Genes are functional segments of DNA molecules. DNA stores genetics information.
Majority of DNA exist in the format of chromosomes. One chromosome contains one long linear DNA molecule which harbors many genes. Chromosomes are visible under a microscope during mitosis. The structure of a chromosome contains two telomeres which are related to DNA replication and senescence, one centromere which is critical for proper segregation. Each species contain different number of chromosomes.
Genes are sections of DNA which code for proteins; thus, genes translate from genetic code to physical appearance. Every gene has a homologous version on a homologous chromosome. This different version of the same gene is called an allele. Some alleles are dominant and some alleles are recessive. Dominant alleles will show up in the physical traits whenever it is present. The recessive allele will not appear unless the dominant alleles are not present. The gene alleles is known as the phenotype, and the physical traits that these genes produce is known as the phenotype.
Other Gene Interactions
Not all genes have the alleles follow dominant/recessive relationship. Genes can also be controlled by incomplete dominance, co-dominance, and polygenic traits. In incomplete dominance, the phenotype is the intermediate of the genotypes. In co-dominance, the phenotype shows both the genotypes. In polygenic traits, many genes produce one trait, so it is not easily predicted, such as height.
Meiosis is the process whereby gametes are produced. The cell replicates DNA once and initiates two cell divisions, resulting in 4 1N gametes. During the first division, homologous chromosomes pair and exchange genetic material, sister chromatids remain together, migrating to same pole. During the second division, sister chromatids segregate and generating 1N gametes.