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Chapter 5: Problem 101

Female heterogamety is found in (a) Human (b) Drosophila (c) Chicks (d) All of these

Short Answer

Expert verified
The correct answer is (c) Chicks. This is because in chicks, the females are the heterogametic sex (ZW), unlike humans and Drosophila where the males are the heterogametic sex (XY).

Step by step solution

01

Understand Heterogamety

First, get an understanding of what heterogamety is. In heterogametic sex, two types of gametes are produced with respect to sex chromosomes. In humans, males are heterogametic with XY sex chromosomes, while females are homogametic with XX sex chromosomes.
02

Analyzing each option

(a) Humans: In humans, males are the heterogametic sex (XY), not the females. So, this option is incorrect.\n\n(b) Drosophila: Similarly, in Drosophila, males are heterogametic (XY) and females are homogametic. So, this option is also incorrect.\n\n(c) Chicks: In birds (like chicks), females are the heterogametic sex, symbolized as ZW, while males are homogametic ZZ. So, this option is correct.
03

Final checking

Therefore, the correct answer to the question which of these organisms presents female heterogamety is 'chicks', and not all of them.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Sex Chromosomes
Sex chromosomes are special types of chromosomes that determine the sex of an organism. Unlike autosomes, which are chromosomes not involved in sex determination, sex chromosomes are different in each sex of a species toward the overall composition of their genetic makeup.

In most mammals, including humans, there are two types of sex chromosomes known as the X and Y chromosomes. Males typically have one X and one Y chromosome (XY), while females have two X chromosomes (XX). These pairings influence physical and reproductive characteristics.
  • XX chromosomes generally lead to female development.
  • XY chromosomes generally lead to male development.
However, this XX/XY system is just one way sex can be determined in the animal kingdom.
Heterogametic Sex
The term "heterogametic sex" refers to the sex of a species that has two different kinds of sex chromosomes. This means that during gamete formation, two different types of gametes are produced with respect to the sex chromosome.

In humans and most other mammals, males are the heterogametic sex, with one X and one Y sex chromosome, producing two different gametes (sperm with either an X or a Y chromosome). This contrasts with the homogametic sex, where the sex chromosomes are the same, such as the XX genotype in human females.
ZW System
The ZW sex-determination system is an alternative to the more widely recognized XY system. It is used by several animal groups, such as birds, reptiles, and some fish and insects. This system is interestingly opposite to the human mechanism in that the female is the heterogametic sex.

  • ZW individuals are female.
  • ZZ individuals are male.
In the ZW system, female gametes (eggs) determine the sex of the offspring, since they can carry either a Z or a W chromosome, unlike the male gametes (sperm), which only carry the Z chromosome.
Birds
Birds, like chicks, utilize the ZW sex determination system, unlike mammals, which generally use the XY system. In birds, females possess ZW sex chromosomes whereas males have ZZ sex chromosomes.

Thus, female birds are heterogametic, producing two types of gametes (Z or W), while males are homogametic, producing only Z-type gametes.

This makes female heterogamety a special feature of bird genetics, while male heterogamety (like in humans) is more common in the mammalian world.
Genetics
Genetics is the scientific study of heredity and the variation of inherited characteristics. It examines how genes, which are the coding units of inheritance, operate and how they are passed on from parents to offspring.

A fundamental concept in genetics is understanding how sex is determined in various species, which involves exploring the roles of sex chromosomes and different systems like XY and ZW. Geneticists explore how traits, including those linked to sex, are transmitted and expressed. This deepens the understanding of biological diversity and also aids in explaining phenomena such as female heterogamety seen in birds and some reptiles.

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Most popular questions from this chapter

In Mendelian dihybrid cross, how many individuals are heterozygous of both the character in \(\mathrm{F}_{2}\) -generation? (a) \(\frac{1}{16}\) (b) \(\frac{2}{16}\) (c) \(\frac{3}{16}\) (d) \(\frac{4}{16}\)

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