I do not think it's more common in a certain group. It's one of the most common genetic birth defects. It's estimated that 1 in 700 babies are born with down syndrome (this is about 6,000). There are over 400,000 people in the US with Down syndrome.
Brain is the central organ of the nervous system and makes the central nervous system with the spinal cord. The brain consists of the cerebrum, the brain stem and the cerebellum.The brain cannot determine where in the nervous system the neuron was stimulated.
The answer to #1 is C, I think. And the answer to #2 is d. Crust
Variation is inherited is one of the four conditions necessary for natural selection to occur in a population
Explanation:
Natural selection is a process in which organisms pass on the heritable trait to their offspring and they adapt to the environment leading to evolution.
Natural selection will occur if the large population is there in which a random mutation has occurred and some organisms in the population have inherited varied characters and passed on these useful characters to the progeny.
Natural selection depends on the environment, random mutation and genetic variation.