3_1 asexual & sexual reproduction, meiosis & life cycles
What has proven to be an essential process for the normal segregation of chromosomes during meiosis?
Crossing over
(chromosomal structure) deletions
a mutation where the end of a chromosome breaks off or two simultaneous breaks lead to the loss of an internal segment
* nucleoid
a region that contains the single circular DNA molecule of bacteria. It is usually coiled on a chromosome;
(chromosomal structure)inversion
a segment of a chromosome is turned around 180 degrees;. The position and sequence of the genes are altered
Poly-X
females that have three or more X chromosomes;
What are the (a) 4 types of chromosomal structure mutation? (b) List some of the factors that may cause them
(a) deletion, translocation, duplication, & inversions (b) radiation, organic chemicals and viruses can cause chromosomes to mutate via breaking.
*Name a process and tell me where it happens in meiosis.
*Name a process and tell me where it happens in meiosis.
How do asexual organisms bring about genetic variation?
Asexual organisms rely on mutations. They do not possess the ability to create genetic variation through recombination.
What is the result of non-disjunction in Anaphase I?
bivalents don't separate properly. Of the four daughter cells, two cells will be n+1 number of chromosomes and two cells will have n-1 number of chromosomes... When primary non disjunction happens there are no normal gametes that form
Compare the processes of Meiosis II to Mitosis
events of Meiosis II are the same as mitosis, except the nucleus contains a haploid number of chromosomes instead of a diploid.
haploid
half the total number of chromosomes of an organism; (n)
What holds non-sister chromatids together (a) initially? (b)finally?
(a) Nucleoprotein lattice. (b) chiasmata
What's the difference between animal, plant and most fungi/ algae in terms of meiosis?
Cells produced via meiosis in animals are called gametes and will need to fuse with another cell to become living organisms. Cells produced via meiosis are called spores and develop into an organism without having to fuse with another spore. Fungi and algae do not ever have a diploid version and will always be haploid.
What causes polyploidy?
Complete failure of meiotic spindle.
In what arrangement do the chromosomes of (diploid) body cells occur?
Diploid body cells occur in pairs;
What would cause certain daughter cells following meiosis II to be identical? What would cause them to not be identical?
If crossing over never took place...if crossing over did happened or independent assortment
Why did early investigators predict that there must be a reduction division in the sexual reproduction process?
If gametes(sex cells) contained the same number of cells as body cells(somatic), then the number of chromosomes would double with each new generation resulting in a completely new organism.
What is the main problem that happens in meiosis?
Non-disjunction: this problem will arise when sister chromatids are joined at centromere and homologues are joined during synapsis at chaismata...during anaphase this is supposed to be broken apart. Nondisjunction is the failure to pull apart sister chromatids during anaphase II or bivalents during anaphase I.
How are prokaryotic and eukaryotic chromosomes different?
Prokaryotic chromosomes have fewer proteins that complex with the DNA than eukaryotic chromosomes. Also the DNA and chromosomal structure is circular where eukaryotic chromosomes are linear.metastasis
anueoploidy
a change in the chromosome number resulting from nondisjunction during meiosis;
meiosis
a type of nuclear division that reduces the chromosome number from diploid(2n) to haploid(n). Unlike mitosis, it involves two rounds of nuclear division and produces four daughter cells with half the total number of chromosomes as there were in the diploid parent nucleus. Daughter cells are not genetically identical to the parent cells or to each other;
Alternation of generation
an organism that has both haploid and diploid phases of their life cycle;
Describe the prokaryotic chromosome...
composed of DNA and associated proteins but much less protein than eukaryotic chromosomes; the chromosome is a circular loop attached to the inside of the plasma membrane;
Telophase II and cytokinesis
daughter cells begin to form; a nuclear envelope forms around each set of chromosomes & cytokinesis takes place. Cytokinesis results in the production of daughter cells; at the end of telophase and cytokinesis there are four daughter cells.
Where do gamete chromosomes come from?
gametes have only one chromosome of each kind derived from the paternal or maternal homologue.
sexual reproduction
process that creates a new organism by combining the genetic material of two organisms;
*chiasmata
regions where non-sister chromatids are attached and exchange parts due to crossing over;
Barr body
the X chromosome that becomes an inactive mass in males and females with an extra X;
euploidy
the correct number of chromosomes in a species;
Trisomy 21
the most common autosomal trisomy seen in humans; it is also called Down syndrome; it occurs when three copies of chromosome 21 are present and is caused by nondisjunction.
diploid
the total number of chromosomes of an organism; (2n)
Compare the processes of Meiosis I to Mitosis
(1)Before both meiosis 1 and mitosis, DNA is replicated only once; (2)During prophase I of meiosis, homologues pair and undergo crossing over; this does not happen in mitosis; (3) during metaphase I of meiosis, bivalents align at the metaphase plate; in mitosis individual chromosomes align. (4) during anaphase I of meiosis, homologues separate and move to opposite poles; in mitosis, sister chromatids separate and move to opposite poles.
monosomy
(2n-1):a form of aneuploidy that occurs when an individual has only one chromosome(instead of the typical two) from a pair of homologues; this condition is the result of nondisjunction
Why are newborns with an abnormal sex chromosomes number more likely to survive than those with an abnormal autosome number?
