocodilians) or an XY-type system (in some lizards/snakes), not uniformly ZW-ZZ. Option (c) Fishes show a wide diversity of …

XX and XY are the sex chromosomes (allosomes) that determine the sex of an individual.

Chromosomes that determine the sex of an organism are called sex chromosomes or allosomes, as distinguished from autosomes, which do not determine sex. In humans, the female has a homomorphic pair (XX) and the male has a heteromorphic pair (XY); this XX-XY system of sex determinatio …

The XX-XO sex-determination system really does occur in bedbugs, cockroaches and grasshoppers, and it works exactly because the sex-determining sperm may or may not carry an X chromosome.

In the XX-XO system, females have two X chromosomes (XX) while males have only a single X and no corresponding sex chromosome (XO); this pattern is documented in several insect groups including bedbugs, cockroaches and grasshoppers, confirming the assertion. During spermatogenesis in XO males, meiosis produces two classes of sperm -- one carrying the single X chromosome and one carrying no sex chromosome at all -- so whichever type of sperm fertilises the female's X-bearing egg determines whether the offspring becomes XX (female, if X-bearing sperm fertilises) or XO (male, if the X-less sperm …

(b) Honey bee — shows haplo-diploid sex determination, where fertilised (diploid) eggs develop into females and unfertilised (haploid) eggs develop into males.

Honeybees show haplo-diploidy: diploid eggs become female, haploid eggs become male.

In the haplo-diploid mechanism of sex determination, seen in honeybees and many other Hymenoptera, sex is not determined by a pair of sex chromosomes but by chromosome number itself. Fertilised eggs are diploid (having received both a maternal and a paternal set of chromosomes) and develop into females (queens or worker bees), while unfertilised eggs rema …

(c) Bird — in birds, the female is the heterogametic sex (ZW) and the male is homogametic (ZZ), the ZW-ZZ mechanism of sex determination.

Birds show ZW (female) - ZZ (male) sex determination.

Sex-determination mechanisms vary across animal groups. In the ZW-ZZ type (found in birds, and also in some fish, reptiles and butterflies/moths), it is the female that is heterogametic, carrying one Z and one W chromosome (ZW), while the male is homogametic, carrying two Z chromosomes (ZZ) — the reverse pattern from the familiar human XX (female)-XY (male) system. Hon …

The X chromosome is comparatively large and metacentric/submetacentric, while the Y chromosome is much smaller and acrocentric. The X chromosome carries many genes (X-linked traits such as colour blindness and haemoph...

X and Y chromosomes differ markedly in size, shape and gene content, though both are involved in human sex determination.

The X and Y chromosomes, while both classified as sex chromosomes, differ in several respects. In size and shape, the X chromosome is comparatively large, roughly metacentric to submetacentric in structure, whereas the Y chromosome is significantly smaller and acrocentric. In gene content, the X chromosome carries a large number of genes, including many unrelated to sex determination (giving rise to X-linked traits such as red-green colour blindness and haemophilia), while the Y chromosome carries relatively very few genes, the most important being the SRY (sex-determining region Y) gene, which triggers development of the testes and male characteristics in the embryo. Additionally, the X chromosome is present in two copies in females and one copy in males, wherea …