Chapter 2 - Chromosomes, Mitosis, and Meiosis Flashcards
(262 cards)
1
Q
chromosomes
A
Chromosomes contain genetic information
most chromosomes contain a single
molecule of double-stranded DNA that form a complex with proteins
Chromosomes are complex and dynamic structures consisting of DNA and proteins (chromatin)
2
Q
The degree of chromatin compaction
A
involves proteins and varies between heterochromatic and euchromatic regions and among
stages of the cell cycle.
3
Q
T/F Chromosomes can be distinguished cytologicaly based on their length, centromere position, and banding patterns when stained
dyes or labeled with sequence-specific probes.
A
TRUE Chromosomes can be distinguished cytologicaly based on their length, centromere position, and banding patterns when stained
dyes or labeled with sequence-specific probes.
4
Q
Homologous chromosomes
A
Homologous chromosomes contain the same series of genes along their length, but not necessarily the same alleles.Sister
chromatids initially contain the same alleles.
5
Q
Chromosome replication
A
Chromosomes are replicated by DNA polymerases and begin at an origin. Replication is bi-directional. Eukaryotes have
multiple origins along each chromosome and have telomerase to replicate the ends.
6
Q
how mitosis and meiosis affect the c and n numbers
A
Mitosis reduces the c-number, but not the n-number.Meiosis reduces both c and n.
7
Q
T/F Homologous chromosomes pair (sysnapse) with each other during mitosis
A
false, Homologous chromosomes pair (sysnapse) with each other during meiosis, but not mitosis
8
Q
Aneuploidy
A
results from the addition or subtraction of one or more chromosomes from a group of homologs, and is usually
deleterious to the cell.
9
Q
Polyploidy
A
is the presence of more than two complete sets of chromosomes in a genome.Even-numbered multiple sets of
chromosomes can be stably inherited in some species, especially plants
10
Q
Endopolyploidy
A
is tissue-specific type of polyploidy observed in some species, including diploids
11
Q
T/F Organelles also contain chromosomes
A
TRUE, Organelles also contain chromosomes, but these are much more like prokaryotic chromosomes than the nuclear chromosomes
of eukaryotes.
12
Q
A
13
Q
What is the primary function of mitosis?
A
A: To ensure that each daughter cell inherits identical genetic material—one copy of each chromosome.
14
Q
During which phase of mitosis do replicated chromosomes condense?
A
A: Prophase
15
Q
What happens during metaphase?
A
A: Chromosomes are positioned near the middle of the dividing cell.
16
Q
What occurs during anaphase?
A
A: Sister chromatids migrate to opposite poles of the dividing cell.
17
Q
At which phase are unreplicated chromosomes completely separated into two sets?
A
A: Telophase
18
Q
What is cytokinesis?
A
A: The division of the cytoplasm to complete the formation of two daughter cells.
19
Q
What helps move chromosomes during mitosis?
A
A: Microtubules that attach to the chromosomes at the centromeres.
20
Q
What occurs in metaphase of mitosis?
A
A: Chromosomes align at the center (metaphase plate) of the cell.
20
Q
What happens in prophase of mitosis?
A
A: Chromosomes condense and become visible; spindle fibers begin to form.
21
Q
What occurs in anaphase of mitosis?
A
A: Sister chromatids are pulled apart to opposite poles of the cell.
22
Q
What happens in telophase of mitosis?
A
A: Two new nuclei begin to form; chromosomes begin to de-condense.
23
Q
What is the result of cytokinesis in mitosis?
A
A: Two genetically identical diploid daughter cells.
24
What happens in metaphase I?
A: Homologous chromosome pairs line up at the metaphase plate.
24
What happens in anaphase I?
A: Homologous chromosomes are pulled to opposite poles.
24
What occurs in prophase I of meiosis?
A: Homologous chromosomes pair up and crossing over may occur.
25
What happens in telophase I?
A: Nuclei may reform; the cell prepares for division into two.
26
What is the result of cytokinesis I?
A: Two haploid cells with duplicated chromosomes.
27
What happens in prophase II?
A: Chromosomes re-condense and spindle fibers form again.
28
What happens in telophase II?
