Class 12 Biology - KERALA
Principles of Inheritance and Variation
Principles of Inheritance and Variation forms the core of classical genetics in Class 12 Biology under the Kerala SCERT syllabus. This chapter explores how hereditary characters pass from parents to offspring, building upon Gregor Mendel's groundbreaking hybridization experiments with garden peas. You will study Monohybrid and Dihybrid crosses, Mendel's laws of inheritance, and deviations like incomplete dominance and co-dominance. The latter half covers chromosomal theory of inheritance, linkage, crossing over, sex determination in various organisms, and genetic disorders like hemophilia, sickle-cell anemia, and Down syndrome. Scoring well here requires a clear grasp of ratios and pedigree analysis for board exams.
Start Learning FreeKey Concepts
Mendel's Law of Segregation
Alleles do not show any blending and that both the characters are recovered as such in F2 generation though one of these is not seen at the F1 stage.
Incomplete Dominance
A phenomenon where the F1 hybrid exhibits a phenotype intermediate between the parental traits, as seen in the flower color of Mirabilis jalapa (4 o'clock plant).
Chromosomal Theory of Inheritance
Proposed by Sutton and Boveri, it states that chromosomes are vehicles of genetic information and their behavior during meiosis parallels the segregation of Mendelian factors.
Linkage and Crossing Over
Linkage is the physical association of genes on the same chromosome, while crossing over is the recombination of non-sister chromatids during meiosis that breaks this linkage.
Pedigree Analysis
The study of family history tracing the inheritance of a specific trait or genetic disorder over several generations using standard genealogical symbols.
Important Formulas
Board Exam Info
In the Kerala (SCERT) Class 12 Biology board examination, this chapter is a high-weightage area, typically contributing 8 to 12 marks. Questions frequently include numerical problems on dihybrid crosses, identifying pedigree charts, explaining chromosomal disorders, and differentiating between linkage and crossing over.
Frequently Asked Questions
What is the difference between incomplete dominance and co-dominance?
In incomplete dominance, the F1 hybrid shows a blended intermediate trait (e.g., pink flowers). In co-dominance, both alleles are expressed equally and independently without blending (e.g., AB blood group).
How do I solve pedigree analysis questions in the exam?
First check if the trait skips generations (recessive) or appears in every generation (dominant). Then look for sex-bias; if mostly males are affected, it is likely X-linked recessive.
What causes Down syndrome?
Down syndrome is caused by the trisomy of chromosome 21, resulting from non-disjunction of chromosomes during egg or sperm formation, giving the individual 47 chromosomes.
Learn Principles of Inheritance and Variation with Your AI Tutor
10 different ways to study this chapter. Free for 3 chapters per day.
Lecture
Key Points
Interactive
Quiz
Flashcards