Chapter 13 and Sexual Life Cycles Chromosome number Human cells Diploid 46 total per cell 46 Diploid number Humans cells 23 pairs of homologous 23 Haploid number The number of different kinds of An Overview of Human cells are considered diploid because each cell has two copies Some organisms Haploid triploid tetraploid Overview of Process of a single diploid cell dividing to produce four haploid cells Cells that contain a single set of For reproduckon 1
Gametes Overview of Haploid cells produced through meiosis are Female gametes are eggs Male gametes are sperm. They are the reproduckve cells of human beings and many other organisms. Compared to Mitosis homologous pairs means the same in size and function 1. Both mitosis and meiosis are initiated in cells that are diploid or, meaning cells that contain paired sets of Mitosis. The members of each pair are homologous the same in size and function. Two pairs of homologous are shown within the cells in both the mitosis and meiosis figures. In each somatic gamete cell precursor homologous pair, one chromosome (in red) comes from the mother of the person whose cell is undergoing meiosis, while the other chromosome (in blue) comes from the father of this person. 2. Prior to the initiation of both mitosis and meiosis, the duplicate. In both processes, each chromosome is now composed of two sister chromatids. 3. In mitosis, the line up on the metaphase plate, one sister chromatid on each side of the plate. In meiosis, homologous not sister chromatids line up on opposite sides of the 4. In mitosis, the sister chromatids separate. In meiosis, the homologous pairs of separate. 5. In mitosis, cell takes place, and each of the sister chromatids from step 4 is now a full-fledged chromosome. Mitosis is finished. In meiosis, one member of each homologous pair has gone to one cell, the other member to the other cell. Because each of these cells now has only a single set of, each is in the haploid or state. Next, these single line up on the metaphase plate, with their sister chromatids on opposite sides of the plate. 6. The sister chromatids of each chromosome then separate. 7. The cells divide again, yielding four haploid cells. Figure 10.1 Overview of When the haploid sperm and haploid egg fuse, a diploid ferklized egg (or zygote) is produced, sesng into development a new generakon of organism. Chapter 13 and Sexual Life Cycles 10.2 The Steps in 2
The Steps in one round of chromosome duplicakon followed by two rounds of cell No second chromosome duplicakon aver first The Steps in Two primary stages in meiosis meiosis I meiosis II homologous pairs means the same in size and function 1. Both mitosis and meiosis are initiated in cells that are Mitosis diploid or, meaning cells that contain paired sets of. The members of each pair are homologous the same in size and function. Two pairs somatic gamete of homologous are shown within the cells cell precursor in both the mitosis and meiosis figures. In each homologous pair, one chromosome (in red) comes from the mother of the person whose cell is undergoing meiosis, while the other chromosome (in blue) comes from the father of this person. 2. Prior to the initiation of both mitosis and meiosis, the duplicate. In both processes, each chromosome is now composed of two sister chromatids. 3. In mitosis, the line up on the metaphase plate, one sister chromatid on each side of the plate. In meiosis, homologous not sister chromatids line up on opposite sides of the 4. In mitosis, the sister chromatids separate. In meiosis, the homologous pairs of separate. 5. In mitosis, cell takes place, and each of the sister chromatids from step 4 is now a full-fledged chromosome. Mitosis is finished. In meiosis, one member of each homologous pair has gone to one cell, the other member to the other cell. Because each of these cells now has only a single set of, each is in the haploid or state. Next, these single line up on 6. the The metaphase sister chromatids plate, with of each their chromosome sister chromatids then separate. on opposite sides of the plate. 7. The cells divide again, yielding four haploid cells. Prophase I (aver chromosome duplicakon) First pairing of homologous Crossing over occurs exchange reciprocal seckons of themselves Increases variakon Results in no two sperm or eggs being idenkcal Metaphase I chromosome pairs line up at the metaphase plate One member of each homologous pair is on one side of the plate, the other member is on the other side Random assortment 3
