Asked by shellby
If exact copies are produced in Mitosis, why do we look different from each other?
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Answered by
GPT-5 mini
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Mitosis does make copies of a cell’s DNA, but that only explains how one organism’s cells stay the same as it grows and repairs itself. It does not explain why different people look different. The main reasons:
- Different starting genomes. Every person starts as a unique fertilized egg (zygote). Meiosis (in sperm and egg formation) shuffles genes by recombination and independent assortment, and fertilization mixes two parents’ genomes. That produces different DNA sequences between individuals long before mitosis makes copies of those sequences.
- Gene regulation and cell differentiation. Even within one person most cells have the same DNA, but different cells turn different genes on or off. That’s why a skin cell looks and acts unlike a nerve cell despite identical genomes.
- Somatic mutations and mosaicism. Cells can acquire mutations after conception. Over growth and lifetime these small changes can make patches of the body genetically different from others.
- Epigenetics. Chemical marks on DNA and chromatin (methylation, histone modifications) change how genes are expressed without altering sequence. These marks are influenced by development and environment and can differ between people.
- Environment and chance. Nutrition, infections, sun exposure, hormones, and random events during development (e.g., where cells migrate) all shape phenotype. Two people with similar DNA can still look different because of different life histories.
- Microbiome and other non-genetic factors. Microbes living on and in us affect metabolism, skin, and even behavior.
Example: identical twins form from one zygote and therefore have (nearly) identical DNA copied by mitosis, yet they still develop differences over time because of somatic mutations, epigenetic changes, and different environments.
In short: mitosis copies cells within an individual; meiosis + fertilization, plus epigenetics, mutations, and environment, create the differences you see between people.
- Different starting genomes. Every person starts as a unique fertilized egg (zygote). Meiosis (in sperm and egg formation) shuffles genes by recombination and independent assortment, and fertilization mixes two parents’ genomes. That produces different DNA sequences between individuals long before mitosis makes copies of those sequences.
- Gene regulation and cell differentiation. Even within one person most cells have the same DNA, but different cells turn different genes on or off. That’s why a skin cell looks and acts unlike a nerve cell despite identical genomes.
- Somatic mutations and mosaicism. Cells can acquire mutations after conception. Over growth and lifetime these small changes can make patches of the body genetically different from others.
- Epigenetics. Chemical marks on DNA and chromatin (methylation, histone modifications) change how genes are expressed without altering sequence. These marks are influenced by development and environment and can differ between people.
- Environment and chance. Nutrition, infections, sun exposure, hormones, and random events during development (e.g., where cells migrate) all shape phenotype. Two people with similar DNA can still look different because of different life histories.
- Microbiome and other non-genetic factors. Microbes living on and in us affect metabolism, skin, and even behavior.
Example: identical twins form from one zygote and therefore have (nearly) identical DNA copied by mitosis, yet they still develop differences over time because of somatic mutations, epigenetic changes, and different environments.
In short: mitosis copies cells within an individual; meiosis + fertilization, plus epigenetics, mutations, and environment, create the differences you see between people.
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