Meiosis and Sexual Life Cycles Flashcards
1
Q
Heredity
A
The transmission of traits from one generation to the next
2
Q
Variation
A
Differences between members of the same species
3
Q
Genetics
A
The scientific study of heredity and hereditary variation.
4
Q
What must happen to a chromosome before a cell starts mitosis?
A
The single DNA molecule in the chromosome must be replicated
5
Q
What phases make up the stages of mitosis?
A
- Prophase
- prometaphase
- metaphase
- anaphase
- telophase
6
Q
Characterize the events in metaphase of mitosis:
A
Alignment of chromosomes at the equator
7
Q
Genes
A
A discrete unit of hereditary information consisting of a specific nucleotide sequence in DNA (or RNA in some viruses).
8
Q
The ______ we inherit from our mothers and fathers are our genetic link to our parents and they account for family resemblances such as shared eye color or freckles.
A
Genes
9
Q
Gamete
A
- A haploid reproductive cell (such as an egg or sperm) that is formed by meiosis or is the descendant of cells formed by meiosis.
- Gametes are united during sexual reproduction to produce diploid zygote.
10
Q
In animals and plants reproductive cells called ____ are the vehicles that transmit genes from one generation to the next.
A
Gametes
11
Q
Somatic cell
A
Any cell in a multicellular organism except a sperm or egg in their precursors
12
Q
Locus
A
A specific place along the length of a chromosome where a given gene is located
13
Q
A gene’s specific location along the length of a chromosome is called the gene’s _____.
A
Locus
14
Q
Only organisms that reproduce _____ have offspring that are exact genetic copies of themselves.
A
Asexually
15
Q
Asexual reproduction
A
- The generation of offspring from a single parent that occurs without the fusion of gametes.
- Offspring are genetically identical to the parent.
16
Q
Clone
A
- An individual that is genetically identical to another individual
17
Q
Sexual Reproduction
A
Reproduction arising from fusion of two gametes
18
Q
In _____; two parents give rise to offspring that have unique combinations of genes inherited from the two parents.
A
Sexual reproduction
19
Q
Using what you know of gene expression in a cell, explain what causes the traits of parents (such as hair colour) to show up in their offspring.
A
- Parents pass genes to their offspring; by dictating the production of messenger RNAs (mRNAs)
- the genes program cells to make specific enzymes and other proteins whose cumulative action produces an individual’s inherited traits.
20
Q
How does an asexual eukaryotic organism produce offspring that are genetically identical to each other and to the parent?
A
- Via mitosis
21
Q
A horticulturalist breeds orchids trying to obtain a plant with a unique combination of desirable traits. After many years she finally succeeds. To produce more plants like this one should she crossbreed it with another plant or clone it? Why?
A
She should clone it. Crossbreeding it with another plant would generate offspring that have additional variation which she no longer desires now that she has obtained her ideal orchid.
22
Q
Life cycle
A
The generation-to-generation sequence of stages in the reproductive history of an organism.
23
Q
In humans: each somatic cell has __ chromosomes.
A
46
24
Q
Karyotype
A
A display of the chromosome pairs of a cell arranged by size and shape.
25
Homologous chromosomes (or homologs)
- A pair of chromosomes of the same length, centromere position and staining pattern that possess genes for the same characters at the corresponding loci.
- One maternal and one is paternal
26
The X and Y chromosomes play a role in sex determination and are called ____
Sex chromosomes
27
Autosome
A chromosome that is not directly involved in determining sex; not a sex chromosome.
28
Diploid cell
A cell containing two sets of chromosomes (2n) one set inherited from each parent.
29
Haploid cell
A cell containing only one set of chromosomes (n).
30
Fertilization
- The union of haploid gametes to produce a diploid zygote.
31
Zygote
The diploid cell produced by the union of haploid gametes during fertilization; a fertilized egg.
32
The only cells of the human body not produced by mitosis are the ____________ which develop from specialized cells called germ cells in the gonads - ovaries in females and testes in males.
