Unit 4 Study guide
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This 14 page Study Guide was uploaded by Danielle Francy on Monday April 25, 2016. The Study Guide belongs to Bio 190 at Towson University taught by Joseph Velenovsky in Fall 2015. Since its upload, it has received 63 views. For similar materials see Intro Biology for Health Professions in Biology at Towson University.
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Date Created: 04/25/16
Unit 4 Study Guide Cells must divide because: ● Growth ● Replacement of damaged cells ● Development embryo into an adult organism Asexual Reproduction: ● No sperm or egg involved ● Not just singlecelled organisms ● Sea stars fragmented parts ● Plants growing from a clipping ● Parent and offspring identical in terms of genetic makeup ● One parent cell ● Is mitotic division ● Parent no longer exists after reproduction ● Minimal genetic variation ○ Mutation(primarily, but rare) Sexual Reproduction: ● Fertilization of an egg by a sperm ● Gametes= egg and sperm ● Testes and ovaries ● Meiosis ● Only half as many chromosomes as parent cell ● Diploid(2n) ● Haploid(n) ● Unique combination of genes ● Crossing over ● Not identical to parents or siblings ● Identical twins ● Two parents(multicellular organisms) ● Parents still exist after reproduction ● Requires: ○ Meiotic division ■ Each parent produces a gamete(half genetic info) ○ Fertilization(Gamete fusion) ■ Gametes fuse together to create a new individual with mixture of maternal and paternal genetic info Somatic Cells: ● Body cells ● 46 chromosomes ● Metaphase of mitosis ● 2 sister chromatids ● Arranged into matching pairs based primarily on size ● Centromere position ● Banding pattern ● 23 pairs of duplicated chromosomes ● Homologous chromosomes ● Genes are located at the same loci ● Allelic versions may be different ● Locus, banding patterns ● In females, 46 chromosomes are arranged neatly into 23 pairs of homologous chromosomes ● In males, X and Y (partly homologous) ● Determine sex and other functions ● Autosomes Human Life Cycle: ● Two sets of chromosomes in each person; one from mother and one from father ● Species that reproduce sexually, share this characteristic with humans ● Diploid ● Somatic cells contain pairs of homologous chromosomes ● Total number is diploid number (2n) ● Humans diploid number = 46 ● 2n = 46 ● Gametes= egg and sperm ● Single set of chromosomes ● 22 autosomes ● 1 sex chromosome ● Either X or Y ● All eggs have X ● Sperm determines sex of offspring ● Haploid cells ● One chromosome of each homologous pair ● Homologous number = 23 ● N = 23 ● Haploid sperm, haploid egg ● Fertilized egg ● Fertilization ● Zygote ● Two sets of homologous chromosomes ● Diploid ● One set from each parent ● Development occurs *****Homologous Chromosome Pairs: ● Each body/somatic cell contains two copies of each human chromosome/DNA molecule ● Are present in all stages of cell cycle ○ G1, G0, S, G2, MP, M,A,T,C ● Can be in chromatin (fully extended) or chromosomes (fully compacted) form depending on stage of cell cycle ● Can be replicated or unreplicated ● These two copies are: ○ A pair ○ “Homologous” because they have: ■ Same length ■ Same centromere position ■ Same sequence of genes, but… ■ Not necessarily same “variants” (alleles) for each gene because each member of the pair is from a different parent ● Same length, same centromere position, and same sequence of genes because they are the same chromosome ● Not same sequence of alleles because ○ One= maternal (a, b, c, d, e, F) ○ One= paternal (a, B, C, D, e, f) ● Never attached at centromere ****Sister Chromatids: ● Each= one side (one half) of a replicated chromosome ● Each contains one of the 2 daughter DNA molecules made during the S phase ● Are identical in both gene and allele sequence ● Always held together by the centromere ● When separated at anaphase, they become independent chromosomes Know the difference between: Chromosome: Thread like structures located inside the nucleus of plant and animal cells. Chromatid: One half of two identical threadlike strands of a replicated chromosome Chromatin: A complex of DNA and proteins that forms chromosomes within the nucleus of eukaryotic cells. Chromosomes: ● Tightly packaged DNA ● Found only during cell division ● DNA is not being used for macromolecule synthesis Chromatin: ● Unwound DNA ● Found throughout interphase ● DNA is being used for macromolecule synthesis Three Subphases: 1. G1 phase 2. S phase 3. G2 phase ● First gap ● Second gap ● Cell grows during all three ● Chromosomes duplicated during S phase ● Synthesis of DNA(S