1.When did the modern science of genetics begin and who was its founder?
The modern science of genetics began in the 1860s, when an Augustinian monk named Gregor Mendel deduced the fundamental principles of genetics by breeding garden peas.
2.What does the law of segregation states?
It states that a perm or egg carries only one allele for each inherited charcater because allele pairs separate from each other during the production of gametes.
3.Do sex-linked disorders affect more men or women?
Sex-linked disorders affect mostly males.
Five main facts from the reading:
1. The science of genetics has ancient roots.
2.Genetic traits in humnas can be tracked through family pedigrees
3.Many inherited disorders in humans are controlled by a single gene.
4.Many genes have more than two alleles in the population.
5.A single character may be influence by many genes.
Diagram:
This is an example of a Punnet square, which represents the fertilization between a male and female flower.
Link: http://bio8.wikispaces.com/4%29Mendelian+Genetics
Summary:
The introduction section of the chapter talks about that there are many different types of dogs, due to the fact that when one type of a dog fertilizes another type of a dog, the production is a new type of a dog, similar to its parents. Genetics is the science of heredity and it has ancient roots. The first person to purpose an explanation to genetics was the physician Hippocrates, and even though he was not right, he put the basis of genetics. Experimental genetics began in an abbey garden. The modern science of genetics began in the 1860s, when an Augustinian monk named Gregor Mendel deduced the fundamental principles of genetics by breeding garden peas. He correctly argued that parents pass on to their offspring discrete heritable factors. A heritable feature that varies among individuals, such as flower color, is called a character. Each variant for a character, such as purple or white flowers, is called a trait. Perhaps the most important advantage of pea plants as an experimental model was that Mendel could strictly control matins. Consequently, pea plants usually self-fertilize in nature. That is, sperm-carrying pollen grains released from the stamens land on the egg-containing carpel of the same flower. He also used cross-fertilization sometimes, which is fertilization of one plant by pollen from a different plant. Mendel worked with his plants until he was sure he had true-breeding varieties - that is, varieties for which self-fertilization produced offspring all identical to the parent. In the language of plant and animal breeders and geneticists, the offspring of two different varieties are called hybrids, and the cross-fertilization itself is referred to as a hybridization, or simply a cross. The true-breeding parental plants are called the P generation, and their hybrid offspring are the F1 generation. When F1 plants self-fertilize or fertilize each other, their offspring are the F2 generation. Mendel's law of segregation describes the inheritance of a single character. A cross between a pea plant with purple flowers and one with white flowers is called a monohybrid cross, because the parent plants differ in only one character. There are alternative versions of genes that account for variations in inherited characters. For example, the gene for flower color in pea plants exists in two versions, one for purple and the other for white. The alternative versions of a gene are now called alleles. For each character, an organism inherits two alleles, one from each parent. These alleles may be the same or different. An organism that has two identical alleles for a gene is said to be homozygous for that gene. An organism that has two different alleles for a gene is said to be heterozygous for that gene. If the two alleles of an inherited pair differ, then one determines the organism;s appearance and is called the dominant allele; the other has no noticeable effect on the organism;s appearance ans is called the recessive allele. A sperm or egg carries only one allele for each inherited character because allele pairs separate from each other during the production of gametes. Because an organism's appearance does not always reveal its genetic composition, geneticists distinguish between an organism;s expressed, or physical, traits, called its phenotype, and its genetic makeup its genotype. Homologous chromosomes bear the alleles for each character. The law of independent assortment is revealed by tracking two characters at once. A dihybrid cross is a mating of parental varieties differing in two characters. Each pair of alleles segregates independently of other pairs of alleles during gamete formation. This is called Mendel's law of independent assortment. Geneticists use the testcross to determine unknown genotypes. A testcross is a mating between an individual of unknown genotype and a homozygous recessive individual. Mendel's laws reflect the rules of probability. Genetic traits in humans can be tracked through family pedigrees, by going back to the previous generations and finding out if they had the trait or not. many inherited disorders in humans are controlled by a single gene. Most human genetic disorders are recessive. They range in severity from relatively mild, such as albinism, to life-threatening, such as cystic fibrosis. Most people who have recessive disorders are born to normal parents who are both heterozygous - that is who are carriers of the recessive allele for the disorder but are phenotypically normal.Although many harmful alleles are recessive, a number of human disorders are caused by dominant alleles. New technologies can provide insight into one's genetic legacy. There are several ways of testing: genetic testing, fetal testing, fetal imaging, which uses ultrasound imaging, newborn screening, and ethical considerations. Incomplete dominance results in intermediate phenotypes. The F1 offspring of Mendel's pea crosses always looked like one of the two parental varieties. This situation is called complete dominance; the dominant allele has the same phenotypic effect whether present in one or two copies. But for some characters, the appearance of F1 hybrids falls between the phenotypes of the two parental varieties, an effect called incomplete dominance. Many genes have more than two alleles in the population. For instance, the ABO blood group phenotype in humans involves three alleles of a single gene. A single gene may affect many phenotypic characters. Most gene influence multiple characters, a property called pleiotropy. A single character may be influenced by many genes. Mendel studied genetic characters that could be classified on an either-or basis, such as purple or white flower color. However, many characteristics, such as human skin color and height, vary in a population along a continuum. Many such features result from polygenic inheritance, the additive effects of two or more genes on a single phenotypic character. The environment also affects many characters. Chromosome behavior accounts for Mendel's laws. Genes on the same chromosome tend to be inherited together. Genes located close together on the same chromosome tend to be inherited together and are called linked genes. Crossing over produces new combinations of alleles. Geneticists use crossover data to map genes. Chromosomes determine sex in many species. Many animals, including all mammals, ahve apir of sex chromosomes, designed X and Y, that determine an individual's sex. Sex-linked genes exhibit a unique pattern of inheritance. A sex-linked gene is a gene located on either sex chromosome, and it is a lot different than a linked-gene. Sex-linked disorders affects mostly males. Hemophilia, red-green color blindness. and Duchenne muscular dystrophy are disorders caused by sex-linked genes, and they are seen more often in males, than in females. The Y chromosome is also very valuabe, because provides clues about human male evolution.
Key Terms:
1.Character - a heritable feature that varies among individuals, such as flower color.
2.Trait - each variant for a character, such as purple or whit flowers.
3.Hybrids - the offspring of two different varieties.
4.Alleles - the alternate versions of a gene.
5.Homozygous - an organism that has two identical alleles for a gene.
6.Heterozygous - an organism that has two different alleles for a gene.
7.Achondroplasia - a serious dominant disorder; a form of dwarfism.
8.Huntington's diseas - a degenerative disorder of the nervous system that usually does not appear until 35 to 45 years of age.
9.Complete dominance - the dominant allele has the same phenotypic effect whether present in one or two copies.
10.Incomplete dominance - the appearance of F1 hybrids falls between the phenotypes of the two parental varieties.
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