AP Biology 13

If the progenitor cell of a gamete has 12 pairs of chromosomes during G1 of interphase, how many chromosomes will the following cells have? After S Phase of Interphase:

A. After S phase of interphase After the S phase the chromosomes have duplicated = 24 chromosomes.

Explain how asexual reproduction is different from sexual reproduction.

Asexual reproduction generates offspring that are genetically identical to a single parent, while in sexual reproduction, two parents contribute genetic information to produce unique offspring.

If the progenitor cell of a gamete has 12 pairs of chromosomes during G1 of interphase, how many chromosomes will the following cells have? A daughter cell immediately following cytokinesis 1 of meiosis

B. a daughter cell immediately following cytokinesis 1 of meiosis After cytokinesis I the homologous pairs have separated, each daughter cell = 12 chromosomes.

If the progenitor cell of a gamete has 12 pairs of chromosomes during G1 of interphase, how many chromosomes will the following cells have? A daughter cell during anaphase 2 of meiosis

C. a daughter cell during anaphase 2 of meiosis During anaphase the sister chromatids are separated but new daughter cells not yet formed= 24 chromosomes.

If the progenitor cell of a gamete has 12 pairs of chromosomes during G1 of interphase, how many chromosomes will the following cells have? A daughter cell immediately following cytokinesis 2 of meiosis

D. a daughter cell immediately following cytokinesis 2 of meiosis Meiosis yield haploid cell-- in each daughter cell of meiosis II = 12 chromosomes.

Explain what happens during crossing over and when it occurs in meiosis.

In crossing over, sections of DNA move between homologous chromosomes and allows for independent assortment. Independent assortment states that genes are inherited independently of one another. For meiosis to occur, the chromosomes contributed by each of the organism's parents are duplicated to form sister chromatids. During meiosis I, the sister chromatids of one parent match up with the corresponding sister chromatids of the other parent (synapsis), or its homologous non-sister chromosome, along the metaphase plate. Crossing over then occurs. At a point called a chiasma, homologous chromosomes trade genetic information so that each chromosome is complete but has different information. This random exchange of information is what allows for unique gametes to form and genetic recombination to occur.

How is metaphase 1 different from metaphase of mitosis?

In metaphase 1, tetrads, groups of four chromatids, line up at the metaphase plate with one chromosome facing each pole. The microtubule from one pole are attached to the kinetochores of one chromosome of each tetrad, the same with the other microtubule. In metaphase of mitosis, the centrosomes have now moved all the way to the opposite poles of the cell. The chromosomes are now in the middle of the cell and convene on the metaphase plate, an imaginary plane that is equidistant from the two poles. The kinetochores of sister chromatids, only two, on each chromosome are attached to kinetochore microtubules coming from opposite poles. The number of chromatids connected to each other differ in metaphase 1 and metaphase of mitosis. Tetrads are in metaphase 1 and sister chromatids are connected in metaphase of mitosis

How is sexual reproduction related to gender determination in mammals?

One pair of chromosomes in a human cell is the sex chromosomes. In sexual reproduction, two distinct gametes fuse to form a zygote. The gametes are produced through the process of the meiosis. Each individual gamete only contains one set of chromosomes. So when the male and female gamete fuse, the zygote is diploid, which means it contains two sets of chromosomes. In humans, the sex chromosomes are either X or Y. The female gametes are X only, while the male can have either X or Y. Therefore, the male sperm cell determines the sex of the individual. If the sperm cell gives an X, the zygote will be a female. If the sperm cell gives a Y, the zygote results in a male.

Explain why sexual reproduction increases variation among offspring much more than asexual reproduction does.

There are many reasons sexual reproduction increases variation among offspring. Sexual reproduction increases variation among offspring because the sperm and egg have different combinations of genes than their parent organisms. Asexual reproduction does not have variation from sperm and egg because the offspring is an exact copy of a single parent. In sexual reproduction, crossing over in meiosis shuffles the genes to produce genetic diversity. This is where homologous chromosomes pair up and exchange parts with another. Since homologous chromosomes can only have the same pair of genes or slightly different, the crossing provides shuffling and variation of genetic material. Each cell that carries out meiosis has 23 pairs of homologous chromosomes. Independent assortment is the process in which each homologous chromosome in a pair goes into a separate gamete. Thus, each gamete has only one copy of each gene and that copy may be a different version of the same gene that is in another gamete. Another reason is the process of fertilization, or gamete fusion. Gametes only contain half the amount of DNA of a normal cell, so the two gametes must form together in fertilization. This creates a cell that will be able to form a new organism with a unique combination of genes.

How many possible genetic variations can be produced during meiosis and sexual reproduction?

Three mechanisms that contribute to genetic variation include the independent assortment of chromosomes, crossing over, and random fertilization. In the independent assortment of chromosomes, homologous chromosomes orient randomly at metaphase 1 of meiosis. Each pair of chromosomes will then independently sort maternal and paternal homologues from the other pairs. The possibility of chromosomes increases by the millions during independent assortment. Crossing over produces recombinant chromosomes, that combines genes inherited from a single parent. This happens by homologous portions of nonsister chromatids trading places. DNA from two parents is combined into one chromosome. Random fertilization is when any sperm can fuse with any ovum, an unfertilized egg. This fusion produces a zygote with about 70 trillion diploid combinations. The number of combinations is so high from the 8.4 million possibilities in independent assortment. This is without the addition of combinations from crossing over.

asexual reproduction

the nucleus divides and each chromosome is copied, giving each nucleus the same genetic material. Once the cell divides, the two daughter cells are exact copies of each other. This process is also used in the continual growth and development of a cell and if a cell is damaged.

sexual reproduction

the sperm and egg cells combine in fertilization, creating unique combinations of genes. The process is special cell division following nuclear division which produces sex cells. After fertilization, there are subsequent normal divisions.