This set of Class 12 Biology Chapter 5 Multiple Choice Questions & Answers (MCQs) focuses on “Inheritance and Variation Principles – Sex Determination”.
1. Which of the following animals rely on environmental factors for sex determination?
Explanation: Turtles are one of the organisms which rely on environmental factors for sex determination completely. They usually depend upon temperature for this purpose.
2. How is the sex of grasshopper determined?
Explanation: The sex of a grasshopper is determined genetically. Some experiments were carried out by some of the scientists on insects to study the genetic or chromosomal mechanism of sex determination.
3. The chromosomal basis of sex determination was discovered by which of the following scientists?
Explanation: The foundation of the chromosomal basis of sex determination was laid down by Henking in 1891. He studied a specific nuclear structure though spermatogenesis in a few insects.
4. Henking gave the term X chromosome.
Explanation: Henking was studying spermatogenesis in insects where he observed that only 50% of the sperms received a structure which he later termed as ‘X body’. But he could not explain the significance of this body.
5. Which of the following scientists discovered the Y-chromosome.
b) Ernst Haeckel
c) Francis Crick
Explanation: Stevens was the scientist who first discovered Y-chromosome. Many scientists concluded that the ‘X body’ which was discovered by Henking was a chromosome. Therefore, in 1905, X and Y chromosomes were named as sex chromosomes by Stevens and Wilson.
6. In which of the following organisms, the male heterogametic condition is not observed?
Explanation: Birds do not show male heterogametic conditions. Instead, they show the female heterogametic condition. Male heterogametic condition is characterised by male individuals producing two different types of gametes.
7. Which of the following determines the sex of the offspring in male heterogametic conditions?
c) Both egg and sperm
d) It cannot be determined
Explanation: When the condition of male heterogamety is present, then sperm determines the sex of the offspring because two kinds of sperms are present, one with X-chromosome and the other with Y-chromosome. Eggs of an individual are the same as both of them contain 22+ X chromosomes.
8. In which of the following animals, there is a difference between the male and female numbers of chromosomes?
Explanation: In a grasshopper, male and female individuals have a different number of chromosomes because grasshoppers exhibit XO type of male heterogamety where 2 kinds of sperms are formed- one with X-chromosome and the other with no sex chromosome.
9. Which of the following does not show XY type of male heterogametic condition?
b) Human beings
Explanation: Grasshoppers do not show XY type of male heterogametic condition. XY type of male heterogametic condition is shown by a number of insects like Drosophila and mammals including human beings and elephants, the males in this type bear two types of sex chromosomes- X and Y type.
10. Y chromosome is always larger than the X-chromosome.
Explanation: Y-chromosome is not larger than X-chromosome, instead, it is often shorter than X-chromosome. In XY type of male heterogametic condition, both males and females have the same number of chromosomes.
11. What is the probability of having a girl child in sixth pregnancy if the first five progenies are boys?
Explanation: The probability of having a girl child in the sixth pregnancy, where the first five progenies were male is 50%. As humans show XY type of male heterogamety, where 50% sperms carry 22+ X chromosomes and the other 50% carry 22+Y chromosomes, therefore in each pregnancy there is 50% probability of either a male or a female child.
12. What is the full form of TDF?
a) Testis determining factor
b) Testes development factor
c) Thyroxine determining factor
d) Thyroid developing factor
Explanation: TDF stands for testis determining factor. TDF is essential for the development of male sex organs and if it is not produced in the body then it leads to the formation of the female sex organ.
13. The given figures show which of the following species of organisms?
Explanation: The 1st figure represents a male fruit fly and 2nd figure represents a female fruit fly. Drosophila melanogaster which is used as a material for experimental genetics because it could be easily grown on a simple synthetic medium in the laboratory and a single mating produces a large number of offspring. Also, females are easily distinguishable from the males by the larger body size and the presence of an egg-laying structure.
14. Which of the following organisms does not show female heterogametic conditions?
Explanation: Grasshoppers do not show female heterogametic conditions. Butterflies, moths, and birds show female heterogametic conditions where female individuals produce two different kinds of gametes.
15. In which of the following organisms, male has half the number of chromosomes than female?
c) Honey bees
Explanation: The female progeny of a honey bee develops from the union of a sperm and an egg whereas a male progeny develops from an unfertilised egg by the means of parthenogenesis. This means that the males have half the number of chromosomes than that of a female.
16. What kind of sex-determination system is present in honey bees?
d) XY type
Explanation: Honey bees exhibit a haplodiploid type of sex-determination system. This type of system has special characteristic features like the males produce sperms by mitosis. The male individuals do not have a father and thus cannot have sons, but can have a grandfather and a grandson.
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