How do Mendel's laws explain inheritance patterns?

Mendel's Laws and Inheritance Patterns

Gregor Mendel, through his experiments with pea plants, established two fundamental laws that explain how traits are inherited from one generation to the next:

1. Law of Segregation: Each individual has two alleles for each gene, and these alleles separate (segregate) during gamete formation. Each gamete receives only one allele.
2. Law of Independent Assortment: Genes for different traits assort independently of one another during gamete formation, provided the genes are on different chromosomes.

These laws explain why offspring inherit predictable combinations of traits from their parents.

Worked Example: Monohybrid Cross

Suppose we cross two pea plants for flower color:

• Purple (P) is dominant to white (p)
• Parent genotypes: $Pp \times Pp$

Step 1: Gamete Formation

Each parent produces two types of gametes: $P$ and $p$.

Step 2: Punnett Square

P (Parent 1)	p (Parent 1)
P (Parent 2)	PP	Pp
p (Parent 2)	Pp	pp

Step 3: Genotype and Phenotype Ratios

• Genotypes: $1,PP : 2,Pp : 1,pp$ - **Phenotypes:** $3$ purple $(PP, Pp)$ : $1$ white $(pp)$

Step 4: Probability Calculation

Probability of white flowers:
$$ P(\text{white}) = P(pp) = \frac{1}{4} $$

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Takeaways

• Mendel's laws predict inheritance patterns using simple probability.
• The law of segregation explains why alleles separate during gamete formation.
• The law of independent assortment accounts for the independent inheritance of different traits.