BSC 2011 Exam 2 Review Slide Set VI I Chromosomes A Germ cells gametes are haploid n B Somatic cells are diploid 2n C Homologous chromosomes D Karyotypes i Homologous pairs of chromosomes ii Autosomes iii Sex chromosomes II The Cell Cycle and Mitosis A Two components Growth Division B Functions C Eukaryotes Interphase i ii Mitotic phase III Meiosis and Sexual Reproduction A Stages of meiosis i Meiosis I ii Meiosis II B Differences between mitosis meiosis i Segregation of alleles Important aspects of meiosis C i Law of Segregation and haploid gametes ii Law of Independent Assortment and genetic variation iii Crossing over and genetic variation I Chromosomes 1 chromosome 1 DNA molecule bound to proteins 1 chromosome has many genes Each gene codes for a heritable trait protein or RNA a Germ Cells gametes i Gametes are haploid n Ex sperm egg cells ii Haploid having only 1 set of chromosomes n Ex 1 maternal chromosomes from egg 1 paternal chromosome from sperm b Somatic cells i Somatic cells are diploid 2n Ex skin muscle cells ii Diploid 2 sets of chromosomes Ex A maternal set a paternal set Can be arranged into homologous pairs c Homologous chromosomes Diploid chromosomes can be arranged into homologous pairs o For every maternal chromosome there is a matching paternal chromosome with the same and kind of genes o Chromosomes is species specific Each species has their own specific number of diploid 2n chromosomes d Karyotypes Karyotype an orderly display showing the number and types of chromosomes in a diploid cell and arranged in homologous pairs Uses visible condensed chromosomes from a cell undergoing mitosis A human somatic diploid cell has 23 homologous pairs for a total of 46 chromosomes i Homologous pairs of chromosomes Allele different versions of the same kind of gene on a pair of homologous chromosomes Alleles for a gene code for the same protein but they can have the same or different DNA sequence ii Autosomes Human pairs 1 22 autosomes iii Sex chromosomes Human pair 23 pair of sex chromosomes o Male X and Y chromosomes o Female 2 X chromosomes II The Cell Cycle and Mitosis a Two components Growth Division Mitosis cell division that preserves the original number of parental chromosomes in 2 daughter cells b Functions 1 Asexual Reproduction ex binary fission 2 Development ex cleavage 3 Tissue Growth Repair c Eukaryotic Cell Cycle i Two Parts Steps Interphase G1 S G2 Mitotic Phase M Phase Mitosis Cytokinesis 1 Two new daughter cells are created 2 G1 A new cell grows 3 S Chromosomes DNA replicates 4 G2 The cell prepares to divide 5 M Phase nucleus divides mitosis and then cytoplasm divides cytokinesis 2 daughter cells each with the same of chromosomes as parent cell Interphase G2 Phase After DNA replicates in the S Phase the cell synthesizes proteins and structures to prepare for cell division The centrosome Replicates The centrosome is a microtubule organizing center Each centrosome a pair of cylindrical centrioles Centrioles synthesize microtubules needed to make the spindle apparatus Centrioles are absent in plant cells M 1 Prophase Centrosomes move to opposite poles Spindle microtubules and asters begin to form Replicated chromosomes begin to condense o 1 replicated chromosome 2 sister chromatids o Joined at centromere by cohesion proteins M 2 Prometaphase Nuclear membrane breaks down why Replicated chromosomes are now clearly distinct condensed A kinetochore kt protein complex appears at each centromere and attaches the centromeres of sister chromatids to spindle fibers The spindle is now complete o Non kt microtubules go pole to pole o Kt microtubules go pole kt Aster microtubules anchor the centrosome to cell Spindle microtubules move the chromosomes Chromosomes line up single file along the midline equator or metaphase plate Note the 2 sister chromatids of a replicated chromosome face Centromeres split Spindle microtubules shorten and pull apart sister chromatids toward opposite poles Once separated each chromatid is now called a daughter membrane M 3 Metaphase opposite poles M 4 Anaphase chromosome M 5 Telophase Spindle disassembles Nuclear membrane reforms Mitosis nuclear division is now complete M 6 Cytokinesis Cell membrane pinches in at the cleavage furrow Cytoplasmic division is now complete Result 2 daughter cells with the same of chromosomes and identical DNA as parent cell III Meiosis and Sexual Reproduction 1 diploid somatic cell 4 haploid gamete cells a Stages of meiosis Requires 2 cell divisions Reduces chromosome number in half from 2n i Meiosis I n 1 Interphase 2 Prophase I Chromosomes replicate in diploid parent cell during S Synapsis homologous chromosomes pair up and form tetrad Non sister chromatids in a tetrad exchange equivalent segments at a chiasma crossing over 3 Metaphase I Tetrads line up at metaphase plate Note orientation of poles is North South 4 Anaphase I Homologous chromosomes separate Sister chromatids remain attached They still need to be separated 5 Telophase I Cytokinesis Results in 2 haploid n cells Each haploid cell now skips G1 and S and goes to Meiosis II just separates sister chromatids ii Meiosis II 1 Prophase II 2 Metaphase II 3 Anaphase II Attached sister chromatids line up at the middle Note orientation of poles in East West Sister chromatids separate 4 Telophase II Cytokinesis Results in 4 haploid daughter cells with only one set of chromosomes Meiosis I Meiosis II b Differences between mitosis meiosis Mitosis 2 daughter cells are diploid and genetically identical to parent Meiosis 4 daughter cells are haploid and genetically different than parent due to crossing over c Important aspects of meiosis i Law of Segregation and Alleles This is makes gametes haploid 2 homologous chromosomes in a pair along with their alleles separate or segregate from each other into different gamete cells during meiosis I ii Law of Independent Assortment and genetic variation This is makes gametes genetically different each pair of homologous chromosomes tetrad line up during Metaphase I independent of how all other pairs line up This can create MANY different combinations of maternal and paternal chromosomes This makes games genetically different iii Crossing over and genetic variation During synapsis non sister chromatids exchange equivalent pieces at chiasma This creates new allele combinations in gametes This also makes gametes genetically different Allele different versions of the same gene o Ex blue eye allele brown eye allele 2n of
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