Gametes
33
Meiosis
A modified type of cell division in sexually reproducing organisms consisting of two rounds of cell division but only one round of DNA replication.
- Results in cells with half the number of chromosome sets as the original cell.
34
____ and ____ alternate in sexual life cycles to maintain a constant number of chromosomes in each species from one generation to the next.
Fertilization; meiosis
35
____ occurs in germ cells during the production of gametes which undergo no further cell division prior to fertilization. After fertilization the diploid zygote divides by ____ to produce a multicellular organism that is diploid.
Meiosis; mitosis
36
Alternation of generations
A life cycle in which there is both a multicellular diploid form( the sporophyte) and a multicellular haploid form (the gametophyte; characteristic of plants and some algae.)
37
Note that either haploid or diploid cells can divide by _________ depending on the type of life cycle. Only ________________ cells can undergo meiosis because __________ cells have only a single set of chromosomes that cannot be further reduced. Though the three types of sexual cycles differ in the timing of meiosis and fertilisation they share a fundamental result: _____________ among offspring.
Mitosis; diploid; haploid; genetic variation
38
A certain eukaryote lives as a unicellular organism but during environmental stress it produces gametes. The gametes fuse and the resulting zygote undergoes meiosis which generates new single cells. What type of organism could this be?
Most fungi and some protists
39
Describe Meiosis I
The first division of a two-stage process of cell division in sexually reproducing organisms that result in cells with half the number of chromosome sets as the original cell
40
Describe Meiosis II
The second division of a two-stage process of cell division in sexually reproducing organisms that results in cells with half the number of chromosome sets as the original cell
41
In Meiosis the two divisions result in __________ daughter cells (rather than the ___________ daughter cells of mitosis) each with only half as many chromosomes as the parent cell - one set rather than two.
Four; two
42
Sister chromatids are two copies of _______ chromosome that is closely associated all along their lengths; this association is called _______.
One; sister chromatid cohesion
43
Homologs appear alike in the microscope but they may have different versions of genes at corresponding loci; each version is called an _____ of that gene.
allele
44
Meiosis produces ____ haploid cells. Each cell has _____ the chromosomes of the parent cell. The cells differ______ from each other and the cells of the parents.
4; half; genetically
45
During early prophase I each chromosome pairs with its homologs (aligned gene by gene) and _____ occurs: The DNA molecules of no sister chromatids are broken (by proteins) and are rejoined to each other.
Crossing over
46
Each homologous pair has one or more X-shaped regions called _____ where crossovers have occurred.
Chiasmata
47
The meiosis division of one parent cell produces ____ daughter cells each with a haploid set of (unduplicated) chromosomes. The daughter cells are genetically distinct from one another and from the parent cell.
Four
48
Imagine that the two daughter cells are undergoing another round of mitosis → yielding four cells. Compare the number of chromosomes in each of those four cells after mitosis with the number in each cell. What is it about the process of meiosis that accounts for this difference even though meiosis includes two cell divisions?
- If a cell with six chromosomes undergoes two rounds of mitosis each of the four resulting cells will have six chromosomes while the four cells resulting from meiosis. - In mitosis DNA replication (and thus chromosome duplication) precedes each prophase ensuring that daughter cells have the same number of chromosomes as the parent cell. - In meiosis DNA replication occurs only before prophase I (not prophase II). - Thus in two rounds of mitosis the chromosomes duplicate twice and divide twice while in meiosis the chromosomes duplicate once and divide twice.
49
The synaptonemal complex is fully formed; the two homologs are said to be in ________. During ______ the DNA breaks are closed up when each broken end is joined to the corresponding segment of the nonsister chromatid producing ______.
Synapsis; Synapsis; crossovers
50
After interphase the chromosomes have been duplicated and the sister chromatids are held together by proteins called ________.
Cohesins
51
synaptonemal complex
A zipper-like structure composed of proteins which connects a chromosome to its homolog tightly along their lengths during part of prophase I of meiosis
52
Synapsis
The pairing and physical connection of one duplicated chromosome to its homologs during prophase I of meiosis
53
During ______ the DNA breaks are closed up so that each broken end is joined to the corresponding segment of the ______ chromatid.