A: Nuclear membranes form around separated chromatids.
28
What occurs in metaphase II?
A: Chromosomes line up at the metaphase plate in both haploid cells.
28
What happens in anaphase II?
A: Sister chromatids are pulled apart to opposite poles.
29
What is the final result of cytokinesis II?
A: Four genetically unique haploid daughter cells.
30
How many cells are produced in mitosis vs meiosis?
A: Mitosis: 2 cells; Meiosis: 4 cells.
31
Are mitosis products diploid or haploid?
A: Diploid (2n).
32
Are meiosis products diploid or haploid?
A: Haploid (n).
33
Does crossing over occur in mitosis?
A: No.
34
Does crossing over occur in meiosis?
A: Yes, during prophase I.
35
What is the main purpose of meiosis in eukaryotic organisms?
A: To reduce the chromosome number by half in the cells that will fuse to form a new organism, preventing chromosome doubling in each generation.
36
Why is chromosome number reduction necessary in sexual reproduction?
A: Without reduction, each generation would have double the chromosome number of the previous one, leading to genetic imbalance.
37
What happens during Meiosis I?
A: Homologous chromosomes segregate—each pair separates and moves to different cells.
38
What type of reproduction involves meiosis?
A: Sexual reproduction, where a cell from one individual joins with a cell from another to create the next generation.
39
What occurs in Meiosis II?
A: Sister chromatids segregate—each duplicated chromosome splits into two chromatids which go to different cells.
40
Do only multicellular organisms undergo meiosis?
A: No, some single-celled eukaryotes like yeast also use meiosis.
41
How many divisions occur in meiosis?
A: Two rounds: Meiosis I and Meiosis II.
42
What are the diploid cells that undergo meiosis called?
A: Meiocytes
43
Why is Meiosis I called a "reductional division"?
A: Because it reduces the number of chromosomes inherited by daughter cells.
44
Why is Meiosis II called an "equational division"?
A: Because sister chromatids separate, similar to mitosis, maintaining chromosome number.
45
What is synapsis in meiosis?
A: The pairing up of homologous chromosomes during prophase I of meiosis I.
46
When do homologous chromosomes line up and separate in meiosis I?
A: They line up in the middle during metaphase I and separate during anaphase I.
47
What structure helps homologous chromosomes attach along their length?
A: The synaptonemal complex.
48
What is the synaptonemal complex?
A: A protein structure that forms between homologous chromosomes during synapsis to keep them aligned and connected.
49
What is a bivalent?
A: A transient structure formed by a pair of homologous chromosomes held together by the synaptonemal complex.
50
When is the synaptonemal complex released?
A: When the cell enters anaphase I.
51
What is crossing over?
A: The exchange of genetic material between non-sister chromatids of homologous chromosomes during prophase I.
52
Where does crossing over occur?
A: Within the synaptonemal complex at specific DNA regions.
53
How does crossing over occur?
A: DNA repair enzymes break the DNA in non-sister chromatids and then reattach them in a way that exchanges segments.
54
What is the result of crossing over?
A: Genetic recombination—new combinations of alleles in the gametes.
55
Why is crossing over important for meiosis?
A: It ensures homologous chromosomes stay together for proper segregation and increases genetic diversity.
56
How does crossing over contribute to evolution?
A: By reshuffling gene/allele combinations, it creates genetic diversity, which natural selection can act upon.
57
Into how many stages is Prophase I divided?
A: Five stages: Leptotene, Zygotene, Pachytene, Diplotene, and Diakinesis.
58
What happens during leptotene?
A: Chromatin begins to condense into long, visible threads—chromosomes.
59
What occurs in zygotene?
A: Homologous chromosomes pair up (synapse) and begin forming the synaptonemal complex.
60
What is significant about pachytene?
A: Homologous chromosomes are fully synapsed and form bivalents (two chromosomes, four chromatids).
61
What important event occurs during pachytene?
A: Crossing over—exchange of genetic material between non-sister chromatids.
62
What is observed during diplotene?
A: Homologous chromosomes start to loosen, and the individual chromatids become visible.
63
What structure marks crossing over during diplotene?
A: Chiasmata (singular: chiasma), the visible sites of crossover.
