Biol Chapter 13
DNA content of daughter cells compared to parent cell
Mitosis- Reduced to half because it goes from replicated to unreplicated. Meiosis- Reduced 1/4 because it goes from replicated diploids to replicated haploids to unreplicated haploid sets
Role in organism life cycle
Mitosis- asexual reproduction in some eukaryotes; cell division for growth and wound healing. Meiosis- Halfing chroosome number in cells that will produce gametes
Why is asexual reproduction more efficient?
No men!!
Number of Cell divisions
Mitosis 1, Meiosis 2
Make up of chromosomes in daughter cells
Mitosis Identical, Meiosis diffrent
Synapsis of homologs
Mitosis No, Meiosis Yes
Number of chromsomes in daughter cells compared with parent cell
Mitosis Same, Meiosis Half
Spindle fiver attachment
Mitosis indivisual chromtids in each chromosome attach to spindle fibera from different spindle poles Meiosis both chromatids in each chromosome attach to spindle fibers from the same spindle pole
Why is sexual variation favorable?
Offspring that aren't clones have differential thrive-ability in different environments and benefit from inheriting diverse, eveolving genes so they arent doomed & die at once
_ results in a combination of chromosomes sets from different individuals
Outcrossing
homologous chromosomes or homologs (same proportion)
Pair of chromosomes that are the same size, same appearance and same genes.
The pair of homologous chromosomes, connected by at least one _, is moved to the _
chiasma; metaphase plate
non-sister chromatids
chromatids on different members of a homologous chromosome pair. one of the chromatids is on one homolouge, and the other is on the other homolog. (legs on different bodies)
replicated chromsomes
chromosome after DNA replication. consists of two identical chromatids (two of the "unreplicated" Dna strands),
metaphase II
chromosomes line up at metaphase plate
homologs / homologous chromosomes
chromosomes that have the same genes in same position same size and shape with differing alleles - NOT identical
homologous pair
contain same genes in same positions along the two chromosomes,in same position, but NOT inherently identical.
Because of _, each chromosomes contains a random assortment of paternal and maternal alleles
crossing over
metaphase I
kinetochore microtubules move pairs of bivalents to metaphase plate. each bivalent straddles the plate with one homolog on either side; the alignment of each bivalent is independent of any other bivalent, meaning that the m/p placement on the plane has no affect of another binavent's m/p placement
Anapahse and Telophase I
m/p homologs separated from each other NOT sister chromatids, moved to opposite poles and separated.
2n = 6
means that there are six chromosomes total in three distinct types in pairs of two
3n = 6
means that there are six chromosomes total, two distinct types in sets of three
6n = 1
means that there is one set of six identical copies
During _, sister chromatids of the replicated chromosomes seperate and are distributed to two daughter cells.
meiosis II
gametes
reproductive cells such as sperm and eggs
cells replicate each of their chromosomes before starting meiosis,
same state they are in at the start of mitosis
gene
segment of DNA, found at a specific place on a chromosome, that influences a hereditary trait.
anaphase II
sister chromatids separated
meiosis I differs from meiosis II and mitosis because
sister chromatids stay together, reduces chromosome number to haploid
bivalent
structure resulting from synapsis. paired homologous chromosomes, each homogolog consisting of 2 sister chromatids.
Meiosis I
the diploid cells homologs (m/p) of each chromosome pair separate into two haploid daughter cells (that are still condensed, still replicated, X shaped, two sister chromatids attached by centromere)
chiasmata / chaisma
the homologs were so tigthly paired little x's developed on their path, at least one occuts in every pair of homologs. mark particular sites of DNA breakage and rejoining, crossing over. red and blue mix segments.
karyotype
the number and visual appearance of the chromosomes in the cell nuclei of an organism or species.
sister chromatids
two identical chromatid copies in a replicated chromosome
gametes of a nondisjunction
two will have an extra chromosome n+1 , and two will be missing a chromosome n-1, resulting gametes after meiosis II can be missing a chromosome
The _ versions are called _. One homolog is inherited from the mother, one from the father. _ organisms just have one of each type of chromosome.
two; homolog; haploid
In diploid _ organisms, individuals have _ versions of each type of chromosome.
(2n); two
why isnt an unreplicated chromsome just called a chromatid?
(it would make it alot easier to understand but its biology, fuk easy).
synapsis
(m/p) homologous chromosomes pair side-by side tighly along corresponding regions.
early prophase I
-nuclear envelope breaks down, spindle apparatus forms. homologous chromosomes pair together (unique to meiosis I)
What proportion of chromosomes in a man's skin cell are maternal chromosomes?
