Heredity and Variation Drive Evolution All living organisms reproduce, passing traits from parents to offspring through heredity. This process results in similarities between generations but also introduces variations, which are differences among individuals of the same species. Variations can arise during both sexual and asexual reproduction; however, they tend to be more pronounced in sexually reproducing organisms. Over time, these accumulated variations contribute significantly to evolution.
Types of Traits: Inherited vs Acquired Traits inherited from parents fall into two categories: inherited traits and acquired traits. Inherited traits come directly from genetic information passed down at birth and remain unchanged by environmental factors—examples include eye color or hair type. Acquired traits develop throughout an individual's life due to experiences or environmental influences but do not affect DNA—skills like playing instruments exemplify this category.
Mendel’s Laws Define Genetic Inheritance The inheritance of characteristics occurs via genes transferred equally from both parents during reproduction; each parent contributes one gene for every trait resulting in dominant (expressed) or recessive (masked) expressions based on their alleles' interactions. Gregor Mendel's experiments with pea plants established foundational laws governing inheritance patterns including dominance, segregation of alleles during gamete formation, and independent assortment across different character pairs.
Genetic Basis for Sex Determination Sex determination varies across species but is genetically defined in humans by sex chromosomes carried within gametes produced by each parent—the combination determines whether a child will be male (XY) or female (XX). Males produce sperm carrying either X or Y chromosomes while females only provide X chromosomes through eggs; thus fertilization outcomes dictate the newborn's sex based on paternal contribution alone.