phase) DNA replication ● At the end of S phase, chromosomes are doubled ● 92 sister chromatids ● Growth duplication, growth Checkpoints: ● Critical ● Need specific signals ● G1, G2, M ● Progress cell cycle ● Stop progression ● Detected by control system determine if progression should occur ● Key cellular processes ● First gap checkpoint is the most important ● If signal never arrives, switch to G0 ● Control system at G1 checkpoint ● Growth factor ● Cyclins, etc. not located in one place, but throughout cell ● Signals can override the brakes ● Progression through cell cycle Preparing to Divide: ● Chromatin coils up into chromosomes ● It must coil because DNA must be compacted into a structure that is easily moved ● Histones ● Chromosomal structure and gene regulation ● The number of chromosomes varies widely among eukaryotes Mitosis M Phase ● 10% of time during cell cycle ● Mitosis and cytokinesis ● Nucleus and its contents (duplicated chromosomes) divide ● Two daughter nuclei ● Cytokinesis is divided in two ● Two genetically identical daughter cells ● Single nucleus ● Cytoplasm; organelles ● Plasma membrane ● Each daughter cell begins the cell cycle in the first gap ● Mitosis unique to eukaryotes ● Development of human body ● Single cell ● Fusion of mother’s egg and father’s sperm ● Mitotic division results in embryonic growth Interphase: ● Animal cell ● Cell growth ● Synthesize new molecules and organelles ● Late interphase (G2) doubled much of its contents ● Two centrosomes (microtubuleorganizing centers) found in cytoplasm ● Each centrosome one pair of centrioles (microtubules) ● Chromosomes are duplicated but are still in chromatin form (cannot tell individual chromosomes apart) Prophase: ● Changes in the nucleus and cytoplasm ● Formation of discrete chromosomes (folding and coiling) ● Two identical sister chromatids joined together at centromere ● Different from centrosome and centrioles ● Mitotic spindle begins to form (early mitotic spindle) ● Microtubules grow out of the centrosomes ● Centrosomes (2) move away from each other Prometaphase: ● Nuclear envelope breaks down ● Microtubules from centrosomes are present at the poles (ends) of the mitotic spindle ● Microtubules reach the chromosomes which at this point are higher condensed ● Within the centromere region, each sister chromatid has a kinetochore ● This protein structure attaches to a portion of the microtubules from the mitotic spindle(both poles) ● This attachment causes the chromosomes to begin an agitated motion ● Other microtubules (not attached to kinetochores) contact microtubules that have extended from the opposite pole ● ***Protein motors (enzymes called kinesins use ATP) associated with spindle microtubules move the chromosomes toward the center of the dividing cell ● Kinesins similar to myosin ● ***Dynein also involved; a separate motor protein complex ● Kinesins and Dynein work together Metaphase: ● Mitotic spindle fully formed and functional ● Poles are completely at opposite ends of the cell ● Chromosomes converge on the metaphase plate ● Metaphase plate is an imaginary area equidistant between the two ends of the spindle ● Centromeres are lined up on the metaphase plate ● Within each chromosome, the kinetochores face opposite poles ● Microtubules attached to a particular chromatid are from one pole; its sister Anaphase: ● Sister chromatids are separated as the two centromeres of each chromosome come apart ● Upon this separation, each sister chromatid is labeled a daughter chromosome ● Kinesins and Dynein walk daughter chromosomes centromere first along microtubule towards opposite poles of the dividing cell ● At the same time, spindle microtubules attached to kinetochores shorten ● Spindle microtubules not attached to kinetochores lengthen ● Poles are moved farther apart Telophase: ● Cellular expansion or elongation that started in anaphase continues ● Daughter nuclei appear at opposite ends of the cell ● Nuclear envelopes form around the chromosomes at each pole ● Telophase is reverse of prophase ● Chromatin structure starting ● Presence of a nuclear envelope ● Shrinking of the mitotic spindle ● By the end of telophase, chromosomes are nearly coiled as chromatin ● Mitotic spindle has disappeared ● Mitosis is complete after telophase ● Defined as the equal division of one nucleus into two genetically identical daughter nuclei ● Still undergo cytokinesis ● Cytokinesis occurs often concurrently with telophase Cytokinesis: ● Two daughter cells completely separate after the end of mitosis ● Begins concurrently with telophase ● Animal and plant cells undergo cytokinesis