64
What happens during diakinesis?
A: Chromosomes condense further and individualize, preparing for metaphase I and segregation.
65
What follows diakinesis in meiosis?
A: Metaphase I, where homologous chromosomes align on the metaphase plate.
66
What is the overall goal of the stages of Prophase I?
A: To ensure accurate pairing, recombination, and segregation of homologous chromosomes
67
What is the ploidy of the daughter cells after Meiosis I?
A: Haploid (n) – homologous chromosomes have been separated.
68
What separates in Meiosis I?
A: Homologous chromosomes.
69
What separates in Meiosis II?
A: Sister chromatids.
70
What separates in Mitosis?
A: Sister chromatids.
71
Does crossing over occur in Meiosis I?
A: Yes – during Prophase I (pachytene), homologous chromosomes exchange genetic material.
72
Does crossing over occur in Meiosis II or Mitosis?
A: No – crossing over only happens during Prophase I of meiosis.
73
Are daughter cells genetically identical after Meiosis I and II?
A: No – they are genetically unique due to crossing over and independent assortment.
74
Are daughter cells genetically identical after Mitosis?
A: Yes – they are clones of the parent cell.
75
Where does Meiosis occur?
A: In germ cells to produce gametes (sperm and egg).
76
Where does Mitosis occur?
A: In somatic (body) cells for growth, development, and tissue repair.
77
What happens during the leptotene stage of Prophase I?
A: Chromatin condenses into long, visible chromosomes that appear as thin threads.
78
What is the key visual feature of chromosomes in leptotene?
A: They are single-thread-like and not yet synapsed.
79
What key event begins in zygotene?
A: Homologous chromosomes begin pairing in a process called synapsis.
80
What structure begins forming during zygotene?
A: The synaptonemal complex, which helps align homologous chromosomes.
81
What happens to chromosome pairs during pachytene?
: Homologous chromosomes are fully synapsed and form bivalents (tetrads).
82
What major genetic process occurs in pachytene?
A: Crossing over – exchange of genetic material between non-sister chromatids.
83
Why is crossing over important?
A: It creates genetic diversity by reshuffling alleles.
84
What happens during diplotene?
A: The synaptonemal complex dissolves, and homologs begin to separate slightly.
85
What remains attached during diplotene?
A: Homologous chromosomes remain connected at chiasmata (sites of crossing over).
86
What becomes visible during diplotene?
A: Individual chromatids and chiasmata.
87
What occurs during diakinesis?
A: Chromosomes are fully condensed, individualized, and prepare for metaphase I.
88
What happens to the nuclear envelope during diakinesis?
A: It breaks down, enabling spindle fibers to interact with chromosomes.
89
What is the last event before metaphase I?
A: Paired homologs align on the metaphase plate.
90
What ensures genetic diversity in the gametes formed after meiosis?
A: Allelic differences caused by crossing over and recombination.
91
What are the four products of meiosis called in male animals?
A: Spermatids, which mature into sperm cells.
92
What happens to spermatids in male animals?
A: They grow tails and become functional sperm cells.
93
In female animals, how many products of meiosis become functional eggs?
A: Only one out of four becomes an egg; the other three become polar bodies.
94
What is the function of polar bodies in female meiosis?
A: They are tiny, disposable cells that receive minimal cytoplasm and do not become gametes.
95
Why does only one egg form in female meiosis?
A: To ensure the egg receives the maximum amount of nutrients.
96
What are the four main stages of the typical eukaryotic cell cycle?
A: G₁ (Gap 1), S (Synthesis), G₂ (Gap 2), and M (Mitosis).
97
What is the function of the G₁ phase?
A: It's a lag period where the cell grows and prepares for DNA replication.
98
What occurs during the S phase of the cell cycle?
A: DNA synthesis (replication)—each chromosome is replicated.
99
What is the G₂ phase and when does it occur?
A: A second lag phase that follows DNA replication and precedes mitosis.
100
What is interphase?
A: The portion of the cell cycle that includes G₁, S, and G₂ phases—everything except mitosis and meiosis.
101
Why is interphase important?
A: It’s when the cell grows, performs normal functions, and prepares for division.
