Meiosis consists of one DNA replication and two nuclear divisions resulting in 4 daughter cells. The process which provides for genetic variation is crossing over. Crossing over occurs in the early stages when homologous chromosomes move together so that their chromatids form a tetrad. This is called synapsis and allows for the exchange of chromosome sections.
These bivalents line up along the equator during metaphase I, the arrangement of the bivalent is completely random and relative to the orientation of the other bivalents, this is known as the independent assortment of chromosomes. This is followed by anaphase I where the homologous chromosomes separate and move to the opposite poles of the cell. At telophase I the cell divides into two, each cell contains one chromosome from each homologous pair. The second stage of meiosis is similar to mitosis.
6. Gather data: On the DESCRIPTION tab, click Reset. Set DD and dd to any values you like. Fill in the initial values in the table below, and then run the Gizmo for five generations. Record the allele and genotype percentages for each generation in the table below.
A) Meiosis consists of two cell divisions and is broken up into Meiosis I and Meiosis II. At the beginning of the Cell Cycle, in this case there are four chromatids each from the homologous pairs being A, a, B, b. This is the Diploid number (4) meaning it is 2 times the haploid number that will be seen at the end of meiosis II. During the S phase of interphase, the chromatids replicate and reach the end of G2 phase. Now starting meiosis, during the first stage of prophase I the chromosomes condense and pair up through synapsis with their sister chromatids creating AA, aa, BB, bb. After they pair up they go through a process called crossing over, where the homologous chromosomes share a piece of their genetic material with each other. Crossing over allows for the genetic diversity of chromosomes. Now there are four homologous chromosomes Aa, Aa, Bb, Bb, each containing heterozygous alleles because the sister chromatids exchanged genetic information with their homologous pair. During late prophase I, spindle fibers being to form where they will later attach to a homologous chromosomes centromere. The next stage is Metaphase I. During metaphase I, the homologous pairs line up at the metaphase plate, also known to be the center of the cell. The homologous pairs form a tetrad which is considered a group of four homologous chromosomes. These homologous chromosomes orient themselves randomly, which is know as the process of independent
2. How will the alleles for these traits assort into the gametes that each parent might produce? (Hint: For a reminder on how alleles sort independently into gametes, refer to the illustration in Part 2, Question 2, in the Student Guide.)
Human cells carry two copies of each chromosome they have two versions of each gene and the different versions are called alleles. Alleles can be either dominant or recessive. Dominant alleles means you have one copy of the gene or your heterozygous. Recessive alleles means you have two copies of the gene or your homozygous.
The two recessive alleles are both on the same chromosome. Genes A and B completely follow Mendel’s principles of inheritance; genes B and C are physically connected together and never are separated from each other at any time during any cell division cycle or fertilization event. Draw below the gamete genotypes that this individual could produce.
So in this case, the crosses that involve the law of segregation would be the cross between Group 1 (XWY x X+XW) and Group 3 (ap/ap x ap+/ap+). This is also the law of segregation as the cross deals with two different alleles being passed to the offspring (The Linkage, p174). Group 3 specifically deals with the two alleles separating from each other during the crosses (in group 3 apterous is being separated from the other apterous allele and wildtype is separated from wildtype)(Gen.: Analysis & Principles, p23).
First is the law of dominance, this is when one trait is dominant over the other, that other trait is the recessive trait. An example is, when you have an ebony body one parent may be yellow while the other may be ebony. In this case, the yellow body parent was recessive in the offspring. The second law is the law of random fertilisation. This is when any fly can mate with any fly, an example is a normal fly can mate with a normal or apterous fly with normal fly. This occurred in our lab because all of our types of flies were in the one container and they decided which flies wanted to mate with each
The principle of segregation is based on the non-blending of the particles that an offspring would receive from each parent. The principle of segregation relates to question 1 because question 1 talks about traits coming in discrete units, and the principle
In meiosis the pairs of chromosomes (that code for possible outcomes of characteristics) temporarily join and exchange information (crossing over) creating different combinations of gene types (alleles). For example; a pair of chromosomes could be a dominant allele (gene type) and a recessive allele which might code for brown hair. After crossing over it might be recessive which could be blond hair.