Synapsis; nonsister
54
What's the difference between mitosis and meiosis?
- Meiosis reduces the number of chromosome sets from two (diploid) to one (haploid) whereas mitosis conserves the number of chromosome sets. Therefore meiosis produces cells that differ genetically from their parent cell and from each other. - Mitosis produces daughter cells that are genetically identical to their parent cell and to each other.
55
Number of Divisions: - ____ = One including prophase prometaphase metaphase anaphase and telophase - ____ = wo each including prophase metaphase and telophase
Mitosis; Meiosis
56
Synapsis of homologous chromosomes: - ___ Does not occur - ____ Occurs during prophase I along with the crossing over between nonsister chromatids; resulting chiasmata hold pairs together due to sister chromatid cohesion
Mitosis; Meiosis
57
What occurs in both diploid and haploid cells?
Mitosis
58
What can only occur in diploid cells?
Meiosis
59
What are the three unique events to meiosis that occur during meiosis I?
Synapsis and crossing over; alignment of homologous pairs at the metaphase plate; separation of homologs
60
In meiosis at the onset of anaphase I the release of cohesion along sister chromatid ________ allows homologs to separate. At anaphase II the release of sister chromatid cohesion at the _________ allows the sister chromatids to separate.
Arms; centromeres
61
Compare the chromosomes in a cell at metaphase of mitosis with those in a cell at metaphase II.
- The chromosomes are similar in that each is composed of two sister chromatids and the individual chromosomes are positioned similarly at the metaphase plate.
- The chromosomes differ in that in a mitotically dividing cell sister chromatids of each chromosome are genetically identical but in a meiotically dividing cell sister chromatids are generally distinct because of crossing over in meiosis I.
- Moreover the chromosomes in metaphase of mitosis can be a diploid set or a haploid set but the chromosomes in metaphase of meiosis II always consist of a haploid set.
62
After the synaptonemal complex disappears how would any pair of homologous chromosomes be associated if crossing over did not occur? What effect might this have on gamete formation?
- If crossing over did not occur the two homologs would not be associated in any way; each sister chromatid would be either all maternal or all paternal and would only be attached to its sister chromatid not to a non sister chromatid.
- This might result in incorrect arrangements of homologs during metaphase I and ultimately in the formation of gametes with an abnormal number of chromosomes.
63
What is a recombinant chromosome?
A chromosome created when crossing over combines DNA from two parents into a single chromosome
64
___ are individual chromosomes that carry genes (DNA) from two different parents
Recombinant Chromosomes
65
What is the original source of genetic variation among the different alleles of a gene?
Mutations in a gene lead to the different versions (alleles) of that gene.
66
The diploid number for fruit flies is 8 and the diploid number for grasshoppers is 46. If no crossing over took place would the genetic variation among offspring from a given pair of parents be greater in fruit flies or grasshoppers? Explain
- Without crossing over independent assortment of chromosomes during meiosis I theoretically can generate 2n possible haploid gametes and random fertilization can produce 2n x 2n possible diploid zygotes. - Because the haploid number (n) of grasshoppers is 23 and that of fruit flies is 4 two grasshoppers would be expected to produce a greater variety of zygotes than would two fruit flies.
67
WHAT IF? maternal and paternal chromatids had the same two alleles for every gene. Will crossing over lead to genetic variation?
- No if the segments of the maternal and paternal chromatids that undergo crossing over are genetically identical and thus have the same two alleles for every gene then the recombinant chromosomes will be genetically equivalent to the parental chromosomes.
- Crossing over contributes to genetic variation only when it involves the rearrangement of different alleles.
68
Each _______ in an organism's DNA exists at a specific ___ on a certain chromosome.
Gene; locus
69
In ____ a single parent produces genetically identical offspring by mitosis.
