This chapter explains the concept of heredity and how traits are passed from parents to offspring, highlighting the importance of genetic variation.
Heredity – Formula & Equation Sheet
Essential formulas and equations from Science, tailored for Class X in Science.
This one-pager compiles key formulas and equations from the Heredity chapter of Science. Ideal for exam prep, quick reference, and solving time-bound numerical problems accurately.
Key concepts & formulas
Essential formulas, key terms, and important concepts for quick reference and revision.
Formulas
F1 Generation: TT (Tall) x tt (Short) → All Tt (Tall)
TT represents homozygous tall, tt represents homozygous short, and Tt represents heterozygous tall. This shows dominance of tall trait over short.
F2 Generation Ratio: 1 (TT) : 2 (Tt) : 1 (tt)
This ratio demonstrates Mendelian inheritance patterns, showing 3 tall (TT or Tt) to 1 short (tt) plant.
Dihybrid Cross Ratio: 9:3:3:1
Represents the phenotypic ratio for two traits independently assorting, e.g., seed shape and color in peas.
Sex Determination: XX (Female) x XY (Male)
Females contribute an X chromosome; males contribute either X or Y, determining the offspring's sex.
Probability of Sex: 50% Male (XY), 50% Female (XX)
Based on the equal chance of a sperm carrying an X or Y chromosome fertilizing an X-bearing egg.
Gene Expression: Dominant (T) vs. Recessive (t)
Dominant traits are expressed when at least one dominant allele is present; recessive traits require two recessive alleles.
Phenotypic Ratio in Monohybrid Cross: 3:1
Shows the ratio of dominant to recessive phenotypes in the F2 generation.
Genotypic Ratio in Monohybrid Cross: 1:2:1
Represents the ratio of homozygous dominant:heterozygous:homozygous recessive genotypes in the F2 generation.
Law of Segregation
Alleles separate during gamete formation, ensuring each gamete carries only one allele for each gene.
Law of Independent Assortment
Genes for different traits are inherited independently of one another, leading to varied combinations in offspring.
Equations
Punnett Square for Monohybrid Cross
A grid used to predict the genotype and phenotype combinations of offspring from parental alleles.
Punnett Square for Dihybrid Cross
Extends the monohybrid concept to two traits, predicting more complex inheritance patterns.
Blood Group Inheritance: IA, IB, i
IA and IB are codominant; i is recessive. Determines blood groups A, B, AB, or O.
Chromosome Pairing: 22 Autosomes + 1 Sex Chromosome Pair
Humans have 23 chromosome pairs, with sex determined by the 23rd pair (XX or XY).
Mutation Rate and Variation
Mutations during DNA copying introduce variations, some of which may be inherited.
Environmental Influence on Traits
Some traits are influenced by both genetic and environmental factors, e.g., height and nutrition.
Genetic Diversity Calculation
Diversity increases with the number of gene combinations possible through sexual reproduction.
Homozygous vs. Heterozygous
Homozygous individuals have identical alleles (TT or tt); heterozygous have different alleles (Tt).
Pedigree Analysis Symbols
Standard symbols represent males, females, affected individuals, and carriers in genetic diagrams.
Test Cross: Tt x tt
Used to determine the genotype of a dominant phenotype individual by crossing with a homozygous recessive.
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