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Meiosis
Why You Both Do and Don’t Look
Like Your Parents
DIPLOID
 SOMATIC CELLS (BODY CELLS) ARE
DIPLOID OR 2n
– PAIRS OF CHROMOSOMES
– 1 FROM MOTHER
– 1 FROM FATHER
– 2 FACTORS (ALLELES) FOR EACH TRAIT
 GENE--HEIGHT
 ALLELE--TALL OR SHORT
 ONE ALLELE ON EACH CHROMOSOME
HAPLOID
 GAMETES (SEX CELLS) ARE
HAPLOID OR n
– 1 OF EACH CHROMOSOME
– FROM 1 PARENT
– 1 ALLELE FOR EACH TRAIT
ZYGOTE
 SPERM + EGG = ZYGOTE
– 1 ALLELE FOR EACH TRAIT FROM EACH
PARENT
– DIPLOID OR 2n
– # OF CHROMOSOMES ARE SPECIES
SPECIFIC
– CHROMOSOME # IS NOT RELATED TO
COMPLEXITY
What is the difference between a
somatic cell and a gamete?
5%
76%
19%
0%
1. Somatic cells are used for reproduction
and gametes are body cells
2. Somatic cells are diploid and gametes
are haploid
3. Somatic cells are haploid and gametes
are diploid
4. They are the same
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What is the product of the union
of two gametes?
94%
6%
0%
0%
1.
2.
3.
4.
A zygote
Somatic cells
Stem cells
A haploid cell
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%
%
%
%
What is the difference between a
gene and an allele?
1. A gene is the chemical form of a trait
while the allele is the specific type of
gene
2. An allele is the chemical form of a trait
while the gene is the specific type of a
allele
3. A gene is part of a chromosome while an
allele is what you see
10
4. Alleles are part of a chromosome while a
gene is what you see
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HOMOLOGOUS
CHROMOSOMES
 PAIRED CHROMOSOMES
– GENES FOR THE SAME TRAITS
– ARRANGED IN THE SAME ORDER
– NOT IDENTICAL
WHY MEIOSIS?
A chimp has 48 chromosomes in its
somatic cells, how many will be in a
gamete?
20%
25%
0%
55%
1.
2.
3.
4.
48
96
12
24
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10
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%
%
%
%
What would happen if gametes
were produced by mitosis?
1. Offspring would have half the
chromosomes of the parents
2. Offspring would have random numbers of
chromosomes
3. Offspring would have unmatched pairs of
homologous chromosomes
4. Offspring would have twice the number of
chromosomes of their parents
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What makes homologous
chromosomes homologous?
5%
47%
21%
26%
1. Size shape and color
2. The number of chromatids in each
chromosome
3. Size shape and genes
4. Size shape and alleles
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MEIOSIS I--DIPLOID TO
HAPLOID
 MEIOSIS I (DIPLOID TO HAPLOID)
 MEIOSIS II (HAPLOID TO HAPLOID)
 INTERPHASE
– GROWTH
– METABOLISM
– CHROMOSOME REPLICATION
 SISTER CHROMATIDS WITH CENTROMERE
PROPHASE I
 CHROMOSOMES COIL
 SPINDLES FORM
 TETRAD FORMS
– CROSSING OVER (NEW COMBINATIONS)
METAPHASE I
 TETRADS ON MIDLINE OF SPINDLE
ANAPHASE I
 HOMOLOGOUS CHROMOSOMES
SEPARATE
 MOVE TO POLES
 CENTROMERES INTACT
TELOPHASE I
 SPINDLES DISAPPEAR
 CHROMOSOMES UNCOIL
 CYTOKINESIS
 Meiosis CellsAlive
Tetrads form during this stage of
meiosis.
25%
25%
25%
25%
1.
2.
3.
4.
Prophase I
Metaphase I
Anaphase I
Telophase I
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Crossing over happens during
this phase of meiosis.
25%
25%
25%
25%
1.
2.
3.
4.
Prophase I
Metaphase I
Anaphase I
Telophase I
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The germ line cell goes from diploid to
haploid during this phase of meiosis.
25%
25%
25%
25%
1.
2.
3.
4.
Prophase I
Metaphase I
Anaphase I
Telophase I
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Two new haploid cells are formed during
this stage of meiosis.
25%
25%
25%
25%
1.
2.
3.
4.
Prophase I
Metaphase I
Anaphase I
Telophase I
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10
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Prophase II
 SPINDLES FORM
II METAPHASE
 SISTER CHROMATIDS ON MIDLINE OF
SPINDLE
ANAPHASE II
 CENTROMERES SPLIT
 SISTER CHROMATIDS SEPARATE
 MOVE TO POLES
TELOPHASE II
 NUCLEI REFORM
 SPINDLES DISAPPEAR
 CYTOKINESIS
 Meiosis CellsAlive
_______ produces 4 sperm cells while
______ produces three polar bodies and
an ova.
25%
25%
25%
25%
1.
2.
3.
4.
Spermatogenesis, oogenesis
Oogenesis, spermatogenesis
Meiosis, mitosis
Fertilization, meiosis
During which phase of meiosis do sister
chromatids become daughter
chromosomes?
25%
25%
25%
25%
1.
2.
3.
4.
Prophase I
Prophase II
Anaphase I
Anaphase II
MEIOSIS PROVIDES GENETIC
VARIATION
 MITOSIS-EQUAL DIVISION-IDENTICAL GENETICS
 MEIOSIS-REDUCTION DIVISION-SHUFFLES GENES
GENETIC RECOMBINATION
 8 MILLION DIFFERENT
POSSIBILITIES FOR SPERM AND
EGG (223)
 7 TRILLION DIFFERENT POSSIBLE
OFFSPRING (223 x 223)
GENETIC VARIATION
 CROSSING OVER
– 2 TO 3 CROSSOVERS PER CHROMOSOME
DURING MEIOSIS
GENETIC RECOMBINATION
AND VARIATION
 RANDOM ASSORTMENT
– CROSSING OVER
– INDEPENDENT SEGREGATION OF
HOMOLOGOUS CHROMOSOMES
 THIS IS THE RAW MATERIAL FOR
EVOLUTION