Chromosomes and Cell Division Flashcards
Name the stages of the cell cycle.
There are 9.
- Interphase: G1, G0 (nondividing), S phase, G2
- Prophase
- Prometaphase
- Metaphase
- Anaphase
- Telophase
What is the chromosome structure during interphase?
loosely coiled, replicated chromosomes
What is the chromsome structure during prophase?
Chromosomes condense
What is the chromosome structure during prometaphase?
Spindle fibers attach to chromosomes and the chromosomes condense
What is the chromosome structure during metaphase?
The chromosomes align in the center
What is the chromosome structure during anaphase?
Centromeres divide and sister chromatids move to opposite poles
What is the chromosome structure during telophase?
Chromosomes decondense, nuclear membrane reforms
What is the chromosome structure during cytokinesis?
The cytoplasm divides, and the chromosomes uncoil.
What is the goal of mitosis?
production of two cells with the same number of chromosomes as the parent cell
What is the goal of meiosis?
production of sex cells that contain 1/2 the number of chromosomes (haploid), with genetic diversity through recombination
Describe the stages within interphase.
intensive metabolic activity, cell growth, and cell differentiation are evident
* G1 (gap I): period during interphase where no DNA synthesis occurs. Before S phase
* S Phase: DNA is synthesized before the cell enters mitosis
* G2 (gap II): period during interphase where no DNA synthesis occurs. After S phase
* G0 stage: Cells that enter G0 remain viable and metabolically active but are not proliferative
* During interphase, the nucleus is filled with chromatin fibers that are formed as the chromosomes uncoil and disperse after the previous mitosis
* Once G1, S, and G2 are completed, mitosis is initiated
Briefly describe the stages of mitosis.
- prophase: centrioles migrate to opposite ends of the cell, nuclear envelope begins to break down, chromatin fibers begin to condense, sister chromatids are visible
- prometaphase: chromosome movement
- metaphase: chromosomes begin to line up in center of cell, spindle fibers bind to kinetochore (in centromere) to move them
- anapase: sister chromatids disjoin from each other and are pulled to opposite ends of the cell
- telophase: cytokinesis occurs, chromosomes uncoil and become diffuse, spindle fibers disappear and nucleolus reforms
What is an allele?
alternative forms of the same gene
what is a locus?
gene sites along the lengths of chromosomes
what is a metacentric chromosome?
the centromere is in the middle of the chromosome
what is a submetacentric chromosome?
the centromere is located between the middle and the end of the chromosome
What is an acrocentric chromosome?
the centromere is close to the end
What is a telocentric chromosome?
the centromere is at the end
What is a karyotype?
An individuals complete set of chromosomes. Shows the double structure of two parallel sister chromatids connected by a centromere
What is a zygote?
a single-celled fertilized egg. most multicellular diploid organisms begin life as zygotes.
Briefly describe the stages of meiosis.
Prophase I: diploid cell w/ duplicated genetic material. Tetrads are two sister chromatids joined at the centromere. Cross over occurs.
Metaphase I: tetrad interacts with spindle fibers and starts moving to metaphase plate
Anaphase I: one half of the tetrad (dyad) is pulled to each pole
Telophase I: nuclear membrane forms
Prophase II: dyad is composed of one pair of sister chromatids
Metaphase II: centromeres are positions onto the metaphase plate
Anaphase II: sister chromatids of each dyad are pulled to opposite poles
Telophase II: cytokinesis occurs and monads are in each daughter cell (4 total)
What is spermatogenesis?
Production of male gametes
* occurs in testes
* undifferentiated diploid germ cell, spermatogonium grows to become a primary spermatocyte
* spermatocyte undergoes meiosis I
* secondary spermatocytes undergo meiosis II and produces spermatids
* spermatids go through spermigenesis to become spermatozoa (sperm)
onset: species reproductive cycles. may be continuous/occur periodically
What is oogenesis?
production of female gametes
* oogonium matures into a primary oocyte
* in meiosis I, primary oocyte divides unequally:
* daughter cells receive equal amounts of the genetic material but all of the cytoplasm goes to the primary oocyte, first polar body is produced
* at puberty (once a month), the oocyte divides through meiosis II and then is arrested as an ootid, second polar body is produced
* differentiates into a ovum
what is a heterogametic sex?
the sex of a species where an individual’s gametes have non-matching sex chromsomes
e.g. in humans, men have an XY
What is homogametic sex?
the sex has sex chromosomes that do not differ in morphology. Results in one kind of gamete. Female humans are homogametic because they contain XX chromosomes.
