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Master Genetics for NEET 2026 with comprehensive notes on Mendel's laws, inheritance patterns, chromosomal basis, linkage, and genetic disorders. NCERT-aligned content with diagrams and PYQs.
Remember these points for your NEET preparation
Genetics is the highest weightage chapter in NEET Biology, contributing 8-12 questions annually. This comprehensive guide covers all NCERT concepts essential for NEET 2026.
| Advantage | Description |
|---|---|
| Contrasting traits | 7 pairs of clearly visible differences |
| Annual plant | Short generation time |
| Self-pollination | Easy to maintain pure lines |
| Cross-pollination | Can be artificially done |
| Large number of seeds | Statistical analysis possible |
| Trait | Dominant | Recessive |
|---|---|---|
| Seed shape | Round (R) | Wrinkled (r) |
| Seed color | Yellow (Y) | Green (y) |
| Pod shape | Inflated (I) | Constricted (i) |
| Pod color | Green (G) | Yellow (g) |
| Flower color | Purple (P) | White (p) |
| Flower position | Axial (A) | Terminal (a) |
| Stem height | Tall (T) | Dwarf (t) |
Statement: When two organisms with contrasting characters are crossed, only one character appears in F1 (dominant), while the other remains hidden (recessive).
Key Points:
Statement: During gamete formation, the two alleles of a gene separate so that each gamete receives only one allele.
Monohybrid Cross Example:
Test Cross: Cross with homozygous recessive to determine genotype.
Statement: Alleles of different genes assort independently of each other during gamete formation, provided genes are on different chromosomes.
Dihybrid Cross Example:
| Phenotype | Ratio | Genotypes |
|---|---|---|
| Round Yellow | 9 | R_Y_ |
| Round Green | 3 | R_yy |
| Wrinkled Yellow | 3 | rrY_ |
| Wrinkled Green | 1 | rryy |
Neither allele is completely dominant; heterozygote shows intermediate phenotype.
Example: Snapdragon flower color
Both alleles express equally in heterozygote.
Example: ABO blood groups
More than two alleles exist for a gene in a population.
Example: ABO blood groups (3 alleles: I^A, I^B, i)
Single gene affects multiple traits.
Example: Sickle cell anemia - single mutation causes multiple effects:
One gene masks the expression of another gene.
Example: Coat color in dogs
Multiple genes control one trait; shows continuous variation.
Example: Skin color in humans (3+ genes)
Proposed by: Sutton and Boveri (1902)
Genes on the same chromosome tend to inherit together.
Types:
Coupling (Cis): Dominant alleles on same chromosome (AB/ab) Repulsion (Trans): Dominant alleles on different homologs (Ab/aB)
| Sex | Chromosomes | Gametes |
|---|---|---|
| Female | 44 + XX | All carry X |
| Male | 44 + XY | Half X, half Y |
Sex of offspring determined by father's sperm.
Characteristics:
Examples:
| Cross | Offspring |
|---|---|
| X^C X^C × X^C Y | All normal |
| X^C X^c × X^C Y | 1 normal female : 1 carrier female : 1 normal male : 1 colorblind male |
| X^c X^c × X^C Y | All females carriers : All males colorblind |
Abnormal number of chromosomes.
| Type | Definition |
|---|---|
| Monosomy | 2n - 1 (one less) |
| Trisomy | 2n + 1 (one extra) |
| Nullisomy | 2n - 2 |
| Tetrasomy | 2n + 2 |
| Feature | Description |
|---|---|
| Karyotype | 47, +21 |
| Cause | Non-disjunction in meiosis |
| Risk factor | Advanced maternal age |
| Features | Intellectual disability, flat face, short stature, congenital heart defects |
| Feature | Description |
|---|---|
| Karyotype | 45, X (monosomy X) |
| Sex | Female |
| Features | Short stature, webbed neck, sterile, underdeveloped ovaries |
| Feature | Description |
|---|---|
| Karyotype | 47, XXY |
| Sex | Male |
| Features | Tall, gynecomastia, sterile, small testes |
| Feature | Description |
|---|---|
| Karyotype | 47, XXX |
| Sex | Female |
| Features | Usually normal, may have reduced fertility |
| Disorder | Affected Gene/Protein |
|---|---|
| Huntington's disease | Huntingtin protein |
| Polydactyly | Extra fingers/toes |
| Brachydactyly | Short fingers |
| Disorder | Cause | Features |
|---|---|---|
| Phenylketonuria (PKU) | Phenylalanine hydroxylase deficiency | Mental retardation if untreated |
| Sickle cell anemia | Abnormal hemoglobin (HbS) | Sickle-shaped RBCs, anemia |
| Thalassemia | Reduced/absent globin chains | Severe anemia |
| Cystic fibrosis | CFTR protein defect | Thick mucus, lung infections |
| Albinism | Tyrosinase deficiency | No melanin pigment |
| Pattern | Characteristics |
|---|---|
| Autosomal dominant | Affected in every generation, both sexes equally |
| Autosomal recessive | May skip generations, both sexes equally |
| X-linked recessive | More males affected, never father to son |
| X-linked dominant | Affected father → all daughters affected |
Q1 (NEET 2023): A cross between two tall plants produced 75 tall and 25 dwarf plants. The genotype of parents would be:
Q2 (NEET 2022): Which of the following is an example of co-dominance?
Q3 (NEET 2021): Down syndrome is caused by:
Q4 (NEET 2020): In a dihybrid cross, F2 generation ratio is:
Q5 (NEET 2019): Color blindness is more common in males because:
Q: Why is the 9:3:3:1 ratio not always observed? A: This ratio assumes: (1) genes are on different chromosomes (no linkage), (2) no gene interactions (epistasis), (3) complete dominance. Deviations occur when these conditions aren't met.
Q: Why is color blindness more common in males? A: The gene for color vision is on the X chromosome. Males (XY) have only one X, so a single mutant allele causes the condition. Females (XX) need mutations on both X chromosomes to be affected.
Q: How does non-disjunction cause chromosomal disorders? A: Non-disjunction is failure of chromosomes to separate during meiosis. This produces gametes with extra or missing chromosomes, leading to conditions like Down syndrome (trisomy 21) when fertilized.
Q: Why do carriers of sickle cell anemia have malaria resistance? A: Carriers (HbA HbS) have some sickle-shaped RBCs under low oxygen. The malaria parasite cannot survive well in these cells, providing selective advantage in malaria-endemic regions.
Q: What is the difference between linkage and crossing over? A: Linkage keeps genes on the same chromosome together during inheritance. Crossing over (during meiosis) breaks this linkage by exchanging segments between homologous chromosomes, creating recombinant offspring.
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How many hours should I study Biology daily for NEET?
For NEET Biology, aim for 3-4 hours of focused study daily. Quality matters more than quantity!
Is NCERT enough for Biology in NEET?
Yes! NCERT covers 95% of NEET Biology questions. Master it completely before any reference book.
Which chapters have maximum weightage?
Human Physiology (20%), Genetics (18%), and Ecology (12%) are the highest-scoring areas.
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