Principles of Inheritance and Variation in Poetic Form 🌿 – A Class 12 Biology Study Guide"
Inheritance, oh such a tale,
From genes to traits, it will unveil.
A Mendelian story we'll tell today,
With variation leading the way.
Let’s explore each Mendelian law,
With poetic rhythms, without a flaw.
From monohybrid to dihybrid cross,
Learn the basics without a loss.
🌱 Laws of Inheritance: Mendel’s Legacy
In a monastery garden so green,
Mendel observed what could be seen.
Pea plants with traits so clear and bright,
Brought genetics into the light.
🌟 Law of Dominance
Dominance stands, bold and tall,
One gene’s shadow covers all.
Tall over dwarf, purple over white,
Dominant alleles rule the fight.
But recessive traits, hidden they lie,
Till homozygous, they’ll multiply.
Two recessives? Then they’ll rise,
Nature’s surprises meet our eyes!
🌱 Law of Segregation
In gametes, alleles segregate,
Each trait decides its unique fate.
Half the genes from each we take,
One from mom, one from dad’s stake.
No mixing or blending, Mendel said,
Alleles keep pure until they're wed.
Chance decides what trait appears,
In each generation over the years.
🌿 Law of Independent Assortment
Traits don’t depend on others’ game,
Each shuffles genes without shame.
Color doesn’t pair with height,
Each walks its genetic flight.
Pea pods yellow, peas tall or small,
Mix together—one, or all.
Genes follow their own free rule,
As taught by Mendel, nature’s school.
🌱 Monohybrid Cross
One trait we cross, just one seed,
Like tall or dwarf, or flower breed.
Ratios arise: three-to-one,
Dominance plays, recessive’s done.
🌱 Dihybrid Cross and Ratios
Mendel took height and seed’s hue,
A dihybrid cross—what would it do?
Nine tall yellow, three tall green,
Three short yellow, and one unseen.
One-fourth of the time, all recessive,
Mendel’s findings, truly impressive!
This 9:3:3:1 pattern we praise,
In genetic studies, it forever stays.
🌿 Incomplete Dominance
Not all genes follow Mendel’s law,
Some mix their traits without a flaw.
Red and white in snapdragons blend,
To make pink flowers in the end.
No allele is fully bold,
Together they make a trait of gold.
This incomplete dominance shines,
Nature writes its genetic lines.
🌸 Co-dominance
In co-dominance, traits stand tall,
Each shows fully—no hiding at all.
Like cows with patches, black and white,
Both alleles take center light.
In blood types too, we see this play,
AB’s alleles both on display.
No trait overpowers, no one hides,
Co-dominance equally resides.
🌱 Multiple Alleles and ABO Blood Group
Blood types tell of allelic tales,
More than two alleles, nature prevails.
A, B, and O are genes in play,
Determine blood type in this way:
A and B co-dominantly act,
O is recessive, that’s a fact.
Mix them right, and you will see,
The wonders of genetic chemistry.
🌸 Polygenic Inheritance
Some traits are not one-gene-made,
Height and skin tone, in shades displayed.
Many genes combine their might,
To give a trait that’s complex, bright.
These traits show variation wide,
Nature’s rainbow we cannot hide.
No simple ratio here you’ll find,
For polygenes, the rules aren’t confined.
🌿 Pleiotropy
One gene, but many traits will rise,
A pleiotropic gene’s surprise.
Sickle cell anemia, an example pure,
One gene, many symptoms endure.
🌱 Sex Determination
In humans, XX means girl is seen,
XY, a boy, with genes so keen.
Father’s gamete decides the fate,
The sex of the child is nature’s date.
In birds and reptiles, sometimes reversed,
Z and W alleles are immersed.
Nature’s way is wild and grand,
Sex determination rules the land.
🌸 Mutation: Nature’s Change
Mutation comes, sudden, wild,
Changing traits in parent or child.
Sometimes silent, sometimes grand,
Mutations shift the genetic stand.
Point mutations—just one base,
Frame shifts, causing gene’s disgrace.
Mutagens speed up the rate,
Causing errors, sealing fate.
🌱 Pedigree Analysis
A family tree, in black and white,
Tracks genetic traits in sight.
Squares for males, circles for dames,
Shaded ones bear traited names.
Through generations, traits can pass,
Dominant, recessive, genes amass.
Pedigrees trace disease and health,
Nature’s stories told in stealth.
🌿 Chromosomal Disorders
Down’s Syndrome, a trisomy tale,
Chromosome 21 carries the trail.
Klinefelter’s brings an extra X,
Turner’s misses one, no Y connects.
Nondisjunction tells the cause,
Chromosomes break genetic laws.
Errors in meiosis may arise,
Causing chromosomal surprise.
🌱 Genetic Disorders
Sickle cell anemia changes the shape,
Red blood cells in crescent’s cape.
Hemophilia causes endless bleed,
Lack of clotting factor we need.
Cystic fibrosis thickens the mucus,
Genetic mutations, there to spook us.
Each disorder tells a tale,
Of inheritance—genetic grail.
🌸 Variation in Population
No two beings exactly the same,
Variation is life’s genetic flame.
Crossing over, mutation’s spark,
Brings diversity, bold or stark.
Nature’s way to adapt and grow,
Through variation’s genetic flow.
Survival of fittest, variation leads,
Evolution fulfills its genetic needs.
🌱 Conclusion: Genetics’ Symphony
Inheritance, a symphony grand,
Conducted by nature’s unseen hand.
From Mendel’s peas to modern gene,
The principles of life are keen.
Genetics weaves its timeless tale,
Through generations, genes prevail.
Understanding traits, from start to end,
Helps us heal, evolve, and mend.
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