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90 Cards in this Set
- Front
- Back
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telomere
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a type of counter that keeps track of how many times a cell has divided - located at the tip of every chromosome, right next to the genes that direct the processes that keep an organism alive
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problems with cell division
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most cells that rebuild there telomeres with each cell division present a big problem: they don't know when to stop dividing - this is called cancer
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telomere
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every time a cell divides - the telomere gets shorter. after a critical number of cell divisions, functional DNA is lost, which means almost certain death for the cell
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some chromosomes are circular, others are linear
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in most bacteria and the other prokaryotes, the genetic information is carried in a single, circular chromosome, a strand of DNA that is attached at one site to the cell membrane. Eukaryotes have much more DNA than do bacteria and organize it into free-floating linear chromosomes within the nucleus
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histones
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long, linear strands are wrapped around these proteins - which keep the DNA from getting tangled and enable an orderly, tight, and efficient packing of the DNA inside the cell
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binary fission
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time for bacteria and the other prokaryotes to reproduce - tuse this method. means division in 2. begins with replication
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replication
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the process by which a cell's DNA duplicates itself - begins as the double-stranded DNA molecule unwinds from its coiled-up configuration, once un-coiled they split apart like a zipper, as it unzips free-floating nucleotides bases attach to the bases exposed on each of the 2 separated, single-stranded circular molecules of DNA, matching A to T and G to C to create 2 identical double-stranded DNA molecules
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parent cell
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original cell - pinches into 2 new cells
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daughter cells
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the 2 new cells from the parent cell - each of them has an exact and precise 2 stranded copy of the original 2 stranded circular chromosome
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asexual reproduction
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binary fission can be considered this - because the daughter cells inherit their DNA from a single parental cell
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sexual reproduction
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a combination of DNA from 2 separate individuals is passed on to offspring, resulting in offspring that are genetically different both from one another and from their parents
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cell cycle
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alternation of activities between processes related to cell division and processes related to growth
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somatic cells
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cells forming the body of the organism
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reproductive cells
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the sex cells, or gametes
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2 main phases in cell cycle:
-interphase -mitotic phase (M phase) |
-during which the cell grows and prepares to divide
-during which first the nucleus and genetic material within the cell divides, and then the rest of the cellular contents divides |
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interphase - gap 1
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a cell grows and performs all cellular functions (making proteins, getting rid of waste, and so on). cells that divide infrequently, such as most neurons and heart muscle cells, spend most of their time in the Gap 1 phase
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interphase - dna synthesis
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the cell begins to prepare for cell division - every chromosome creates an exact duplicate of itself by replication. before replication, each chromosome is a long linear strand of genetic materal. after replication, each chromosome has become a pair of identical long linear strands, held together near the center
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centromere
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region where the chromosomes are in contact - held together near the center
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centromere position
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can be at any location on a chromosome = middle-metrocentric/end - telocentric/also subtelocentric
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interphase - gap 2
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cell continues to grow and prepare for cellular division - phase differs from gap 1 because the genetic material has now been duplicated - gap 2 is usually shorter than gap 1
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mitotic phase - mitosis
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a process in which the nucleus of the parent cell duplicates - generally followed by cytokinesis
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mitotic phase - cytokinesis
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during which the cytoplasm, organelles, and the rest of the materials in the cell duplicate and the cell separates into 2 daughter cells, each of which has a complete set of the parent cell's DNA and other cellular structures
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complementarity
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feature of DNA - the characteristic that in the double-stranded DNA molecule, the base on one strand always has the same pairing partner (called the complementary base) on the other strand. A pairs with T, and G pairs with C (and vice versa) - one strand carries all the info needed to construct its complementary strand
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process of DNA replication
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1) unwinding - replication begins when the coiled, double stranded DNA molecule unwinds and separates into 2 strands (like zipper unzipping)
2) rebuilding - each of the single strands becomes a double strand as an enzyme connects the appropriate complementary base to the exposed base. |
