Because through natural selection, only the fittest survive. when the fittest come together and reproduce then the species continues and evolves with only the fittest and strongest genes.
Increase and decrease in oestrogen and progesterone.
Answer:
A. chromosomes
Explanation:
Chromosomes are structures found in the center (nucleus) of cells that carry long pieces of DNA. DNA is the material that contains genes and is the building block of the human body.
Chromosomes come in pairs. Normally, each cell in the human body has 23 pairs of chromosomes (46 chromosomes in all), of which half comes from the mother and half from the father.
Bonds between the strands are relatively weak hydrogen bonds, whereas bonds within the strands are relatively strong covalent bonds.