________ combines genes from two parents leading to genetically diverse offspring.
asexual reproduction; sexual reproduction
70
Explain why human offspring resemble their parents but are not identical to them.
- Genes program specific traits and offspring inherit their genes from each parent accounting for similarities in their appearance to one or the other parent.
- Humans reproduce sexually which ensures new combinations of genes (and thus traits) in the offspring.
- Consequently the offspring are not clones of their parents (which would be the case if humans reproduced asexually).
71
Normal human ___________ are diploid. They have ________ chromosomes made up of two sets of ______, one set from each parent.
Somatic cells; 46; 23
72
Human diploid cells have 22 pairs of homologs that are __________ and one pair of ________. The latter typically determines whether the person is female (XX) or male (XY)
Autosomes; sex chromosomes
73
In humans ovaries and testes produce haploid gametes by _________ each gamete containing a single set of 23 chromosomes (n=23). During ____________ an egg and sperm unit forming a diploid (n=46) single called _________ which develops into a multicellular organism by mitosis
Meiosis; fertilization; zygote
74
Sexual life cycles differ in timing of ____ relative to _____ and in the points of the cycle at which a multicellular organism is produced by mitosis.
Meiosis; fertilization
75
Compare the life cycles of animals and plants.
- Animals and plants both reproduce sexually alternating meiosis with fertilisation.
- Both have haploid gametes that unite to form a diploid zygote which then goes on to divide mitotically forming a diploid multicellular organism.
- In animals haploid cells become gametes and don't undergo mitosis while in plants the haploid cells resulting from meiosis undergo mitosis to form a haploid multicellular organism the gametophyte.
- This organism then goes on to generate haploid gametes. (In plants such as trees the gametophyte is quite reduced in size and not obvious to the casual observer).
76
The two cell divisions of meiosis ____ and ____ produce ____ haploid daughter cells. The number of chromosome sets is reduced from two (diploid) to one (haploid) during _____.
1; 2; 4; meiosis
77
Meiosis is distinguished from mitosis by three events of meiosis I: 1. ____: Each pair of homologous chromosomes undergoes synapsis and crossing over between nonsister chromatids and with subsequent appearance of chiasmata. 2. ___: Chromosomes line up as homologous pairs on the metaphase plate. 3. ____: Homologs separate from each other; sister chromatids remain joined at the centromere
Prophase I; Metaphase I; Anaphase I
78
_____ separates the sister chromatids.
Meiosis II
79
____ and ____ allow chiasmata to hold homologs together until anaphase I. Cohesins are cleaved along the arms at anaphase I allowing homologs to separate and at the centromeres in anaphase II releasing sister chromatids.
Sister chromatid cohesion; crossing over
80
Explain how independent assortment generates genetic variation
Each pair of homologous chromosomes lines up independent of each other pair at the metaphase plate so a daughter cell of meiosis I randomly inherits either a maternal or paternal chromosome of each pair.
81
Explain how crossing over generates genetic variation
- Paired homologous chromosomes undergo synapsis, and non-sister chromatids (one from each homologous chromosome) break and reattach to each other, exchanging genetic material.
- This exchange creates new combinations of alleles on the chromosomes.
82
Explain how random fertilisation generates genetic variation
It ensures even more variation since any sperm of a large number containing many possible genetic combinations can fertilize any egg of a similarly large number of possible combinations.
83
If the DNA content of a diploid cell in the G1 phase of the cell cycle is x then the DNA content of the same cell at metaphase of meiosis will be __
2x
84
How many genes are present in the human genome?
Tens of thousands - Each chromosome has hundreds or thousands of genes; the entire human genome has on the order of 20000 to 25 000 genes.
85
What is a locus?
The precise location of a gene on a chromosome
86
Name for an ordered displays of an individual's chromosomes are useful in identifying chromosomal abnormalities.
Karyotype
87
Sister chromatids are _____
identical copies of each other formed through DNA synthesis
88
When we say that an organism is haploid we mean that ____
It's cells have a single set of chromosomes
89
Multiplication of body cells is a function of ___ in humans. It is ___ that enables a multicellular adult to form from a fertilized egg and produces cells for growth and tissue repair.
