Answer: Genetic variation can be caused by mutation (which can create entirely new alleles in a population), random mating, random fertilization, and recombination between homologous chromosomes during meiosis (which reshuffles alleles within an organism's offspring).
By the end of meiosis, the resulting reproductive cells, or gametes, each have 23 genetically unique chromosomes. The overall process of meiosis produces four daughter cells from one single parent cell.
Explanation:
During meiosis, homologous chromosomes (1 from each parent) pair along their lengths. The chromosomes cross over at points called chiasma. At each chiasma, the chromosomes break and rejoin, trading some of their genes. This recombination results in genetic variation.
Answer:
d. Nucleus
Explanation:
the nucleus stores the DNA which is the genetic code for the organism.
There are two things that occur in aquarium ammonia chemisty. 1. the build up of natural ammonia and nitrate in the water. 2. displacement of oxygen in the water caused by the ammonia. This is a very real threat especially when you have a new tank that is still cycling or when the biological filter has been upset or removed.
Look for these main symptoms if you suspect ammonia poisoning in your fish tank:
-loss of appetite
-lethargic fish
-fish gasping for air/breath at the top of the water
-fish laying at the bottom of the tank
-red/purple gills
-red streaking on the fish's body
- fins becoming torn and jagged
-scales on fish falling off or turning black
Answer:
Greenhouse gases
Explanation:
Teddy is working for a nonprofit organization that urges people to stop using products with CFCs. Through this Initiative, Teddy's organization hopes to reduce the concentration of greenhouse gases in the atmosphere.
Greenhouse gases deplete the ozone layer thereby causing global warming as a result often increase in the intensity of Sun rays reaching the earth.
Example of greenhouse gases include chlorofluorocarbon, nitrogen, water vapor etc
Answer:
The correct option is b. lower esophageal sphincter
Explanation:
The esophagus is the initial part of the digestive tract and its function is the transport of the alimentary bolus from the pharynx to the stomach, through the thorax and avoid the reflux thereof. It begins and ends in two sphincter structures, the upper esophageal sphincter and the lower esophageal sphincter, which separate it from the pharynx and stomach. The lower esophageal sphincter has two functions: relax during swallowing and prevent reflux of the gastric contents into the esophagus in the postdeglutory period. After swallowing, there is a relaxation of the lower esophageal sphincter, pressure dropping to levels similar to those of the gastric fundus, which allows the bolus to enter the stomach. This relaxation lasts a few seconds and is followed by a strong contraction that prevents backflow of food.
