Meiosis and Chromosomal Abnormalities Flashcards
What is Meiosis?
The Process of forming haploid cells.
What do most haploid cells?
They are gametes.
What is the process of meiosis involve?
The replication of DNA followed by 2 sets of cell division so the daughter cells contain only one member of each homologous pair and one sex chromosome.
What happens prior to meiosis?
Single stranded chromosomes are replicated to become 2 identical chromatids.
Meiosis steps…
- Prophase I
- Metaphase I
- Anaphase I
- Telophase I
- Prophase II
- Metaphase II
- Anaphase II
- Telophase II and Cytokinesis
What happens in prophase I…
The DNA condenses and the chromosomes appear. spindles start to form and similar chromosomes pair. Adjacent chromatids wrap around each other. The nuclear membrane starts to break down towards the very end.
What is Synapsis?
The act of similar chromosomes pairing.
In prophase where to the chromatids wrap around..
The Chiasmata.
What is Crossing over recombination?
In prophase 1… it is the chance of chromosomes breaking and swapping pieces.
What happns during Metaphase I…
The breakdown of nuclear membrane completed. Spindle fibers attach to the centromeres of chromosomes. Homologous pairs move to the equator of spindle which is now fully formed.
What happens during Anaphase I…
Spindles retract towards poles of the cell causing pairs to separate.
What happens during Telophase I…
Chromosomes unwind. spindle breakdown and a nuclear membrane forms around each set of chromosomes.
What happens during Prophase II…
New spindle forms and DNA condenses. Chromosomes appear and are double stranded but the daughter cells are haploid.
What happens during Metaphase II…
Chromosomes consisting of sister chromatids line up in a single file across equator of cell. Spindle is corrected to the centromere of chromosome.
What happens during Anaphase II…
Spindle fibers contract and pull sister chromatids to the poles of the cell.
What happens during Telophase II…
New nuclear membrane forms around each bundle of cells. Spindles break down. chromosomes unwind and disappear and a new nucleoli forms.
What happens after Telophase II?
Cytokinesis is completed and 4 daughter cells are formed.
What are Mendel’s Laws?
Mendel’s Law of Segregation and Mendel’s Law of independent Assortment.
What is Mendel’s Law of Segragation?
Two chromosomes of homologous pairs separate during meiosis I and end up in different gametes. The separation of maternally and paternally derived members of the homologous pair is random.
What is Mendel’s Law of Independent Assortment?
How one pair of chromosomes, and hence alleles, separates is independent of how a different pair on different chromosomes separate. All combinations are possible.
What is the action of Fertilisation?
Occurs when two haploid gametes fuse to form a diploid cell.
What is a fertilized diploid cell called?
A zygote.
What happens to the Zygote once fertilized?
It divides down by meiosis to form an individual (human, animal…)
What are some errors in meiosis?
The separation of chromosomes fails in meiosis II or meiosis II. Aneuploidy. Polyploidy.
What is a fail in chromosomal separation called?
A non disjunction.
What is Aneuploidy?
A condition which occurs when a gamete carrying a chromosomal non-disjunction fuses with a normal gamete and the resulting zygote develops. Normally someone with Aneuploidy has more or less then the normal number of chromosomes.
What is having 3 copies of a chromosome called?
A trisomy.
What is having 1 copy of a chromosome called?
A monosomy.
