Biology 2 Unit 2 study guide Slide set 5 The cell cycle Mitosis and Meiosis Chromosomes o 1 chromosome 1 DNA molecule bound to proteins o Many genes occur along the length of 1 chromosome o Each gene codes for a heritable trait a protein or RNA Gametes o Gametes are haploid n Haploid having only 1 set n of chromosomes 1 maternal set of chromosomes in an egg 1 paternal set of chromosomes in a sperm Somatic Cells o Somatic cells are diploid 2n Diploid having two sets of chromosomes A maternal set and a paternal set of chromosomes Homologous Chromosomes homologous pairs o The 2 sets of chromosomes in a diploid 2n cell can be arranged as Meaning for every kind of maternal chromosome there is a matching homologous paternal chromosome carrying the same kind of genes The 2 homologous chromosomes in a pair have the same number and kind of genes Pairs of homologous chromosomes in a human diploid cell Chromosome number is series specific o All somatic cells of an organism have their species specific diploid number of chromosomes Example Humans diploid chromosomes 46 and a goldfish diploid chromosomes 94 Karyotype o A Karyotype is an orderly display showing the number and types of chromosomes in a diploid cell and arranged in homologous pairs o Karyotypes are important because They are useful to detect abnormal chromosome number abnormal chromosome size and gender because they are displayed orderly They can also detect if there is any breakage in the chromosomes If some are missing or added on o Are Karyotypes from gametes or somatic cells Somatic cells because chromosomes are paired diploid o Amniocentesis withdraw a sample of mother s amniotic fluid that contains fetal cells makes a fetal karyotype o They do this to older women to see defects or down syndrome Alleles o Alleles are different versions of the same kind of gene o Alleles for a gene code for the same protein but they can have the same or different DNA sequence o Example o This pair of homologous chromosomes has 2 DIFFERENT ALLELES for the flower color gene o They still will code for a pigment protein same gene but it will be a different color different version Human pairs of chromosomes o 1 22 Autosomes o 23 a pair of sex chromosomes they carry sex determining genes Males an X Y chromosome Female two X chromosomes I clicker question o How might the members of a pair of homologous chromosomes differ from each Answer in the sequence of DNA making up each chromosome other The cell cycle o There are two parts to one full cell cycle cell growth and cell division o Mitosis cell division that preserves the original parental number of chromosomes in the 2 daughter cells Same number of chromosomes in 2 daughter cells Example 6 chromosomes and they undergo mitosis and the daughter cells have 6 chromosomes what has to happen They must replicate and then divide evenly o Side note in cleavage cells don t grow before they divide Some functions of the mitotic cell division include 1 Asexual Reproduction without gametes 2 Development cleavage 3 Tissue growth and repair adding cells Parts of the eukaryotic cell cycle o Two parts Interphase g1 s g2 stages and Mitotic Mitosis Cytokinesis o Blue arrow represents interphase o G s stand for gaps o Yellow Mitotic phase division phase Mitosis Cytokinesis The nucleus divides and then the cytoplasm divides o Side note in cleavage cells bypass G1 and go straight to S o In g1 a new cell grows o In S chromosomes DNA replicates o In g2 the cell prepares to divide G2 of Interphase o After DNA replication in S the cell synthesizes proteins and structures to prepare for cell division o The centrosome replicates when a cell is not replicating it has only one centrosome o The centrosome is a microtubule organizing center o Each centrosome is made up of a pair of cylindrical centrioles o Centrioles synthesize microtubules needed to make the spindle o Now have two centrosomes and four centrioles o Centrioles are absent in plant cells Prophase 1 o Centrosomes move to opposite poles o Spindle microtubules and asters begin to form o Replicated chromosomes begin to condense o ONE REPLICATED CHROMOSOME 2 sister chromatids joined at a centromere joined by cohesion proteins It is still one chromosome until the sister chromatids spread apart proteins is where the 2 sister proteins are joined by cohesion o Centromere o KNOW THIS one chromosome BEFORE replication has no sister chromatids and one chromosome AFTER replication has two sister chromatids Pro metaphase 2 o Nuclear membrane breaks down why Have to get rid of membrane in order to be able to pull them apart into two daughter cells This is where you can see distinct chromosomes o A kinetochore protein complex appears at each centromere and it attaches the centromeres of sister chromatids to spindle fibers you need kinetochore because the bind to the chromosome o The spindle is now complete o Aster microtubules anchor the centrosome to cell membrane Metaphase 3 o Spindle microtubules move the chromosomes o Chromosomes line up in SINGLE FILE along the midline equator or metaphase plate o NOTE the 2 sister chromatids of a replicated chromosome face opposite poles Anaphase 4 o Centromeres split o Spindle microtubules shorten and pull apart chromatids towards o Once pulled apart they are now called opposite poles chromosomes Telophase 5 o Spindle dissembles o Nuclear envelope reforms o Mitosis nuclear division is now complete Cytokinesis last part of M phase o Cell membrane pinches in at the cleavage furrow o Cytoplasmic division is now complete o End result 2 daughter cells each with the SAME number of chromosomes as parent cell and identical DNA sequence as parent cell Cytokinesis in animal vs plant cells o In animal cells a cleavage furrow forms separating the two daughter cells o In plant cells a cell plate is formed that creates a new cell wall to separate the daughter cells Meiosis o Requires two cell divisions and reduces the diploid chromosome number in half o 1 diploid somatic cell 4 haploid gamete cells o Meiosis 1 a reduction division go from 2n to n o Interphase o Prophase 1 chromosomes replicate in diploid parent cell during S 2n 6 Synapsis homologous chromosomes pair up and form tetrads Non sister chromatids in a tetrad exchange equivalent segments at a Chiasma crossing over o Metaphase 1 o Anaphase 1 Tetrads line up at the metaphase plate chromosomes in each pair aka one blue and one red homologous chromosomes separate the two o Picture of Meiosis 1
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