Both males and females only have one function X chromosome. So extra copies don't really effect gene expression
What accounts for the genetic dissimilarity between daughter cells and the parent cell following meiosis?
Crossing over.
zygote
the cell that forms when gametes fuse; zygote has a full (diploid 2n) number of chromosomes;
nondisjunction
the failure of chromosomes to separate at meiosis or mitosis;
Describe how crossing over happens
(1) At synapsis, homologues line up side by side and a nucleoprotein lattice forms between. This lattice functions to hold the bivalent together; (2) Crossing over takes place (meaning non-sister chromatids of the homologous chromosomes exchange parts) (3) the nucleoprotein lattice breaks down. Homologues are temporarily held together by chaismata. (4)[not part of crossing over but happens next] during anaphase 1 the homologues separate and are distributed to daughter cells.
Excluding process, what are the overall fundamental differences between meiosis and mitosis?
(1)Meiosis requires two nuclear divisions; mitosis requires only one. (2) Meiosis produces four daughter nuclei, while mitosis produces two. (3)Meiosis daughter cells are haploid, while mitosis daughter cells are diploid like parent cells. (4)In meiosis, daughter cells are not genetically identical to each other or parent cells, while in mitosis, daughter cells are genetically identical to each other and the parent cell (5) Occurrence: meiosis only happens during certain times in life cycle of sexual organism; while mitosis happens often because it is how multicellular organism replaces damaged cells or evidence of growth in size.
Independent assortment
(1)in genetics, the principle that genes are inherited independently of one another, although genes close together on the same chromosome have a higher likelihood of being inherited together (2) when homologues align at the metaphase plate, the maternal & paternal homologue orient toward either pole randomly; (3) homologous chromosome pairs separate independently or in a random manner. [caveat: do not confuse maternal & paternal chromosomes with the fertilized egg diploid. We are still talking about gametes, maternal and paternal refer to the organisms set of chromosomes he received from his/her parents. Not the chromosomes he will deliver to his/her offspring.]
trisomy
(2n+1) a type of aneuploidy in which an individual has three of a particular chromosome instead of the normal two; this conditions results from nondisjunction;
Explain independent assortment with an example of a cell that has (a) 3 pairs of homologous chromosomes.(b) compare to humans who have 23 pairs...
(a) A cell with only three pairs of chromosomes(6 total) independently assort into 8(two cubed) combinations of maternal and paternal chromosomes. This variation was produced without even considering crossing over. If we consider an example where crossing over happens just once, the number of orientation jumps to 64(4 cubed). For humans who have 23 pairs, the possible orientations jumps to (2 raised to the 23rd) 8,338,608 arrangements.
How does binary fission in prokaryotes differ from mitosis and cytokinesis in eukaryotes?
Both processes are similar in that a parent cell forms genetically identical daughter cells. Said another way both processes produce copies of the original cell. Binary fission is asexual reproduction for prokaryotes which produces two new individuals, albeit identical ...Mitosis and cytokinesis is part of the growth process and is used for renewal and repair of damaged or old cells....binary fission does not involve the use of a mitotic spindle;
binary fission:
DNA is replicated and attaches to a special place on the plasma membrane indicating fission will happen. The cell elongates its plasma membrane and cell wall and the replicated DNA is pulled apart by the elongation. When the cell is approximately double its original length, the plasma membrane grows inward dividing the cell into two daughter cells.
What causes down-syndrome?
Down syndrome is caused by an extra copy of chromosome 21. Reduced levels of crossing over have been linked to this issue.
What happens to the haploid cells following meiosis?
In animals, haploid cells mature and develop into gametes(egg or sperm cells); In plants they become spores which becomes the haploid generation; the haploid generation then produces gametes which fuse to produce a diploid generation;
What is the fate of meiosis daughter cells?
In animals, the daughter cells become gametes that fuse during fertilization to become a diploid zygote; in plant cells, daughter haploid cells become spores that germinate and develop into a haploid generation;
How is meiosis 1 similar to and different from mitosis?