What is Klinefelter Syndrome (47, XXY)
There is an extra X chromosome
* result of nondisjunction: failure of sex chromosomes to segragate properly
* tall, long arms and legs
* 50% affected produce sperm (low sperm count, most are sterile)
* no cognitive reduction
* occurs in 1/660 male births
What is Turner syndrome? (45,X)
There is a missing sex chromosome
* result of nondisjunction: failure of sex chromosomes to segregate properly
* female internal and external genitalia
* ovaries are rudimentary
* short stature
* skin flaps on neck
* underdeveloped breasts
* intelligence is normal usually
* occurs in 1/2000 female births
What is 47, XXX Syndrome?
- additional X chromosome
- triplo-X
- often are completely normal
- sometimes women have underdeveloped secondary characteristics or intellectual disability
What is 47, XYY Condition?
- additional Y chromosome
- above average in height and more frequently violent
- subnormal intelligence, personality disorders
- some may be completely normal
What is the Lyon Hypothesis?
the inactivation of X chromosomes occurs randomly in somatic cells early in embryonic development
* once inactivation occurs, all descendant cells ahve the same X chromosome inactivated as their progenitor cell
What is Down Syndrome or Trisomy 21?
- extra 21st chromosome
- share similar physical characteristics
What is aneuploidy?
When an organism gains or loses one or more chromosomes but not a complete set
* monosomy: the loss of a single chromsome from an otherwise diploid genome
* trisomy: the gain of one chromosome in an otherwise diploid genome
What is euploidy?
When complete haploid sets of chromsomes are present
(this is preferred)
What is Polypoidy?
When two or more sets of haploid chromosomes are present
* triploid: three sets
* tetraploid: four sets … etc.
What is a nondisjunction?
When pair homologs fail to disjoin during segregation
* disrupts normal distribition of chromosomes into gametes
What causes chromsomal abberations?
Nondisjunctions, deletions, translocations, inversions, duplications
Why does advanced maternal age increase risk in nondisjunctions resulting in syndromes such as Trisomy 21?
- meiosis is initiated in all eggs of a female when she is a fetus, and then development is arrested
- when ovulation begins, meiosis is reinitatied in one each during each ovulatory cycle
- each ovum that is released is a month older than the one before it
- genetic counselling is recommended for women who get pregnant late in her reproductive years
What is Patau Syndrome and Edwards Syndrome?
- the two other human trisomies that survive to term (excluding Down syndrome)
- Patau: 47, 13+
- Edwards: 47, 18+
What is deletion?
Distinguish between a terminal and intercalary deletion
a missing piece of a chromosome when it breaks in one or more places and a portion of it is lost
* terminal: deletion at the end of a chromosome
* intercalary: deletion in the interior of a chromosome
What is Cri du Chat Syndrome?
- result of a deletion of a small terminal portion of chromosome 5
- 46,5p- :meaning all 46 chromosomes are there but some or all of the p arm of one member of chromsome 5 pair is missing
- characteristic crying sound in infants
- intellectual and developmental disabilities
What is a duplication?
- when any part of the genetic material is present more than once in the genome
- a repeated segment of a chromosome
- may be the result of unequal crossing over between synapse chromosomes during meiosis
- or thorugh a replication error prior to meiosis
What is an inversion?
Distinguish between paracentric and pericentric inversions.
- a chromsomal abberaiton in which a segment of a chromsome is turned around 180º within a chromosome
- rearranges the linear gene sequence
- requires a break along two points and then reinsertion of inverted segment
- paracentric: the centromere is not part of the rearranged chromosome segment
- pericentric: the centromere is part of the inverted segment
What is a translocation?
Include the definition of a reciprocal translocation.
the movement of a chromsomal segment to a new location in the genome
* reciprocal translocation: exchange of segments between two nonhomologous chromosomes
* genetic information is not lost or gained, there is a rearrangement of material
Name the chromosomal abberations where there is NO loss of genetic material
- translocations
- inversions
Name the chromsomal abberation(s) where there IS a loss of genetic material
- deletion
Name the chromomal abberation(s) where there is a gain of genetic material
- duplication
What is the difference between genotype and phenotype?
- phenotype: physical appearance
- genotype: genetic consitution
