Biology · Class 12 · Chapter 4
Principles of Inheritance and Variation
11 lessons 85 min 2 simulations 10 practice questions
This chapter explains how characters pass from parents to offspring: Mendel's pea experiments and laws, deviations such as incomplete dominance, co-dominance and multiple alleles, the chromosomal basis of inheritance with linkage, and how sex is determined. It closes with mutation and human genetic disorders, both single-gene and chromosomal, and leads into the molecular view of the gene in the next chapter.
What the exam asks
NEET tests cross ratios (3:1, 1:2:1, 9:3:3:1, 1:1 test cross), ABO blood group problems, Morgan's recombination data, sex-determination systems, and the inheritance pattern and cause of each disorder. Students lose marks by mixing up genotypic and phenotypic ratios, by assuming ZW females are homogametic, and by confusing the karyotypes of Klinefelter and Turner syndromes.
Lessons
11 lessons · 85 min
1Mendel's laws of inheritanceNCERT § "Mendel's Laws of Inheritance"6 min2Inheritance of one gene: dominance and segregationNCERT § "Inheritance of One Gene"10 min 1 sim3Incomplete dominance, co-dominance and multiple allelesNCERT § "Inheritance of One Gene"7 min4Inheritance of two genes: independent assortmentNCERT § "Inheritance of Two Genes"10 min 1 sim5Chromosomal theory, linkage and recombinationNCERT § "Inheritance of Two Genes"7 min6Polygenic inheritance and pleiotropyNCERT § "Polygenic Inheritance" and § "Pleiotropy"7 min7Sex determinationNCERT § "Sex Determination"7 min8MutationNCERT § "Mutation"6 min9Genetic disorders: pedigree and Mendelian disordersNCERT § "Genetic Disorders"7 min10Chromosomal disordersNCERT § "Genetic Disorders"6 min11Chapter reviewMust-know facts, traps and formulas12 min