Unit 4 - Cell Cycle and Communication Flashcards
List 3 differences between asexual reproduction and sexual reproduction
Sexual reproduction begins from two parents while asexual reproduction begins from a single individual.
In sexual reproduction, both parents contribute genes to the offspring in the form of the fusion of gametes during fertilization. Asexual reproduction does not have a fusion of gametes since the single parent passes copies of all its genes to the offspring
Sexual reproduction results in more genetic variation in the offspring, as their genomes are different from each other and the parents. Asexual reproduction results in genetically identical offspring because they arise from mitosis and have the exact copies of the parent’s genes. Asexual offspring are called clones.
What are gametes? (definition, function, chrromosomes)
Reproductive cells that transmit genes from one generation to the next; haploid (n = 23 chromosomes)
Contain 22 autosomes and one sex chromosome (X in females, X or Y in males)
EX: sperm and ova (eggs)
What is a locus?
The location of a gene on a chromosome
What is a somatic cell?
All cells in the body that are not gametes; diploid (2n = 46 chromosomes)
Contain 46 autosomes
What is a karyotype? What are the similarities in homologous chromosomes?
Picture of an organism’s complete set of chromosomes, arranged in pairs of homologous chromosomes or homologs.
One homologous chromosome was inherited from your mother and one from your father. Both chromosomes in a pair carry genes at the same loci that control the same inherited characteristics (EX: eye color) but may have different alleles (EX: blue eyes vs brown eyes). Both are similar in length + centromere position and have the same staining pattern
Sex chromosomes (X and Y)
Human females have a homologous pair of chromosomes, XX, but human males have one X chromosome and one Y chromosome (XY).
Autosome
Nonsex chromosomes (all other 22 pairs)
How do meiosis and fertilization contribute to the life cycles of sexually reproducing organisms?
Meiosis halves the number of chromosome sets from two (2n) to one (n), and then fertilization combines two gametes to double it from one (n) to two (2n), thus restoring the diploid number to form a zygote, or a fertilized egg, that eventually grows into an organism with diploid somatic cells. Fertilization and meiosis alternate in the life cycles of sexually reproducing organisms.
List 4 differences between meiosis and mitosis
Mitosis occurs in somatic (body) cells while meiosis occurs in gametes (sex cells)
Mitosis produces 2 diploid daughter cells (46 chromosomes) that are genetically identical to the parent and to each other. Meiosis produces 4 haploid daughter cells (23 chromosomes, one from each homologous pair) that genetically vary from one another and the parent
The # of divisions in mitosis is 1 while the # of divisions in meiosis is 2. However, they both experience DNA replication only once
The purpose of mitotic division is to grow and repair identical cells and also for asexual reproduction while the purpose of meiosis is to create unique gametes for fertilization
What do 2n and n each represent?
Diploid number (2n) = # of chromosomes
Haploid number (n) = # of homologous pairs
List 3 unique events that occur during meiosis I but do not occur in mitosis.
- Synapsis and crossing over between homologous chromosomes, which creates genetically varied daughter cells [prophase I]
- Alignment of homologous pairs (tetrads) at the metaphase plate. In mitosis, individual chromosomes line up, but in meiosis I, pairs of homologous chromosomes line up. This results in independent assortment (two ways in which the maternal pair and the paternal pair can line up), which increases genetic variation [metaphase I]
- Separation of homologous chromosomes. In mitosis, the sister chromatids separate while in meiosis I the pairs separate so that the sister chromatids remain attached [anaphase I]
List 3 ways in which meiosis creates genetic variation.
- Independent Assortment of Chromosomes
Random orientation of homologous pairs occurs at the metaphase plate in metaphase I. There is a 50% chance that a given daughter cell gets the maternal chromosome pair and a 50% chance it gets the paternal chromosome pair. Each pair is positioned independently of the other pair which means they are sorted independently.
- Crossing Over
During prophase I, genetic material is exchanged between homologous chromosomes (nonsister chromatids) which produces recombinant chromosomes that carry genes from both parents. All the chromatids that make up the tetrad are different due to crossing over. On top of that, at metaphase II, chromosomes can be oriented in two different ways because their sister chromatids are no longer identical. This creates even more genetic possibilities in the daughter cells
- Random Fertilization
Due to the previous two mechanisms, each gamete is already unique. There are even more possible combinations from the fusion of a male gamete (a sperm cell) with a female gamete (an egg) to produce a diploid zygote
Formula for # of possibilities of daughter cells?
2^n with n being the haploid number
How does negative feedback help maintain homeostasis?
In a negative feedback loop, feedback serves to reduce an excessive response and keep a variable within the normal range. Examples of processes controlled by negative feedback include body temperature regulation (sweating when you’re hot to lower your body temp) and control of blood glucose.
How does positive feedback affect homeostasis?
In a positive feedback loop, feedback serves to intensify a response until an endpoint is reached. Examples of processes controlled by positive feedback in the human body include blood clotting and childbirth
Centromere
The region where two sister chromatids are most closely attached to each other
What are the 3 stages of interphase?
