Cell Division (Chapter 16) Flashcards
What are the three main reasons for cell division?
- Growth/Differentiation:
Mitosis enables organisms to grow from a single-celled zygote into a mature organism that might contain hundreds of trillions of specialized cells - Maintenance:
New cells produced to replace worn out/dead cells - Repair:
They can regenerate damaged tissues (finger cut → new skin). Some organisms can regenerate entire body parts.
True or False…
There is no new combination of cellular material as a result of single cell reproduction
True; all new cells contain same DNA as original cell
Where does asexual reproduction occur?
Occurs in all somatic (body) cells, unicellular organisms, and simple multicellular organisms (budding, runners)
What are the five levels DNA is organized into?
- DNA Molecule
- Histones (DNA wraps around histones forming a bead-like structure)
- Chromatin Strands (the bead-like structure is packed tightly, producing chromatin strands)
- Chromatin Fibres: Stands from loops which are attached to a supporting protein scaffold
- Chromosomes: Protein scaffold folds further to condense the genetic material into chromosomes (duplicate during replication)
True or False…
Chromosomes may be found as individual chromatids (during late stages of cell division) or as paired/sister chromatids (connected at the centromere)
True
Fill in the Blank:
Sister chromatids are _________ to each other
Sister chromatids are IDENTICAL to each other
How many pairs of chromosomes do humans have?
23 pairs (46 total)
Define: Homologs
- Homologous chromosomes carry the same genes, in the same order
- Despite this, homologous chromosomes often have slightly different DNA sequences resulting in different alleles (different form of the same gene)
- Share several other characteristics including: length, centromere location, and banding pattern
What is the cell cycle?
Refers to the life cycle of a cell where it alternates between haploid and diploid form
What are the two MAIN parts of the cell cycle?
- Cell division (mitosis): division of genetic material & nucleus
- Interphase: cell growth and synthesis stages
What are the 3 stages of interphase?
- G1 (first cell growth stage): cell grows (organelle replication)
- S (synthesis phase): Cell DNA is replicated
- G2 (second cell growth stage): cell grows, rebuilds energy reserves, and prepares for mitosis
What are the five stages of cell division?
- Prophase
- Metaphase
- Anaphase
- Telophase
- Cytokinesis
What are the five stages of cell division?
- Prophase
- Metaphase
- Anaphase
- Telophase
- Cytokinesis
Define: mitosis
Cell division in somatic cells
True or False…
All of the cells produced by mitosis are identical in genetic makeup to the original cells
True
Define: alleles
A alternative form of the same gene caused by slight variations in DNA base sequences
The appearance and functionality of a cell is a result of…
a) difference in cellular content
b) difference in the way that content is expressed
Answer: B
The unique appearance and functionality found in different cells of the body is NOT due to difference in cellular content, but instead, a difference in the way that content is expressed (differentiation)
Define: differentiation
The process during which young, immature (unspecialized) cells take on individual characteristics and reach their mature (specialized) form and function
Explain the steps of prophase in cell division
- Nuclear envelope breaks down and the contents of the cell’s nucleus becomes visible
- DNA strands shorten and thicken, causing chromatin to condense into visible chromosomes
- Centrioles move to opposite poles of cell and begin growing spindle fibres
Explain the steps of metaphase in cell division
- Chromosomes move to center of cell
- Centromeres align across equator
- Spindle fibres attach to the centromeres
Explain the steps of anaphase in cell division
- Spindle fibres shorten and start pulling the sister chromatids apart
- Chromatids separate at centromeres
- Chromatids move to opposite poles of cell (same number of single-copy chromosomes should be at each pole)
Explain the steps of telophase in cell division
- Chromosomes at opposite ends of cell
- Chromosomes un-condense to form chromatin
- Nuclear envelope and nucleolus reappears
Explain the steps of cytokinesis in cell division
- Division of the cytoplasm
- In plant cells, a cell-plate forms first, separating two cells by forming cell wall
- In animal cells, cell membrane pinches in at the cleavage furrow to form two distinct daughter cells
Define: Stomaic Cells
- Somatic cells are found all throughout the body, except in cells that divide by meiosis to produce gametes (sperm and eggs)
- Somatic cells are diploid cells
- They have DNA from maternal and paternal sides combined
Define: Gamete Cells
- Gametes (sperm or eggs) are haploid cells
- They only hold half the DNA from somatic cells from which they came
- When an ovum is fertilized by a sperm, the original number of chromosomes (46 = 2n) is restored, forming a zygote
Define: Zygote
A diploid cell that results from the fusion of two haploids gametes
What is the purpose of meiosis?
Creates gamete cells by reducing the number of chromosomes from 46 to 23 by copying chromosomes once, but dividing twice
What is separated during Meiosis I?
Homologous chromosome
What is separated during Meiosis II?
Sister chromatids
What is crossing over?
Paired homologous chromosomes overlap and occasionally break, exchanging identical sized segments of DNA
Fill in the Blank:
Crossing over leads to more __________ ___________
GENETIC VARIATION
When can crossing over occur?
Only during prophase I
What is chromosome segregation?
Chromosome segregation is a process where chromatids (individual or sister chromatids) are separated from each other and migrate to opposite poles of the nucleus.
When does chromosome segregation occur?
The process of chromosome segregation occurs during both mitosis and meiosis
Define: Oocyte
A cell located in an individual’s ovary which may undergo meiotic division to form an ovum (egg cell)
What type of cell puts meiosis I on hold after prophase I?
