Genetics PDF

Genetics is the branch of biology that focuses on the inheritance of traits. Heredity is the transmission of traits from parent to offspring. Passing down traits. Trait is a characteristic of an individual. Gene is a sequence of DNA that codes for a specific protein. An allele is different versions...

Genetics is the branch of biology that focuses on the inheritance of traits. Heredity is the transmission of traits from parent to offspring. Passing down traits. Trait is a characteristic of an individual. Gene is a sequence of DNA that codes for a specific protein. An allele is different versions of a gene. Genes divide during mitosis and meiosis which involves the separation of the chromosomes that carry genes. In Meiosis genetic material is accurately passed on and mixed to create genetic diversity in offspring, particularly during sexual reproduction. Meiosis has two divisions. Meiosis 1 and Meiosis 2. The crossing over occurs in prophase 1 in meiosis. The chromatids of these homologous chromosomes physically exchange segments of DNA in a process called crossing over or recombination. Meiosis produces haploid cells which are gametes. Those gametes are phenotypes which determine your eye color, hair color, etc. Phenotypes are observable characteristics or traits of an organism. Genotype refers to the genetic construction of an individual. We use letters to name the alleles to have them as place holders for the whole genetic sequence. Dominant allele is an allele that determines the phenotype of a heterozygous individual. Recessive allele: is an allele whose phenotype is only expressed in homozygous individuals. Homozygous means having two identical alleles of a certain gene. Heterozygous means having two different alleles of a certain gene. We get one chromosome from our mom and one from our dad. Gregor Mendel was the father of genetics. He discovered the inheritance of traits in pea plants. He used peas because they produce in large numbers, are small, and are inexpensive to care for. They can be manipulated experimentally because peas can self fertilize and are easy to breed. He began artificial selection which is creating what you want to create, for example purple corn. In his first experiment he had heterozygous offspring even though he had a homozygous recessive and homozygous dominant female and male. Punnett squares are used to predict the cross between two individuals. Mendel’s law of segregation states alleles of each gene segregate during the formation of gametes (meiosis). Every egg and sperm carries only one copy of each gene. An individual with a dominant phenotype does not have to be homozygous dominant for that trait. It could also be heterozygous. A dominant allele is one that expresses its trait even if only one copy(allele) is present. A recessive allele requires two copies (homozygous recessive) to express its trait. Recessive alleles are only expressed when both parents contribute the recessive gene. Incomplete dominance occurs when the phenotype of a heterozygous individual is a blend or intermediate of the two homozygous parental phenotypes. Complete dominance is a genetic phenomenon where one allele completely masks the expression of the other allele in a heterozygous individual. In complete dominance, the dominant allele completely determines the organism’s phenotype and the recessive allele only influences the phenotype when the organism is homozygous recessive. Monohybrid is a genetic cross that examines the inheritance of one trait. Dihybrid is a genetic cross that examines the inheritance of two traits. Codominance is a genetic phenomenon where both alleles in a heterozygous individual are fully expressed. For example blood type. Multiple alleles occur when three or more alleles for the same gene exist within a population. Multiple alleles allow for a high variation. Polygenic inheritance refers to the pattern of inheritance where multiple genes determine a single trait either phenotype or genotype. An example: human height, bmi, weight, eye color. Both alleles are expressed in blood types. Polygenic means many genes. Discrete traits:inherited traits that exhibit distinct phenotypes. Each gene has a small effect on the trait resulting in a normal distribution of the trait in a population. The distribution is measured using bell curves. An example of a polygenic inheritance is your skin color. Species variation refers to the differences in the physical behavioral, and genetic characteristics of individuals within a species. A species refers to a group of organisms that share common characteristics and are capable of interbreeding to produce fertile offspring. Species variation helps with evolutionary adaptation. Genetic variation and evolution is influenced by the environment for example the food resources, predators, prey, weather conditions.