1/2 (half from mom, half form dad)
An n+1 gamete will have the resulting zygote
2n+1, a trisomy.
An n-1 gamete will have the resulting zygote
2n-1, a monosomy, or aneuploid cell
The domestic dog has a diploid number (n) of 78. ; 76 of the chromosomes are autosomes and two 2 are sex chromosomes (X and Y). As in humans, female dogs contain two X chromosomes and male dogs contain an X and a Y chromosome. How many kinds of chromosomes are present in the karyotype from a diploid cell from a female dog? See Section 13.1
39. One of each type of chromosomes 1--38, plus the X chromosome.
The domestic dog has a diploid number (n) of 78. ; 76 of the chromosomes are autosomes and two 2 are sex chromosomes (X and Y). A karyotype taken from a dog's mature egg cell would have how many kinds of chromosomes? See Section 13.1
39. The mature egg would contain 38 autosomes and one 1 sex chromosome, either X or Y
Why would meiosis and sexual reproduction be favorable?
A parent with a harmful allele can produce offspring without that allele, and generically diverse offspring are likely to include some that are better able to resist evolving pathogens and parasites
If you followed a womans cells through meiosis would the amount of DNA in one of these cells be equal to the amount of DNA in one of her other G1 phase (before DNA replication) kidney cells?
At the end of meiosis I, when kidney cell before DNA replication, there are pairs of each chromosome, with one double-helical molecule of DNA per chromosome; at the end of meiosis I, the cell has one of each type of chromosome, with each chromosome having two double-helical molecules of DNA
explain why mitosis in triploid would be easy but meiosis difficult
Because mitosis separates sister chromatids of single chromosomes and there is (no need) for homologous chromosomes to pair, mitosis in a triploid cell, or a cell of any level of ploidy, can occur easily. In contrast, chromosome pairing is essential for proper separation of homologous chromosomes in meiosis. Since it's impossible to pair three of anything, the three copies of each chromosome in a triploid cannot be separated into daughter cells in a reproducible way.
autosomes
Chromosomes that are not directly involved in determining the sex of an individual.
sex chromosomes
Chromosomes that determine the sex of an individual
Fertilization
Creating Zygote (2n) from Sperm (n) + Egg (n)
Discuss how crossing over influences the genetic diversity of the daughter cells produced by meiosis
Crossing over increases the genetic diversity of daughter cells by creating many different combinations of maternal and paternal alleles along each of the daughter chromosomes
If mistakes occur during meiosis, the resulting egg and sperm cells may contin the wrong number of chromosomes. Most often embryos with an incorrect number of chromosomes do no complete development. Children with _ syndrome, who have an extra copy of chromosome _, are an exception.
Down; 21
Identify event that makes meiosis a reduction division and explain how it reduces chromosome number
During anaphase I, homologs (not sister chromatids, as in mitosis) are separated, making the cells produced by meiosis I haploid.
A circle containing ten blue sausage-shaped forms of varied lengths, with colored bands at one or both ends. Two are tiny with a yellow band near the bottom. Two are very small with a red band near the top and a dark-blue band near the bottom. Two are small with a green band near the bottom. Two are medium-length with a black band near each end. Two are long with one pink and one purple band near the top, and a gray band near the bottom.
Each chromosome contains one long molecule of double-stranded DNA and proteins. True There are five different lengths of chromosomes in this cell. True The chromosomes are replicated. False This cell is 2n = 10. True This cell is diploid. True The bands on the chromosomes represent certain genes. True
Explain how genetic variation would be affected if maternal chromosomes always lined up on one side of the metaphase plate during meiosis I and paternal on the other
Each gamete would inherit either all maternal or all paternal chromosomes. This would limit genetic variation in the offspring by preventing many possible combinations of maternal and paternal chromosomes in gametes.
One set, haploid 1n=6
Each of the chromosomes in the cell is a different length so you can infer that each has unique genetic information.
gametogenesis
Formation of gametes
State haploid number, ploidity, and total number of chromosomes present in male Drosophila.
Haploid number is n = 4; the organism is diploid, and 2n = 8
Which statement about the difference between homologous chromosomes and sister chromatids is correct? See Section 13.1
Homologous chromosomes contain the same genes, but may contain different alleles. Sister chromatids contain the same genes and the same alleles. Sister chromatids are produced by the process of DNA replication, whereas homologous chromosomes are inherited from the mother and father.
How many different combinations possible?
If diploid 2^n So, humans are capable of 2^23 gametes that differ in their combination of maternal and paternal chromosome sets
Predict how many genetically different offspring could be produced by outcrossing two 2n=4 individuals
In outcrossing of 2n = 4 individuals, each parent produces four types of gametes. Using the logic developed in the description of how many different combinations are possible in human fertilization, there would be 4 × 4 = 16 genetically different offspring produced by outcrossing in this situation.