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6.2 - mitosis replaces worn-out old cells with fresh new duplicates
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2 reasons for mitosis:
-growth -replacement |
-during development, organisms get bigger; happens in part through the creation of new cells
-cells must be replaced when they die, the wear and tear that come from living can physically damage cells |
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apoptosis
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cells that must be replaced actually die on purpose - in a planned process of cell suicide (those at high risk of becoming cancer cells - those in the digestive track or liver)
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mitosis process
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to begin, parent cell duplicates its DNA, creating a duplicate copy of each chromosome - once task is completed, other materials in the cell duplicate and cell divides into 2 new duplicate cells (the daughter cells)
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mitosis in depth
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interphase: in preparation for mitosis, the chromosomes replicate
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- every chromosome replicates itself - after replication, each chromosome is a pair of indentical long, linear strands held together at the center (by the centromere)
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prophase: the long, linear chromosomes that have replicated condense
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chromosomes in the cell's nucleus become more and more tightly coiled - at this point each chromosome looks like the letter X (not actually, they are linear)
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chromatid
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1 DNA molecule after replication - together called pairs of 'sister' chromatids - attached at centromere
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spindle
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when membrane around nucleus is dismantled and disappears near the end of this first stage - spindle is assembled. Part of cytoskeleton - thought of as a group of parallel threads stretching from one pold of the cell to the other
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spindle fibers
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protein in cytoplasm attached to chromosomes in mitosis - pull the sister chromatids to the middle of the cells and will eventually be used to pull the chromatids apart as cell division proceeds
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metaphase: the chromosomes congregate at the cell center
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chromosomes line up at the cell's center - pulled by spindle fibers attached to the centromere. Lined up in an orderly fashion, straddling the center in a "single-file" congregation that is called teh metaphase plate.
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anaphase: chromatids separate and move in opposite directions
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fibers attached to the centromeres begin pulling each chromatid in the sister chromatid pairs toward opposite poles of the cell; one strand of DNA is pulled in 1 direction and other identical strand is pulled in opposite direction. at end, one full set of chromosomes is at one of of cell and another identical full set is at the other end
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telophase: new nuclear membranes form around the 2 complete chromosome sets
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cell is now prepared to divide into 2 genetically identical cells - chromosomes begin to uncoil and fade from view, nuclear membranes reassemble, and the cell begins to pinch into 2
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cytokinesis
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the cell's cytoplasm is also divided into approximately equal parts, with some of the organelles going to each of the 2 new cells
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cancer
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defined as unrestrained cell growth and division can cause serious health problems (2nd leading cause of death in US - occurs when some disruption of the DNA in a normal cell interferes with the cell's ability to regulate cell division (caused by chemicals that mutate DNA or sources of high energy)
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2 most significant differences of cancer cells
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1) lose their "contact inhibition" - they ignore the signal that they are at high density and they continue to divide instead of bumping up against other cells and stopping
2) cancer cells can divide indefinitely - never lose ability to divide and continue to do so even in conditions that would otherwise prevent so |
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benign and malignant tumors
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benign - masses of normal cells that do not spread
malignant - result of unrestrained growth of cancerous cells - shedding of cancer cells from malignant tumors is how cancer spreads (called metastasis) |
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chromosome
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1 DNA molecule
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homologue
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DNA molecule with virtually complete identity to another chromosome
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Tetrad=4
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4 homologous chromatids pairing after replication and before anaphase
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simply - chromatid = chromosome = 1 DNA double helix = 2 molecules of complementary single stranded deoxyribonucleic acid
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"chromosome" should be considered an archaic term, which intially referred to the staining bodies found in the nucleic of eukaryotic cells. in modern usage it refers to any molecule with replicable nucleotide based info
- in modern usage, each unique, nucleic-acid-based, info bearing molecule is called a chromosome |
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DNA double stranded helix
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consists of 2 complementary single strands; each strand is a molecule (length can go up to a million bases)
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single strand of a helix
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each can serve as a template for the synthesis of the new complementary strand with complementary bases to the template strand at every position along the nucleotide sequence (DNA strands are each a mirror image of the other)
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therefore...
