Class 10 Exam  >  Class 10 Notes  >  Science Class 10  >  DNA & Sex Determination

DNA & Sex Determination | Science Class 10 PDF Download

How do Traits get Expressed?

Deoxyribonucleic Acid (DNA)


The expanded form of DNA is deoxyribonucleic acid. It was first isolated by the scientist Frederick Meisher from the nucleus of the pus cells in 1869. He named it as 'nuclein' or nucleic acid because of its acidic nature. Later, it was experimentally proved by the scientists Griffith (1928), Avery, McLeod and McCarty (1944) that DNA is the carrier of the genetic information from generation to generation. It transmits the hereditary characters in a coded language from parents to the offspring (i.e., from one generation to another).

DNA is a macro-molecule or polymer. It is made of very large number of `nucleotide' units and hence is termed as polynucleotide.

Each nucleotide unit in a DNA molecule is made up of three components:

1. Deoxyribose sugar :- It is a pentose sugar.

2. Nitrogenous base :- Each nucleotide unit has a nitrogen containing base. In a DNA molecule, nitrogenous bases are of two types :

(a) Purines :- The purines in a DNA molecule are — Adenine (A) and Guanine (G). 

(b) Pyrimidines :- The pyrimidines in a DNA molecule are — Cytosine (C) and Thymine (T). 

3. Phosphate group :- The phosphate group contains one phosphorus atom and four specifically linked oxygen atoms.

Double Helical Mode of DNA

DNA & Sex Determination | Science Class 10

Double Helical Mode of DNA

J. D. Watson and F.H.C. Crick proposed the double helical mode of DNA in 1953. They were awarded the Nobel Prize for this discovery in 1962. The important features of the double helical modes are:

(i) DNA molecule is made up of two long polynucleotide strands forming a double helical structure (double helix) just like a spiral staircase. Each helical turn of the DNA molecule is 3.4 nm in length in which ten nucleotide base pairs are present.

(ii) Deoxyribose sugar and phosphate molecules are joined alternately to form the backbone of each polynucleotide strand. The nitrogenous base of each nucleotide is attached to the sugar molecule and projected towards the interior of the double helix.

(iii) In the interior of double helix, the nitrogenous bases of two polynucleotide strands form a pair with the help of hydrogen bonds. Adenine (A) always pairs with thymine (T) and guanine (G) always pairs with cytosine (C).

Thus, the two polynucleotide strands of the DNA molecule are joined by hydrogen bonds between specific nitrogenous bases. Such a specific pairing of the bases of the opposite strands of the DNA molecule is called complementary pairing. Adenine (A) and thymine (T) are complementary to each other. Similarly, guanine (G) and cytosine (C) are complementary to each other. The hydrogen bonding between the specific nitrogenous bases keeps the two strands held together. Therefore, all the base pairs remain stacked between the two strands.

Blood Groups

Four different types of blood groups in human beings are : A, B, O, AB

O → universal donor

AB → universal recepient

Blood groupGenotypeDominantRecessive AntigenAntibody
AIIA
 IAIO
IAIOAB
BIBIB
 IBIO
 IBIOBA
ABIAIBIA,IB-A,B-
OIOIO-IO-AB

Sex Determination

How is the sex of newborn individual determined? In human beings, the sex of the individual is largely genetically determined. In other words, the genes inherited from our parents have assumed that similar gene sets are inherited from both parents. If that is the case, how can genetic inheritance determine sex ?

Al human beings these are 23 pairs of chromosomes are present out of these 23 pairs,22 are autosomes (similar in males and females) and 1 pair is called sex chromosome (different in males and females). In males, sex chromosome are XY and in females, sex chromosome are XX.

DNA & Sex Determination | Science Class 10

So, it is clear from above that male is responsible for producing male child.

Points to Remember


  • The term Genetics comes from "gene" word-means "to grow".
  • The term "Genetics" coined by Bateson.
  • Study of heredity and variations is called Genetics.
  • Father of Genetics - Gregor Johann Mendel.
  • Father of Modern Genetics - Bateson.
  • Father of Experimental Genetics - Thomus Hunt Morgan.
  • "Heredity" term coined by Spencer.
  • Bateson coined terms Genetics, Allele, Homozygous, Heterozygous, F1 and F2 Generation.
The document DNA & Sex Determination | Science Class 10 is a part of the Class 10 Course Science Class 10.
All you need of Class 10 at this link: Class 10
105 videos|457 docs|112 tests

FAQs on DNA & Sex Determination - Science Class 10

1. How is DNA related to the expression of traits?
Ans. DNA carries the genetic information that determines the traits of an organism. The sequence of DNA bases contains instructions for the production of proteins, which are responsible for the expression of traits. Through a process called gene expression, the DNA is transcribed into RNA and then translated into proteins, leading to the manifestation of specific traits.
2. What is the role of sex determination in the expression of traits?
Ans. Sex determination plays a crucial role in the expression of certain traits that are specific to males or females. In humans, for example, the presence or absence of the Y chromosome determines the development of male traits. The genes located on the sex chromosomes, such as the SRY gene on the Y chromosome, influence the expression of traits related to sexual characteristics, reproductive organs, and hormone production.
3. How does DNA contribute to the determination of an individual's sex?
Ans. The sex determination of an individual is influenced by the presence or absence of specific genes on the sex chromosomes. In humans, females have two X chromosomes (XX), while males have one X and one Y chromosome (XY). The SRY gene on the Y chromosome initiates the development of male characteristics during embryonic development. The expression of this gene leads to the production of testes and the subsequent development of male reproductive organs and secondary sexual traits.
4. What happens if there are abnormalities in the sex determination process?
Ans. Abnormalities in the sex determination process can result in conditions known as disorders of sexual development (DSD). These conditions can lead to atypical development of reproductive organs and variations in sexual characteristics. For example, individuals with Androgen Insensitivity Syndrome (AIS) have XY chromosomes but are born with female external genitalia due to the body's inability to respond to androgens. Such abnormalities highlight the intricate role of DNA and sex determination in the expression of traits related to sexual development.
5. Can traits be inherited differently based on sex determination?
Ans. Yes, traits can be inherited differently based on sex determination. Some traits are specifically linked to the sex chromosomes and may exhibit different inheritance patterns. For instance, certain genetic disorders, such as color blindness and hemophilia, are X-linked recessive traits. This means that males, who have only one X chromosome, are more likely to express these traits if they inherit a faulty gene on their X chromosome. Females, on the other hand, have two X chromosomes and would need to inherit two faulty genes to express the trait.
105 videos|457 docs|112 tests
Download as PDF
Explore Courses for Class 10 exam
Signup for Free!
Signup to see your scores go up within 7 days! Learn & Practice with 1000+ FREE Notes, Videos & Tests.
10M+ students study on EduRev
Download the FREE EduRev App
Track your progress, build streaks, highlight & save important lessons and more!
Related Searches

MCQs

,

video lectures

,

mock tests for examination

,

DNA & Sex Determination | Science Class 10

,

Important questions

,

Viva Questions

,

Semester Notes

,

Extra Questions

,

Exam

,

pdf

,

ppt

,

past year papers

,

study material

,

Free

,

Objective type Questions

,

Previous Year Questions with Solutions

,

Sample Paper

,

DNA & Sex Determination | Science Class 10

,

Summary

,

practice quizzes

,

shortcuts and tricks

,

DNA & Sex Determination | Science Class 10

;