102
What is the G₀ phase?
A: A permanent, non-dividing state that some cells enter and never leave.
103
What happens in cells that enter G₀ phase?
A: They do not replicate DNA or divide; examples include nerve and muscle cells.
104
What is endoreduplication?
A: A process where a cell repeats DNA synthesis (S phase) without undergoing mitosis, leading to increased DNA content.
105
Do cells undergoing meiosis usually have a G₂ phase?
A: No, they typically do not have a G₂ phase.
106
Why is understanding the cell cycle important in science?
A: Because of its relationship to cell division and cancer; disruptions can lead to uncontrolled growth.
107
In genetics, what does “c” represent?
A: The DNA content in a cell.
108
What does “n” represent in a cell?
A: The number of complete sets of chromosomes (ploidy level).
109
What is the DNA content and chromosome number of a gamete (sperm or egg)?
A: 1c DNA content and 1n chromosome number.
110
What happens to DNA and chromosome content upon fertilization?
A: DNA content becomes 2c, and chromosome number becomes 2n.
111
What is the DNA and chromosome content of a gamete (sperm or egg)?
A: 1N, 1C – haploid chromosome number and one copy of DNA.
112
What happens to DNA and chromosome content after fertilization?
A: It becomes 2N, 2C – diploid with one copy of each chromosome from each parent.
113
What is the DNA and chromosome content during G₁ phase?
A: 2N, 2C – normal diploid content before DNA replication.
114
What change occurs during the S phase of the cell cycle?
A: DNA replicates: the cell becomes 2N, 4C (same chromosomes, but each has a sister chromatid).
115
What is the cell’s state during G₂ phase?
A: 2N, 4C – ready to enter mitosis with replicated chromosomes.
116
After mitosis, what is the DNA and chromosome content of each daughter cell?
A: 2N, 2C – each gets one copy of each replicated chromosome.
117
What is the DNA and chromosome content entering Meiosis I?
A: 2N, 4C – same as G₂, with homologous chromosomes and sister chromatids.
117
After Meiosis I, what is the DNA and chromosome content of each cell?
A: 1N, 2C – homologs are separated but sister chromatids are still joined.
118
After Meiosis II, what is the DNA and chromosome content of each resulting gamete?
A: 1N, 1C – sister chromatids separate; each gamete is haploid with a single DNA copy.
119
How does mitosis affect DNA and chromosome content?
A: Maintains 2N, 2C – creates identical diploid cells.
120
How does meiosis affect DNA and chromosome content?
A: Reduces to 1N, 1C – produces genetically unique haploid gametes.
121
What key cellular events cause shifts in DNA content from 1C → 2C → 4C → 1C?
A: Fertilization, DNA replication (S phase), Meiosis I, and Meiosis II.
122
What is a karyotype?
A: The complete set of chromosomes in an individual, typically viewed during metaphase.
123
What is a karyogram?
A: A visual arrangement of chromosomes in standardized order, used to assess chromosomal abnormalities.
124
What is the difference between a karyotype and a karyogram?
A: A karyotype is the written description of the chromosomes, while a karyogram is the actual image or diagram showing the chromosome pairs.
125
How many chromosomes are in a haploid human nucleus (e.g., sperm or egg)?
A: 23 chromosomes (n = 23).
126
How many chromosomes are in a diploid human nucleus?
A: 46 chromosomes (2n = 46), arranged in 23 pairs.
126
Why are there 46 structures visible in a metaphase karyogram?
A: Because each chromosome is replicated (has two sister chromatids).
127
Why do chromosomes have different lengths?
A: It’s due to their actual physical size and DNA content—chromosome 1 is the longest, followed by chromosome 2, etc.
128
How are chromosomes arranged in a karyogram?
A: By length and centromere position, with chromosome 1 as the longest, down to chromosome 22 and the sex chromosomes (X/Y).
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What does a karyogram help geneticists determine?
A: Any abnormalities in chromosome number or structure in a person’s genome.
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How are chromosomes visualized in a karyogram?
A: Using stains and fluorescent dyes that produce unique banding patterns.
131
Is there a correlation between chromosome number and organism complexity?
