Bio: Meiosis
If nondisjunction happens in anaphase II
1 daughter cell will have 2 copies, 1 will have no copies, and 2 will have 1 copy as normal
What 3 mechanisms contribute to variation in meiosis
1. Independent assortment of chromosomes 2. Crossing over 3. Random fertilization
What are the 4 key differences between mitosis and meiosis
1. Recombination in prophase I in meiosis 2. Homologous pairs allign on the metaphase plate in metaphase I of meiosis, chromosomes allign on the metaphase plate in mitosis 3. Separation of homologos at anaphase I in meiosis sister chromatids remains attached, splits in mitosis 4.Two rounds of cell division in meiosis, one in mitosis
If nondisjunction happens at anaphase I
2 of the daughter nuclei will have both members of that homologous pair, the other 2 will have none
aneuploidy
A chromosomal aberration in which one or more chromosomes are present in extra copies or are deficient in number.
Homologous pairs separate and move to opposite poles during
Anaphase I
Chromatids separate and chromosomes move to opposite poles during which stage of meiosis
Anaphase II
Trisomy and monosomy are examples of
Aneuploidy
Translocation
Change to a chromosome in which a fragment of one chromosome attaches to a nonhomologous chromosome
Polyploidy
Condition in which an organism has extra sets of chromosomes
The most common aneuploidy that allows survival is
Down syndrome (trisomy 21)
A triploid nucleus can undergo meiosis
False, it does not have an even number of chromosomes
Each somatic cell has 46 pairs of chromosomes
False, it has 23 pairs
Attachment points during crossing over is called centromere
False, it's the chiasmata
Haplontic organisms spend most of their time in the diploid stage
False, most time in the haploid stage
A tetrad is visible in prophase I and II
False, only in prophase I
During anaphase I of meiosis sister chromatids are separated
False, sister chromatids remain attached
During meiosis II we still see crossing over, and DNA duplication
False, there is no crossing over and no DNA duplication
Gametes are diploid
False, they are haploid
In metaphase I of meiosis individual chromosomes are positioned in the middle of the cell
False, this happens in mitosis
Matching pairs of chromosomes are called
Homologous chromosomes
Monozygotic is another name for
Identical twins
Contrast prophase I from prophase in mitosis
In prophase I homologous chromosomes stick together in pairs and crossing over occurs and the microtubules attach to the homologous chromosomes not the sister chromatids
The condition of missing a chromosome
Monosomy
How do we get identical twins
One egg is fertilized and early in the cell division the cell will divide in two producing two ppl
During meiosis, segments of nonsister chromatids can trade places. This recombination of maternal and paternal genetic material is a key feature of meiosis. During what phase of meiosis does recombination occur?
Prophase 1
Crossing over produces
Recombinant chromosomes
Diplontic organisms
Spend most of their time in the diploid stage. (ex. humans)
Synpasis
The lining up of homologous pairs of chromosomes so they can cross over
Synapsis
The pairing of replicated homologous chromosomes during prophase I of meiosis.
Most plants and some fungi display alternation of generations which means
They spend an equal amount of time in the haploid and diploid stage
In mitosis during anaphase what would happen to the chromatids
They would separate
What are the goals of meiosis
To reduce the number of chromosomes to haploid To ensure a full complement of chromosomes To generate genetic diversity
What is the condition of having an extra chromosome
Trisomy
Most common form of aneuploidy is
Trisomy 16
A tetraploid nucleus has an even number of chromosomes
True
During early prophase I homologous pairs align and undergo crossing over (recombination)
True
During prophase II the chromosomes condense and attach to the spindle microtubules
True
Each chromosome has one paternal and one maternal copy
True
In both mitosis and meiosis the chromosomes are duplicated during interphase
True
Single celled Eukaryotas and some multicellular organisms can reproduce asexual
True
The 4 chromatids of each pair of chromosomes form a tetrad or bivalent
True
The centromere is also where the spindle microtubules attach during both meiosis and mitosis
True
When starting from a diploid cell meiosis produces two haploid cells by the end of telophase 1
True
When starting from a diploid cell mitosis produces two diploid cells
True
How do we get fraternal (dizygotic) twins
Two eggs are fertilized
Recombination results in
Two recombinant chromosomes and two non recombinant chromosomes
Nondisjunction
When a homologous chromosome pair fails to separate at anaphase I or a pair of chromatids fails to separate at anaphase II
Meiosis starts with a single diploid cell and produces
four haploid cells
What is another name for dizygotic
fraternal twins
During prophase 1 of meiosis
homologous chromosomes stick together in pairs
A cell preparing to undergo meiosis duplicates its chromosomes during
interphase
Gametes-- eggs and sperm-- are made by a special sort of cell division called
meiosis
Each pair of chromosomes lines up independently of the other pairs in which phase of meiosis
metaphase I of meiosis
The correct order of events during meiosis is
prophase I, metaphase I, anaphase I, telophase I, cytokinesis, meiosis II
Meiosis occurs only in
reproductive organs
The part of the chromosome where two sister chromatids are joined
the centromere
Sexual reproduction
two parents give rise to offspring that have unique combinations of genes