1. Genes and Chromosomes: Genes are segments of DNA that contain the instructions for building and maintaining an organism. These genes are organized into structures called chromosomes. Humans have 23 pairs of chromosomes – one set inherited from each parent.
2. Sexual Reproduction: Inheritance happens during sexual reproduction. Each parent contributes one set of 23 chromosomes to their offspring through their sex cells (sperm and egg). These sex cells are produced through a process called meiosis, which shuffles and divides the parent's chromosomes.
3. Meiosis and Genetic Variation: Meiosis is crucial because it creates genetic variation. During meiosis, chromosomes exchange genetic material through a process called crossing over. This means that the chromosomes passed on to the offspring are not identical copies of those in the parent. Furthermore, the selection of which chromosome from each pair goes into a sex cell is random.
4. Fertilization: When a sperm fertilizes an egg, the resulting zygote (fertilized egg) receives a complete set of 46 chromosomes – 23 from each parent. This combination of genes determines the offspring's traits.
5. Alleles and Dominance: Each gene can have different versions called alleles. For example, a gene for eye color might have an allele for brown eyes and an allele for blue eyes. One allele is inherited from each parent. The interaction between these alleles determines which trait is expressed (phenotype). Some alleles are dominant, meaning they mask the effect of recessive alleles. Others are recessive, only showing their effect if two copies are present.
6. Genotype and Phenotype: An organism's genotype is its genetic makeup (the combination of alleles it possesses). The phenotype is the observable trait (e.g., blue eyes, brown hair). The phenotype is often, but not always, a direct result of the genotype.
In short, you inherit a mixture of your parents' genes, shuffled and recombined during meiosis, leading to a unique combination that determines your traits. The interaction between the alleles you inherit determines which traits are actually expressed.