CAMPBELL BIOLOGY IN FOCUS Urry Cain Wasserman Minorsky
CAMPBELL BIOLOGY IN FOCUS Urry • Cain • Wasserman • Minorsky • Jackson • Reece 10 Meiosis and Sexual Life Cycles Lecture Presentations by Kathleen Fitzpatrick and Nicole Tunbridge © 2014 Pearson Education, Inc.
Inheritance of Genes § Each gene has a specific locus (fixed position), on a certain chromosome © 2014 Pearson Education, Inc.
§ Gene: a region of DNA that encodes a function § Ex. Flower color § Allele: one of two or more forms of an alternative gene that are found at the same place on a chromosomes § Ex. Purple flower color, white flower color © 2014 Pearson Education, Inc.
Sets of Chromosomes in Human Cells § A karyotype is an ordered display of the pairs of chromosomes from a cell § The 2 in each pair are called homologous chromosomes, or homologs § These carry genes controlling the same inherited characters § 1 from each parent © 2014 Pearson Education, Inc.
Figure 10. 3 Application Technique Pair of homologous duplicated chromosomes Centromere Sister chromatids Metaphase chromosome © 2014 Pearson Education, Inc. 5 m
§ The sex chromosomes are called X and Y § The remaining 22 pairs are called autosomes © 2014 Pearson Education, Inc.
Figure 10. 4 Key 2 n 6 Maternal set of chromosomes (n 3) Paternal set of chromosomes (n 3) Sister chromatids of one duplicated chromosome Two nonsister chromatids in a homologous pair © 2014 Pearson Education, Inc. Centromere Pair of homologous chromosomes (one from each set)
Three Types of Sexual Life Cycles: • All species that reproduce sexually undergo mitosis and meiosis • Timing of each may vary © 2014 Pearson Education, Inc.
Figure 10. 6 a Key n Gametes n n MEIOSIS 2 n Diploid multicellular organism (a) Animals © 2014 Pearson Education, Inc. FERTILIZATION Zygote 2 n Mitosis Haploid (n) Diploid (2 n)
Figure 10. 6 b Haploid multicellular organism (gametophyte) Mitosis n Key Haploid (n) Diploid (2 n) Mitosis n n Spores MEIOSIS 2 n Diploid multicellular organism (sporophyte) Gametes FERTILIZATION 2 n Mitosis (b) Plants and some algae © 2014 Pearson Education, Inc. n n Zygote
Figure 10. 6 c Haploid unicellular or multicellular organism Mitosis Key Haploid (n) Diploid (2 n) Mitosis n n Gametes FERTILIZATION MEIOSIS 2 n Zygote (c) Most fungi and some protists © 2014 Pearson Education, Inc. n
Concept 10. 3: Meiosis reduces the number of chromosome sets from diploid to haploid § Meiosis: § Two sets of cell divisions…meiosis I and meiosis II § End result: 4 haploid daughter cells (that become gametes) © 2014 Pearson Education, Inc.
Figure 10. 7 Interphase Pair of homologous chromosomes in diploid parent cell Chromosomes duplicate Duplicated pair of homologous chromosomes Sister chromatids Diploid cell with duplicated chromosomes Meiosis I 1 Homologous chromosomes separate Meiosis II Haploid cells with duplicated chromosomes 2 Sister chromatids separate Haploid cells with unduplicated chromosomes © 2014 Pearson Education, Inc.
Figure 10. 7 a Interphase Pair of homologous chromosomes in diploid parent cell Duplicated pair of homologous chromosomes Sister chromatids © 2014 Pearson Education, Inc. Chromosomes duplicate Diploid cell with duplicated chromosomes
Figure 10. 7 b Meiosis I 1 Homologous chromosomes separate Meiosis II Haploid cells with duplicated chromosomes 2 Sister chromatids separate Haploid cells with unduplicated chromosomes © 2014 Pearson Education, Inc.
§ Meiosis I, homologous pair and separate § Meiosis II, sister chromatids separate § https: //www. youtube. com/watch? v=16 en. C 385 R 0 w Animation: Meiosis Video: Meiosis I in Sperm Formation © 2014 Pearson Education, Inc.
Figure 10. 8 a MEIOSIS I: Separates homologous chromosomes Prophase I Metaphase I Anaphase I Telophase I and Cytokinesis Sister chromatids Centromere (with kinetochore) Sister chromatids remain attached Centrosome (with centriole Cleavage pair) furrow Chiasmata Metaphase Spindle plate Fragments of nuclear envelope Homologous chromosomes © 2014 Pearson Education, Inc. Homologous chromosomes separate Microtubule attached to kinetochore
Figure 10. 8 b MEIOSIS II: Separates sister chromatids Prophase II Metaphase II Anaphase II Telophase II and Cytokinesis Sister chromatids separate Haploid daughter cells forming © 2014 Pearson Education, Inc.
