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The last time you saw the sisters pictured above, you considered how different protein molecules in their cells could lead to different traits. Now, you know that genes provide instructions for proteins that lead to traits. How could these sisters have ended up with different genes, leading to their different proteins and traits? Explain your ideas below.

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The sisters, while sharing the same parents and therefore a significant portion of their genetic material, can have different genes due to several factors related to genetics and inheritance. Here are some key points that could explain how they ended up with different genes, leading to different proteins and traits:

  1. Genetic Variation: Each parent contributes half of their genetic material to their offspring. The combination of alleles (different versions of a gene) that each sister inherits can differ due to the random assortment of chromosomes during meiosis. This process shuffles the alleles, resulting in unique genetic combinations for each child.

  2. Recombination: During the formation of eggs and sperm, homologous chromosomes exchange segments of DNA in a process called recombination. This means that the genetic material passed on to each child can be a mosaic of the parents' genes, leading to variations in the genes inherited by each sister.

  3. Mutations: While it's less common for mutations to occur during the process of inheritance, they can contribute to genetic diversity. Random mutations can happen in germ cells (sperm and egg) or early in development and may lead to differences in genes between siblings.

  4. Epigenetics: While the underlying DNA sequence is important, epigenetic factors can influence how genes are expressed without changing the DNA itself. Environmental factors, experiences, and even parental influences during development can lead to different levels of gene expression, further resulting in varied traits despite having similar genetic backgrounds.

  5. Gene Interactions: The effects of one gene can be influenced by other genes. Therefore, even if both sisters carry the same genes, the interaction among their diverse gene sets can produce different phenotypic outcomes.

  6. Environmental Influences: Beyond genetic differences, environmental factors such as nutrition, lifestyle, and social interactions can play a significant role in how genes are expressed, leading to differences in traits.

These factors combine to create unique genetic profiles for each sister, despite their shared ancestry, resulting in different proteins being produced and, consequently, diverse traits manifesting between them.