differently Shortterm explanation of Mitosis(easily able to be drawn): Interphase: Centrosomes and DNA replicate themselves and get ready to split Prophase: Chromosomes form and centrosomes start to spread apart to either side of the cell Metaphase: C hromosomes align in the middle of the cell Anaphase: Separate chromosomes from their copies Telophase: Each of the new cell structures are reconstructed Cytokinesis: Cell movement Mitosis is responsible for: 1. Cell replacement 2. Growth 3. Asexual reproduction This video really helps better understand mitosis: https://www.youtube.com/watch?v=L0kenzoeOM Meiosis I: Interphase: ● Chromosomes duplicate ● Each chromosome consists of two genetically identical sister chromatids ● Centrosome has also duplicated ● Chromatin coils up ● Individual chromosomes are visible ● Synapsis ● Homologous chromosomes(each made of two sister chromatids) are paired Metaphase I: ● Chromosomal tetrads aligned on metaphase plate ● Midway between the two poles of the spindle ● Sister chromatids still attached to each other at centromere ● Spindle microtubules attached to kinetochores ● Homologous chromosomes are held together at the sites of crossing over ● Microtubules from one pole vs other pole ● Opposite movement Anaphase I: ● Chromosomes move towards opposite poles of the cell ● Sister chromatids composing each doubled chromosome remain attached at the centromere ● Only the tertads split up ● Haploid number of chromosomes move towards each spindle pole Telophase I: ● Chromosomes arrive at opposite poles ● Each pole has a haploid chromosome set ● Each chromosome is still duplicated ● Each chromosome consists of two sister chromatids ● Cytokinesis usually occurs concurrently with telophase I ● Two haploid daughter cells are formed Meiosis II: ● Same as mitosis ● Starts with a haploid cell Prophase II: ● Spindle forms ● Chromosomes are moved towards the middle of the cell Metaphase II: ● Aligned on metaphase plate ● Kinetochores face opposite poles Anaphase II: ● Sister chromatids finally separate ● Individual daughter chromosomes move towards opposite poles Telophase II: ● Nuclei envelope reformation ● Cytokinesis occurs concurrently ● Four daughter haploid cells Shortterm explanation of Meiosis I: Interphase I:ong strings of DNA duplicate Prophase I: Centromeres head to either side of the cell and microtubules unspool. DNA clumps and turns to chromosomes. Each is linked to its duplicate copy to make X shaped, double chromosomes. Once attached, they are called a chromatid. Each chromosome has two chromatids. Metaphase I: Each chromosome lines up next to its homologous pair partner in the center of the cell. Anaphase I: The duplicate copies get pulled apart to either end of the cell. Telophase I: ach new cell structure is reconstructed Cytokinesis: The cells pull apart. Shortterm explanation of Meiosis II: Undergoes the same way as mitosis since it has already gone through Meiosis I. The role of meiosis is to reduce the chromosome number in cells from 2n(diploid) to n(haploid). This video better helps understand Meiosis I and II: https://www.youtube.com/watch?v=qCLmR9YY7o Essay Questions: Law of Independent Assortment: Basically, there are two ways chromosomes can line up and that will determine which daughter cell gets which alleles in each cell. Once the mitotic spindle has separated each chromosome pair, they are yet again divided within the daughter cells into chromatids (two on each side of the cell).There are equal numbers of the genotypes. There are a lot of combinations because the alleles can align in many different ways. Video that helps starts at 8:58 (but reviews important terms before that): https://www.youtube.com/watch?v=0OkJK1x_tx4 Law of Segregation: Occurs during meiosis. During gamete formation, alleles from each gene separate (or segregate) from each other so that each gamete carries only one gene. Gametes then randomly unite during fertilization. https://www.youtube.com/watch?v=a5GMp9BPEkA Dihybrid Cross: A 16 Punnett Square. Differ in two traits: color and shape. This video is so helpful, I can’t even try to explain it better myself. Starts at 6:50: https://www.youtube.com/watch?v=Y1PCwxUDTl8 Remember the ratio 9:3:3:1 9 round yellow peas, 3 round green peas, 3 yellow wrinkled peas, and 1 wrinkled green pea. First generation must yield hybrid heterozygous RrYy. P generation: True breeding parents. FF and ff F1 generation: Hybrids. Heterozygous. Ff F2 generation: 3:1 ratio. FF, Ff, ff ***Know how to complete a Punnett Square Short Answers: Process of Mitosis and Meiosis were already discussed above. Number