TH- meiosis Flashcards
1
Q
What is heredity/inheritance?
A
The transmission of traits from one generation to the next
2
Q
what is variation?
A
a change or slight difference
3
Q
What is a genome? and is it comprised of?
A
- organism’s complete set of genetic instructions.
- comprised of many genes from mother and father.
4
Q
what are genes? and where are they found on a chromosome?
A
- segments of DNA
- found at its locus
5
Q
State the difference between asexual and sexual reproduction.
A
- organisms that reproduce asexually can produce offspring that are exact copies of themselves.
- sexual reproduction, two parents produce offspring that have unique combinations of genes inherited from the two parents.
6
Q
What is a clone?
A
a group of genetically identical individuals.
7
Q
How may clones differ?
A
Due to mutations
8
Q
What is a somatic cell?
A
all cells except reproductive cells
9
Q
What is a karyotype display?
A
images of 46 chromosomes arranged in pairs in order of size.
10
Q
What do two chromosomes in a pair need to have in common?
A
have the same length, centromere position, and staining pattern.
11
Q
what is a homologous chromosome pair?
A
carry genes that control the same inherited characters.
12
Q
what are the 2 distinct sex chromosome?
A
X and Y
13
Q
what are the exception to the general pattern of homologous chromosomes in human somatic cells?
A
the sex chromosomes
14
Q
what are autosomes?
A
- chromosomes other than X and Y
- so the 22 other pairs in humans cells.
15
Q
what homologous pair of sex chromosomes do females and males have?
A
- M= XY
- F= XX
16
Q
what is a diploid cell?
A
• Any cell with two sets of chromosomes, 2n
17
Q
what is a haploid cell?
A
• A gamete with a single chromosome set, n
18
Q
How many sets of chromosomes and what type do we have in somatic cells?
A
-two sets of 23, a maternal set and a paternal set
19
Q
How many and what type of chromosomes do sperm cells and ovum have?
A
- sperm= 22 autosomes and X or Y
- ovum= 22 autosomes and X
20
Q
what is syngamy?
A
the fusion of two cells, or of their nuclei, in reproduction.
21
Q
what occurs in fertilisation?
A
Fertilization occurs when the nucleus of both a sperm and an egg fuse (synagmy) to form a diploid cell, known as zygote.
22
Q
what is a zygote?
A
fertilised egg
23
Q
what is gonads?
A
male and female primary reproductive organs.
24
Q
By which process are gametes produced?
A
meiosis
25
why are gametes produced by this process?
- If gametes were produced by mitosis, the fusion of gametes would produce offspring with four sets of chromosomes after one generation, eight after a second, and so on.
- however by meiosis they are halved instead.
26
Briefly describe life cycle from gamete to adult
- gametes divide by meiosis
- haploid sperm and egg cell fuse
- fertilization takes place
- most cells in diploid zygote now divides via mitosis to grow and develop
- forming eventually a adult
- their gametes still divide via meiosis
27
What is the 2nd life cycle of plants and algae called?
alternation of generations.
28
what does the life cycle of plants and algae include?
two multicellular stages, one haploid and one diploid.
29
Describe the alternation of generations
- The multicellular diploid stage is called the sporophyte.
- Meiosis in the sporophyte produces haploid spores that develop by mitosis into the haploid gametophyte stage.
- Gametes produced via mitosis by the gametophyte fuse to form the zygote, which grows into the sporophyte by mitosis.
30
describe the third life cycle of most fungi and protoctists
- Gametes fuse to form a zygote, which is the only diploid phase.
- The zygote undergoes meiosis to produce haploid cells.
- These haploid cells grow by mitosis to form the haploid multicellular adult organism.
- The haploid adult produces gametes by mitosis.
31
which type of cells can undergo meiosis?
Diploid cells
32
which feature do all 3 cell cycles share?
each cycle of chromosome halving and doubling contributes to genetic variation among offspring.
33
what does meiosis I result in?
separation of homologous chromosomes forming a haploid cell
34
what does meiosis II result in?
separates sister chromatids so form 4 daughter cells.
35
what 2 things happenn in interphase before meiosis I?
- chromosomes are replicated to form sister chromatids.
| - single centrosome is replicated, forming two centrosomes.
36
Describe Meiosis I
- Prophase I:
* the chromosomes begin to condense.
* Homologous chromosomes loosely pair up along their length, precisely aligned gene for gene.
* In crossing over, nonsister chromatids exchange DNA segments
* a protein structure called the synaptonemal complex forms between homologues, holding them tightly together along their length.
* As the synaptonemal complex disassembles in late prophase, each chromosome pair becomes visible as a tetrad, or group of four chromatids.