During Prophase I: § Nuclear envelope breaks down § Synapsis occurs: homologous chromosomes pair up, aligned gene to gene and connects § chromosomes in synapsis sometimes called a tetrad © 2014 Pearson Education, Inc.
§ When homologous chromosomes pair up, crossing over may occur § Crossing Over: sharing of genetic material between two non-sister chromosomes § Exchange DNA segments § Chiasma: region where crossing over occurs © 2014 Pearson Education, Inc.
Evolutionary Advantage? © 2014 Pearson Education, Inc.
© 2014 Pearson Education, Inc.
§ 4 events unique to meiosis, all in meiosis l § Synapsis and crossing over (Prophase I) § Homologous pairs line up at the metaphase plate (Metaphase I) § Separation of homologous pairs (Anaphase I) § Telophase I results in in 2 (diploid) daughter cells © 2014 Pearson Education, Inc.
Figure 10. 9 a MITOSIS MEIOSIS Parent cell Chiasma MEIOSIS I Prophase Duplicated chromosome Metaphase Anaphase Telophase 2 n Daughter cells of mitosis © 2014 Pearson Education, Inc. Chromosome duplication 2 n = 6 Chromosome duplication Individual chromosomes line up. Pairs of chromosomes line up. Sister chromatids separate. Homologs separate. 2 n Sister chromatids separate. Homologous chromosome pair Metaphase I Anaphase I Telophase I Daughter cells of meiosis I MEIOSIS II n n Daughter cells of meiosis II
• Some species have a short interphase others do not. © 2014 Pearson Education, Inc.
Meiosis II Events • Prophase II: new mitotic spindle forms; single duplicated chromosomes attach • Metaphase II: Single duplicated chromosomes line up at equatorial plate • Anaphase II: Sister chromatids separate (centromere breaks) • Telophase II: New nuclear envelopes form, results in 4 haploid daughter cells – Are they identical to the parent cell? © 2014 Pearson Education, Inc.
Figure 10. 9 b SUMMARY Property Mitosis Meiosis DNA replication Occurs during interphase before mitosis begins Occurs during interphase before meiosis I begins Number of divisions One, including prophase, prometaphase, anaphase, and telophase Two, each including prophase, metaphase, and telophase Synapsis of homologous chromosomes Does not occur Occurs during prophase I along with crossing over between nonsister chromatids; resulting chiasmata hold pairs together due to sister chromatid cohesion Number of daughter cells and genetic composition Two, each diploid (2 n) and genetically identical to the parent cell Four, each haploid (n), containing half as many chromosomes as the parent cell; genetically different from the parent cell and from each other Role in the animal body Enables multicellular adult to arise from zygote; produces cells for growth, repair, and, in some species, asexual reproduction Produces gametes; reduces number of chromosome sets by half and introduces genetic variability among the gametes © 2014 Pearson Education, Inc.
Concept 10. 4: Genetic variation produced in sexual life cycles contributes to evolution § Mutations …the original source of genetic diversity § Mutations create different alleles § Reshuffling alleles produces genetic variation © 2014 Pearson Education, Inc.
Origins of Genetic Variation Among Offspring § Meiotic mechanisms that contribute to genetic variation: § Independent assortment of chromosomes § Crossing over § Random fertilization © 2014 Pearson Education, Inc.
§ Independent assortment: random distribution of alleles occurs during meiosis § Homologous chromosomes line up and separate independently of each other © 2014 Pearson Education, Inc.
Figure 10. 10 -3 Possibility 2 Possibility 1 Two equally probable arrangements of chromosomes at metaphase I Metaphase II Daughter cells Combination 1 Combination 2 © 2014 Pearson Education, Inc. Combination 3 Combination 4
© 2014 Pearson Education, Inc.
Possible Chromosome Combinations As a result of random alignment, the number of possible combinations of chromosome pairs in a gamete is: 2 n (and this is without crossing over) © 2014 Pearson Education, Inc.
Possible Chromosome Combinations 2 n for humans would be … 223 or… 8, 388, 608 © 2014 Pearson Education, Inc.
Random Fertilization § Random fertilization adds to genetic variation § Random fertilization: the genes within one gamete (such as a sperm cell) do not give that gamete a lesser or better chance than any of the other sperm cell of fusing with an egg cell to produce a zygote. § Problem if they did? © 2014 Pearson Education, Inc.
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