Genetics and Inheritance

Sexual Reproduction in Organisms

• Most animals, plants, and fungi reproduce sexually.
• Inherits two sets of chromosomes: one from mother and one from father.
• Results in two copies of each gene.

Genes and Alleles

• Different versions of genes are called alleles.
• Alleles code for different versions of the same trait.
• Example: Gene coding for flower color in pea plants has two alleles:
• Purple allele (dominant)
• White allele (recessive)

Dominant and Recessive Traits

• When both alleles are present, one may mask the other’s expression.
• Dominant trait: expressed with one or two copies of dominant allele.
• Recessive trait: expressed only when two copies of recessive allele are present.
• Set of genes in an organism = genotype.
• Observable traits = phenotype.

Genotype Representation

• Genotypes are written using single letters:
• Uppercase letters = dominant alleles
• Lowercase letters = recessive alleles
• Example: Flower color in pea plants is represented by the letter F.
• Plant with allele for purple flowers (dominant) = F
• Plant with allele for white flowers (recessive) = f.

Example of Pea Plant Genotype

• A pea plant with one purple and one white allele: Ff
• Phenotype = purple flowers (dominant allele masks recessive).
• Two genotypes yield purple flowers:
• FF (homozygous dominant)
• Ff (heterozygous)
• To have white flowers, the plant must be:
• ff (homozygous recessive).

Terminology

• Homozygous: organism has two identical alleles for a trait.
• Heterozygous: organism has two different alleles for a trait.
• Example: Pea plant Ff is heterozygous for flower color.