* Each tetrad has one or more chiasmata, sites where the chromatids of homologous chromosomes have crossed, and segments of the chromatids have been traded
* Spindle microtubules form from the centrosomes, which have moved to the poles
* The breakdown of the nuclear envelope and nucleoli take place.
* Kinetochores of each homologue attach to microtubules from one of the poles.
- Metaphase I:
* tetrads are all arranged at the metaphase plate, with one chromosome facing each pole.
* Microtubules from one pole are attached to the kinetochore of one chromosome of each tetrad, while those from the other pole are attached to the other.
- Anaphase I:
* homologous chromosomes separate
* One chromosome moves toward each pole, guided by the spindle apparatus.
* Sister chromatids remain attached at the centromere and move as a single unit toward the pole.
- Telophase I and cytokinesis:
* movement of homologous chromosomes continues until there is a haploid set at each pole.
* In animal cells, a cleavage furrow forms. In plant cells, a cell plate forms.
37
Does chromosome replication occur after meiosis I? explain why/ why not
no, chromosomes are already replicated.
38
Describe Meiosis II
- Prophase II:
* spindle apparatus forms and attaches to kinetochores of each sister chromatid.
* Spindle fibers from one pole attach to the kinetochore of one sister chromatid, and those of the other pole attach to kinetochore of the other sister chromatid.
- Metaphase II:
* sister chromatids are arranged at the metaphase plate.
* kinetochores of sister chromatids attach to microtubules extending from opposite poles.
- Anaphase II:
* centromeres of sister chromatids separate
* two newly individual chromosomes travel toward opposite poles.
- Telophase II:
* chromosomes arrive at opposite poles.
* Nuclei form around the chromosomes, which begin expanding
* cytokinesis separates the cytoplasm.
39
Explain the synapsis process
-During prophase I of meiosis, replicated homologous chromosomes line up and become physically connected along their lengths by a zipperlike protein complex, the synaptonemal complex
40
state the differences between meiosis and mitosis
- chromosome number is reduced from diploid to haploid in meiosis but is conserved in mitosis.
- mitosis produces genetically identical daughter cells to parents but Meiosis produces cells that are genetically distinct
- Synapsis and crossing over do not occur in mitosis.
- In mitosis, individual replicated chromosomes line up along the metaphase plate however in Meiosis I homologous pairs line up
- At anaphase I of meiosis, it is homologous chromosomes that separate and are carried to opposite poles of the cell however In mitosis, sister chromatids separate to become individual chromosomes.
41
What is synaptonemal complex ?
zipperlike protein complex used in synapsis
42
What is crossing over?
Genetic rearrangement between nonsister chromatids
43
What is the origin of genetic variation?
Mutations are the original source of genetic diversity
44
What are the three mechanisms contribute to genetic variation?
1. Independent assortment of chromosomes.
2. Crossing over.
3. Random fertilization.
45
Describe Independent assortment of chromosomes (how it affects genetic variation)
- each pair of chromosomes sorts maternal and paternal homologues into daughter cells independently of the other pairs
- Therefore, the first meiotic division results in independent assortment of maternal and paternal chromosomes into daughter cells.
- causing the number of combinations possible.
46
what is the formula for calculating the number of possible combinations for Independent assortment of chromosomes?
- 2^n
| - n= haploid number
47
What are recombinant chromosomes?
DNA are broken and recombined to produce new combinations of alleles.
48
Describe crossing over and when it takes place?
- begins very early in prophase I
- homologous portions of two nonsister chromatids trade places
- paired chromosomes from each parent align so that similar DNA sequences from the paired chromosomes cross over one another.
49
how do crossing over and Independent assortment of chromosomes help provide variation together?
* Crossing over, by combining DNA inherited from two parents into a single chromosome brings about nonidentical sister chromatids
* At metaphase II, nonidentical sister chromatids sort independently from one another, increasing by even more the number of genetic types of daughter cells that are formed by meiosis.
50
Describe Random fertilization
• Any sperm can fuse with any egg.
51
What are the three sources of genetic variability in a sexually reproducing organism?
1. Independent assortment of homologous chromosomes during meiosis I and of nonidentical sister chromatids during meiosis II.
2. Crossing over between homologous chromosomes during prophase I.
3. Random fertilization of an ovum by a sperm.
52
what is natural selection?
Natural selection is the process through which populations of living organisms adapt and change.
53
what is phenotype?
individual's observable traits
54
What develops from natural selection?
adaptation
55
what is adaptation?
A change in structure, function, or behavior by which a species or individual improves its chance of survival in a specific environment
56
What can cause new genes to arise and former ones to decrease?
If the environment changes or a population moves to a new environment, new genetic combinations that work best in the new conditions will produce more offspring, and these genes will increase.
57
Why is adaptation important?
Only those individuals best suited to the local environment will leave the most offspring, transmitting their favorable genes in the process.
