Sally and Harry fall in love. They introduce Sally's identical twin, Emily, to Harry's identical twin, Ken. Soon there is a double wedding where Sally marries Harry and Emily marries Ken. Both Sally and Emily get pregnant. They wonder "Will their babies look exactly alike?" Answer their question, and explain your reasoning. (To answer this question, think about the children that could be produced if both pairs of identical twins are heterozygous Aa.)

No their babies won't look alike.

Both the couples mentioned here i.e. Sally - Harry and Emily - Ken are both identical twins. So they have similar pairs of genetic setup. This was possible because they developed from same zygote.

But during gametogenesis, crossing over and independent assortment occurs which brings about variation in genetic setup among the offspring. And it's very less probable that same crossing over will occur between the gametes of these couples. So, their offsprings won't look same.

answer: the blood-brain barrier is a layer of specialized membranes and cell processes designed to keep undesirable substances from passing from the bloodstream into the precious tissues of the brain. while the blood-brain barrier does keep most bad things out of the central nervous system, it is not impermeable.

explanation: