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Mendelian Genetics explains how traits are inherited and how variation…
Mendelian Genetics explains how traits are inherited and how variation occurs
Inheritance of Traits
Subtopic A: Genes & Alleles
Definition: Genes are units of heredity found on chromosomes, and alleles are different forms of a gene
Details:
Each individual has two alleles (one from each parent)
Alleles can be dominant or recessive
Located on homologous chromosomes
Example: B = brown eyes, b = blue eyes
Subtopic B: Dominant & Recessive
Definition: Dominant alleles mask recessive alleles in heterozygous individuals
Details:
Dominant = uppercase letter
Recessive = lowercase letter
Recessive trait appears only when homozygous
Example: Bb = dominant trait, bb = recessive trait
Subtopic C: Genotype vs Phenotype
Definition: Genotype is the genetic makeup; phenotype is the observable trait
Details: Genotypes: AA, Aa, aa
Same phenotype can have different genotypes
Example: AA and Aa → same phenotype (dominant)
Mendel’s Laws & Meiosis
Subtopic D: Law of Segregation
Definition: Alleles separate during gamete formation
Details: Each gamete carries one allele
Occurs during meiosis (Anaphase I)
Example: Aa → gametes: A or a
Subtopic E: Law of Independent Assortment
Definition: Genes for different traits assort independently
Details:
Occurs in Metaphase I
Applies to genes on different chromosomes
Increases variation
Example: BbRr → BR, Br, bR, br
Subtopic F: Meiosis & Gametes
Definition: Meiosis produces haploid gametes
Details:
Two divisions (Meiosis I & II)
Reduces chromosome number (2n → n)
Produces 4 genetically different cells
Example: Humans: 46 → 23 chromosomes
Genetic Prediction & Variation
Subtopic G: Punnett Squares
Definition: Tool used to predict offspring genotypes and phenotypes
Details: Shows all possible combinations
Used for monohybrid and dihybrid crosses
Example: Bb × Bb → 3:1 ratio
Subtopic H: Probability in Genetics
Definition: Mathematical rules used to predict genetic outcomes
Details: Multiplication rule
Addition rule
Example: Chance of Aa = 1/2
Subtopic I: Non-Mendelian Inheritance
Definition: Patterns that do not follow simple dominance
Types & Details:
Incomplete dominance → blending
Codominance → both traits expressed
Multiple alleles → more than two forms
Example: AB blood type