2.2 Meiosis Flashcards
In what type of cells does meiosis occur?
IN gametes, and results in four nonidentical sex cells.
What is the result of meiosis 1?
What is the result of meiosis 2?
Meiosis 1- homologous chromosomes being separated, resulting in 2 haploid cells (reductional division)
Meiosis 2- similar in mitosis in that it results in separation of sister chromatids without a change in ploidy. (equational division)
You could say that in Meiosis, there is one round of replication and two rounds of division.
What happens in prophase 1?
How is this different than mitosis?
Chromatin condenses into chromosomes
Spindle apparatus forms
Homologous chromosomes come together and intertwine in a process called synapsis, where each chromosome consists of two sister chromatids, so each synaptic pair contains four chromatids and is referred to as a tetrad
The homologous chromosomes are held together by a group of proteins called the synaptonemal complex.
What is crossing over and where does it occur in meiosis?
Occurs during prophase 1
Chromatids of homologous chromosomes may break at the point of contact, called the chiasma and exchange equivalent pieces of DNA.
**Crossing over occurs between homologous chromosomes, NOT sister chromatids, Chromatids are identical, so there would not be any change of information if they did cross over.
Can be characterized as a single crossover or double crossover, depending on the number of cross overs.
What is Mendel’s Second Law of Independent Assortment and which part of meiosis is it related to?
States that the inheritance of one allele has no effect on the likelihood of inheriting certain alleles for other genes.
Related to prophase 1
What happens in Metaphase 1?
Homologous pairs (tetrads ) align at the metaphase plate, and attach to a separate spindle fiber by its kinetochore.
In mitosis- each chromosome is lined up on the metaphase plate by two spindle fibers
In meiosis- homologous chromosomes are lined up across from each other at the metaphase plate and are held by one spindle fiber
What happens during anaphse 1?
Homologous pairs separate and are pulled to opposite poles. This is called disjunction.
During disjunction, each chromosome of paternal origin separates from its homologue of maternal origin, and either chromosome can end up in the either daughter cells.
The separation of the two homologous chromosomes is referred to as segregation.
If a chromosome failed to separate, it may result in a gamete having two copies, such as resulting in trisomy 21, Klinefelter and Turner syndromes.
what is the result of meiosis 1?
The daughter cells are haploid.
What happens during telophase 1?
A nuclear membrane forms around each nucleus.
Then the cell divides into two daughter cells by cytokinesis.
There may be a short rest period during which the chromosomes partially uncoil, called interkinesis
What happens in Meiosis II?
What is splitting from each other in anaphase II vs anaphase 1?
Sister chormatids, NOT the homologues, are separated from each other.
What happens in prophase II?
The nuclear envelope dissolves, the nucleoli disappear, and the centrioles migrate to opposite poles, and the spindle apparatus begins to form.
What happens in metaphase II?
Chromosomes line up on the metaphase plate.
What happens in Anaphase II?
The centromeres divide, separating the chromosome into sister chromatids, and pulled to opposite poles by spindle fibers.
What happens during telophase II?
A nuclear membrane forms around each new nucleus. Cytokienesis follows, and two daughter cells are formed.
What’s the difference between homologous chromosomes and sister chromatids?
Homologous Chromosomes: Homologous chromosomes are related chromosomes of opposite parental origin (i.e. maternal and paternal chromosome 15).
Sister Chromatids: Are identical copies of the same DNA that are held together at the centromere.
