Transcript 8.14 Meiosis reduces the chromosome number from diploid to haploid

MEIOSIS AND
CROSSING OVER –
__________Reproduction
(making gametes)
Copyright © 2009 Pearson Education, Inc.
8.12 Chromosomes are matched in homologous
pairs
 ___________cells have pairs of homologous
chromosomes, receiving ____________________
_______________________
 Homologous chromosomes are matched in
– ____________
– Centromere position
– Gene locations
– A _____________(plural, loci) is the position of a gene
– ______________ (________) of a gene may be found at
the same locus on maternal and paternal chromosomes
Copyright © 2009 Pearson Education, Inc.
8.12 Chromosomes are matched in homologous
pairs
 The human _______________X and Y differ in
_______and genetic composition
 Pairs of __________have the same size and
genetic composition
 Applying Your Knowledge
– Humans have 46 chromosomes; how many
homologous pairs does that represent?
– If there is one pair of sex chromosomes, how many
pairs of autosomes are found in humans?
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_______________of
chromosomes
___________
________________ One duplicated
chromosome
8.13 Gametes have a single set of chromosomes
 Meiosis is a process that converts diploid nuclei to
haploid nuclei
– _______________have _____homologous sets of
chromosomes (_____)
– _____________have ____set of chromosomes (__)
– Meiosis occurs in the sex organs, producing
_______—sperm and eggs
 _____________is the union of sperm and egg
– The _______has a ________chromosome number,
one set from each parent
Copyright © 2009 Pearson Education, Inc.
Haploid gametes (n = 23)
n
Egg cell
n
Sperm cell
Meiosis
Fertilization
Diploid
zygote
(2n = 46)
Multicellular
diploid adults
(2n = 46)
Mitosis and
development
2n
8.14 Meiosis reduces the chromosome number
from diploid to haploid
 Like mitosis, meiosis is preceded by __________
– Chromosomes duplicate during the _____ phase
 Unlike mitosis, meiosis has ______ divisions
– During meiosis I, ______________________separate
– The chromosome number is reduced by ______
– During meiosis II, __________________separate
– The chromosome number remains the same
– Pipe Cleaner Example
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8.14 Meiosis reduces the chromosome number
from diploid to haploid
 Events in the nucleus during meiosis I
– Prophase I
– Chromosomes coil and become ____________
– Homologous chromosomes come together as pairs by
____________
– Each pair, with four ___________, is called a _________
– Nonsister chromatids exchange genetic material by
_______________________
Copyright © 2009 Pearson Education, Inc.
8.14 Meiosis reduces the chromosome number
from diploid to haploid
– Applying Your Knowledge
Human cells have 46 chromosomes. At the end of
prophase I
– How many chromosomes are present in one cell?
– How many chromatids are present in one cell?
Copyright © 2009 Pearson Education, Inc.
8.14 Meiosis reduces the chromosome number
from diploid to haploid
 Events in the nucleus during meiosis I
– Metaphase I
– ____________align at the cell equator
– Anaphase I
– ________________________separate and move toward
opposite poles of the cell
– Applying Your Knowledge
Human cells have 46 chromosomes. At the end of
Metaphase I
– How many chromosomes are present in one cell?
– How many chromatids are present in one cell?
Copyright © 2009 Pearson Education, Inc.
8.14 Meiosis reduces the chromosome number
from diploid to haploid
 Events in the nucleus during meiosis I
– Telophase I
–
Duplicated chromosomes have reached the poles
–
A _____________________forms around chromosomes
in some species
–
Each nucleus has the _____________number of
chromosomes
– Applying Your Knowledge
After telophase I and cytokinesis
–
How many chromosomes are present in one human
cell?
–
How many chromatids are present in one human cell?
Copyright © 2009 Pearson Education, Inc.
MEIOSIS I: Homologous chromosomes separate
INTERPHASE
Centrosomes
(with centriole
pairs)
Nuclear
envelope
PROPHASE I
METAPHASE I
ANAPHASE I
Microtubules Metaphase Sister chromatids
remain attached
plate
attached to
Spindle kinetochore
Sites of crossing over
Sister
Chromatin chromatids
Tetrad
Centromere
(with kinetochore)
Homologous
chromosomes separate
8.14 Meiosis reduces the chromosome number
from diploid to haploid
 Meiosis II follows meiosis I _____________
chromosome duplication
 Each of the two haploid products enters meiosis II
 Events in the nucleus during meiosis II
– Prophase II
– Chromosomes coil and become _____________ (visible)
Copyright © 2009 Pearson Education, Inc.
8.14 Meiosis reduces the chromosome number
from diploid to haploid
 Events in the nucleus during meiosis II
– Metaphase II
– ___________________align at the cell equator
– Anaphase II
– _____________________ separate and chromosomes
move toward opposite poles
Copyright © 2009 Pearson Education, Inc.
8.14 Meiosis reduces the chromosome number
from diploid to haploid
 Events in the nucleus during meiosis II
– Telophase II
– Chromosomes have reached the poles of the cell
– A _____________________ forms around each set of
chromosomes
– With ________________, _____ haploid cells are produced
– Applying Your Knowledge
After telophase II and cytokinesis
–
How many chromosomes are present in one human cell?
–
How many chromatids are present in one human cell?
Copyright © 2009 Pearson Education, Inc.
MEIOSIS II: Sister chromatids separate
TELOPHASE II
AND CYTOKINESIS
PROPHASE I
METAPHASE II
ANAPHASE II
TELOPHASE II
AND CYTOKINESIS
Cleavage
furrow
Sister chromatids
separate
Haploid daughter
cells forming
8.15 Mitosis and meiosis have important
similarities and differences
 Which characteristics are similar for mitosis and
meiosis?
– _______ duplication of chromosomes
 Which characteristics are unique to meiosis?
– _________ divisions of chromosomes
– Pairing of _____________________
– Exchange of genetic material by ________________
Copyright © 2009 Pearson Education, Inc.
8.15 Mitosis and meiosis have important
similarities and differences
 What is the outcome of each process?
– Mitosis: ______ genetically _________ cells, with the
________ chromosome number as the original cell
– Meiosis: ______ genetically _________ cells, with
______ the chromosome number of the original cell
Copyright © 2009 Pearson Education, Inc.
MITOSIS
MEIOSIS
Parent cell
(before chromosome duplication)
Site of
crossing over
MEIOSIS I
Prophase I
Prophase
Duplicated
chromosome
(two sister
chromatids)
Tetrad formed
by synapsis of
homologous
chromosomes
Chromosome
duplication
Chromosome
duplication
2n = 4
Chromosomes
align at the
metaphase plate
Metaphase
Anaphase
Telophase
Sister chromatids
separate during
anaphase
2n
2n
Daughter cells
of mitosis
Tetrads
align at the
metaphase plate
Homologous
chromosomes
separate
(anaphase I);
sister chromatids remain
together
No further
chromosomal
duplication;
sister
chromatids
separate
(anaphase II)
Metaphase I
Anaphase I
Telophase I
Haploid
n=2
Daughter
cells of
meiosis I
MEIOSIS II
n
n
n
n
Daughter cells of meiosis II