Meiosis Book Notes Flashcards
What happens during meiosis?
Consists of two nuclear divisions that together reduce the # of chromosomes to the haploid # in preparation for sexual reproduction
Products in meiosis are
Genetically different
Functions of meiosis
1) reduce chromosome # from diploid to haploid
2) ensure that each of the haploid products has a complete set of chromosomes
3) generate genetic diversity among products
Meiotic division reduces
The chromosome #
Homologous chromosomes come together to pair and homologous chromosome pairs separate
Meiosis I
No DNA replication, product = 4 cells each containing haploid # of chromosomes but not genetically identical
Meiosis II
Chromatid exchanges during Meiosis I generate
Genetic diversity
Homologous chromosomes pair by adhering along their lengths
Synopsis
Chromosomes appear to repel each other but (blank) keep them together
Cohesins
Regions having attachments take on x-shaped appearance
Chiasmata
Chiasma reflects an exchange of genetic material between nonsister chromatids on homologous chromosomes
Crossing over
Result of crossing over- increases genetic variation
Recombinant chromatids
During meiosis homologous chromosomes separate by
Independent assortment
Explain independent assortment during meiosis
- diploid organism has two sets of chromosomes (2n)
- meiosis I (synopsis) maternal chromosomes pair with paternal homólogas
Result of independent assortment
Each newly formed cell receives 1 member of each homologous pair so chromosome # is decreased from diploid to haploid
Steps in meiosis I
Early prophase I Mid-prophase I Late-prophase I Metaphase I Anaphase I Telophase I
Early prophase I
Chromatin begins to condense following interphase
Mid-prophase I
Sysnapsis aligns homóloga and chromosomes condense further
Late-prophase I to prometaphase
Chromosomes continue to coil and shorten. The chiasmata reflect crossing over. The exchange of genetic material between nonsister chromatids in a homologous pair
Nuclear envelope breaks
Metaphase I
The homologous pairs line up on equatorial metaphase plate
Anaphase I
The homologous chromosomes (each with 2 chromatids) move to opposite poles
Telophase I
The chromosomes gather into nuclei and the original cell divides
Steps in meiosis II
Prophase II
Metaphase II
Anaphase II
Telophase II
Products of meiosis II
Each of the 4 cells has a nucleus with a haploid # of chromosomes
Prophase II
Chromosomes condense again, following a brief interphase with no DNA replication
Metaphase II
Centromeres of the paired chromatids line up across the equatorial plates of each cell
Anaphase II
Chromatids finally separate, becoming chromosomes in their own right, and move to opposite poles
Why do cells have different genetic makeup after meiosis
Crossing over and independent assortment
Telophase II
The chromosomes gather into nuclei and the cells divide
Meiosis II =separation of sister chromatids into
Daughter nuclei
Homologous chromosomes fail to separate or remain together and migrate the the same pole which results in the production of andhploid cells
Nondisjunction
Condition in which 1 or more chromosomes are either lacking or present in excess
Aneuploidy
Occurs when gamete has 2 copies of chromosome 21
Down syndrome
3 copies of chromosome
Trisomic
Recognition may lead to miscarriage in humans
A piece of a chromosome may break away and become attached to another chromosome
Translocation
Pictograph of chromosomes made- image of individual chromosomes manipulated to pair them and place in an orderly arrangement
Karotype
#, shapes, and sizes of chronometer in cell Aid in diagnosis of chromosomal abnormalities
Karyotype
Have more than 2 complete sets of chromosomes
Polyploid
Use of polyploid plants in nature because larger example
Wheat
