Big Picture: Genetics, heredity, DNA
Principles and/or Concepts:
Genetics - Genetics is the branch of science that explores genes, heredity, and different traits in living organisms. Geneticists learn about how traits are passed from parents to their offspring, which will benefit us humans in helping us cure and prevent more genetic diseases and allowing us to breed better plants and animals. Genetics includes examining the molecular structure and function of genes, how genes behave in an individual cell or an entire organism, and how genetic variations occur in populations (“Genetics”)
Heredity/Inheritance - Heredity is when traits or characteristics get passed down from parent to offspring, from one generation to the next. This “chain” is also called inheritance; however, not all cases are this simple due to the different arrangement of the chemical bases in DNA (“Heredity and Genetics”).
DNA - DNA stands for deoxyribonucleic acid, the molecule of heredity material and genetic code for all organisms. Four chemical bases, called adenine (A), guanine (G), thymine (T), and cytosine (C), are arranged in a certain order to form sentence-like codes that determine the traits of each particular organism. In order to make base pairs, A always pairs up with T, and G always pairs with C. Each base also attaches to a sugar molecule and a phosphate molecule, forming a nucleotide. Finally, many nucleotides twist around in a spiral-shaped double helix. This double helix looks sort of like a coiled ladder since the two strands that the nucleotides created are parallel. DNA can replicate, which means that when cells divide, each new cell has the exact DNA of the old one, allowing it to continue the same functions and processes (“What is DNA?”).
Gene - Genes, which are located on chromosomes, determine each trait that is inherited. They specify the structure of proteins that make up each cell (Juan).
Chromosome - A chromosome has a structure similar to thread. Many genes are attached to this thread of protein. There is no exact number of chromosomes because it varies for plants and animals. However, a human has 46, or 23 pairs grouped together - 23 inherited from the father and 23 from the mother. Only 1 determines gender; the remaining 22 control other physical characteristics (Purchon).
Gregor Mendel - This scientist discovered the principles of heredity - that the inheritance of traits was more than simply a mixture of the parents’ characteristics. He cross-bred many generations of pea plants in order to form conclusions about genetic inheritance, dominant and recessive traits, and the 3:1 dominant:recessive ratio that commonly occurs when two parents produce four offspring. Medel learned that inheritance of traits is determined by "units" or "factors" (now called “genes”) that are passed on from parents to offspring unchanged, that organisms inherit one of these “units” from each parent for each trait, and that a trait unseen in an organism may still be passed on to its offspring (O’Neil).
Allele - An allele is a variation of a gene. Humans are diploid organisms because they have two alleles (one from each parent) at each genetic locus, which is a position on a chromosome. Each pair of alleles represents the genotype of a specific gene and helps to determine an organism's phenotype (“Allele”).
Dominant - A dominant allele in the genotype, if present, is always expressed, no matter what the other allele may be. They tend to hide or cover up recessive alleles; therefore, dominant traits are more commonly seen than recessive ones (“Allele”).
Recessive - A recessive trait is only expressed in the phenotype when neither of the alleles present is dominant. Often, the recessive allele is present in the genotype but cannot be seen due to a dominant allele masking it. If an organism carries one dominant and one recessive allele, then the dominant phenotype is the one that is expressed (“Allele”).
Genotype - Genotype is the genetic makeup of an individual. It refers to the alleles that are present and not necessarily what is seen (“Genotypes and Phenotypes”).
Phenotype - The phenotype is the actual physical characteristics that are seen in an individual. This includes both genetically determined traits such as height and eye color, as well as health, behavior, and preferences. Not all phenotypes are caused by genotypes; some looks and habits are a result of the environment that the individual was exposed to (“What is genotype? What is phenotype?”).
Heterozygous - Homozygous is defined as having two different alleles, a dominant and recessive allele. In this case, the dominant trait will appear in the phenotype (“Genotypes and Phenotypes”).
Homozygous - Homozygous is when an organism has two identical alleles. A homozygous dominant organism carries two copies of the same dominant allele, and a homozygous recessive organism carries two copies of the same recessive allele (“Genotypes and Phenotypes”).
Meiosis - Meiosis occurs during sexual reproduction. A cell divides twice (called Meiosis I and II) and forms four new “daughter” cells, each with twenty-three chromosomes, half the number of chromosomes in the parent cell. This “half” is referred to as haploid (“Meiosis”).
Law of Segregation - According to this law, for any particular trait, the pair of alleles from each parent separate. Only one allele gets passed from each parent on to the offspring. Which of the two alleles in a parent's pair gets inherited is a matter of chance (O’Neil).
Plant Reproduction - Plant reproduction varies between asexual and sexual reproduction. Asxeual reproduction happens when one cell divides into two cells, which causes both cells to be identical. Sexual reproduction occurs two cells combine and create another living cell. This process only requires half of the DNA needed from both cells (“Plant Reproduction - They'll Make More”).
Pollination - Pollination is the process of transferring pollen from the stamen (male part) to the stigma (female part) in a plant. There are two ways to do this. One method, self-pollination, occurs when the plant’s stamen is carried to the same plant’s stigma. The other process, cross-pollination, is when its stamen is transferred to another plant’s stigma (“Pollination”).
Key Words and Quantities With Their Units: Probability, percentage, chance
Formulas, Charts, and Graphs:
Figure 1: The Punnett Square displays and calculates the probability for receiving a particular gene.
Figure 2: This figure shows the structure of DNA.
Figure 1: The Punnett Square (Stanley)
Figure 2: DNA Structure (Pray)