A cell with haploid number (n) of 3 is undergoing meiosis. Using a microscope, you observe three condensed groups of chromosomes. Within each group, the chromosomes appears to be physically linked by chiasmata. This cell is most likely in what stage of meiosis? See Section 13.1
In prophase I of meiosis, homologous chromosomes pair and exchange sequences in a process called crossing over.
Crossing over
Increases the amount of possible combinations almost listlessly by adding new combinations of alleles along each chromosome.
Each chromosome is replicated well before meiosis begins. This occurs as DNA is replicated during the _ phase of the cell cycle.
S
Meiosis II
Sister chromatids of each cell separate. result: 4 unreplicated haploid DNA
Polyploid
Some species have more than two of each TYPE of chromosome. 3n (triploid), 4n (tetraploid)
Prophase II
Spindle apparatus forms in both daughter cells, microtubles form the spindle poles attach to kinetochores on opposite sides of every chromosome and move them towards the middle, same as mitosis prophase.
Triploid (3n) watermelons are produced by crossing a tetraploid (4n) with a diploid (2n) plant. Explain how this mating produces a triploid indivisual.
Tetraploids produce diploid gamete, which combine with a haploid gamete from a diploid individual to form triploid offspring
explain how DNA content is reduced in half in meiosis I and II, yet chromosome number is only reduced in meiosis I.
The separation of homologous chromosomes at meiosis I reduces both chromosome number and DNA amount in each of the daughter cells. However, each chromosome remains in a replicated state with two double-helical molecules of DNA. In meiosis II, the sister chromatids of the replicated chromosomes separate. This keeps the number of chromosomes in each daughter cell the same, but it reduces the amount of DNA in each daughter cell. The key to understanding this event is that one chromosome can contain either one double-helical DNA molecule or two, depending on whether the chromosome is unreplicated or replicated. In either case, it's still one chromosome
n=6
The six chromosomes are of different lengths, suggesting that each has unique genetic information.
predict double-helical molecules of DNA present in gametes of Drosophlia, the diploid with 8 replicted chromosomes in each cell that enters meiosis
There will be four double-helical molecules of DNA in each fruit fly gamete because the 8 replicated chromosomes in a diploid cell are reduced to 4 replicated chromosomes per cell at the end of meiosis I. Each of these replicated chromosomes contains two double-helical molecules of DNA. In meiosis II, the sister chromatids of each replicated chromosome are separated. Each cell now contains 4 unreplicated chromosomes, each with a single double-helical molecule of DNA. Note how one chromosome may contain one or two molecules of DNA depending on whether it is unreplicated or replicated.
In generation 2 there are only two more child-producing individuals in the asexual population than in the sexual population. If the same two-fold difference continued, how many more child-producing individuals would there be in the asexual population in generation 5.
There would be 240 more. (Notice that the number of child-producing individuals in the sexual population doubles at each generation, but in the asexual population, there is a quadrupling of these individuals at each generation. Therefore, after 4 generations of reproduction [this is what's needed to create generation 5], there will be 24 = 16 child-producing offspring in the sexual population and 44 = 256 in the asexual population. The base in each equation is the fold increase at each generation, and the exponent is the number of generations; look back at Figure 13.14 to see why these numbers make sense.) This diagram shows that slight differences in population growth rate can quickly lead to big differences in the number of individuals over many generations.
Why do they need to split again after meiosis I?
They are still replicated haploids, need to be unreplicated single chromatids.
principle of independent assortment
What principle states that during gamete formation genes for different traits separate without influencing each other's inheritance?
What are homologous chromosomes?
a chromosomes similar in size, shape, and gene content
Each cell produced by mieiosis receives a different combination of chromosomes. Genes are located on chromosomes, and often come in different forms ( _ ), each cell produced by meiosis receives a different complement of alleles for its genes. The resulting offspring are genetically distinct from one another and from their parents.
alleles
each copy of the chromosome 2 in Drophilla carries many different genes, one influencing eye color. this gene comes in different forms- red and purple.
alleles differentiate this. One homolog may have the red allele while the other has the purple allele.
In _, all individuals are capable of bearing offspring. From this standpoint, it is more efficient than _, in which half the offspring (males) are unable to bear offspring.
asexual; sexual
What is the outcome of genetic recombination?
b the new combination of maternal and paternal chromosome segments that result when homologs cross over
Dogs have 78 chromosomes in their diploids. how many chromosomes & double helical molecules of DNA present in each daughter cell at end of meiosis I.
b. (meiosis I reduces it in half 78->39 each retains two double helical molecules of DNA, so 39 chromosomes and 78 double helical molecules of DNA.)