In both meiosis and mitosis DNA replication has previously occurred so each chromosome is made up of two sister chromatids. What's different is that in meiosis 1, 46 chromosomes align into two rows side by side as homologous pairs along the metaphase plate(synapsis). In mitosis, 46 chromosomes align into one row along the metaphase plate. Said another way in meiosis 1, 23 pairs of homologous chromosomes line up along the metaphase place. In mitosis, 46 chromosomes line up along the metaphase plate.
How are homologous chromosomes different in the normal stages of cell cycle compared to their status just before entering meiosis?
In normal stages of the cell cycle, there are 46 chromosomes. Just before entering meiosis chromosomes get duplicated(actually this happens in S stage). There are still 46 chromosomes but now each exist as a pair of daughter chromatids connected at its centromere.
What organisms are these likely to occur in and why?
Likely to occur in plants, because plants can self fertilize and meiotic failure only has to happen once, where as animals would need to separate organisms to undergo meiotic failure and then these daughter cells would need to meet with another 2n, and it would probably combine with a 1n gamete. If you ever get a triploid, you can't reproduce correctly with unaffected organisms. Plants will never create a triploid number of chromosomes.
How does meiosis bring about genetic variation?
Meiosis bring about genetic variation via recombination in two ways: crossing-over & independent assortment
What are the phases of meiosis?
Meiosis consist of two unique cell divisions, meiosis I & meiosis II. The phases of both meiosis I & II are prophase, metaphase, anaphase, and telophase.
Contrast the genetic makeup of sister chromatids with that of non-sister chromatids
Sister chromatids come from the same parent and have genes that code the same trait and same allele . Non sister chromatids come from different parents code for the same trait but may different alleles.
What is the result of non-disjunction in Anaphase II?
Sister chromatids don't separate properly. 1 cell will have n+1 # of chromosomes, another will have n-1 and the other two cells will have the correct haploid number n...
Where do triploids come from?
Triploids form when the spindle apparatus does not form correctly and the 4 gametes consist of two diploid gamete cells and the other 2 having zero chromosomes...the 2n gametes combine via fertilization with a regular haploid gamete to form a 3n individual.
What's the difference between triploidy and trisomy?
Triploidy is when the entire organisms set of chromosomes has an extra chromosome. this produce as 3n individual. In trisomy, only one of the homologous pairs has an extra chromosome.
True or False || abnormal numbers of sex chromosomes are less problematic than abnormal number of autosomes.
True
True or False Chromosomes are duplicated before Meiosis I
True. the 46 parent chromosomes in humans are duplicated into sister chromatids during the S phase of the cell cycle.
*Great apes have 24 haploid chromosomes, while humans have 23 haploid chromosomes...why?
Two chromosomes that were separate probably became fused. it was discovered that chromosome 2 has a fusion point indicating common ancestory between human and great apes...Fusion is a way of reducing the chromosome number, producing an organism that is viable, but possibly not fertile....jumping genes could have caused this or crossing over happened
(chromosomal structure) translocation
a chromosomal segment is removed from one chromosome and inserted into another non-homologous chromosome; in Down syndrome 5% of cases are due to translocation between chromosome 21 & 14.
karyotype
a visual display of chromosomes arranged by shape, size & banding pattern.
*bivalent
also called a tetrad; two homologous chromosomes that undergo synapsis and stay in close association during the first two phases of meiosis 1;
bivalent:
also called a tetrad; two homologous chromosomes that undergo synapsis and stay in close association during the first two phases of meiosis 1;
homologous chromosomes
also called homologues; a pairing of chromosomes, one of paternal origin, the other of maternal origin that pair up with each other during meiosis; they contain genes that code for the same trait, although the genes may code for different variations of that trait;
somatic cells
also known as body cells; any cell in the body that is not a sex cell(or gamete) and has a full (diploid 2n) number of chromosomes;
alleles
alternate forms of the same gene;(ex: a gene that codes for short fingers and a gene that codes for long fingers are alleles)
chromosomal mutations
changes in chromosome number or structure;
autosomes
chromosomes that do not code for an organism's sex; In humans we have 23 homologous pairs or 46 chromosomes; 22( or 44) are autosomal because they code for all traits except sex.