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a double stranded helix has sufficient info to form (from its 2 complementary single strands) 2 complete DNA double helices with a synthesis occuring at the same time for each template
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there is (1) and only (1) double helix in either a) chromosome or b)chromatid
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- a chromatid refers to a chromosome after replication but before physical separation from its sister chromosome (formed from the other DNA template strand)
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after appropriate division step, name changes
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-a chromatid undergoes a name change and is referred to as a chromosome instead of a chromatid - only feature that has changed is the attachment to another strand of DNA
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when info in DNA is obtained - it is first made as a complementary RNA (ribose sugar containing, not deoxyribose containing) copy from one (but nOT both) of the DNA strands
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double helix because of high stability associate with its chemical structure - the copy of the info is separate from the chromosome and the RNA is not considered part of the chromosome
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6.3 - meiosis generates sperm and eggs and a great deal of variation
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fertilization
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organisms including most animals and plants undergo sexual reproduction, in which offspring are produced by the fusion of 2 reproductive cells
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meiosis
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a process that enables organisms, prior to fertilization, to make special reproductive cells, the gametes, which ahve only half as many chromosomes as the rest of the cells in the organism's body - reduces each individual's genome by half in the gametes
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diploid
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cells that have 2 copies of each chromosome (somatic cells) - as a diploid individual, you have 2 copies of every gene in every somatic cell; one from your mother and one from your father
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haploid
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cells that have one copy of each chromosome (gametes)
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euploid
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total number of chromosomes for a particular species ( 23 pairs of chromosomes a healthy human has in each cell)
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meiosis important outcomes
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1) it reduces the amount of genetic material in gametes
2) it produces gametes that differ from one another with respect to the combinations of alleles they carry |
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gonads
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where meiosis occurs (the ovaries and testes in sexually reproducing animals) - diploid cells are found here
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homologous pair/homologues
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the maternal and paternal copies of a chromosome - means that there are 23 pairs in a diploid human
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cells undergoing meiosis divide twice
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1st division: homologues separate - for each of the 23 chromosome pairs, the maternal sister chromatids and the paternal sister chromatids separate into 2 new cells
second division: each of the 2 new cells divides again and the sister chromatids separate from each other into 2 newer cells - at the end there are 4 new cells, each of which has 23 strands of DNA (23 chromosomes) |
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interphase: in preparation for meiosis, the chromosomes replicate
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there is a DNA synthetic phase during which every chromosome creates an exact duplicate of itself by replicating - each chromosome is a pair of identical, long linear strands held together at the centromere
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meiosis division I: the homologues separate
1) prophase I: chromosomes condense and crossing over occurs |
(most complex phase) as sister chromatids become shorter and thicker, the homologous chromosomes come together (maternal and paternal sets of sister chromatids come together so there are 4 versions of the chromosome lined up together, look tlike they are lying on top of each other). Sister chromatids that are next to each other do something that makes every sperm/egg cell unique...nuclear membrane later disintegrates
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crossing over
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some of the genes you inherited from your mother get swapped onto strand of DNA you inherited from your father and the corresponding bit from your father is inserted into the DNA strand from your mother - can take place at several spots on the chromosome - ends up having a unique mixture of the genetic material that you received from your 2 parents
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2)metaphase I: chromosomes all line up at the center of the cell
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each pair of homologous chromosomes moves to the center of the cell, pulled by the spindle fibers to form the arrangement called the metaphase plate
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3) anaphase I: homologues are pulled to either side of the cell
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beginning of first cell division - homologues are pulled toward opposite sides of the cell - one of homologues goes to top pole, the other to the bottom. maternal and paternal chromatides are pulled to the ends of the cell in a random fashion
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4) telophase I and cytokinesis: nucluear membrane reassembles around sister chromatids and 2 daughter cells form
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after chromatids arrive at 2 poles of cell, the nuclear membrane reforms, then cytokinesis occurs and cytoplams divides and cell membrane pinches the cell into 2 daughter cells, each with its own nucleus
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meiosis divison II: separating the sister chromatids
5) prophase II: chromosomes re-condense |
like first division, genetic material in each of the 2 daughter cells once again coil tightly
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6) metaphase II: sister chromatids line up at the center of the cell
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sister chromatids move to the center of the cell, pulled by spindle fibers attached to the centromere, where sister chromatids are held together (metaphase plate)
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7) anaphase II: sister chromatids are pulled to opposite sides of the cell
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phase starts with 46 pieces of DNA in each cell created by meiosis I: 23 chromatid pairs - fibers attached to the centromere begin pulling each chromatid in the 23 sister chromatid pairs toward opposite poles of each daughter cell - each of what will become the 4 daughter cells has one single copy of each the 23 chromosomes
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8) telophase II and cytokinesis: nuclear membranes reassemble and the 2 daughter cells pinch into four haploid gametes
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sister chromatids for all 23 chromosomes have been pulled to opposite poles - cytoplasm divides, cell membrane pinches the cell into 2 new daughter cells, nuclear membranes begin to re-form and the process comes to a close
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difference between male and female gametes
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sperm cells have very little cytoplasm, while eggs have a huge amount - egg division produces lopsided cells, nearly all of cytoplasm from one of cells goes to one and barely none to the other. one of eggs is one large egg with lots of cytoplasm and 3 small cells with very little - small cells degrade and never function as gametes
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crossing over doesn't create new alleles but it does create new combinations of alleles on a chromatid
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all of the alleles from your parents are still carried on one DNA molecule or another - but combination of traits that are linked together on a single chromatid is new
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advantages&disadvantages of sexual production
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1) crossing over during the prodution of gametes - carries a mixture of that individual's maternal and paternal genetic material
2) shuffling and reassortment of homologues during meiosis - extremely large number of different combos of maternal and paternal homologues that might end up in each gamete 3) combining alleles from 2 parents at fertilization - new individual comes from the fusion of gametes from 2 different people BUT takes more time and energy and can be risky |
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asexual production advantages&disadvantages
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can be fast and efficient, but leads to genetically identical offspring that carry all of the genes that their parent carried.
