Passing One Copy is Random
Passing one copy of a gene randomly is a core concept in Grade 6 science from Amplify Science (California), Chapter 3: Investigating Spider Inheritance. Understanding that each parent passes only one of their two gene copies to a child — and that this selection is entirely random — is fundamental to explaining why genetic variation exists within families. Although both parents each carry two copies of every gene, only one copy from each parent is inherited by the child, and chance determines which one. This random inheritance process directly explains why siblings share the same parents yet display different combinations of traits: each sibling received a distinct random mix of gene copies, producing unique genetic combinations and observable differences in appearance or characteristics.
Key Concepts
Although parents have two copies of every gene, they only pass one copy to their child. Which of the two copies gets passed down is a matter of chance . This random selection explains why siblings are not identical. Even though they have the same parents, each sibling likely received a different random mix of gene copies, leading to different combinations of traits .
Common Questions
How many gene copies does a parent pass to their child?
A parent passes only one copy of each gene to their child, even though the parent has two copies of every gene. Which of the two copies is passed down is determined by random chance, not a predictable pattern.
Why do siblings look different if they have the same parents?
Siblings look different because each sibling randomly inherits a different combination of gene copies from their parents. Since which copy gets passed down is a matter of chance, each child ends up with a unique mix of gene copies, leading to different traits.
What determines which gene copy a parent passes to their child?
Chance determines which of a parent's two gene copies gets passed to a child. There is no rule that favors one copy over the other — the selection is entirely random each time a child is conceived.
Why are siblings not genetically identical to each other?
Siblings are not genetically identical because the random selection of gene copies from each parent produces a different combination for every child. Even with the same two parents, the probability that two siblings receive the exact same mix of gene copies from both parents is extremely low.
How does the random passing of gene copies connect to differences in traits?
Because each child inherits a randomly selected copy of each gene from both parents, they end up with a unique combination of gene copies. Different combinations of gene copies lead to different traits, which is why variation in characteristics like appearance can be observed among children of the same parents.