Chapter Text
Modern Cell Theory dictates that all organisms are made of cells (unicellular/multicellular), cells are the smallest unit of life, cells are made from pre-existing cells, DNA is passed from parent to offspring, all cells have the same chemical composition, and energy flow is done within the cell.
Characteristics of Life: cellular organization, metabolism, growth, homeostasis, reproduction, evolution, and response to stimuli.
Chromosomes are a chain of DNA mixed with a group of stabilizing proteins. The genetic material is made into chromatin, a thread-like fibre that is periodically woven with histones. It is only in its chromosome form during mitosis/meiosis. There are 23 pairs of chromosomes (46 singular chromosomes), with 22 being autosomal and 1 being a sex pair.
DNA are a bunch of amino acids called nucleotides formed into a double helix (with the support of phosphate and deoxyribose sugar), with the main 4 being adenine, guanine, thymine, and cytosine. RNA is similar and is considered a 'missing part' of DNA, only having one helix. All of the nucleotides are the same, except for guanine, which is replaced by uracil.
Genes are a special stretch of DNA with specific nucleotides to be read in threes. They control the types of proteins being made and therefore the proteins' function (which is dependant of its size and shape). GMOs are an example of genes being able to be altered, with some genes being removed or replaced entirely. Traits are a mix of environmental and genetic influences.
Terminology so far: chromatin (stringy genetic material), chromosome (coiled DNA consisting of 2 (sister) chromatids), (sister) chromatids (one half of a chromosome, almost like its wing connected by a body (centrosome), homologous (same), somatic cells (body cells), gametes (sex cells/reproductive cells), gene (segment of a DNA strand to create a specific protein), alleles (different forms of the same gene).
Women will have 23 homologous chromosomes, while men will have 22 plus their sex pair that includes an X and a Y chromosome. The Y looks like a slightly deformed X chromosome and can be seen via a karyotype. Different types of things (like non-disjunction) can lead to an odd number of chromosomes. This refers to polysomy (number of chromosomes), with the variation between trisomy (three chromosomes) and monosomy (one chromosome, which is usually unsurvivable).
Diploid refers to a pair of chromosomes (2n), while haploid is one single chromosome per pair (n)
Mitosis is a process of duplicating the cell with 6 phases. Interphase, prophase, metaphase, anaphase, telophase, cytokinesis. Interphase includes the multiplication of the DNA and the life of the maturing cell. Prophase includes the dissolution of the membrane, as well as the formation of the actual chromosomes. Metaphase is the lining up of all the chromosomes and migration of the centrioles (which sit at the side of the cell, producing spindle fibres to pull the chromosomes by the centromeres). Anaphase is the pulling and separation of the chromosomes to the different poles of the cell. Telophase is the uncoiling of said chromosomes, slowly forming the nuclei back together. Cytokinesis is the splitting of the cytoplasm and the final step before having 2 new diploid daughter cells from one mother cell.
Meiosis is a similar process, only that it results in 4 haploid cells and is done in gametes. Meiosis follows the same steps as mitosis, except they do it twice with meiosis I and II. Meiosis I is exactly like mitosis, with the splitting of one adult cell into two daughter cells. There are also different things done during prophase I to ensure genetic diversity, such as pairing up to perform recombination and crossing over. Meiosis II is when the daughter cells split once more to make 4 viable haploid granddaughter cells.
Meiosis is slightly different in women, only resulting in 1 viable egg and 3 polar bodies. Polar bodies are deformed and malnourished eggs that will never mature (though in plants, they are used to feed the embryo).
Non-disjunction is the failure of the centromere during anaphase, resulting in an entire chromosome being pulled towards a cell (meaning there will be a trisomy/monosomy). If it happens during meiosis I, there will be 4 damaged cells (2 monosomy/trisomy). If it happens during meiosis II, there will be 2 healthy cells and 2 damaged cells (1 monosomy/trisomy).
Another error in meiosis can be caused by chromosome mutation (deletion/insertion, duplication, inversion, translocation). These all affect the way the genes are read as they are read in threes!
Aneuploidy refers to the addition or subtraction of a chromosome to the regular diploid system (2n+/-1). Some common trisomies are on 21 (Down syndrome), 18 (Edward's syndrome), and 13 (PATAU syndrome).
Gregor Mendel (1822-1884) is the person responsible for making 'Mendelian genetics,' which provided the basis for the understanding of genetics.
Terminology: p generation (parent generation), F (filial generation/ offspring), homozygous (same), heterozygous (different), phenotype (observable characteristics), genotype (genetic characteristics), hemizygous (only linked to men with sex-linked traits).
For phenotypes, they will always use ratios.
There are dominant (UPPERCASE) and recessive traits (lowercase); the dominant trait will always win. Think of dominant as alpha and recessive as omega.
To determine the phenotype/genotype of an F1/F2, we can use a Punnett square (either 4/16). When doing dihybrid Punnett squares, use foil to determine the distribution of the genes.
Pedigrees are charts of ancestry based on the recorded phenotype/genotype of alive/dead relatives to track a specific trait and its effects. Please refer to notes/ pictures for the correct drawing of a pedigree chart (make sure it includes roman numerals, number labelling under each member, and the appropriate shading/symbols). The roman numerals refer to the generation, while the order lists the oldest to youngest. When referring to a single member, use (roman numeral - order number).
Women are the only people who can be carriers (people affected who are asymptomatic). They can have a child who will either be autosomal dominant (dominant phenotype) or autosomal recessive (recessive phenotype).
Incomplete dominance is when there is a blending of 2 domainant phenotypes. Co-dominance is where there is no blending, with both phenotypes expressed at the same time.
Human blood types also follow these variations in genes, with the blood types A, AB, B, and O as a result. AB are considered the universal recipients, while O are the universal donors. With blood types come antigens (antibody generators) that create proteins to clump/destroy any unrecognized cells.
Some traits can be specifically linked to an X or Y chromosome. Everyone needs at least one X chromosome to survive, as it houses most of the basic genetic information for human functions. Women need at least 2 affected X chromosomes to express the sex linked trait.
In every cell, 1 X chromosome will deactivate before shrinking up into a Barr body, no longer being able to express any alleles. This happens in embryonic cells and is completely random (varies from cell to cell).