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Transcript of Genetics
Work of Mendel
All living things on earth have sets of traits passed down from its parents. The study of heredity known as genetics helps us learn the characteristics of all living organisms. With the work of Gregor Mendel we have the modern science of today. Mendel was born in what known as Czech Republic in 1822. After being accepted a cleric he spent several years on studying mathematics and science at the University of Vienna. He then spent more than a decade in a monastery and educating students at a high school. Situated at the monastery Mendel also worked in the monastery's garden and from that point foward he changed the way we look at Biology forever. Mendel started with pea plants primarily because they are insignificant, easy to grow, and a single pea plant can produce an abundant number of offspring. Scientists call these pea plants, "model systems and these model systems can help scientists know how other organisms function.
Mendel knew that the male part of the flower which contains the reproductive cells called sperm. Like wise with the female part of the flower produces the reproductive cells called eggs. During sexual reproduction the female and male cells accompany each other, this process is called fertilization. This process creates a new cell and this new cell adapts into a insignificant embryo sheathed within a seed. Pea flowers are commonly asexual, and this means that the male and female parts fertilize in the same flower. So the offspring that derived from the parents receives the same traits as the parents who bore the flower. In other words the flower adopts the traits from its parents. Mendel's monastery garden had several stocks of pea plants that were true breeding that meant that they were self pollinating and that their offspring would be identical to themselves. A trait is a specific characteristic such as the unique description of the plant.Mendel then decided to cross pollinate his true breed plants and then decided to prevent self pollination. To do this Mendel had to cut the male part of the pea flower and then dusted the pollen from the male part onto a female part from a different plant known as cross pollination. And cross pollination produces a plant that has two different parents. Mendel then studied the results from the parents' offspring. He studied seven different traits of the pea plants and they had two sets of characteristics and then had those plants mate. Mendel then had those mate and called them hybrids.
Genes and Alleles
Each original pair of plants is known as the parental generation in genetic crossing and their offspring are call f1 which means son and daughter for the Latin words filius and filia. Each trait studied, all the offspring only had one of the characteristics of the parent. In each cross , the nature of the other parent, with regard to each trait, suddenly disappeared.The first conclusion he made is what we now understand as inheritance. An organisms' traits are predisposed by factors passed from parental generation to the next and so on. These factors are called genes. The variations in the plants produced interpretations of each trait.The different forms of a gene are called alleles.
Formation of Gametes
Mendels second conclusions called the
Principle of Dominance
. This conclusion states that some are dominant and others are recessive. An organism will display the trait for at least one dominant allele. the organism will only display that trait when the dominant allele does not exist.
formation, alleles segregate from each other
so that each gamete carries only a single copy
of each gene. Each F1 plant makes two types
of gametes—those with the allele for tallness
and those with the allele for shortness. The
alleles are paired up again when gametes
fuse during fertilization.
During gamete formation, the alleles for each gene segregate from each other,
so that each gamete carries only one allele for each gene.Each plant produced tall and short alleles. A capital letter represents a dominant allele. A lowercase
letter represents a recessive allele, Whenever a gamete that carried the t allele paired with the other gamete that carried the t allele to produce an F2 plant, that plant was short. Every time one or both gametes of the pairing carried
the T allele, a tall plant was produced.
Whenever Mendel performed a cross with pea plants, he carefully organized and counted the offspring. Unfortunately , he had plenty of data to analyze. Whenever Mendel crossed two plants that were hybrids for stem height (Tt), about 75 percent of the resulting plants were tall and about 25 percent were short. When analyzing his data, Mendel realized that the principles of probability could be used to explain the results of his genetic crosses
The F1 Cross
The traits controlled by the recessive alleles reappeared in the
second generation.About a quarter of the F2
plants showed the trait controlled by the recessive
Segregation to predict results
Mendels drive and determination lead him to venture into a world of new possibilities
Alleles segregate during gamete formation in every bit as random as a coin flip. So the principles of probability can be used to predict the results of genetic crosses. Probabilities predict the average outcome of a large number of events. If you fl ip a coin twice, you are likely to get one heads and one tails. However, you might also get two heads or two tails. To get the expected 50 : 50 ratio, you might have to flip the coin many times. The same is true of genetics. The larger the number of offspring, the closer the results will be to the predicted values.
phenotype and genotype
Phenotype and Genotypes
Every organism has a genetic makeup as well as a set of observable characteristics.All of the tall pea plants had the same phenotype, or physical traits. They did not, however, have the same genotype, or genetic makeup. The genotype of an organism is inherited, and the phenotype is largely determined by the genotype. Two organisms may share the same phenotype but have different genotypes.
Punnett squares use mathematical probability to help predict the genotype and phenotype combinations in genetic crosses.following the principle of segregation,
all possible combinations of alleles in the gametes produced by one parent are written along the top edge of the square. The other parent’s alleles are then segregated along the left edge. Next, every possible genotype is written into the boxes within the square.
Futher More Into Dominant and Recessive Alleles
Some alleles are neither dominant or recessive Cases in which one allele is not completely dominant over another are called incomplete dominance.
In incomplete dominance, the heterozygous phenotype lies somewhere
between the two homozygous phenotypes. A Similar situation arises from codominance, in which the phenotypes produced by both alleles are clearly expressed.Many human genes, including one for a protein that controls cholesterol levels in the blood, show codominance, too. People with the heterozygous form of this gene produce two different forms of the protein, each with a different effect on cholesterol levels.
Multiple Alleles/ Polygenic traits
Many genes exist in several different forms and are therefore said to have multiple alleles. A gene with more than two alleles is said to have
. Many traits are produced by the interaction of several genes. Traits controlled by two or more genes are said to be
“many genes". Polygenic traits often show a wide range of phenotypes. The variety of skin color in humans comes about partly because more than four different genes probably control this trait.
Genes and the Envoirment
The characteristics of any organism are not determined solely by the genes that organism inherits. Genes provide a plan for development, but how that plan unfolds also dependson the environment. In other words, the phenotype of an organism is only partly determined by its genotype. Environmental conditions can affectgene expression and infl uence genetically determined traits. An individual’s actual phenotype is determined by itsenvironment as well as its genes.In the case of the western white butterfl y, these changes in wing pigmentation are particularly important. In order to fly effectively, the body temperature of the butterfly must be 28°C–40°C (about 84°F–104°F). Since the spring months are cooler in the west, greater pigmentation helps them reach the body temperature needed for flight. Similarly, in the hot summer months, less pigmentation enables the moths to avoid overheating.
A fruit fly a body cell in an adult fruit fly has eight chromosomes Four of the chromosomes come from its male parent, and four come from its female parent. These two sets of chromosomes are homologous.A cell that contains both sets of homologous chromosomes is said to be diploid, meaning “two sets.” The diploid cells of most adult organisms contain two complete sets of inherited chromosomes and two complete sets of genes Some cells contain only a single set of chromosomes, and therefore a single set of genes. Such cells are haploid, meaning “one set.” The gametes of sexually reproducing organisms.
Phases of Meiosis
Meiosis is a process in which the number of chromosomes per cell is cut in half through the separation of homologous chromosomes in a
diploid cell.Meiosis I Just prior to meiosis I, the cell undergoes
a round of chromosome replication during