Principles of Inheritance and Variation for NEET UG
Genetics questions are among the most scoring in NEET once you can draw a Punnett square. This chapter covers Mendel's laws, exceptions to them, sex determination and genetic disorders.
BiologyClass 1297 MCQs3 lessons14 flashcards4 memory tricks
Practise Principles of Inheritance and Variation free
What you'll learn
- Mendel's monohybrid and dihybrid crosses
Predict ratios from monohybrid, dihybrid and test crosses. - Beyond Mendel: incomplete dominance, codominance and linkage
Recognise non-Mendelian inheritance patterns and their ratios. - Sex determination and genetic disorders
Explain sex determination systems and solve problems on sex-linked and autosomal disorders.
Memory tricks
A recessive trait hidden in F1 reappears in a quarter of F2: monohybrid phenotype ratio 3 : 1, genotype ratio 1 : 2 : 1.
Colour blindness and haemophilia are on the X chromosome. A carrier mother passes the allele to half her sons, who show the disorder because they have only one X.
Klinefelter: 47, XXY, a sterile male. Turner: 45, XO, a sterile female. Down syndrome: trisomy 21.
Iᴬ and Iᴮ are codominant (IᴬIᴮ gives AB); i is recessive. Six genotypes, four phenotypes. This is also an example of multiple alleles.
Try 3 NEET-style questions
Q1. The law of independent assortment was derived mainly from Mendel's
- monohybrid crosses
- test crosses with dwarf plants only
- studies on blood groups
- dihybrid crosses
Show answer
Answer: (4) dihybrid crosses
Based on dihybrid crosses, Mendel proposed that when two pairs of traits are combined, the segregation of one pair is independent of the other.
Q2. Individuals with Turner's syndrome are
- fertile males with gynaecomastia
- sterile males with an extra X chromosome
- sterile females with rudimentary ovaries and lack of secondary sexual characters
- females with an extra chromosome 21
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Answer: (3) sterile females with rudimentary ovaries and lack of secondary sexual characters
Turner's syndrome (44 + XO) results from the absence of one X chromosome. Affected females are sterile, with rudimentary ovaries and poorly developed secondary sexual characters.
Q3. Down's syndrome is caused by
- an extra copy of chromosome 21
- absence of one X chromosome (XO)
- an extra X chromosome in a male (XXY)
- a point mutation in the β-globin gene
Show answer
Answer: (1) an extra copy of chromosome 21
Down's syndrome results from trisomy 21, an extra copy of chromosome 21, usually due to non-disjunction during gamete formation.
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