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Unit 4 test
Transcript of Unit 4 test
By Chance Williams
Describe Mendel's principle of heredity.
The inheritance of biological characteristics is determined by individual units called genes which are passed from parent to offspring.
Where two or more forms (alleles) of the gene for a single trait exist, some alleles may dominant and others may be recessive.
In most sexual reproducing organisms, each adult had two copies of each gene, one from each parent. These genes segregate from each other when gametes are formed.
Alleles for different genes usually segregate independently of each other.
Describe and give the products of Meiosis.
Meiosis-is a process in which the number of chromosomes per cell is cut in half through the seperation of homologous chromosomes in diploid cell.
Meiosis 1- The chromosomes pair up in prophase 1 they each replicate chromosome pairs with its corresponding homologous chromosome. The pairing forms a structure called a tetrad, which contains four chromatids. As the homologous chromosomes form tetrads they undergo a process called crossing-over. The chromosomes cross over one another then exchange alleles and form a new combination of alleles in the cell.
Next Metaphase 1 and Anaphase 1-During metaphase 1 of meiosis,paired chromosomes line up across the centeof the cells. During anaphase 1, spindles fibers pull each chromosome pair toward opposite ends of the cell.
Telophase 1 and cytokinesis-When anaphase 1 is complete, the separated chromosomes cluster at opposite ends of the cell. The next phase is telophase 1 in which a nuclear membrane forms around each cluster of chromosomes. Cytokinesis follows telophase 1 forming two new cells.
Meiosis 2- Both cells now enter a second meiotic division. Unlike the fist division neither cell goes through a round of chromosome replication before entering meiosis 2.
Prophase 2-The chromosomes become visible and do not form tetrads because they are already seprated during meiosis 1.
Metaphase 2 Anaphase 2 telophase 2 and cytokinesis- During metaphase 2 chromosomes line up in the center of the cell a the cell enters anaphase the paired chromatids separate. The final four phases of meiosis 2 are similar to those in meiosis 1, however four haploid daughter cells is the result. The four cells contain just two chromosomes each.
Describe the non-disjunction and give one example.
When homologous chromosomes fail to separate this mistake is known as non-disjunction.For example two copies of an autosomal chromosome fail to separate during meiosis and individual may be born with three copies of that chromosome.This condition is called trisomy.The most common form of trisomy, involving three copies of chromosome 21 is Down syndrome.
Describe the process of transforming genes
Bacteria are organisms that have the unique ability to take in foreign DNA and replicate it. This gives them an evolutionary advantage and helps them survive changes in their environment. For example, bacteria can acquire DNA that makes them resistant to antibiotics.
After death some bacteria release their DNA into the environment.
Other bacteria can come into contact with these fragments, take them up and mix them into their DNA by crossing over.
The genetically transformed cell is called a recombinant cell because it has a different genetic makeup than the two bacteria it descended from.
All of the descendants of the recombinant cell will be identical to it.