Anaphase I pairs separate each will become part of a separate daughter cell. Telophase I separated pairs reach opposite poles Cytokinesis I Two daughter cells fully separated Now haploid 23 per cell No homologous pairs present Each chromosome skll in duplicated state I I Sister chromakds of the duplicated are separated into separate daughter cells No subsequent DNA replicakon Proceeds much like mitosis from this point Only 23 sets of sister chromakds present instead of 46 4
End of interphase DNA has already duplicated Exchange of parts of non-sister chromatids. duplicated maternal chromosome sister chromatids Diploid non-sister chromatids link as they condense, forming tetrads. Crossing over occurs. duplicated paternal chromosome Prophase I First important source of genetic variation tetrad Metaphase I Microtubules move homologous to Independent assortment occurs. Anaphase I Microtubules separate homologous (sister chromatids remain together). Haploid Telophase I Two haploid daughter cells result from cytokinesis. In the sequence above, homologous lined up this way in Metaphase I... Prophase II (Brief) Random alignment of maternal/paternal at the Metaphase I Metaphase I Metaphase II Sister chromatids line up at new Second important source of genetic variation... but they could have lined up this way, yielding a different outcome. Anaphase II Sister chromatids separate. Compare these cells to the cells above Metaphase II cytokinesis cytokinesis Telophase II Four haploid cells result. Telophase II I I Prophase II Nuclear membranes breakdown If they reformed at all aver meiosis I New mitokc spindle forms Metaphase II 23 sister chromakds lined up on metaphase plate A^ached to mitokc spindle at the centromere I I Anaphase II 23 sets of sister chromakds separate at centromere Travel to poles Telophase II Separated at the poles Nuclear envelopes reform Cleavage furrow begins to form Cytokenesis II Cleavage furrow grows to pinch off cell in to two new daughter cells Now FOUR daughter haploid gametes, ready for maturakon I (a) I II Chapter 13 and Sexual Life Cycles 10.3 What is the Significance of? (b) Crossing over (c) Independent assortment Figure 10.2 5
What is the Significance of? Generates Diversity Generates diversity by ensuring that the gametes it gives rise to will differ genekcally from one another. is unlike mitosis In mitosis, TWO daughter cells are exact genekc copies of parent cells Diploid (46 ) 2 copies of each homologous chromosome (23x2) In meiosis, FOUR daughter cells (gametes) are not idenkcal Haploid (23 ) 1 copy of each chromosome Compared to Mitosis somatic cell Mitosis homologous pairs means the same in size and function gamete precursor 1. Both mitosis and meiosis are initiated in cells that are diploid or, meaning cells that contain paired sets of. The members of each pair are homologous the same in size and function. Two pairs of homologous are shown within the cells in both the mitosis and meiosis figures. In each homologous pair, one chromosome (in red) comes from the mother of the person whose cell is undergoing meiosis, while the other chromosome (in blue) comes from the father of this person. 2. Prior to the initiation of both mitosis and meiosis, the duplicate. In both processes, each chromosome is now composed of two sister chromatids. provides variakon in gametes in two ways Crossing over Independent assortment 3. In mitosis, the line up on the metaphase plate, one sister chromatid on each side of the plate. In meiosis, homologous not sister chromatids line up on opposite sides of the 4. In mitosis, the sister chromatids separate. In meiosis, the homologous pairs of separate. 5. In mitosis, cell takes place, and each of the sister chromatids from step 4 is now a full-fledged chromosome. Mitosis is finished. In meiosis, one member of each homologous pair has gone to one cell, the other member to the other cell. Because each of these cells now has only a single set of, each is in the haploid or state. Next, these single line up on the metaphase plate, with their sister chromatids on opposite sides of the plate. 6. The sister chromatids of each chromosome then separate. 7. The cells divide again, yielding four haploid cells. Figure 10.1 6
Generates Diversity Crossing over Prophase I of meiosis pair with each other Chromosomes exchange reciprocal segments with one another Tetrads Aligned replicated homologous pairs Chiasma Point on the where crossing over occurs 7