of cells at the start: Mitosis: 4 Meiosis I: 4 Meiosis II: 2 Number of chromosomes in each cell: Mitosis: 46 Meiosis I: Meiosis II: Are these chromosomes replicated? Mitosis: yes Meiosis I: yes Meiosis II: yes Are these chromosomes condensed? Mitosis: yes Meiosis I: yes Meiosis II: yes Are homologous chromosomes present in prophase? Mitosis: yes Meiosis I: yes Meiosis II: no Are sister chromosomes present in prophase? Mitosis: yes Meiosis I: yes Meiosis II: yes Prophasewhat is visibly different? Mitosis: No tetrads (they don’t form) Meiosis I: Tetrads form and crossing over happens Meiosis II: Sister chromatids. Half the number Metaphasewhat is visibly different? Mitosis: Sister chromatids are lined up Meiosis I: Tetrads are lined up Meiosis II: Sister chromatids are lined up Anaphasewhat is separated? Mitosis: Sister chromatids Meiosis I: Tetrads Meiosis II: Sister chromatids Number of chromosomes in each cell at the end? Mitosis: 4 Meiosis I: 2 Meiosis II: 2 Are homologous chromosomes present in daughter cells? Mitosis: yes Meiosis I: no, tetrads got separated Meiosis II: no Are sister chromatids present in the daughter cells? Mitosis: yes Meiosis I: yes Meiosis II: no Meiosis I: sources of genetic variation: 1. Independent assortment of chromosomes 2. Random fertilization 3. Crossing over Independent assortment of chromosomes: Basically the same as the Law of Independent Assortment. Random fertilization: Cannot get the same exact genes in children. This is due to the fact that you are taking a female’s egg and fertilizing it with a male’s sperm. Each sperm and egg have different DNA and therefore produce different DNA for each offspring. Crossing over: Exchange of corresponding segments between nonsister chromatids of homologous chromosomes and occurs during prophase I of meiosis. Chiasma is the site of crossing over. ***Know how to draw meiosis and mitosis if given 2n=____. Ploidy: Diploid: ● Number of chromosomes in a body cell ● Characteristics of a species ● Always even number because chromosomes occur in pairs ● Both homologous chromosome members of each pair present in the cell ● 2N(or 2n) ● 46 chromosomes Haploid: ● Number of chromosomes in a gamete ● One half the diploid number, but not just any half ● Only one member of each type/pair present ● When two haploid cells fuse, the diploid state is restored ● N(or n) ● 23 chromosomes ● Prokaryotes Bonus: Cyclins: ● A family of proteins that control the progression of cells through the cell cycle by activating Cdk(cyclin dependent kinase) enzymes. ● Key cell cycle regulator in all eukaryotic cells. ● Different cyclins for different stages of the cell cycle ● A cyclin molecule binds to a CDK which changes its shape and allows for phosphorylation of two amino acids. Insect sex chromosomes: ● Cockroaches and other insects use a XO system ● O is the absence of a sex chromosome ● XXfemale ● XOmale ● Sperm either has a X or no chromosome ● Eggs determine sex of offspring ● SRY= sex determining region of the Y chromosome Hypercholesterolemia: ● Too much LDL in the blood ● High levels of blood cholesterol ● hh and HH ● hh= recessive ● HH= normal amount of LDL receptors ● LDL receptors bind to LDL and remove them from blood ● Hh= mild disease, half the amount of LDL ● hh= severe disease, five times the amount of LDL in blood ● Receptor mediated endocytosis (remember from previous unit) ● Negative cholesterol Null allele: A mutant copy of a gene at a locus that completely lacks that gene’s normal function. Other things you should be familiar with: 1. Codominance: ○ Relationship between two versions of a gene ○ Individuals receive an allele from each parent ○ Dominant ○ DD,PP 2. Incomplete dominance: ○ r=null allele ○ One allele does not completely dominate another allele, resulting in a new phenotype ○ Does not support blending ○ However, you could have a red flower and a white flower and end up with a new phenotype of a pink flower. 3. Pleiotropy: ○ One gene influences multiple characteristics or traits, not just one. ○ Ex: sickle cell anemia 4. Polygenic Inheritance: ○ Two or more genes added together to get a single phenotypic characteristic. ○ Ex: height, skin color, eye color, and weight Test Cross: A genetic cross between a homozygous recessive and and a heterozygous to determine the genotype of the second individual. Synapsis: ● Chromatids of homologous chromosomes exchange segments ● Rearrangement of genetic information ● Key component of genetic variability stemming ● Crossing over Histone: Any of a group of proteins found in chromatin
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