Heredity and Evolution Notes Class 10 Notes

Hereditary and Evolution Class 10 Notes: Hereditary is the transmission of traits or characters from parents to their offspring through genes. Offspring may not inherit the same combination of genes from their parents which can result in variations in physical characteristics. This variation causes rise to the evolution of species.

The CBSE Science Heredity and Evolution Class 10 Notes are provided here for quick revision. We have also provided Heredity and Evolution Class 10 important questions for last-minute preparation.

Heredity

Heredity, which is also known as inheritance or biological inheritance, refers to the process by which genetic information, carried in the form of DNA, is passed from parents to offspring.

This can occur through either asexual reproduction or sexual reproduction. Heredity involves the transmission of traits and characteristics from one generation to the next through the transfer of genetic material known as genes. The heredity passing over of genes happens in random combination that gives rise to variation. This variation allows for genetic diversity within a population and gives rise to the possibility of evolution.

Genes

Genes are the basic unit of heredity. These are the short segments of DNA  that encode specific proteins or RNA molecules. This helps in maintaining generational variation and the evolution of species.   

Traits                

Traits refer to any observable characteristic of an organism. There are two types of traits:

• Inherited Traits: They are passed down from parents to offspring through genetic material in the form of genes. For example, if both the parents have brown or black hair, the offspring may inherit either brown or black hair or a combination of the two.
• Acquired Traits: They are the traits which are developed because of the surrounding environments effect. These are not code via DNA.

Mendels Experiment

• Gregor Johann Mendel, widely regarded as the ‘Father of Genetics’, conducted experiments on pea plants with the aim of comprehending the principles of heredity.
• The rules of inheritance of traits are based on the fact that genetic material is contributed equally by both mother and father. Thus, for each trait, a child will inherit two versions, or alleles.
• Mendel proposed 3 laws known as Laws of Inheritance.
• Mendel’s experiments demonstrated the principles of inheritance and the concept of dominant and recessive traits.

Characteristics of Mendel Experiment

Dominant and Recessive Traits

A dominant trait is one that is expressed when at least one copy of the dominant allele is present in an organism’s genotype. For example In Mendel’s experiment height is the dominant trait.                                          

A recessive trait, on the other hand, is expressed only when two copies of the recessive allele is present in an organism’s genotype. For example Mendel’s short height of pea plant.      

Monohybrid Cross

A cross between two organisms that involves only one character is referred to as a monohybrid cross.                                                                           

Monohybrid Cross

Mendel bred pea plants that differed in one specific trait, such as the height of the pea plant. He first crossed two plants that were true-breeding for different heights, one with tall height and the other with short height. The height of the plant offspring was all tall. He called this generation as F1 generation. Next, he crossed two of the F1 plants with each other and observed that the resulting offspring, the F2 generation, had a 3:1 ratio of tall to short plants. This meant that the trait for tall height was dominant over the trait for short height.

Dihybrid Cross                                           

A cross between two organisms that involves two characters is referred to as a Dihybrid cross.

Mendel chose two pea plant characteristics, seed color, and seed shape, and crossed two true-breeding plants that had different alleles of both traits. One parent had a round, yellow seeds (RRYY), and the other had wrinkled, green seeds (rryy). The offspring, called the F1 generation, all had a round, yellow seeds (RrYy), which showed that one allele of each trait was dominant over the other.

Dihybrid Cross

Mendel then crossed two of the F1 plants with each other to create the F2 generation. He observed that the offspring had a 9:3:3:1 ratio of seed types, with 9 plants having round and yellow seeds, 3 plants having round and green seeds, 3 plants having wrinkled and yellow seeds, and 1 plant having wrinkled and green seeds.    

Laws of Inheritance                 

The laws of inheritance were given by Mendel to describe how traits are passed from parents to offspring through genetic mechanisms such as segregation and independent assortment.

Laws of Mendel

• Law of dominance: Also known as the first law of inheritance. In organisms having contrasting traits, only one trait of the pair appears in the F1 generation during the crossing. This trait is called a dominant trait while the trait not expressed is called a a recessive trait.
• Law of segregation: states that traits for each pair of genes separate or segregate from each other during gamete formation, so that each gamete carries only one trait for each gene
• Law of independent assortment: States that alleles for separate or contrasting traits are passed independent of each other during gamete formation. For example Mendelian Dihybrid cross.   

How do These Traits Get Expressed?

• The DNA present in the cells serves as a source of information for synthesizing proteins. A gene is a segment of DNA that provides the instructions for making a specific protein.
• Every cell contains a pair of each chromosome, with one chromosome inherited from each parent. During germ cell formation, each germ cell acquires one chromosome from each pair, randomly inherited from either the mother or the father. When two germ cells combine during fertilization, they restore the original number of chromosomes in the offspring, ensuring the stability of the species’ DNA.

Sex Determination

The process of sex determination is influenced by genetic factors that determines the sex of the offspring.

Sex Determination

• The determination of the sex of a newborn, varies among different species, with each utilizing a unique approach. In some species, environment influences the sex of their offspring implying genetic factors do not exclusively determine sex.
• Human chromosomes are present in pairs, with one copy inherited from each parent.  
• 22 pairs of such chromosomes are called an autosomal chromosomes. One pair of chromosomes that determines the sex of an individual is known Sex chromosome.
• Women have XX chromosomes and Men have XY chromosomes(The Y chromosome is smaller than the X chromosome).
• The sex of a child depends on the chromosome they receive from their father.  

Heredity and Evolution Class 10 Important Questions for Last-Minute Preparation

Heredity and Evolution Class 10 Notes question answer is given here. These are some of the important questions that can be asked in the Class 10 and hence helpful for the last minute preparation.

What is the Difference between Heredity and Variation?

Heredity is the passing over of traits from parents to offspring that maintains consistency in characteristics, while variation denotes the differences observed among individuals within a species due to genetic and environmental factors.

What is the Role of DNA in Heredity?

DNA carries genetic information in the form of genes, which are inherited from parents to offspring. Through processes like replication, transcription, and translation, DNA directs the synthesis of proteins responsible for traits passed down through generations.

What is the Difference between Dominant and Recessive Alleles?

Dominant alleles exhibit their effect in the presence of a recessive allele, whereas recessive alleles are only expressed when two copies are present. Dominant alleles mask the expression of recessive alleles in heterozygous individuals, resulting in observable traits.

How does Sex Determination Occur in Humans?

Sex determination in humans is influenced by the combination of sex chromosomes inherited from parents. Females typically have two X chromosomes (XX), while males have one X and one Y chromosome (XY). The presence of the Y chromosome determines male development, while its absence leads to female development.

How can Mendel’s Experiment help in Knowing if the traits are Dominant or Recessive?

Mendel’s experiments involve cross-breeding pea plants with different traits and observing the traits expressed in offspring. By analyzing the ratios of dominant to recessive traits in subsequent generations, Mendel could determine whether a trait was dominant or recessive based on the patterns of inheritance observed.

What are the Mendel’s Laws of Inheritance?

Mendel’s Laws of Inheritance describe the patterns of inheritance for traits in organisms. They include:

1. Law of dominance: In organisms having contrasting traits, only one trait of the pair appears in the F1 generation during the crossing. This trait is called a dominant trait while the trait not expressed is called a a recessive trait.
2. Law of Segregation: During gamete formation, the alleles for each gene spearates from each other so that each gamete carries only one allele for each gene.
3. Law of Independent Assortment: Genes for different traits are inherited independently of each other. This means the inheritance of one trait does not influence the inheritance of another trait.