Intro-
#Mendel’s idea was that distinct differences between individuals are determined by differences in single yet powerful hereditary factors.
#These single hereditary factors were identified as genes.
#Copies of genes are transmitted through sperm and egg and guide the development of the offspring.
#Genes are also responsible for reproducing the distinct features of both parents that are visible in their children.
#Experimented on Garden pea Pisum sativum.
Characters studied by Mendel
Mendel chose seven pairs of contrasting traits, namely plant height, flower position, pod colour, pod shape, seed colour, seed shape and flower colour. The terminal flower position was recessive to axial position; yellow seed colour was recessive to green colour; green pod colour was dominant to yellow and round seed shape was dominant to wrinkled shape.
Laws of inheritance-
Law of Dominance-
#Mendel’s law of dominance states that:
“When parents with pure, contrasting traits are crossed together, only one form of trait appears in the next generation. The hybrid offsprings will exhibit only the dominant trait in the phenotype.”
# first law of inheritance. I
# In this law, each character is controlled by distinct units called factors, which occur in pairs.
#Law of dominance explains that in a monohybrid cross between a pair of contrasting traits, only one parental character will be expressed in the F1 generation and both parental characters will be expressed in the F2 generation in the ratio 3:1.
#The one which is expressed in the F1 generation is called the dominant trait and the one which is suppressed is called a recessive trait. In simple words, the law of dominance states that recessive traits are always dominated or masked by the dominant trait.
Law of segregation-
#Mendel’s law of segregation states that:
“During the formation of gamete, each gene separates from each other so that each gamete carries only one allele for each gene.”
# second law of inheritance
#In a monohybrid cross, both the alleles are expressed in the F2 generation without any blending. Thus, the law of segregation is based on the fact that each gamete contains only one allele.
#This law is based on four basic concepts:
1-A gene exists in more than one form of an allele.
2-When gametes are produced by meiosis, the allelic pairs separate, leaving each gamete with a single allele.
3-Every organism inherits two alleles for each trait.
4-The two alleles of a pair are different, i.e., one is dominant and one is recessive.
Law of independent assortment
#“The law of independent assortment states that the allels of different genes are inherited independently within the organisms that reproduce sexually.”
#According to the law of independent assortment, the alleles of two more genes get sorted into gametes independent of each other. The allele received for one gene does not influence the allele received for another gene.
#Reasons for Independent Assortment
Independent assortment takes place during the process of meiosis. In this process, the chromosomes are halved and are known as haploid.
#Law of independent assortment states that the gene of different trait all situted in different places in a chromosome.
Each trait have pair of gene.
During gamete formation, each character are independent from each other during segrigation of gametes.
#Mendalian recombination was due to independent assortment.
#This law was proved by Di_Hybrid cross and phenotypic ration i.e=9:3:3:1
NCERT Solutions for Class 12 Biology Chapter 5 This topic
Exercise : Solutions of Questions on Page Number : 93
Q1 : Mention the advantages of selecting pea plant for experiment by Mendel.
Answer :
Mendel selected pea plants to carry out his study on the inheritance of characters from parents to offspring.
He selected a pea plant because of the following features.
(a) Peas have many visible contrasting characters such as tall/dwarf plants, round/wrinkled seeds, green/yellow pod,
purple/white flowers, etc.
(b) Peas have bisexual flowers and therefore undergo self pollination easily. Thus, pea plants produce offsprings with
same traits generation after generation.
(c) In pea plants, cross pollination can be easily achieved by emasculation in which the stamen of the flower is
removed without affecting the pistil.
(d) Pea plants have a short life span and produce many seeds in one generation.
Q2 :
Differentiate between the following -
(a) Dominance and Recessive
(b) Homozygous and Heterozygous
(c) Monohybrid and Dihybrid.
Answer : (a) Dominance and Recessive Dominance Recessive
1. A dominant factor or allele expresses itself in the
presence or absence of a recessive trait.
A recessive trait is able to express itself only in
the absence of a dominant trait.
2. For example, tall plant, round seed, violet flower,
etc. are dominant characters in a pea plant.
For example, dwarf plant, wrinkled seed, white