The changes during puberty take place slowly over months and years. For example, facial hair growth in boys starts with a few scattered hairs and gradually becomes more uniform.
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These changes do not occur at the same time or at a specific age for everyone. The onset and pace can vary widely among individuals.
Boys develop new thick hair on the face, experience voice cracking, and may witness occasional enlargement and erection of the penis, often in daydreams or at night.
Girls experience an increase in breast size and darkening of the skin of the nipples. Menstruation also begins during this period.
Sexual reproduction, by combining germ cells from two individuals during fertilization, ensures the reestablishment of the proper number of chromosomes and DNA content in the new generation. This process helps maintain genetic stability and control over cellular functions.
Specialized organs, particularly those involved in reproduction, contain germ cells with half the number of chromosomes and DNA content to maintain a balance and prevent the accumulation of excessive genetic material in each generation.
Meiosis is a cell division process that reduces the chromosome number by half. In specialized organs, germ cells undergo meiosis, resulting in cells with half the chromosomes and DNA content. This ensures that when germ cells from two individuals combine ...
Many multicellular organisms solve this challenge by having specialized lineages of cells in dedicated organs. These germ cells, involved in reproduction, undergo a process called meiosis, resulting in cells with half the number of chromosomes and DNA content compared to ...
If DNA copying mechanisms were less accurate, many resultant DNA copies might not function properly within the cellular apparatus, leading to cellular dysfunction or death.
The process of making variants is accelerated by the accumulation of variations in DNA copies across generations. Each new variation occurs in a DNA copy that already carries accumulated variations from previous generations.