- G1 phase - cell grows by producing proteins + cytoplasmic organelles such as mitochondria
- S phase - replication of DNA and centromeres
- G2 phase - more growth, preparation for mitosis
Definition of mitosis
Division of one nucleus into two genetically identical nuclei
Centrosome
Where the assembly of microtubules for the mitotic spindle begins in animals
Name the stages of mitosis in order
Prophase Prometaphase Metaphase Anaphase Telophase
Prophase
chromatin fibers condense into discrete chromosomes viewable under a light microscope
mitotic spindle begins to form (centrosomes, microtubules, asters)
centrosomes move away from each other toward the poles of the cell, propelled by lengthening microtubules between them
Prometaphase
nuclear envelope fragments
kinetochore microtubules (which are attached to the centromere of each chromosome on each side) jerk them back and forth
non-kinetochore microtubules interact with those from the opposite pole of the spindle, elongating/shortening the cell
Metaphase
centrosomes are at opposite poles of the cell
chromosomes line up at the metaphase plate
Anaphase
cohesin proteins holding the sister chromatids together at the centromere are cleaved –> two sister chromatids separate –> each becomes its own chromosome
the daughter chromosomes begin moving toward opposite ends of the cell as their kinetochore microtubules shorten
non-kinetochore microtubules lengthen, elongating the cell
Telophase
two daughter nuclei form in the cell
two nuclear envelopes arise from the fragments of the parent cell
chromosomes become less condensed and loosen up into chromatin fiber
the mitotic spindle is disbanded
Nondisjunction
Occurs when the members of a pair of homologous chromosomes don’t separate properly during meiosis I or sister chromatids don’t separate properly during meiosis II/mitosis. One daughter cell gets two and one gets none
Spindle fibers don’t attach
Definition of cytokinesis
Division of the cytoplasm into two identical daughter cells
Cytokinesis in animal cells
- Formation of a cleavage furrow - a shallow groove in the cell surface in the middle
- A contractile ring of actin microfilaments with the protein myosin pinches the cell in two like a drawstring - process is called cleavage
- Two separate daughter cells arise
Cytokinesis in plant cells
- Vesicles from the Golgi Apparatus carry materials to form a cell plate between daughter cells
- After it finishes growing, it fuses with the plasma membrane
- Two separate daughter cells arise
Binary fission
Division of prokaryotes (bacteria) and the asexual reproduction of unicellular eukaryotes
- The single circular chromosome replicates and the cell elongates
- Once the cell has reached twice its size, the plasma membrane pinches inward and divides the cell into two separate daughter cells
Which phase do nerve cells and muscle cells spend the most time in?
G0 phase where they do not undergo mitosis/cell division
Growth factor
A protein released by certain cells that stimulates other target cells to divide
Why can only diploid cells undergo meiosis?
Only diploid cells can undergo mitosis because haploid cells have a single set of chromosomes (n = 23) that can’t be further reduced
Prophase I
Centrosome movement, spindle formation, chromosome condensation, and nuclear envelope breakdown occur just like in prophase of mitosis
Each chromosome pairs with its homolog, aligned gene by gene, and crossing over occurs
Chiasmata
These are X shaped regions each homologous pair has where crossovers have occurred (where the different colors meet)
Hold homologous chromosomes together until anaphase I
Metaphase I
Pairs of homologous chromosomes line up at the metaphase plate, with one facing each pole
Anaphase I
Kinetochore microtubules pull the homologous chromosomes apart while the sister chromatids remain attached together at the centromere (essentially separate the maternal chromosome and the paternal chromosome)
homologous chromosomes move toward opposite poles
Telophase I and Cytokinesis
Each half of the cell has a haploid set of chromosomes (n) with chromatids that contain regions of non-sister chromatid DNA
Cytokinesis forms 2 haploid daughter cells
No chromosome duplication occurs between meiosis I and meiosis II
Metaphase II
Homologous chromosomes line up at the metaphase plate just like in mitosis
because of crossing over, the two sister chromatids of each chromosome are not genetically identical, which creates genetic variation in offspring
Anaphase II
Cohesin proteins holding the sister chromatids together at the centromere are cleaved –> two sister chromatids separate –> each becomes its own chromosome
the daughter chromosomes begin moving toward opposite ends of the cell as their kinetochore microtubules shorten
non-kinetochore microtubules lengthen, elongating the cell
Telophase II and Cytokinesis
Two nuclei form, chromosomes decondense, cytoplasm divides
4 haploid daughter cells are produced from 1 parent cells; they are all genetically distinct from each other and from the parent
How does synapsis/crossing over occur?
Synapsis is the joining of homologous chromosomes along their length. This newly formed structure is called a tetrad and it aligns the chromosomes gene by gene
In crossing over, the DNA from one homolog (or parent) is cut and exchanged with an exact corresponding portion of DNA from the other homolog (or parent). The points of attachment where crossovers occurred are crisscrossed regions called chiasmata, which hold the homologs together until anaphase I
G1 checkpoint
Go ahead checkpoint
If a cell gets a signal to divide (signaling molecules called growth factors), then it will bypass the check point and divide
If not, the cell will enter a nondividing state (G0 phase)
G2 checkpoint
This will determine if the cell has enough size and organelles, that the DNA has been replicated (completely & correctly). The cell is now ready to divide
M checkpoint
Occurs near the end of metaphase stage of mitosis
Determines that all the spindle microtubules are attached to the sister chromatids to prime for their separation
Describe the process in eukaryotes that ensures that the number of chromosomes will not double from
parent to offspring when gametes fuse during fertilization.
Homologous pairs of chromosomes separate in meiosis I which results in haploid (n) gametes, each receiving only one member of each chromosome pair.
