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Key Terminologies and Concepts in Genetics For Easy Reference
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Table 1- Basic Genetic Concepts
| Term | Definition | Example/Notes |
| Gene | A segment of DNA that encodes for a protein or RNA. | BRCA1 gene for DNA repair. |
| Allele | A variant form of a gene. | Dominant (A) or recessive (a). |
| Locus | The specific physical location of a gene or DNA sequence on a chromosome. | The CFTR gene is located at 7q31.2. |
| Homologs | Genes that share a common ancestry, either within the same species (paralogs) or across species (orthologs). | Human hemoglobin genes (HBA1, HBA2) are paralogs. |
Table 2: Patterns of Inheritance
| Term | Definition | Example/Notes |
| Dominant Trait | Expressed when at least one dominant allele is present. | Brown eyes (B) over blue eyes (b). |
| Recessive Trait | Expressed only when both alleles are recessive. | Blue eyes (bb). |
| Codominance | Both alleles are expressed equally in the phenotype. | ABO blood group (IAIB = AB blood type). |
| Incomplete Dominance | A blend of two alleles is expressed in the phenotype. | Red × White → Pink flowers. |
| Epistasis | Interaction where one gene masks or modifies the expression of another. | Coat color in labrador retrievers (e.g., E and B genes). |
| Compound Heterozygous | The presence of two different mutant alleles at the same locus. | One CFTR mutation from each parent (e.g., ΔF508 and G542X in cystic fibrosis). |
Table 3- Genetic Processes
| Term | Definition | Example/Notes |
| Mutation | A change in the DNA sequence. | A point mutation in CFTR gene (cystic fibrosis). |
| Recombination | Exchange of genetic material between homologous chromosomes. | Crossing over in meiosis I. |
| Transcription | Copying DNA sequence into RNA. | mRNA synthesis from DNA template. |
| Translation | Synthesizing a protein from mRNA. | Ribosomes convert codons into amino acids. |
Table 4- Genetic Structures and Tools
| Term | Definition | Example/Notes |
| Genome | The complete set of DNA in an organism. | The human genome has ~3 billion base pairs. |
| Epigenetics | Heritable changes in gene expression without DNA sequence changes. | DNA methylation can silence genes. |
| Karyotype | A visual representation of chromosomes in a cell. | The human karyotype shows 46 chromosomes. |
| Single Nucleotide Polymorphism (SNP) | A single base pair variation in DNA. | SNPs can indicate genetic predispositions. |
| Genetic Engineering | Manipulation of DNA to alter traits. | CRISPR-Cas9 for gene editing. |
Table 5- Population Genetics and Evolution
| Term | Definition | Example/Notes |
| Genetic Drift | Random changes in allele frequency in a population. | The bottleneck effect reduces genetic diversity. |
| Gene Flow | Movement of alleles between populations. | Migration introduces new genetic material. |
| Natural Selection | Differential survival and reproduction due to advantageous traits. | Antibiotic resistance in bacteria. |
Table 6- Complex Traits
| Term | Definition | Example/Notes |
| Polygenic Trait | A trait controlled by multiple genes. | Height, skin color. |
| Pleiotropy | A single gene influences multiple traits. | PKU mutation affects pigmentation and brain development. |
| Epistasis | Interaction between genes where one gene affects the expression of another. | Fur color in animals like mice or labradors. |
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