Living Environment Translated English 2014 | Page 20

16. Meiosis is the process that produces sex cells ( eggs and
sperms). This process results in FOUR new cells that have HALF
of the normal chromosome number.
17. Haploid cells ( ½ the original number of chromosomes) are
formed during meiosis.
18. Diploid cells ( have the normal number of chromosomes) are
formed during mitosis.
19. Fertilization- egg and sperm are united to form a fertilized egg
( zygote).
20. Cell division begins after fertilization.
21. A human body cell has 46 chromosomes, and a human sex cell
has 23 chromosomes.
22. DNA is a molecule that stores genetic information in all
organisms.
23. Watson and Crick, two scientists, discovered that DNA is
shaped like a double helix ( a twisted ladder).
1. The sides of the ladder alternating molecules of sugar
and phosphates.
2. The rungs of the ladder are made up of paired nitrogen
bases.
a. Adenine (A) always pairs with Thymine (T)
b. Cytosine (C) always pairs with Guanine (G)
24. When DNA is copied, the new DNA has bases that are
IDENTICAL to those of the original DNA.
25. A mutation ( a change in DNA) may cause proteins to be made
incorrectly.
a. Mutations may be caused by chemicals or
radiation which breaks the DNA.
b. Crossing Over- the exchange of chromosome
segments between similar chromosomes during
meiosis
26. The instructions for making a specific protein are found in
genes in the cell nucleus.