Homologous pairs of chromosomes synapse early in meiosis I, forming a _- two closely paired homologous chromosomes. Non-sister chromatids undergo crossing over.
bivalent
if n=3 for a given organism and no crossing over, what is the chance that a gamete will receive ONLY paternal chromosomes
c (since 2n=3, independent assortment creates 2^n, 2^3 = 8 different combinations. only one is made from paternal only. 1/8 chance.
Nondisjuntion that leads to problems in offspring occur in:
c meiosis I and II
primary oocytes
diploid precursor to eggs enter meiosis I during emrbyonic development and arrest in prophase I until the female reaches sexual maturaity. each month, a small group enters meiosis, only one produces an egg. so some oocytes may wait 50 years before it completes mitosis, spindle function and proper separation of chromosomes decline after that long
From one _ cell with replicated chromosomes, mieosis produces _ _ daughter cells with unreplicated chromosomes.
diploid; four haploid
n / halpoid number
distinct types of chromosomes in a given cell. sex chromosomes are unpaired but count as ONE distinct type. humans have 23.
Independent assortment
during meiosis one, bivalents can line up in two different ways before the homologs separate, different combinations occur with different results
Zygote
first cell of a new individual; diploid formed from fusion of union of gametes.
what must be perfectly executed to get one complete set of chromosomes
first the chromosomes in each homogolous pair must separate in Meiosis I, so one homolog ends up in each daughter cell. second, sister chromatids must separate from each other & move to opposite poles of the dividing poles of the dividing cell during meiosis II.
outcrossing
gametes of different individuals combine/fuse to form offspring. so one human can produce 2^23 = 8.4 mil genetically distinct offspring TWO humans can make 8.4 mil x 8.4 mil = 70.6 x 10^12 , which is far greater than the total amount of people that have ever lived
At the end of meiosis I, the homologous chromosomes are seperated and distributed to two daugher cells. The daughter cells are _, because each receives one of each type of chromosome.
haploid
bivalent
homogolous replicated chromosomes (two big x's one from mom one from dad) joined during prophase I and metaphase I of meiosis
Most of the mistakes in meiotic are failures of either _ or _ to separate.
homologous chromosomes; sister chromatids
Explain the relatioship between homologous chromosomes and sister chromatids?
homologous similar is size and shape, same genes but different allele originating from different parents. sister chromatids in replicated chromosomes, exact same cope held by proteins
Gametes receive a random assortment of maternal and paternal chromosomes when _ separate in _. This is _
homologs;meiosis I;independent assortment
an unreplicated chromosome and a replicated chromosome are both SINGLE chromosomes, even though the replicated chromosomes contains two SISTER chromatids
if you have two copies of the same book you have more paged overall but its still the same information. the number of information does not double. The number of chromosomes does not double every time DNA replicates.
At the start of _, each chromosome contains a pair of sister chromatids, each with a double-helical _ molecule identical to that of the other sister chromatid.
mitosis I; DNA
telophase II
move to diffrent daughter cells.
synaptonemal complex
network of proteins holding bivalent together, dissasmebles in late prophase I, leaving only chiamasma to hold them together.
genetic recombination
new combination of genetic information in a gamete as a result of crossing over during prophase I of meiosis
At the chisasma,
non-sister chromatids attach to each other at corresponding points.
If both homologs in meiosis I or both sister chromatids in meiosis move to the same daughter cell, products are a
nondisjuction
late prophase I
nuclear envelope breaks down, two homlogs within each bivalent become attached to microtubule fibers coming from opposite poles of the spindle apparatus- each homolog in the bivalent is attached to a different pole. form of attachment unique to meiosis I to separate homogolous pairs.
ploidy
number of chromosome sets. diploid has 2, read 2n. haploids have 1, so read as just n.
chromosomes come in distinct sizes and shapes
occur in pairs
unreplicated chromosome
one helical dna molecule packed with proteins
.Meiosis is a nuclear division resulting in cells that only have _ of each type of chromosomes and _ as many chromosomes as the parent cell. In animals it leads to the formation of eggs and sperm.
one; half
halpoid
organisms like bacteria, archaea and algae and fungi. have one copy of each chromosome, one allele of each gene
diploid
organisms that have two versions (homologs) of each type of chromosome. They have two alleles of each gene (Aa/ AA/ aa)
self-fertilization
pretty rare, but common among intersex plants, produces genetically diverse offspring.
asexual reproduction
producing offspring without the production and fusion of gametes (based on mitosis in eukaryotes). produces clones.