Unit 10: Genetics Chapter 9: Read P. 145-167
10.0 Genetics
The Definition of Genetics The study of heredity and how traits are passed on through generations.
Gregor Mendel: The Father of Genetics Gregor Mendel studied various characteristics of pea plants. His results were many and significantly important to all and any living organism that sexually reproduces. From his experiments, he listed simple rules, known as patterns of inheritance that make it easier to understand the characteristics received by offspring that are may or may not be different than their parents. It is these patterns of inheritance that we will examine in detail and involves all of Mendel's work over time. Here, in the course content, the theory or definition of these rules will be given.
Mendel's Laws of Heredity Gregor Mendel, through his work on pea plants, discovered the fundamental laws of inheritance. He deduced that genes come in pairs and are inherited as distinct units, one from each parent. Mendel tracked the segregation of parental genes and their appearance in the offspring as dominant or recessive traits. He recognized the mathematical patterns of inheritance from one generation to the next. 1) The Law of Segregation: Each inherited trait is defined by a gene pair. Parental genes are randomly separated to the sex cells so that sex cells contain only one gene of the pair. Offspring therefore inherit one genetic allele from each parent when sex cells unite in fertilization. 2) The Law of Independent Assortment: Genes for different traits are sorted separately from one another so that the inheritance of one trait is not dependent on the inheritance of another. 3) The Law of Dominance: An organism with alternate forms of a gene will express the form that is dominant.
Principle of Segregation
Law of Independent Assortment
Law of Dominance
Key Terms Important for Genetics True-Breeding: Varieties or organisms for which their genetics are identical to their parents, such as a pure breed animal. Hybrids: The result in offspring of two different true breeding varieties that have been cross- fertilized or simply crossed. P Generation: Parental organisms. F1 Generation: Offspring from the P generation. F2 Generation: Offspring from the F1 generation. Monohybrid Cross: Parental organisms that differ in one trait only and mate. Genes: units that determine heritable traits Allele: Alternate form of genes of which each organism has two; one from each parent which may be the same allele or different. Dominant Allele: the gene that is expressed or 'shows' in an organisms' pair of different allele genes. Symbolized with a capital letter. For example, brown eye color allele is dominant and would be symbolized as 'B. Recessive Allele: the gene that is 'masked' by the dominant allele but makes up the pair of 90 different allele genes. Symbolized with a lower-case letter. For example, blue eye color allele is recessive to any other eye color and would be symbolized as 'b. Punnett Square: a diagram or 'box' that predicts the results of genetic crosses.
Phenotype: the physical traits that the organism displays, such as brown hair, blue eyes. Genotype: the genetic makeup for the phenotype expressed. Cannot be seen by just looking at the organism. For example 'bb' would be the genotype for blue eyes, while 'BB' or 'Bb' would be the genotype to express the same phenotype of brown eyes. https://www.youtube.com/watch?v=n LVulUy7T7E
Homologous Chromosomes: A pair of chromosomes that is identical in structure, shape, size and location of genes. Chromosomes 1-22 of your mother are homologous to chromosomes 1-22 of your father. These chromosomes are known as the autosomes. The only difference in homologous chromosomes is the alleles that are found at gene locations which create genetic variation on fertilization.
Gene Loci: Location of genes on a homologous chromosome. Homozygous: On a pair of homologous chromosomes belonging to an organism, if the alleles at specific gene loci, from each chromosome are identical, it is homozygous. Example: bb (blue eye allele from father and same from mother), BB (brown eye allele from father and same from mother) Heterozygous: On a pair of homologous chromosomes belonging to an organism, if the alleles at specific gene loci, from each chromosome are different, it is heterozygous. Example: Bb (one allele each from mother or father but different from each other). In this case, the dominant allele (B) will be expressed and the recessive masked so the offspring's phenotype will be brown eyes. Dihybrid Cross: Parental organisms that differ in two traits and mate.
Rules of Probability: Is a statistical and mathematical way of determining the results of a genetic cross based on the rule of multiplication. This rule states that to predict the genotype of an organism is by multiplying the separate probabilities of each allele occurring in both gametes (egg and sperm). Autosomes: all other chromosomes except sex chromosomes. Sex Chromosomes: Chromosomes (X and Y) which determine sex of the offspring. XX for female, XY for male.
Monohybrid and dihybrid crosses https://www.youtube.com/wat ch?v=ff6aewmsote https://www.youtube.com/watch?v=p rkhkjfumms
Monohybrid Cross testing just one trait
Dihybrid Crosses Sort out male and female alleles State Genotype and Phenotype
Principle of Independent Assortment: Each pair of alleles separate independently of the other pairs during gamete formation. Results are genetically different and random formation of gametes.
Incomplete Dominance: when offspring have phenotypes that are in between those of their two parents. For example; grey would be an analogy of incomplete dominance between black and white.
Multiple Alleles: when more than two possible alleles exist in a population, however organisms will only carry two of these alleles. Example is blood type for which there are three alleles; A, B, O and as a result of possible combinations after fertilization, four phenotypes, A, B, O, AB.
Codominance: The blood type AB is an example of codominance because when the two alleles A and B are paired neither dominant over the other but codominant and therefore exists a new and separate phenotype. (see both alleles in the phenotype Roan Cow color
How is Sex determined?
Sex Linked Gene: any gene that is found on the sex chromosomes, X and/or Y.
Examples of Sex-linked Traits: Male Pattern Baldness Duchenne Muscular Dystrophy Muscular weakness, progressive deterioration of muscle tissue, and loss of coordination.
Red-green colorblindness Inability differentiate between read and green.
Hemophilia Causes the blood not to clot. If get a cut it may take a along time to clot or internal bleeding may result from a bruise.
Mutations A mutation involving a long segment of DNA. These mutations can involve deletions, insertions, or inversions of sections of DNA. In some cases, deleted sections may attach to other chromosomes, disrupting both the chromosomes that loses the DNA and the one that gains it. Also referred to as a chromosomal rearrangement.
Chromosomal Mutations Linked Genes: genes that are so close together in location on the chromosome that they tend to be 'linked' or carried together during meiosis or formation of gametes and during fertilization of gametes, and are therefore inherited together in the offspring. Crossing Over: an event that occurs during meiosis, when homologous chromosomes that line up at the metaphase plate, may cross over and exchange pieces of chromosome segments resulting in entirely new and different chromosomes.
Genetic disorders Turner syndrome (45,X0), Klinefelter syndrome (47, XXY), and Cri du chat syndrome, or the "cry of the cat" syndrome (46, XX or XY, 5p-). cystic fibrosis, sickle cell anemia, Marfan syndrome, Huntington's disease, and hemochromatosis. an eye disease called Leber's hereditary optic atrophy; a type of epilepsy called MERRF which stands for myoclonic epilepsy with Ragged Red Fibers; and a form of dementia called MELAS for mitochondrialencephalopathy, lactic acidosis and stroke-like episodes. https://www.youtube.com/watch?v=lox_59rsf68