Mitosis; mitosis
90
At the end of telophase I of meiosis and the first cytokinesis there are ____
Two haploid cells
91
What is the typical result when a diploid cell has completed meiosis?
Four haploid cells
92
What is synapsis?
Where homologous chromosomes physically connect in prophase 1
93
What happens during anaphase II?
Sister chromatids separate and migrate toward opposite poles
94
What happens during anaphase I?
Homologs separate and migrate toward opposite poles
95
Cytokinesis is the ____
division of the cytoplasm
96
Crossing over occurs during ___
Prophase I
97
Regions of chromosomes where nonsister chromatids crossover are called ____
Chiasmata
98
Which event occurs in meiosis but NOT mitosis?
Homologous chromosomes separate
99
Ignoring crossover events how many kinds of gametes can be produced by an organism with a diploid number of 8?
16 - The number of combinations possible when chromosomes assort independently into gametes during meiosis is 2^n where n is the haploid number of chromosomes.
100
In a diploid set of chromosomes one member of each pair of homologous chromosomes is derived from the father (paternal) and the other comes from the mother (maternal). If 2n=6 what is the probability that a particular gamete will contain only paternal chromosomes?
1/8 - The chance of any one paternal chromosome ending up in a particular gamete is 1/2 so the chance that all three would be of paternal origin would be (1/2)^n where n = 3.
101
The major contribution of sex to evolution is that _____
It provides a method to increase genetic variation
102
How are sister chromatids and homologous chromatids different from each other?
Homologous chromosomes contain the same gene loci but may have different alleles of a particular gene. Sister chromatids are identical copies of each other produced during DNA replication.
103
Which processes lead to the most genetic variation in sexually reproducing organisms?
1. Crossing over
2. random fertilisation
3. independent assortment of chromosomes in meiosis
104
The egg (ovum) of a rabbit contains 22 chromosomes. How many chromosomes are in the somatic (body) cells of a rabbit?
44
105
A life cycle in which the only multicellular form is haploid is most typical of ____
Fungi
106
Unless the chromosomes were stained to show band patterns a karyotype would be least likely to show ____
Part of a chromosome turned around
107
The process called ___ reduces the chromosome number by ____
Meiosis; two consecutive cell divisions
108
A clone is the product of _____
Asexual reproduction and mitosis
109
What chromosomes have genes for the same traits at the same loci?
Homologous chromosomes
110
How many genes are present in the human genome?
tens of thousands
111
Most DNA is packaged into _____
Chromosomes
112
A _____ is the generation-to-generation sequence of stages in the reproductive history of an organism: including meiosis fertilization and mitosis.
Life cycle
113
Females have two __ chromosomes
X
114
Males have an _ and a _ chromosome
X; Y
115
Non sexual chromosomes
Autosomes
116
Which are the only types of human cells produced by meiosis rather than mitosis?
Gametes
117
Meiosis I is a reduction division going from diploid to ______.
Haploid - They are haploid but still contain replicated chromosomes in addition to having a random assortment of maternal and paternal chromosomes
118
Crossing over and synapsis occur during __. After interphase the sister chromatids are held together by proteins called ______.
Prophase I; cohesins
119
During ________ DNA breaks are repaired joining DNA from one non-sister chromatid to the corresponding segment of another.
Synapsis
120
What are the key events of prophase I?
1. condensation
2. synapsis (bivalent formation)
3. crossing over and chiasmata formation
4. partial separation of homologs
121
Mutations create different versions of genes called ______.
Alleles
122
Reshuffling of ____ during reproduction facilitates genetic reproduction.
Alleles.
123
What are the key differences between mitosis and meiosis?
Mitosis vs Meiosis:
1. Number of divisions (one vs. two)
2. Chromosome number in daughter cells (unchanged vs halved)
3. Genetic variation in outcomes (identical vs varied)
4. Purpose (growth/repair vs gamete production)
