genetics question?

Question

hello,
i need help understanding from a molecular perspective why siblings do not look alike.

Answer 1

Siblings do not look alike because they share only 50% of each other's DNA. A child gets 50% of its DNA from its mother and 50% from its father, but subsequent children (siblings) will not get the same 50% from each parent each time. For each new child, the 50% contribution is random. Think of it like this: You have 100 marbles in one jar (mother's genes) and 100 marbles in another jar (father's genes) and you make a new jar of marbles (offspring) by taking 50 marbles from each of the other jars and putting them together. If you then put all the marbles back into the jars from which they came (and shake well) and then make another jar by bringing together 50 marbles from each parental jar, the new jar won't possibly contain the same 50 marbles from each parental jar as did the previous mixed jar that you made.

The other reason that siblings don't look alike is that we are not only products of our genes, but also of our environments. Identical twins share 100% of their DNA and look exactly the same at birth. By the time they have reached adulthood, chances are that the non-shared elements of their respective environments will have created differences between them. By the time they are 40 or so, chances are they will look nothing alike any more.

Answer 2

Well, this should be something you went over in class. When a child is formed between two people, the child gets 50% of the genes from either side. The father will have some dominant traits and some recessive traits. The mother will have the same. Now, if the father's got a trait for black hair that is dominant, and the mother has a dominant black hair gene, but a recessive red hair gene, the child is going to have a better chance of having black hair than red, but the possibility of red is still there. It's kind of like yahtzee. You throw all your traits in there, shake it up, and toss it out to see what you get.