Name
Date
Class
4-1 Notes: Sexual Reproduction and Meiosis
A. What is sexual reproduction?
1. __Sexual reproduction___
produces offspring when genetic materials from two different sex cells combine.
a. The female sex cell is called a(n) _____egg______.
b. The male sex cell is called a(n) ___sperm_____.
2. During ____ fertilization____, an egg cell and a sperm cell join together.
The new cell that forms is called a(n) ____zygote____.
B. Diploid Cells
1. Organisms that reproduce sexually make two kinds of cells; _body
cells and _sex__ cells.
2. Body cells are___ diploid____; they have pairs of chromosomes.
3. Different organisms have different __number___ of chromosomes.
4. Homologous chromosomes__ are pairs of chromosomes that have genes for the same traits arranged in the same
order.
C.
Haploid Cells
1. Sex cells are __haploid______; they have only one chromosome from each pair of chromosomes.
2. In ___meiosis______, one diploid cell divides and makes four haploid cells.
D. Why is meiosis important?
1. Meiosis forms sex cells with the correct haploid number of ___chromosomes______.
2. Meiosis creates genetic variation by producing __haploid cells.
E.
How do mitosis and meiosis differ?
1. During __mitosis___, a body cell and its nucleus divide once and produce_2_ identical cells.
2. During __meiosis___, a reproductive cell and its nucleus divide twice and produce__4__ cells, each with half the
number of chromosomes as the parent cell
F.
Advantages of Sexual Reproduction
1. Sexual reproduction produces ___offspring_____ that have a new combination of DNA. This results in genetic
___variation_______ among individuals.
2. Genetic variation gives individuals within a population slight differences that might be an advantage if the
__environment_______ changes.
3. ___Selective__ _breeding has been used to develop desirable traits in plants and animals.
G. Disadvantages of Sexual Reproduction
1. One disadvantage of sexual reproduction is that organisms have to grow and develop until they are mature enough to
produce __sex____ cells.
2. Another disadvantage is that searching for a mate takes time and energy and might expose individuals to predators,
_____disease_________, or harsh environmental conditions.