Oocyte cells
When do oocytes cells complete meiosis I?
Once the female reaches puberty
What is the G-0 phase of the cell cycle?
A resting phase where the cell is neither dividing nor preparing to divide.
When do oocytes cells complete meiosis II?
If/when the oocytes is fertilized
Define: Gametogenesis
The process by which gametes, or germ cells, are produced via meiosis
How many sperm cells are produced from gametogenesis?
Four sperm cells are produced
How many egg cells are produced per oocyte?
One egg cell; the other 3 haploid cells sacrifice their cytoplasm to produce one large egg
Define: Karyotyping
A method of identification of chromosomes
How are chromosomes matched up together during karyotyping?
Chromosomes are matched up based on:
- Size (largest to smallest)
- Centromere position
- G-banding
What is an amniocentesis?
- Procedure where a small amount of amniotic fluid is removed from the sac surrounding the fetus
- The sample of amniotic fluid contains fetal cells and chemicals produced by the baby
- Amniotic fluid is then taken for testing
What is chorionic villi sampling?
- A prenatal procedure where a sample of chorionic villi tissue is removed from the placenta
- Sample is then tested for chromosomal abnormalities and certain other genetic problems
What is chorionic villi sampling?
- A prenatal procedure where a sample of chorionic villi tissue is removed from the placenta
- Sample is then tested for chromosomal abnormalities and certain other genetic problems
Define: Nondisjunction
When chromosomes fail to seperate correctly, resulting in daughter cells with abnormal numbers of chromosomes
What is the impact of nondisjunction?
- One daughter cell produced during separation will be lacking information, the other will have too much
- The impact is usually so severe to zygote that miscarriage occurs very early in pregnancy
- If the baby survives, the set of traits is called a syndrome (trisomy 21, 13 and 18 are the only trisomies that result in surviving offspring)
What is a trisomy? How do they occur?
A condition in which an extra chromosome is present in the cell’s nucleus (forming a triplet) and occur as a result of nondisjunction
What is a monosomy? How do they occur?
A condition where a chromosome is absent from the cell’s nucleus (forming a singlet) and occur as a result of nondisjunction
What condition does trisomy 21 cause?
Down’s Syndrome
What condition does trisomy 18 cause?
Edward’s Syndrome
What condition does trisomy 13 cause?
Patau’s Syndrome
True or False…
Nondisjunction of the sex chromosomes is usually fatal
False; They can be fatal, but most people survive just fine
Fill in the Blank:
XXY sex chromosomes causes ___________
Klinefelter’s Syndrome
- Tall, sterile males
- Normal intelligence
- Has female characteristics
What syndrome does XYY sex chromosomes cause?
Jacob’s Syndrome (super male)
- Somewhat taller than average
- Extra testosterone
- Slightly below normal intelligence
- Delayed emotional development
- Learning problems in school
A set of XXX sex chromosomes would cause ____________
Triple X Syndrome (super female)
- Normal intelligence
- Fertile
- No physical problems
Note: There are some women who are XXXX and XXXXX (each increasing X results in lesser intelligence and fertility)
What is Turner’s Syndrome (X sex chromosome)?
- The ONLY surviving monosomy
- Do not mature sexually at puberty
- Sterile
- Short stature
- Short, broad neck
- Broad chest
What is chromosomal deletion?
A segment of the chromosome is missing/deleted
What is chromosomal duplication?
A segment of the chromosome is duplicated
Define: Polyploidy
The condition in which a normally diploid cell or organism acquires one or more additional sets of chromosomes.
Describe cloning
- A process in which identical offspring are formed from a single cell or tissue (clone = cutting)
- All cells formed in this manner are identical (or almost – some small variations due to mutation are expected)
- Used in some plants and animals for reproduction
What is binary fission?
- Equal division of the cytoplasm and nucleus of an organism resulting in two new organisms
- Bacteria and other prokaryotes have a single, circular chromosome and no nucleus, therefore, a bacterial cell does not undergo mitosis.
- Instead, it replicates via binary fission. In favourable conditions, bacteria can divide at exponential rates (creating huge populations in little amounts of time).
What is budding?
- When the nucleus of an organism’s cell divides equally but the cytoplasm divides unequally
- The new cells formed may live as individuals or as colonies
What is sporulation?
- The production of spores; single, specialized cells which are released from the parent
- Spores are enclosed in a protective case and develop when environmental conditions are favourable
Define: Alternation of Generation
Refers to the alternation of diploid & haploid generations.
Define: Vegetative Propagation
A process of regeneration in plants where new plants develop from part of the original plant.
What are the seven methods of vegetative propagation?
- Bulbs
- Tubers
- Runners
- Rhizomes
- Layering
- Cutting
- Grafting
What is cancer?
The abnormal/uncontrolled growth of cells
Define: Metastasis
spreading of cancer cells throughout the body
What are the advantages of sexual reproduction?
- Offers population a way to adapt to changing environment.
- Competition among siblings may be reduced if genetically diverse.
- Pairing of homologous chromosomes and crossing over opportunities to replace or repair damaged chromosomes and increase variation.
What are the advantages of asexual reproduction?
- Proceeds quickly and does not require presence of second organism
- Usually requires less energy than sexual reproduction
- Many forms, such as budding, help to maximize the chances of survival (as daughter cell does not fully separate until capable of independence).
