AP Inter 2nd Year Botany Notes Chapter 9 Principles of Inheritance and Variation

Students can go through AP Inter 2nd Year Botany Notes 9th Lesson Principles of Inheritance and Variation will help students in revising the entire concepts quickly.

AP Inter 2nd Year Botany Notes 9th Lesson Principles of Inheritance and Variation

→ Gregor Johann Mendel, an Austrian Monk, discovered the basic principles of heredity through experiments on the pea plant.

→ He published the results of his studies under the title. Experiments on plant hybrids.

→ Inheritance is the process by which characters are passed on from parent to progeny. It is the basis of heredity.

→ Mendel selected garden pea plant for his hybridisation experiments, because

  • It is an annual plant that has well defined characters.
  • It can be grown and crossed easily.
  • It has bisexual flowers and has a short life cycle.

→ Mendel studied some centrastic traits in pea. They were
a) Stem height – Tall or dwarf
b) Flower colour – Violet or white
c) Flower position – Axial orterminal
d) Pod shape – Inflated / constricted
e) Pod colour – Green or yellow
f) Seed shape – Round or wrinkled
g) Seed colour – Yellow or green

AP Inter 2nd Year Botany Notes Chapter 9 Principles of Inheritance and Variation

→ Genes are the units of inheritance.

→ Genes which code for a pair of contrasting characters are known as alleles.

→ Phenotypic Ratio of monohybrid cross is = 3 : 1

→ Genotypic Ratio of monohybrid cross is = 1 : 2 : 1

→ Crossing between F1 plant with a recessive parent is called Test cross.

→ Crossing between F1 plant with a dominant parent is called Back cross.

→ The two alleles of a gene when present together in a heterozygous state do not fuse or blend in any way, but remain distinct and seggregate during meiosis or in the formation of gametes so that each meiotic product or genetic will carry one of them – law of purity of gametes or law of segregation.

→ The phenomenon in which a character is expressed phenotypically in both homozygotes and heterozygotes -Law of Dominance.

→ Where one allele of a gene is not completely dominant over the other allele and results in the heterozygous having phenotype different from the dominant and recessive homozygous-incomplete Dominance.

→ The phenomenon in which where heterozygotes have features of both the homozygotes, that is an allele is neither dominant nor recessive to the other – Co-dominance.

→ When two pairs of traits are combined in a hybrid, seggregation of one pair of character is independent of the other pair of characters – law of Independent Assortment.

AP Inter 2nd Year Botany Notes Chapter 9 Principles of Inheritance and Variation

→ Sutton and Boveri proposed chromosomal theory of inheritance.

→ Physical association of genes on a chromosome is called linkage.

→ Mutations were first-noticed by Hugo devries in Oenothera Lamarckiana.

→ UV radiation can cause mutations in organisms (Mutagen).

→ Mutations generate a large amount of variability in a population from which breeder can select the desirable types.

→ Inheritance is the basis ofheredity by which characters are passed on from parent to progeny.

→ Variation is the degree by which progeny differ from their parents as well as among themselves.

→ Genetics is a branch of biology which deals with the principles of inheritance and its practices.

→ Mendel proposed the principles of inheritance, which are called ‘Mendel’s laws of inheritance’.

→ Law of dominance: Some characters are dominant oyer others and these characters are expressed when factors are either in homozygous or in heterozygous condition.

→ A recessive character that was not expressed in heterozygous condition may be expressed again when it becomes homozygous.

→ Law of segregation: Characters segregate during the formation of gametes.

→ Later it was found that Mendel’s Laws of Inheritance did not hold true for the genes that were located on the same chromosome. These genes are called ‘Linked genes’.

AP Inter 2nd Year Botany Notes Chapter 9 Principles of Inheritance and Variation

→ It was proved that closely located genes assort together and distantly located genes, due to recombination, assort independently.

→ Mutations involve changes in chromosomes and genes. [IPE]

→ Mutations help to increase variability which are useful in crop improvement. [IPE]

→ A mutation that occurs due to a change in a single base pair of DNA is called point mutation.

→ The physical appearance of a character is called Phenotype.

→ The genetic makeup of an individual is called Genotype. [IPE]

→ Monohybrid cross: The cross made between two individuals differing in one character is called Monohybrid cross. [IPE]

→ Test cross: Crossing between F1 individuals with the recessive parent is called test cross. [IPE]

→ Incomplete Dominance: It is the phenomenon in which neither of the genes is completely dominant or completely recessive. [IPE]

→ The mechanism that causes a gene to move from one linkage group to another is called translocation. [NEET-2015]

→ An abnormal human baby with ‘XXX’ sex chromosomes was born due to formation of abnormal ova in the mother. [NEET-2015]

→ Number of pairs of contrasting characters in pea plants which were studied by Mendel in his experiments is seven. [NEET-2015]

→ Expressed sequence Tags (ESTs) refer to_’genes expressed as RNA’. [NEET-2019]

AP Inter 2nd Year Botany Notes Chapter 9 Principles of Inheritance and Variation

→ Variations caused by mutation as proposed by Hugodevries are ‘random & directionless’. [NEET-2019]

→ Experimental verification of the chromosomal theory of inheritance was done by Morgan. [NEET-2020]

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