Chapter 13 - Meiosis Flashcards
1
Q
A
A
= not or without
2
Q
Auto
A
= self
3
Q
Chiasm
A
= marked crosswise
4
Q
Di
A
= two
5
Q
Fertil
A
= fruitful
6
Q
Haplo
A
= single
7
Q
homo
A
= like
8
Q
Karyo
A
= Nucleus
9
Q
Meio
A
= less
10
Q
Soma
A
= body
11
Q
Tetra
A
= four
12
Q
Asexual Reproduction
A
A type of reproduction involving only one parent that produces genetically identical offspring by budding or by the division of a single cell or the entire organism into two or more parts.
13
Q
Autosome
A
A chromosome that is not directly involved in determining sex, as opposed to a sex chromosome.
14
Q
Chiasma(plural, chiasmata)
A
The X-shaped, microscopically visible region representing homologous chromatids that have exchanged genetic material through crossing over during meiosis.
15
Q
Crossing Over
A
The reciprocal exchange of genetic material between nonsister chromatids during prophase I of meiosis.
16
Q
Diploid Cell
A
A cell containing two sets of chromosomes(2n), one set inherited from each parent.
17
Q
Fertilization
A
The union of haploid gametes to produce a diploid zygote.
18
Q
Gene
A
A discrete unit of hereditity information consisting of a specific nucleotide sequence in DNA(or RNA, in some viruses)
19
Q
Haploid Cell
A
A cell containing only one set of chromosomes(n).
20
Q
Heredity
A
The transmission of traits from one generation to the next.
21
Q
Homologous Chromosomes
A
Chromosomes pairs of the same length, centromere position, and staining pattern that possess genes from the same characters at corresponding loci.
22
Q
Karyotype
A
A display of the chromosome pairs of a cell arranged by size and shape.
23
Q
Life Cycle
A
The generation-to-generation sequence of stages in the reproductive history of an organism.
24
Q
Locus(plural, loci)
A
A specific place along the length of a chromosome where a given gene is located.
25
Meiosis
A two-stage type of cell division in sexually reproducing organisms that results in cells with half the chromosome number of the original cell.
26
Recombinant Chromosome
A chromosome created when crossing over combines the DNA from two parents into a single chromosome.
27
Sex Chromosome
One of the pair of chromosomes responsible for determining the sex of an individual.
28
Sexual Reproduction
A type of reproduction in which two parents give rise to offspring that have unique combinations of genes inherited from the gametes of the two parents.
29
Synapsis
The pairing of replicated homologous chromosomes during Prophase I of meiosis.
30
Tetrad
A paired set of homologous chromosomes, each composed of two sister chromatids.
31
Zygote
The diploid product of the union of haploid gametes in conception; a fertilized egg.
32
Genes
Units of heredity(the molecules that pass genetic information from parent to offspring)
- located on chromosomes and are linear sequences of DNA nucleotides.
- Each gene encodes the instructions ultimately for making a protein or RNA molecule.
- Located in specific locations along the chromosomes(locus, plural: loci)
33
Sexual Production requirement
Requires the genetic contribution of 2 parents.
34
The life cycle: Meiosis and fertilization
- one haploid gamete formed by meiosis comes from each parent and when the egg is fertilized by the sperm, a fertilized egg or zygote if formed.
- the zygote is diploid and will undergo MITOSIS to grow and develop into a multi-cullular adult
- Fertilization and meiosis must alternate to maintain the proper chromosome number.
35
Somatic Cells and chromosome number
- Always diploid(containing 2 copies of all the chromosomes and therefore 2 copies of every gene located on those chromosomes)
- diploid number = 2n
- 8 chromosomes, 2n = 8
36
Gamete Cells and chromosome number
- Always haploid(only 1 copy of each chromosome and each gene on each chromosome)
- Haploid number = n
- 2n = 8 then n = 4
- haploid number is always 1/2 diploid number
37
Pairs of Chromosomes with same gene loci
- called homologous chromosomes or homologs
- somatic cells will have both members of the homologous pair
- gametes will have only one member
38
Sex Chromosome
X and Y chromosomes
- contain genes that determine sex of the offspring
- Human Female = 2XX chromosomes
- human Male = 1X and 1 Y chromosome
39
Autosomes
All chromosomes EXCEPT sex chromosomes.
40
Human Female chromosome number
23 total
23 pairs of homologous chromosomes
22 autosomal pairs
1 pair of X(sex) chromosomes
normal femals NEVER have a Y chromosome
41
Human Male chromosome number
23 total
22 pairs of Homologous autosomes
1X and 1Y chromosome that are not homologous
only 1 copy of every gene on the X and Y chromosomes
42
Chromosome duplication and S Phase
- forms a pair of identical sister chromatids, joined at a centromere
- Chromatids in the other member of a homologous pair are called non-sister chromatids and contain the same gene loci, may not have identical versions of all genes as the other homologue's sister chromatids
43
Meiosis with Gametes
- involves one duplication of DNA and TWO cell divisions.
- Meiosis I: first division. Forms haploid cells with replicated chromosomes.
- Meiosis 2: second division. forms 4 haploid daughter cells with unreplicated chromosomes.
44
Meiosis I Stages
Duplicating centrosomes occurs in G2
1. Prophase I
- Synapsis occurs creating tetrads(homologous chromosome pairs come together) so that crossing over between non-sister chromatids of homologues pairs occurs; microtubule spindle forms.
