শিক্ষামূলক নোট: এই পৃষ্ঠা একাডেমিক জীববিজ্ঞান শেখা ও পরীক্ষার প্রস্তুতির সহায়ক।
Genetics Lecture 02: Genetic Terminology
Concept Overview
Genetics শেখার সবচেয়ে বড় বাধা হলো terminology confusion. Gene, allele, locus, genotype, phenotype, homozygous, heterozygous, dominant, recessive—এই শব্দগুলো পরিষ্কার না হলে Mendelian ratio, Punnett square, test cross, pedigree or gene interaction বোঝা কঠিন হয়ে যায়।
এই lecture হলো Genetics vocabulary map. এখানে প্রতিটি term শুধু সংজ্ঞা হিসেবে নয়, inheritance reasoning-এর tool হিসেবে শেখানো হয়েছে।
Why This Matters
Genetics problems সাধারণত শব্দ দিয়ে শুরু হয়, ratio দিয়ে শেষ হয়। যদি learner বুঝতে না পারে কোন parent homozygous, কোন trait recessive, কোন genotype heterozygous, কোন phenotype visible, তাহলে calculation ঠিক হলেও biological interpretation ভুল হতে পারে। তাই terminology হলো Genetics problem-solving-এর grammar.
LBFL Educational Framework
Use the central framework pages below for the full method. This page keeps only the topic-specific learning path so learners do not meet the same boilerplate repeatedly.
Terminology Learning Focus
এই lecture central LBFL framework-কে Genetics vocabulary learning-এ প্রয়োগ করে। Learner-এর focus হবে term-definition, term-example, term-confusion, and term-use in inheritance logic.
Core Vocabulary Map
Gene
DNA-এর functional unit that influences a trait.
Use: explains inherited biological information.
Allele
একই gene-এর alternative form.
Example: T and t for plant height.
Locus
Chromosome-এ gene-এর নির্দিষ্ট অবস্থান।
Use: tells where a gene is located.
Character
Broad heritable feature.
Example: seed shape, plant height.
Trait
Character-এর specific form.
Example: round seed, dwarf plant.
Factor
Mendel's historical term for hereditary unit; now understood as gene/allelic factor.
Genotype and Phenotype
Genotype
Allele combination or genetic constitution.
Example: TT, Tt, tt.
Phenotype
Observable or measurable expression.
Example: tall or dwarf.
Genotype + Environment + Developmental context
↓
Phenotype
Homozygous and Heterozygous
| Term | Meaning | Example | Learning point |
|---|---|---|---|
| Homozygous dominant | two dominant alleles | TT | true-breeding dominant possible |
| Heterozygous | two different alleles | Tt | dominant phenotype may appear |
| Homozygous recessive | two recessive alleles | tt | recessive phenotype appears |
Dominant and Recessive
Dominant allele
Heterozygous condition-এ phenotype প্রকাশ করতে পারে।
Example: T in Tt gives tall phenotype.
Recessive allele
Dominant allele উপস্থিত থাকলে masked থাকে; homozygous condition-এ প্রকাশ পায়।
Example: tt gives dwarf phenotype.
Important: Recessive allele does not disappear. It can be hidden in heterozygous condition and reappear in later generations.
Pure Line and Hybrid
| Term | Meaning | Example |
|---|---|---|
| Pure line | genetically stable true-breeding line | TT tall line or tt dwarf line |
| Hybrid | offspring from genetically different parents | Tt from TT × tt |
| Monohybrid | hybrid for one character | Tt for plant height |
| Dihybrid | hybrid for two characters | RrYy for seed shape and colour |
Parental, F1 and F2 Generations
P generation = parental generation
↓ cross
F1 generation = first filial generation
↓ selfing / crossing
F2 generation = second filial generation
These terms describe generation sequence in genetic crosses.
Test Cross and Back Cross
Test cross
Unknown dominant phenotype individual is crossed with homozygous recessive individual to identify genotype.
Back cross
F1 individual is crossed with one of its parents or parent-like genotype.
Test cross logic:
Unknown tall plant = TT or Tt?
↓ cross with tt
All tall offspring → likely TT
Tall + dwarf offspring → likely Tt
Term Relationship Flow
Gene located at locus
↓
Gene has alleles
↓
Allele pair forms genotype
↓
Genotype contributes to phenotype
↓
Phenotype appears as trait
↓
Traits are followed through generations
Common Confusions
Gene vs Allele
Gene is the unit; allele is a version of that gene.
Character vs Trait
Character is the category; trait is the specific form.
Genotype vs Phenotype
Genotype is genetic constitution; phenotype is expressed result.
Dominant vs Common
Dominant does not always mean more common in population.
Recessive vs Weak
Recessive does not mean biologically weak; it means masked in heterozygous state.
Test cross vs Selfing
Test cross identifies genotype; selfing follows inheritance pattern within same line.
Worked Mini Example
A pea plant is tall. Tallness is dominant over dwarfness. The plant may be TT or Tt. To identify its genotype, cross it with a dwarf plant tt.
If TT × tt → all Tt → all tall
If Tt × tt → Tt and tt → tall and dwarf
So offspring pattern helps reveal the hidden genotype.
Synaptic Bridge
Genetic terminology teaches precision. One word can change the whole meaning of a problem. In life and leadership too, vague language creates wrong decisions; precise language builds clear thinking.
Critical Thinking Questions
- Why is allele not exactly the same as gene?
- How can two plants have the same phenotype but different genotype?
- Why does recessive allele reappear in later generations?
- How does test cross reveal hidden genotype?
- Why is dominant not always equal to common?
Related Learning Paths
References
- Standard HSC Biology Genetics notes.
- Integrated Genetics references on genetic terminology and Mendelian vocabulary.
- NCERT Biology: Principles of Inheritance and Variation.