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CHAPTER 8 The Cellular Basis of Reproduction and Inheritance. Modules 8.12 – 8.18. MEIOSIS AND CROSSING OVER. 8.12 Chromosomes are matched in homologous pairs. _____ cells of each species contain a specific number of chromosomes - PowerPoint PPT Presentation
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BIOLOGYCONCEPTS & CONNECTIONS
Fourth Edition
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Neil A. Campbell • Jane B. Reece • Lawrence G. Mitchell • Martha R. Taylor
From PowerPoint® Lectures for Biology: Concepts & Connections
CHAPTER 8The Cellular Basis of
Reproduction and Inheritance
Modules 8.12 – 8.18
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
• _____ cells of each species contain a specific number of chromosomes– Human cells have
46, making up 23 pairs of ________ chromosomes
MEIOSIS AND CROSSING OVER
8.12 Chromosomes are matched in homologous pairs
Chromosomes
Centromere
Sister chromatids Figure 8.12
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Karyotype
______Cells
HaploidCells
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
• Cells with two sets of chromosomes are said to be ______
• Gametes are ______, with only one set of chromosomes
8.13 Gametes have a single set of chromosomes
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
• At fertilization, a sperm fuses with an egg, forming a diploid ______– Repeated mitotic divisions lead to the
development of a mature adult– The adult makes haploid gametes by
_____– All of these processes make up the _____
___ cycle of organisms
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
• The human life cycle
Figure 8.13
MEIOSIS FERTILIZATION
Haploid gametes (n = 23)
Egg cell
Sperm cell
Diploidzygote
(2n = 46)Multicellular
diploid adults (2n = 46)
Mitosis anddevelopment
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
• Meiosis, like mitosis, is preceded by chromosome duplication– However, in meiosis the cell divides ____
to form _____ daughter cells
8.14 Meiosis reduces the chromosome number from diploid to haploid
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
• In the first division, meiosis I, homologous chromosomes are _____– While they are paired, they ____ ___ and
exchange genetic information– The homologous pairs are then
separated, and two daughter cells are produced
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings 9
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Figure 8.14, part 1
MEIOSIS I: Homologous chromosomes separate
INTERPHASE PROPHASE I METAPHASE I ANAPHASE I
Centrosomes(withcentriolepairs)
Nuclearenvelope
Chromatin
Sites of crossing overSpindle
Sisterchromatids
Tetrad
Microtubules attached tokinetochore
Metaphaseplate
Centromere(with kinetochore)
Sister chromatidsremain attached
Homologouschromosomes separate
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
• Meiosis II is essentially the same as ______– The sister ______ of each chromosome
separate– The result is four haploid daughter cells
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Figure 8.14, part 2
MEIOSIS II: Sister chromatids separate
TELOPHASE IAND CYTOKINESIS PROPHASE II METAPHASE II ANAPHASE II
Cleavagefurrow
Sister chromatidsseparate
TELOPHASE IIAND CYTOKINESIS
Haploiddaughter cellsforming
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
• For both processes, chromosomes replicate only once, during interphase
8.15 Review: A comparison of mitosis and meiosis
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
• Each chromosome of a homologous pair comes from a different parent– Each chromosome thus ____ at many
points from the other member of the pair– Cross-Over (Does it happen) and where
cross-over Occurs
8.16 Independent orientation of chromosomes in meiosis and random fertilization lead to varied offspring
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
• The large number of possible _______ of chromosome pairs at metaphase I of meiosis leads to many different combinations of chromosomes in gametes• _____ fertilization also increases variation in offspring
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Figure 8.16
POSSIBILITY 1 POSSIBILITY 2
Two equally probable
arrangements of chromosomes at
metaphase I
Metaphase II
Gametes
Combination 1 Combination 2 Combination 3 Combination 4
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Figure 8.18A
TetradChaisma
Centromere