2. Metaphase I
- Tetrads move to metaphase plate independently from other tetrads by action of microtubules in spindle.
3. Anaphase I
- Homologous chromosomes are pulled to separate ends of cell, still pairs of sister chromatids.
4. Telophase I
- Nuclei form around pairs of chromatids at each end of cell, now haploid
45
Meiosis II Stages
After Cytokinesis of MI, both daughter cells go through MII
1. Prophase II
- New spindle forms and attaches to individual chromatids
2. Metaphase II
- pairs of sister chromatids line up at metaphase plate, one chromatid on each side
3. Anaphase II
- Sister chromatids are pulled apart and to opposite sides of cell; called chromosomes again
4. Telophase II
- Re-forming of nuclei around chromosomes; Cytokinesis occurs forming a total of 4 haploid daughter cells
46
Sources of Gene Variation
1. Random Mutation
- permanent changes in DNA nucleotide sequence
2. Random fertilization between egg and sperm
3. Crossing Over
- Occurs only during tetrad formation during Prophase I in Meiosis I.
- Switching of genes sequences between non-sister chromatids in homologous pairs.
- Creates new combination of maternal and paternal genes in gametes: Recombinant gametes
4. Independent Assortment
- Each pair of homologues comes to the metaphase plate during Metaphase I on its own
- Allows for variation in maternal and paternal genes in gametes
- The more pairs of chromosomes, the more possible variation: 2n possible combinations
47
Following Chromosome/chromatids in Meiosis
The final number of chromosomes in 4 daughter cells will always be haploid
Ex. Somatic cell has 4 chromosomes
- G1: 4 chromosomes
- S: 4 chromosomes; 8 total chromatids, 4 pairs
- G2: 4 chromosomes; 8 total chromatids, 4 pairs
- PI: 4 chromosomes; 8 total chromatids, 4 pairs
- MI: 4 chromosomes; 8 total chromatids, 4 pairs
- AI: 4 chromosomes; 8 total chromatids, 4 pairs but 2 chromosomes moving to one end, 2 chromosomes moving to other end
- TI: 2 chromosomes in each daughter nucleus(4 total chromatids in each daughter nucleus)
- After CI: 2 chromosomes in each daughter cell, each chromosome is still a pair of chromatids. Cells are haploid now
- PII (each cell): 2 chromosomes; 4 chromatids, 2 pairs
- MII (each cell): 2 chromosomes; 4 chromatids, 2 pairs
- AII (each cell): 4 chromosomes
- TII (each cell): 2 chromosomes at either end in daughter nucleus
- After CII: 2 chromosomes in each of 4 daughter cells
Check: Somatic (2n) was 4 so haploid (n) should be 2
48
How are traits transmitted from parents to offspring?
An organism’s traits and appearance are controlled by specific forms of proteins. The instructions for making proteins are contained in our genetic material, the nucleic acid DNA. DNA remains in the nucleus of our cells in the form of linear structures called chromosomes. When gametes are formed, the male and female parents pass along their DNA into their respective gametes. Fertilization fuses
the gametes and combines the genetic contribution of each parent into the new offspring. This DNA is now responsible for directing the making of proteins in the offspring.
49
Haploid V Diploid Cells
Haploid cells have only one member of each pair of homologous chromosomes while diploid cells have both members of each pair of homologous
chromosomes. The gametes (egg and sperm) are haploid and therefore have half the normal chromosome number for the given species. All other cell types, other than gametes, are called somatic cells and they have the diploid number which is the full number of chromosomes for that species.
50
Why must fertilization and meiosis alternate in all sexual life cycles?
Meiosis is the process of cell division that produces the gametes which have the haploid number (n) of chromosomes. If meiosis did not make haploid gametes, when gametes joined to form a fertilized egg or zygote, the chromosome number
would double. Meiosis maintains the normal diploid number by halving the number to make the gametes and then allowing the diploid number to be restored
through fertilization.
51
Meiosis I
Prophase I:
- Chromosomes condense
- Crossing over occurs
- Centrosomes move apart
- Mitotic spindle forms
- Nuclear envelope disappears
Metaphase I:
- Homologues at metaphase plate
- Independent assortment
Anaphase I:
- Homologues separate
Telophase I:
- Each pole has 1 of each homologue, still but each a pair of sister chromatids
Cytokinesis: Division of cytoplasm
52
Meiosis II
Prophase II:
- Mitotic spindle reforms
Metaphase II:
- Sister chromatids on opposite sides metaphase plate
Anaphase II:
- Sister chromatids separate
Telophase II:
- Nuclear membrane
53
Meiosis VS Mitosis
Both are forms of cellular division.
Mitosis makes 2 diploid daughter cells that
are identical in genetic makeup to each other and the parental cell.
Meiosis creates 4 unique daughter cells that have their genetic material shuffled through
crossing over and independent assortment. The 4 daughter cells of meiosis are haploid.
54
Independent assortment, crossing over, and random fertilization effect on genetic variation in sexually reproducing organisms
Crossing over occurs during prophase I of meiosis I. It involves the switching of genes between the non-sister chromatids of homologues which allows the novel mixture of maternal and paternal genetic material with new, recombinant
chromosomes.
Another layer of variation occurs during independent assortment which is the random lining up of the homologues during metaphase I of meiosis I.
Between different gametes, there are 2n different possibilities of how the homologues could line up. chromosomesmaternal and paternal chromosomes
line up during.
Finally, it is complete random which sperm fertlizes which egg which creates even more potential variation in the offspring.