**Synapsis
during meiosis 1, chromosomes that are homologues migrate towards each other and line up side-by-side;
*Synapsis
during meiosis 1, chromosomes that are homologues migrate towards each other and line up side-by-side;
Synapsis
during meiosis 1, chromosomes that are homologues migrate towards each other and line up side-by-side;
Telophase I
during telophase I, daughter cells are starting to form; completion of telophase I is not necessary during meiosis. When it does occur, the nuclear envelope reforms, nucleoli reappear and the mitotic spindle disappears. This phase may or may not be accompanied by cytokinesis;
Turner syndrome
females that only have one sex chromosome; XO; ovaries of Turner females never become functional;
Why are meiosis and sexual reproduction important in responding to changing environments?
identical copies of a duplicated chromosome that have not been pulled apart and are connected at their centers(the centromere)
sister chromatids
identical copies of a duplicated chromosome that have not been pulled apart and are connected at their centers(the centromere)
How does interkinesis differ from interphase?
it differs in that interkinesis has no DNA replication phase
Klinefelter syndrome
males that have one Y chromosome and two or more X chromosomes; •
Jacobs syndrome
males with two Y chromosomes instead of one; results from nondisjunction during spermatogenesis;
primary nondisjunction
nondisjunction that happens during meiosis I; both members of a homologous pair go into the same gamete; when primary nondisjunction happens, there are no normal gametes produced.
secondary nondisjunction
nondisjunction that happens during meiosis II; sister chromatids fail to separate and both daughter chromosomes go into the same daughter cell. When secondary nondisjunction happens there will be two normal gametes and two aneuploid gametes;
Why does the zygote have pairs of each kind?
one member of a homologous chromosome was inherited from the male parent and the other was inherited from the female parent by way of the gametes.
chiasmata
regions where non-sister chromatids are attached and exchange parts due to crossing over;
asexual reproduction
reproduction in which the offspring are genetically identical to the parent; this type of reproduction is common of unicellular organisms;
spores
reproductive cells that develop into a new multicellular structure without the need to fuse with another reproductive cell;
Anaphase II
the centromeres separate, and the two non-identical sister chromatids of each chromosome move to opposite poles. The separated chromatids are now called (daughter) chromosomes in their own right;
*crossing over
the exchange of genetic material between non-sister chromatids of a bivalent during meiosis I. this process is a method genetic recombination used to create genetic variation; after the non-sister chromatids exchange parts, they are no longer genetically identical. Therefore the offspring will have a different set of alleles than their parents.
crossing over
the exchange of genetic material between non-sister chromatids of a bivalent during meiosis I. this process is one genetic recombination method for creating genetic variation; after the non-sister chromatids exchange parts, they are no longer genetically identical to each other or the original chromosome. Therefore the offspring will have a different set of alleles, than their parents.
Metaphase I
the following events happen during this phase: (1) bivalents(homologues) held together by chiasmata move towards each other and then align themselves on the metaphase plate; bivalents align themselves independently(meaning the orientation of one bivalent is not dependent upon the orientation of others (2) mitotic spindle is now fully formed;
Anaphase I
the following happens during Anaphase I: (1)the homologues of each bivalent separate and move towards opposite poles; with that said the non-identical sister chromatids do not separate(like the would during mitosis). Each chromosome still has two chromatids
Metaphase II
the following occurs during metaphase II: (1)the haploid number of chromosomes align at the metaphase plate; in humans, 23 chromosomes align at the metaphase plate; (2) spindle apparatus formation completes; (3) for each chromosome, the kinetochore of the non-identical sister chromatids face opposite poles; each is attached to a kinetochore microtubule coming from that pole
Prophase II
the following occurs during prophase II: nuclear envelope breaks down, and the spindle apparatus starts to form; centrosomes duplicate;
Prophase I
the following processes take place during prophase I: (1) nucleolus disappears, (2)nuclear envelope fragments; (3) chromatin condense into chromosomes and become visible (4) centrosomes migrate away from each other (5) spindle apparatus starts to form; (6) homologous chromosomes, each consisting of two chromatids, undergo synapsis to form bivalents; (6) crossing over of non-sister chromatids occur resulting in (sister) chromatids that are no longer identical;
Interkinesis
the period between meiosis I & meiosis II. It is similar to interphase between mitotic divisions except DNA replication does not occur;
(chromosomal structure) duplication
the presence of a chromosomal segment more than once on the same chromosome; (1) often this manifest in a broken segment of from one chromosome attaches to its homologue or unequal crossing over may occur;
genetic recombination
the process of forming new allelic combinations in offspring either naturally, by crossing over or independent assortment.
gamete
the reproductive cell of an organism which will undergo sexual reproduction. Gametes have a haploid number of chromosomes; if the gamete contained the same number as body cells, the number of chromosomes would double with each new generation(creating a new species each time); egg & sperm cells are gametes;
At the beginning of meiosis 2, describe the state of the two daughter cells
the two daughter cells do not have a full number of chromosomes (diploid 2n). They have the haploid (n) number. Said another way, they have one chromosome from each pair of homologues. In humans, these daughter cells would contain 23 chromosomes; with each chromosome still consisting of two non-identical sister chromatids.