A: No—chromosome number does not indicate complexity or total genomic DNA content.
132
Why is metaphase the best stage to observe chromosomes in a karyogram?
A: Because chromosomes are highly condensed and visible under a microscope.
133
What are autosomes?
A: Chromosomes that are paired and present in equal numbers in both males and females. They do not determine sex.
134
What are sex chromosomes?
A: Chromosomes that differ in males and females and are responsible for determining the sex of an individual.
135
In humans, what are the sex chromosome combinations for males and females?
A: Males: XY, Females: XX.
135
Why was the X chromosome originally named “X”?
A: Because its function was unknown at the time—X stood for the mystery.
135
What is the naming sequence for sex chromosomes?
A: X, Y, Z, then W.
136
What is the sex chromosome system in birds, moths, and butterflies?
A: Males: ZZ, Females: ZW.
137
Do all organisms with X and Y chromosomes determine sex the same way?
A: No. Even with similar chromosomes, the molecular mechanisms differ across species.
138
Give an example of species with X and Y chromosomes but different sex-determining mechanisms.
A: Humans and Drosophila both have X and Y, but use different mechanisms for sex determination
139
When did sex chromosomes evolve in mammals?
A: After the divergence of monotremes from placental and marsupial mammals.
140
What gene is found only on the Y chromosome and determines male development?
A: TDF (Testis-Determining Factor).
140
What happens in XX embryos lacking the TDF gene?
A: Their gonads mature into ovaries by default.
141
What do the testes produce after forming in XY embryos?
A: Male sex hormones that guide the rest of male development.
141
What do the ovaries produce in XX embryos?
A: Female sex hormones that guide female development.
142
What role do testes and ovaries play in gamete production?
A: They are the organs that produce gametes—sperm in males, eggs in females.
143
What are homogametic sexes?
A: Individuals with two of the same sex chromosome, such as XX females and ZZ males.
144
How do sex chromosomes behave in homogametic individuals during meiosis?
A: They pair and segregate like autosomes during Meiosis I.
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What are heterogametic sexes?
A: Individuals with two different sex chromosomes, such as XY males or ZW females.
146
How do sex chromosomes behave in heterogametic individuals during meiosis?
A: The different sex chromosomes (e.g., X and Y) pair with each other and segregate during Meiosis I.
147
What sex chromosome do all egg cells carry in mammals?
A: An X chromosome.
148
What sex chromosomes can sperm carry in XY mammals?
A: Either an X or a Y chromosome.
149
What is the final result of meiosis in XY mammals regarding sex chromosomes?
A: Production of two types of sperm: one with an X chromosome and one with a Y chromosome.
150
What is aneuploidy?
A: A chromosomal abnormality involving the addition or subtraction of a chromosome from a pair of homologs.
151
What is monosomy?
A: The absence of one chromosome from a pair (only one homolog present), symbolized as 2n - 1.
151
What is trisomy?
A: The presence of three homologous chromosomes instead of two, symbolized as 2n + 1.
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What does 2n represent?
A: The normal number of chromosomes in a diploid cell.
153
What does the addition or loss of a whole chromosome cause?
A: A mutation that changes the genotype of the cell or organism.
154
What is the most well-known example of human aneuploidy?
A: Trisomy 21, which causes Down syndrome.
155
Why are most other human aneuploidies lethal?
A: They disrupt development during early embryogenesis.
156
How is aneuploidy different from polyploidy?
A: Aneuploidy affects one chromosome pair, while polyploidy affects the entire set.
157
Is aneuploidy always harmful?
A: It is almost always deleterious, especially in humans.
158
Can polyploidy ever be beneficial?
A: Yes, particularly in plants, such as food crops.
159
What is non-disjunction?
A: The failure of chromosomes or chromatids to segregate properly during mitosis or meiosis.
160
What does non-disjunction lead to?
A: Gametes with extra or missing chromosomes, which can result in aneuploid offspring.
161
What are chromosomal abnormalities?
A: Structural defects in chromosomes that involve changes in their segments, detectable in karyotypes.
162
Name the 5 major types of chromosomal structural abnormalities.
A:
Deletion
Duplication
Inversion
Insertion
Translocation
163
What is a deletion?