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kinetochore
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protein structure on chromosomes where the spindle fibers attach during division to pull the chromosomes apart
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karyotype
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total number, type, and morphology of chromosomes in the cell
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zygote
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fusion of haploid cells to produce a diploid product
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6.4 - there are sex differences in chromosomes
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X and Y chromosomes
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the human sex chromosomes - 1 pair of sex chromosomes, 22 pairs of nonsex chromosomes. Female: XX -one X inactive except for PseudoAutosomal (PsA), Male: XY -equivalent to female in terms of X because X + PsA ~ XX and some expression from Y means not equal to female
X - relatively large and carries a great deal of genetic info Y - is tiny and carries genetic info only about a very small number of traits |
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how babies sex is determined
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at fertilization an egg bearing a single X chromosome is fertilized by a sperm bearing one copy of all the non-sex chromosomes and either an X chromosome or a Y chromosome (if X, a female, if Y, a male)
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hermaphrodites
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organisms capable of producing both male and female gametes because both male and female gametes are produced by an individual
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sex determination for species
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presence or absence of sex chromosomes, number of chromosome sets, and environmental factors such as incubation temperature
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down syndrome
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named after the doctor who discovered it - syndrome is revealed by the presence of an extra copy of the chromosome 21
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nondisjunction
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the unequal distribution of chromosomes during meiosis - can occur at 2 different points in meiosis (homologues can fail to separate during meiosis I or sister chromatids can fail to separate during meiosis II) - results in an egg or sperm with zero or 2 copies of a chromosome rather than a single copy.
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Turner Syndrome: X_
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women carrying only 1 X chromosome and no Y - only condition in humans in which a person can survive without one pair of chromosomes - women are usually relatively short (4'8"); develop a web of skin between the neck and shoulders; ovaries never fully mature, so women are almost always sterile; breasts and other secondary sex characteristics develop incompletely; intelligence is normal, but some learning difficulties
-no additional gene expression since lacking PsA |
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Klinefelter Syndrome: XXY
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causes a man to be feminized (can be treated somewhat with testosterone supplementation) individuals have testes, but they are smaller than average so levels of testosterone are low and almost always infertile; develop some female features like reduced facial hair and breasts; have long limbs and taller than average (6'); learn to speak at later age than average and have language impairments; if more X's - usually results in mental retardation
-triplo PsA + SRY + other Y genes = male characteristics in addtion to female |
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XYY males
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referred to as super males; live lives normally, not really detected but are relatively tall (6'2"); tend to have moderate to severe acne; intelligence usually falls within same range as that of XY males - although average may be lower
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female can be male?
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testosterone production originally regulated SRY on Y chromosome by translocations can transfer SRY from Y to X chromosome or autosome
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male can be female?
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receptor for testosterone and other androgens is termed androgen-receptor resistant and this gene is one the X chromosome; mutation that removes/deletes/mutates and means that testosterone cannot be taken up into somatic cells; females may have this mutation but without the effect on XX's since testosterone is not produced (in high quantities); these individual can be XY (X with mutation) from mother and Y from father, but phenotype will be that of female
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