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Chromosomes and genes

Review your understanding of chromosomes and genes in this free article aligned to NGSS standards.

Key points:

  • All organisms inherit traits, or observable characteristics, from their parents. Inherited traits can include physical features, behaviors, and risks of getting certain diseases.
  • Information about inherited traits is found in genes. Genes are pieces of hereditary material that are passed from parents to offspring.
  • Genes are part of cell structures called chromosomes. In multicellular organisms, chromosomes are found in the nucleus of the cell.
  • Each of these chromosomes contains one, long molecule of DNA, or deoxyribonucleic acid. A gene is a specific stretch of this DNA molecule.
  • Each chromosome in the cell contains many genes.
A diagram shows a cell with six X shaped chromosomes in its nucleus. Extending from one of the chromosomes is a stretch of a DNA molecule. A section of the DNA molecule is labeled as a gene.
Chromosomes are found in the nucleus of the cell. Each chromosome is made up of a single DNA molecule that contains many genes. Image created with Biorender.com.

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  • blobby green style avatar for user victoria.gibson
    How many genes are in a cell?
    (24 votes)
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  • duskpin ultimate style avatar for user Shlok Mamidi
    How is DNA formed?
    (3 votes)
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    • hopper cool style avatar for user Constant Blais
      DNA, or deoxyribonucleic acid, is formed through a process called DNA replication. DNA replication occurs during the cell division process known as the S phase of the cell cycle. Here are the key steps involved:

      1. Initiation: The DNA double helix unwinds and separates into two strands. An enzyme called DNA helicase breaks the hydrogen bonds between the base pairs, causing the DNA strands to separate and form a replication fork.

      2. Primer Binding: Primers, which are short RNA sequences, are synthesized and bind to the DNA template strands. These primers provide a starting point for DNA synthesis.

      3. Elongation: DNA polymerase, an enzyme, attaches to the primer and begins synthesizing new DNA strands. It reads the template strand and adds complementary nucleotides to each growing daughter strand. Adenine (A) pairs with thymine (T), and cytosine (C) pairs with guanine (G), maintaining the base pairing rules.

      4. Leading and Lagging Strand Synthesis: DNA replication occurs in a semi-discontinuous manner due to the antiparallel nature of the DNA strands. The leading strand is synthesized continuously in the 5' to 3' direction, while the lagging strand is synthesized discontinuously in small fragments called Okazaki fragments. These fragments are later joined together.

      5. Termination: Once the entire DNA molecule has been replicated, termination signals halt the replication process. The DNA strands are fully synthesized, and the new double-stranded DNA molecules are ready for further cellular processes.

      DNA replication is a highly precise and complex process that ensures accurate transmission of genetic information from one generation of cells to the next. It plays a crucial role in the growth, development, and reproduction of organisms.
      (29 votes)
  • blobby green style avatar for user MorganD
    why do some kids look like there grandparerents?
    (8 votes)
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  • aqualine tree style avatar for user Hermen
    what's the difference between Adams and molecules
    (2 votes)
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    • leaf yellow style avatar for user SP
      I think you mean atoms :)

      If you are talking about Adams, be informed that all things are made up of atoms, so all Adams are made up of atoms.

      If you do mean atoms, the thing is, molecules are made up of atoms. For example, a molecule may contain 2 hydrogen atoms and 1 oxygen atom. This creates a water molecule.
      (21 votes)
  • aqualine sapling style avatar for user ya girl nini
    Why do some kids look like their dad more than there mom?
    (5 votes)
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    • hopper cool style avatar for user Constant Blais
      According to a study published in Scientific American, babies tend to look more like their fathers than their mothers. This is because fathers are less certain that a baby is theirs and are more likely to invest whatever resources they have in their own offspring. However, there is no scientific evidence that supports this claim.

      Another theory suggests that genetics cause people to look and behave more like their dads than their moms. This is because children inherit half of their genetic material from each parent, and some traits are determined by genes on the sex chromosomes (X and Y). Since males have only one X chromosome, they will pass on all of their X-linked genes to their daughters but none to their sons. On the other hand, females have two X chromosomes, so they will pass on one of their X chromosomes to both their sons and daughters.

      It's important to note that while some children may resemble one parent more than the other, this does not mean that they are more related to one parent than the other. Children inherit half of their genetic material from each parent, so they are equally related to both parents.
      (8 votes)
  • aqualine ultimate style avatar for user momothemoos
    if a cell can multipluy and the genes are in the cell do the genes multipluy
    (4 votes)
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  • aqualine ultimate style avatar for user Wolfy
    I see many questions about genes and appearance, so I will try to explain some. Your gender (you being male or female), is decided by your mother and father's genes, whether you have XX chromosomes, which make you female, or XY chromosomes, which make you male.
    Now, along with this, your father and mother's genes which are passed onto you, do a fun sort of dance while you are in your mother's womb, to create entirely new combinations to make an entirely new person, which is you!

    Why do some people look like one parent or the other? One parent may have stronger genes then the other parent, so certain traits are more visible or apparent, which is why some people look very like the parent with stronger genes, but this does not mean you are like that parent in every way because genes decide much more then appearance, just because you look like, say, your dad, doesn't mean you act like him, or have the same health he does. Some people are a mix of their parents.

    Sometimes, kids look like their grandparents, or a grandparent, in this case, it's likely that your grandparent's genes, which are carried their child, which is your parent, has been passed to you, and they just strongly show in you.
    (6 votes)
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    • female robot amelia style avatar for user Johanna
      Thanks for sharing this. You might want to put each answer under its question, even though that could take more time. This post is technically in the wrong category, and I don’t want your post just taken down or anything.

      I was wondering about how you said parents’ genes “do a fun sort of dance while you are in your mother's womb, to create entirely new combinations.” It was my understanding that one parent’s genes combine with themselves during meiosis. Then both parents’ genes combine during fertilization, which is what makes you (the zygote). The genes don’t combine while you’re in utero, but they do eventually combine to make you, right?
      (2 votes)
  • leafers seed style avatar for user DonavenH
    can your DNA change through experiments
    (4 votes)
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  • blobby green style avatar for user lillian.olsey
    what happens if you have too little chromosomes?
    (4 votes)
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  • blobby green style avatar for user Ludovica
    Can we change the genes of a person also after the birth?
    (2 votes)
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