A: Loss of a chromosome segment.
163
What is a duplication?
A: A chromosome segment is repeated or copied more than once.
164
What is an inversion?
A: A chromosome segment is reversed in orientation (flipped end to end).
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What is an insertion?
A: A segment from one chromosome is moved to a non-homologous chromosome in a unidirectional manner.
166
What is a translocation?
A: A bidirectional exchange of chromosome segments between two non-homologous chromosomes.
167
What is a reciprocal translocation?
A: A type of translocation where the DNA exchange is equal and mutual between two chromosomes.
168
How are structural chromosome abnormalities usually detected?
A: Through karyotype analysis using banding patterns and microscopy.
169
Can these abnormalities affect health or development?
A: Yes. They can lead to genetic disorders, miscarriages, or birth defects, depending on the genes affected.
170
How harmful are structural defects compared to aneuploidy?
A
: They tend to be less harmful than aneuploidy.
170
Do structural chromosome defects affect the entire chromosome?
A: No, they affect only part of a chromosome (a subset of genes).
171
Can duplications of small chromosome segments ever be beneficial?
A: Yes, they can provide extra gene copies which may evolve in new and beneficial ways.
172
Give an example of how structural rearrangements have been evolutionarily significant.
A: Many ancient rearrangements in the genomes of species (including humans) have led to beneficial adaptations.
173
What natural process can cause chromosomal abnormalities?
A: Errors during DNA replication.
174
What is chromosome breakage?
A: It’s the breaking of chromosomes due to physical damage (like ionizing radiation), transposon movement, or other factors.
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176
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What events may be introduced during the repair of broken chromosomes?
A:
Deletions
Insertions
Translocations
Inversions
178
What is diploidy?
A: The condition of having two homologous copies of each chromosome (2n), as seen in humans and most animals
179
What are polyploids?
A: Organisms that have more than two sets of chromosomes, i.e., more than two homologs of each chromosome per cell.
180
In what types of organisms is polyploidy most commonly found?
A: Plant species, though a few animal species can also be polyploid.
181
What is ploidy?
A: The number of complete sets of chromosomes in a cell.
182
Define monoploid.
A: An organism with only one set of chromosomes (1x).
183
What is a triploid organism?
A: An organism with three sets of chromosomes (3x).
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What is a tetraploid organism?
A: An organism with four sets of chromosomes (4x).
185
List the next levels of polyploidy after tetraploid.
A:
Pentaploid (5x)
Hexaploid (6x)
Higher orders are also possible.
186
How is the “x” notation different from the “n” notation?
A:
x = number of chromosome sets.
n = number of chromosomes in a gamete.
For diploids: n = x, 2n = 2x
For tetraploids: n = 2x, 2n = 4x
187
In a hexaploid organism, what are the values of n and 2n?
A: n = 3x, and 2n = 6x
188
What are monoploids?
A: Organisms with only one set of chromosomes. Usually inviable in most species.
189
What is the ploidy of male bees (drones)?
A: Monoploid/haploid (n = 16) – they develop from unfertilized eggs.
190
What is the ploidy of female bees?
A: Diploid (2n = 32) – they develop from fertilized eggs.
191
Do male bees undergo meiosis?
A: No. They produce sperm through mitosis.
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Do female bees undergo meiosis?
A: Yes. They produce eggs via meiosis.
193
What type of sex determination system do bees follow?
A: A haploid-diploid system (not based on X/Y chromosomes).
194
What is the biological role difference between male and female bees?
Males (drones): Only needed for reproduction.
Females (workers): Do most of the work in the colony.
195
What makes polyploids similar to diploids in terms of chromosome count?
A: Stable polyploids have an even number of chromosome sets, like diploids (2n=2x), tetraploids (2n=4x), and hexaploids (2n=6x).
196
Why do odd-number polyploids (e.g., triploids 2n=3x) tend to be sterile?
A: Because meiosis cannot evenly divide an odd number of chromosome sets, making proper gamete formation difficult.
197
What is the key difference in how meiosis vs. mitosis handles polyploidy?
A: Meiosis requires even chromosome sets for accurate halving, while mitosis does not require pairing, so it functions in all ploidy levels.
