Go to the Prenatal Testing page for more details. If one parent has sickle cell trait (HbAS) and the other has sickle cell anaemia (HbSS) there is a one in two(50%) chance that any given child will get sickle cell trait and a one in two chance that any given child will get sickle cell anaemia.
        
             
        
        
        
<span>Facilitated Diffusion- 
Does not use energy. Membranes in the cell membrane pick up molecules & carry them across the membrane from high to low concentration</span>
        
             
        
        
        
Answer:
I would write "terrestrial/lives on land during all life stages" between the frog and pigeon branches.
Explanation:
Jaw evolution has started with fish, so i'd place that before the perch, evolution of four limbs is next and I would plate it between the perch and the frog. Evolution of an egg has ensured that organisms remain terrestrial during all stages of life and don't need to rely on water to lay their eggs. So I would place that between the frog and the pigeon. True mammary glands and true hair, as we know it formed on mammals so i'd place that between the pigeon and the rats (although synapsids evolved similar structures long before birds even existed). And lastly, I would place "walking on two legs" between rats and human branches. Because our ancestors evolved bipedalism relatively late. 
 
        
             
        
        
        
If the pH/temperature fluctuates, the enzyme conditions would no longer be favorable, meaning the enzyme would no longer be able to perform its assigned function. If the conditions become too unfavorable, the enzyme would change shape (denature).