The yolk sac functions to form blood cells in early development (embryonic phase) for nourishment of the embryo and early fetus. Towards the end of the 1st trimester, the yolk sac disappears and the placenta takes over for the fetus.
Answer:
The modern evolutionary synthesis defines evolution as the change over time in this genetic variation. The frequency of one particular allele will become more or less prevalent relative to other forms of that gene.
Explanation:
A substantial part of the phenotypic variation in a population is caused by genotypic variation.
Darwin's theory of evolution by natural selection can explain how antibiotics are becoming defective because the bacteria that is trying to be fought off might have had a mutation making it more likely to survive. Once that surviving bacteria makes offspring most of the first generation will die from the antibiotic but soon all of their offspring will produce a resistance to that antibiotic.