198
How do homologous chromosomes behave during meiosis in polyploids?
A: During metaphase I, homologous chromosomes pair—sometimes as tetravalents (4 chromosomes align) or bivalents (2 pairs).
199
What is a tetravalent?
A: A group of four homologous chromosomes aligning together during meiosis in tetraploid species.
200
Are even-number polyploids fertile or sterile?
A: They are generally fertile, as their chromosomes can pair and segregate properly during meiosis.
201
Can odd-number polyploids undergo mitosis effectively?
A: Yes. Mitosis does not require homologous pairing, so it works in both even- and odd-number polyploids.
202
What is the underlying reason meiosis fails in triploids (2n=3x)?
A: The chromosomes cannot pair evenly, making gamete formation and proper segregation impossible or error-prone.
203
Why are polyploid plants preferred in agriculture?
A: They tend to be larger and healthier than their diploid counterparts and often exhibit greater vigor and size.
204
What is an example of an octoploid (8x) crop plant?
A: Strawberries sold in grocery stores are octoploid and larger than wild diploid strawberries.
205
What is an example of a hexaploid (6x) crop plant?
A: Bread wheat, which has 42 chromosomes and is genetically represented as AABBDD.
206
Which three diploid wheat species contributed to the genome of hexaploid bread wheat?
A:
Triticum monococcum (AA)
Triticum searsii (BB)
Triticum tauschii (DD)
207
How many chromosomes does each diploid wheat species have?
A: 2n = 2x = 14 chromosomes, with 7 chromosomes per set.
208
Why is bread wheat fertile even though it's a polyploid?
A: Because during meiosis I, homologous chromosomes pair accurately (A with A, B with B, etc.), allowing for equal segregation and gene balance.
209
What ensures gene balance and fertility in polyploid bread wheat?
A: Each chromosome set behaves independently during mitosis, and homologs pair correctly during meiosis.
210
What is the chromosomal formula of hexaploid bread wheat?
A: 2n = 6x = 42
Chromosome sets: AABBDD
211
What type of ploidy do grocery store bananas (Cavendish) have?
A: They are triploid (chromosome set = AAA).
212
Why are triploid plants sterile?
A: Because they have three copies of each chromosome, which cannot properly pair during meiosis I, leading to failed chromosome segregation and no seed formation.
213
What species is Cavendish banana derived from, and what is its diploid designation?
A: Musa acuminata with AA chromosome sets.
214
Why are seedless fruits easier to eat?
A: Because meiosis fails in triploids, seeds cannot form, making fruits seedless and more convenient for consumption.
215
How are triploid bananas propagated?
A: Asexually, through cuttings from existing triploid plants.
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How are seedless watermelons typically produced?
A: By crossing a tetraploid (4x) watermelon with a diploid (2x) watermelon, producing triploid (3x) offspring that develop normally through mitosis but can't perform meiosis or produce seeds.
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What happens to the gametes in tetraploid and diploid watermelons during this cross?
A:
Tetraploid produces gametes with 2x chromosomes
Diploid produces gametes with 1x chromosomes
They fuse to form 3x (triploid) zygotes
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How does polyploidy affect plant size?
A: Polyploid plants are larger and often healthier than diploid counterparts.
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What ploidy are most grocery store strawberries?
A: Octoploid (8x), while wild strawberries are diploid.
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Does endoreduplication affect germline or gametes?
A: No. Endoreduplication does not affect the germline or gametes, so organisms with it are not considered polyploid
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What is endoreduplication?
A: A tissue-specific genome amplification process where cells undergo extra rounds of DNA synthesis (S-phase) without mitosis or cytokinesis, resulting in endopolyploid cells with multiple chromatids per chromosome.
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Is polyploidy common in animals?
A: No, it is rare, usually seen only in lower life forms that often reproduce via parthenogenesis.
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In what organisms and cells does endoreduplication occur?
A: It occurs in many plant cells and some specialized animal cells, including humans.
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What is an example of endoreduplication in animals?
A: Salivary gland polytene chromosomes of Drosophila melanogaster, which can have over 1,000 chromatids per chromosome.
