Crossing over happens in Meiosis 1 only. In Prophase 1 a cells chromatin (chromatin = chromosomes that have not condensed yet) condense and pair up forming homologous chromosomes (paired = XX (2 chromosomes together)). When this happens segments/ alleles of the chromosomes pairing up swap over. This creates genetic diversity as each chromosome is different, it has parts from its pair. This leaves every chromosome unique and individual.
I hope this helps, sorry some of the vocab is rather technical. By the way I would suggest watching the
'Crash Course: Meiosis' on YouTube, this really helped me when I was learning this topic. :D
ANSWER:
Lesions are areas of damage to motor neurons. Damage to upper motor neurons stops the signals your muscles need to move. When your muscles don't move for a long time, they become weak and stiff. Over time, it can become harder to walk and control your movement.
Explanation:
I hope it will help you
I think it’s D vacuoles, I’m not certain but it don’t hurt to try if it’s not that try A
A myelinated axon has a sheath around it and a bore axon doesn't have it, it's open or exposed so to speak. T<span>he myelin is made up of fat and protein and works like insulation. these axons make up the white matter in the brain since it appears white. The sheath helps to keep the electrical current from leaving the axon and the myelin sheath provides a tract along which regrowth can occur. </span>