Diploid cells have two pairs of chromosomes (one from each parent).
In humans, this number is 46 (23 pairs).
Gametes (sex cells) have 23 chromosomes, called haploid.
Terminology:
Diploid (2N): Somatic/body cells.
Haploid (N): Gametes.
Mendelian Genetics
Gregor Mendel:
Austrian monk known for his experiments with pea plants in the 1800s.
Published findings in 1865 about how traits are inherited.
Experiments and Findings:
Used artificial pollination to control fertilization.
Examined 7 characteristics, found a 3:1 dominant to recessive ratio.
Purebred tall vs. short plants showed all offspring were tall, indicating dominance.
Genetic Representation
Alleles:
Versions of a gene.
Homozygous: Same alleles (e.g., TT or tt).
Heterozygous: Different alleles (e.g., Tt).
Punnett Squares:
Tool to show potential genetic combinations.
Monohybrid cross: Examines one trait.
Dihybrid cross: Examines two traits.
Plant Reproduction
Flowering Plants:
Produce pollen (male genetic material).
Ovaries house female genetic material.
Cross-pollination vs. self-pollination.
Genotype and Phenotype
Genotype: Pair of alleles represented symbolically (e.g., TT, Tt).
Phenotype: Observable trait based on genotype.
Dominant vs. Recessive:
Dominant alleles are expressed if present.
Recessive alleles are expressed only if both alleles are recessive.
Phenotypic Plasticity
Definition: Changes in phenotype based on environmental factors.
Examples:
Birds altering foraging behaviors and physiological changes in response to environment.
Genetic Disorders
Autosomal Recessive Disorders:
E.g., PKU (Phenylketonuria): Mutation in PAH gene affecting brain development.
Requires both parents to be carriers (heterozygous) for manifestation.
Gene Pool and Alleles:
Multiple alleles for a single gene exist in a population.
Complexity in Genetics
Single Nucleotide Polymorphisms (SNPs):
Variations in a single nucleotide.
Affect traits like taste sensitivity to bitterness (e.g., PTC).
Blood Typing:
Multiple Alleles: Blood type has three alleles (IA, IB, i).
Co-Dominance: Both IA and IB alleles can be expressed together (AB blood type).
Universal Donor: Type O blood, no antigens causing clotting.
Conclusion
Understanding genetic inheritance involves grasping complex concepts like alleles, genotype, phenotype, and the impact of environmental factors on gene expression. The study of Mendelian genetics lays the foundational understanding of how traits are passed on and expressed in organisms.