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What is a polytene chromosome?
A: A giant chromosome formed by many chromatids aligned together, typically produced by repeated endoreduplication without cell division.
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Why are polytene chromosomes important in genetics research?
A: Their large size and visible banding patterns make them ideal for studying gene locations, DNA sequence organization, and chromosome aberrations under the microscope.
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What do the bands on polytene chromosomes represent?
A: They reflect the underlying DNA sequence and gene content of that chromosome region.
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What is endopolyploidy commonly associated with?
A: Cells that are metabolically active, producing enzymes and proteins rapidly.
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What is gene balance?
A: Gene balance refers to the idea that genes, and the proteins they encode, work within complex regulatory and metabolic networks that function best when gene copy numbers are maintained in proper ratios.
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Why can aneuploidy (like trisomy) be harmful while polyploidy can be tolerated or even beneficial?
A: Aneuploidy disrupts gene balance by altering the copy number of a subset of genes, upsetting protein ratios in critical networks. In contrast, polyploidy increases all genes equally, preserving gene balance.
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What happens when gene copy number increases or decreases for just one part of a network?
A: It can throw the entire network out of balance, causing overproduction or underproduction of metabolites, which may be toxic or limit essential cellular functions.
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Are small-scale gene duplications always harmful?
A: No. Duplication of just a few genes is often tolerated because gene networks are regulated in many other ways.
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When does gene imbalance typically result in abnormal or lethal phenotypes?
A: When large chromosomal segments or entire chromosomes are duplicated (e.g., in trisomy), causing widespread dosage imbalances across many genes that cellular networks cannot compensate for.
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What role do cellular networks play in gene balance?
A: They attempt to compensate for changes in gene dosage, but when the imbalance is too widespread, such as in trisomy, the networks fail, resulting in abnormal or lethal effects.
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Which organelles in eukaryotic cells contain their own DNA?
A: The chloroplast and mitochondrion both contain circular chromosomes and their own DNA.
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What are organellar chromosomes?
A: These are DNA molecules found in mitochondria and chloroplasts. They are typically circular, like bacterial chromosomes, and are inherited from one parent (usually the mother).
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What is the mode of inheritance for organellar genomes?
A: Uniparental inheritance, usually maternal (inherited through the egg, which provides the cytoplasm and organelles).
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What theory explains the origin of mitochondria and chloroplasts?
A: The endosymbiont theory – which proposes that mitochondria and chloroplasts are derived from prokaryotic endosymbionts that entered early eukaryotic cells.
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How do organellar chromosomes differ from nuclear chromosomes in terms of cell division?
A: They do not undergo mitosis or meiosis. Their division resembles that of bacteria, i.e., simple replication.
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Are genes required by mitochondria only encoded by the mitochondrial genome?
A: No. Some are encoded in the nuclear genome, translated in the cytoplasm, and then imported into the mitochondria.
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Why are mitochondrial genomes important for evolutionary studies?
A: Mitochondrial DNA (mtDNA) is widely used in evolutionary studies because it’s maternally inherited and mutates at a predictable rate, allowing scientists to trace lineages—e.g., studies show mammoths are closer to Indian elephants than to African ones.
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What was unclear before Mendel's experiments on heredity?
A: The basic rules of heredity were not understood, such as how traits like seed color or plant height were passed from one generation to the next.
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What observation puzzled scientists before Mendel regarding pea plants?
A: Green-seeded pea plants occasionally produced offspring with yellow seeds, raising questions about whether traits disappeared and reappeared across generations.
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What questions did early scientists have about inheritance?
A: They questioned whether the same hereditary factors controlled different traits, like seed color and plant height, and how traits were transmitted or masked.
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Who used pea plants to study the fundamental laws of genetics?
A: Gregor Mendel used pea plants to discover foundational genetic principles.
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What was the state of genetic understanding before Mendel’s work?
A: Heredity was poorly understood. People observed that traits like seed color could change across generations, but the mechanisms behind it were unclear.
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What genetic mystery did green-seeded pea plants present before Mendel’s findings?
.
A: They sometimes produced yellow-seeded offspring, raising questions about whether traits skipped generations or reappeared randomly
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