Name_______________________
Lakeland High School
Date________________________
Biology – Mrs. Cropsey –Packet #41
Meiosis
Vocabulary to know with this topic:
Asexual Reproduction
One parent organism
Sexual Reproduction
Two parent organisms
Somatic cells
Body cells
Gamete
Sex cells
Sperm -
Male sex cell
Ova (egg) -
Female sex cell
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Fertilization
The joining of sperm and egg
Zygote
The name given to the fertilized egg cell
Diploid
The normal number of chromosomes for the species,
also written as 2n
(ours is 46)
Haploid
Half the number of chromosomes for the species, also written as n
Meiosis is the process by which our sex cells are produced with half the chromosome
number.

Why is meiosis a necessary process in sexually reproducing organisms?
To keep the chromosome number the same

sperm
+

=
egg

zygote
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
How is meiosis different from mitosis when referring to chromosome
number?
Mitosis keeps the chromosome number the same
Meiosis cuts the chromosome number in half
Before meiosis begins, the chromosomes in the nucleus replicate, so the chromosome
number is doubled.

This occurs during the same phase as mitosis. What is that stage?
Interphase
After replication, the sister chromatids (doubled chromosomes) pair up with their
homologues.
Homologues –
Paired chromosomes that are about the same size and shape
And code for the same traits
3
Crossing over – When homologous chromosomes exchange pieces of
themselves – results in new chromosomes
4
After pairing up homologous pairs, the cell goes through the process below:
Meiosis involves two rounds of cell division, but only one round of cell doubling.
This is how we end up with cells with half the chromosome number.
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Summary Questions
1. What is meiosis?
2. Do asexually reproducing organisms need the process of meiosis? Why or why
not?
3. What is meant by homologous chromosomes?
4. Define the following terms:
a. Gamete
b. Zygote
c. Fertilization
d. Haploid
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5. If a sexually reproducing species has a chromosome number of 28, how many
chromosomes would you expect to find in its gametes?
6.
How does crossing over increase variety I a sexually reproducing species?
7.
Why is meiosis necessary in sexually reproducing species?
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