Match each event with the appropriate stage of meiosis.
you have to know the stages the cell division is in you wont be able to answer this without a photo
1. Meiosis 1.
2. Meiosis 2.
4A. The chromosome theory of inheritance states that chromosomes are the main carriers of the genetic factors responsible for inheritance.
B. Body cells have two sets of chromosomes while sex cells have one set. Therefore, when two sex cells meet, they form an embryo with two copies of each chromosomes thereby producing a body cell with the exact number of chromosomes. In essence, meiosis maintains the right number of chromosomes of body cells by creating half the number of chromosomes of sex cells.
The synaptonemal complex is formed during the prophase 1 of meiosis. The synaptonemal complex is a s a protein structure that is formed between the homologous chromosomes that form a bivalent. This structure binds and holds homologous chromosomes together and allows crossing over and genetic recombination between them. Crossing over and recombination occur in prophase 1, therefore, the synaptonemal complex disintegrates before the end of prophase 1.
B (Metaphase I)
Meiosis is one of the two types of cell divisions that results in 4 daughter cells (gametes) with each having half the number of chromosomes as the parent cell. During meiosis, cell division occurs twice because before the separation of two halves of a duplicated chromosome called sister chromatids, there still need to be separation of homologous pairs, which is a similar but non-identical pair of chromosome received from both parents. Hence, meiosis occurs in a two step division process; meiosis I and meiosis II.
During Prophase I, which is the first stage of meiosis I, homologous chromosomes pair up side by side to form a structure called TETRAD or BIVALENT and likely undergo crossing over( when segments of homologous chromosomes get broken and refixed interchangeably).
After crossing over, the spindle fibres (from the centrosomes) begin to attach to the centromeres of each chromosomes and move them towards the center of the cell called METAPHASE PLATE. Hence, they become aligned on the equator towards either side of the pole. Each chromosome attaches to microtubules from one pole of the spindle and the two homologues of a pair bind to microtubules from opposite poles. Hence, in Metaphase I, homologous pairs, not individual chromosomes, line up at the Metaphase plate/equator for separation.
The orientation of the line up of homologous chromosomes determines which chromosomes enter into the same cell i.e. the alignment of chromosomes towards the same pole determines which chromosomes enter into the same cell to form the genetic composition of gametes. In an organism with two sets of chromosomes (diploid), there are four possible combinations in which chromosomes are arranged in the metaphase plate, resulting in differences in chromosomal distribution in daughter cells/gametes, the process of independent assortment
The answer is II. Metaphase I VI. Metaphase II
The correct answer is option d.
Based on the given question, the genotype of the male parent is aa, the genotype of the female parent is Aa, and the genotype of the offspring is AAa, showing trisomy characteristics. In the given case, the existence of two A chromosomes shows that the chromosomes non-disjunction at the time of gametogenesis have taken place in the female as she is the only one possessing A allele. Hence, it can be concluded that the disjunction is maternal in characteristic.
The duplication of chromosomes takes place at the time of the S-phase of meiosis. Thus, after going through S-phase, the karyotype of the cell will be (maternal gametogenesis), this set of the chromosome is termed as homologous pair, and the pair of AA or aa is termed as sister chromatids.
The meiotic disjunction takes place in two phases. First, in meiosis I disjunction, in this separation of homologous chromosomes takes place, that is, the maternal cell get differentiated into aa and AA daughter cells. Secondly, in meiosis II disjunction, the separation of sister chromatids takes place into two independent chromosomes, that is, the formation of two cells each comprising chromosome A from the AA cell and the formation of two cells each with chromosome a from the aa cell.
Thus, the phenomenon of non-disjunction would have taken place at the time of meiosis II in the case of a female gamete to exhibit two A chromosomes. Hence, the correct answer is option d.
Prophase I - homologous chromosomes form a tetrad, where they begin cross-over through the process of synapses.
Metaphase - homologous chromosomes then align along the metaphase plate.
Anaphase I - spindles then separate the homologous chromoses, pulling them to opposite poles of the cell
Telephase I - the cell creates a cleavage burrow inwhich the cell divides into two new cells with 46 chromosomes in the process of cytokinesis
The same as mitosis
Prophase II - Nuclear envelope disintegrates, Sister chromatids migrate towards the metaphase plate.
Metaphase II - Sister chromatids align along the plate by their centromere.
Anaphase II- spindles pull the chromatin to opposites poles
Telephase II- cleavage burrow forms and cells seperate through cytokinesis
4 haploid gametes are formed