A guide to studying for the MCAT.
A guide to making a study plan for the MCAT.
Useful information and important MCAT links.
My review notes for the MCAT.
When I was planning to take the MCAT I checked the available date I wanted, September 11th, but not the location that it was given that day (only in Australia)...
The last time I can take the test in California is August 17th, exactly 1 month away from now.
Now I have to abandon writing and reading, and really step up the pace on chemistry and physics.
I don't think I will be ready by then, so I plan on taking it then, but expect to retake it the following year...
I have enough study materials (but for others), why not donate books or materials you don't want anymore? Those of you that have a great score already, what are you going to do with your old books?
If anyone wants to list there old material available here and their email,
people who want that material can email those generous, thoughtful people and let them know the shipping address for the books.
Senders ask for media mail at the post office (very inexpensive), as long as you are being a good person donating books, why not donate the shipping too?
I will definitely donate my books as soon as I have a good score...
The Father of Genetics: Gergor Mendel (1822-1884)[1]
1. Phenotype and Genotype (Definitions, Probability Calculations, Pedigree Analysis) Definitions:
Phenotype is the gene that is used/observed. Ex. I have brown hair.
Genotype is the genes that are carried. Genotypes can be written as dominant and non-dominant using capital and lower case letters: TT (homozygous dominant), Tt (heterozygous) and tt (homozygous recessive), or as two different equally dominant genes A1A2 (heterozygous for A1 and A2), A1A1 (homozygous for A1), A2A2 (homozygous for A2). Ex. I probably carry the genes for brown and black hair (I am heterozygous for hair color). Since my father and both his parents have black hair, I think he is homozygous for black hair. Having only black hair genes my father must have passed a black hair gene to me. Since I have visible brown hair (therefore having a brown hair gene), but also carry a black hair gene I am heterozygous. My children may have black or brown hair from my side.
Probability:
Both parents can contribute either of their genes (odds are equal between all genes the parents carry). Ex. I may pass on brown or black hair. If someone has two genes for black hair (homozygous, same genes), they can pass on either gene, but both will be black (there may still be a difference between the black hair genes if one carries a disease or malfunction).
There is an equal chance of passing on either gene. The pink flowers below will pass on red 50% of the time and white 50% of the time. Statistically I should pass on brown hair 50% of the time and black hair 50% of the time, but in reality I may happen to pass on one hair color over and over (just due to random chance). The probability for two parents that are heterozygous is: 50% mixed (heterozygous) children, 25% pure (homozygous) children of one hair color, and 25% pure (homozygous) children of the other color. There are two genes for hair, one controls level of darkens (blond, brown and black) and one controls level of red. Brown hair is dominant, black is less stable then brown, blond is recessive. Red is also recessive.
Incomplete Dominance in Flowers of Mirabilis Jalapa)[2]
Calculations:
To make a Punnett Square the genes of both parents' genes are lined up (one on the top and one on the left side). The genes get copied into boxes under and across. The offspring of a certain type are counted and divided by the number of boxes (usually 4)to find a percent. For genotype the same letters of the genes are counted, for phenotype expression is counted, that is any box with a dominant letter (one or two) counts as a dominant offspring and double recessive letters count as a recessive offspring.
In the example below one parent has two recessive genes (green) the result is 1:1.
If both parents were hybrids (monohybrid cross) the result is 3:1 (25% pure dominant, 50% mixed, 25% recessive; note that 75% show the dominant trait and 25% show the recessive trait).
If both parents were hybrids in a two gene system (dihybrid cross) the result is 9:3:3:1 (9/16 -> 56% show double dominant, 3/16 -> 19% show one dominant trait and one recessive, 19% show the opposite dominant trait and the opposite recessive, 1/16 -> 6% show both recessive traits.
Punnett Square (Easy Calculation Method)[3]
Pedigree Analysis:
The idea of pedigree is to determine whether genes are recessive or dominant by looking at breeding history and traits of offspring. A simple chart is made using phenotype. Genotype can be inferred depending on what information is present.
Pedigree Symbols[4]
Pedigree of My Family's Hair Color: Generation I is My Grandparents, Generation II is My Parents Generation III is My Generation.
Other then looking up on the internet that brown hair is dominant, it is easy to tell based on my family history. My mother's father had dark blond hair, my mother's mother had auburn hair (brown component). All their children had brown hair. Brown showed dominance over blond in the II generation. My mother has brown hair and my father has black hair. All their children have brown hair. Brown showed dominance over black in the III generation. I know that my brown hair comes from my mother's side, since my father's side has none. It is extremely likely that I carry a black hair gene, since my father would only show black hair if he carried black and black or black and blond. There are 0 blonds on my father's side of the family for 6 generations, so it is highly likely he carries black and black. My phenotype is brown and my genotype is brown and black.
My mother's mother had red (auburn) hair, there is a 100% chance she passed it to my mother (since she only red hair genes), there is a 50% chance my mother passed the gene to me. Hypothetically, if I had children with someone expressing red hair (someone showing red hair has double genes for red hair, since it is recessive) if I do carry the red hair gene 50% of the children would have red hair and 50% would not have red hair. If I do not carry the red hair gene (50% likely) then none of the children would express red hair (even though they would all carry it from the father's side).
There are 2 other genes for presence of grey hair. No gene is currently known that explains why hair color changes with age. I was born with black hair and my sister with red-blond hair, but both ended up brown (possibly dominant genes take time to exert control?). Pedigrees and Punnett Squares work best for traits that are not linked to the same chromosome and have few genes controlling them (1-2).
Human Eye Color is Complex, Controlled by at Least 15 Genes[5]
2. Gene A gene is a piece of DNA that has the information of one trait. The DNA is a specific blueprint used to build a protein that will result in a trait. Hypothetical example, a yard can have either a gazebo or a pool or a barbecue area (only one), the blueprints for the whole house would be DNA, the blue prints for just the gazebo, the pool or the barbecue area are a gene, the building materials would be proteins and the final product (the gazebo, pool or barbecue area) is the trait.
3. Locus The location of a specific gene on a chromosome. Like a page of a book containing the information for a specific information in question.
4. Allele (Single, Multiple)
Alleles are like ice-cream flavors.
There are two alleles for each gene, one from each parents. These can be different or the same. I have different alleles for hair color, one black and one brown. My father has the same alleles for hair color, two black alleles.
Genes can have more then two alleles. Cells can only hold two alleles (two scoops of ice-cream each, but any combination of flavors). Blood type has three possible alleles (IA,IB, andi). Since the body can only hold 2 alleles, multiple blood types are created. Blood type A is:IA andIA, or IAand i. Blood type B is:IB andIB, or IBand i. Blood type O is: i and i. Blood type AB is:IA andIB. Japan and South Korea relate personality to blood type. There is even blood type harassment (burahara). I am blood type A: conservative (no), introverted (yes), reserved (no), patient (yes), a perfectionist (yes), obsessive (no), self-conscious (no), uptight (no) and stubborn (yes, very much). 44% Correct, doesn't seem very accurate to me. My mother is also A, her personality is 11%. Type B is supposed to be forgetful, irresponsible, creative, flexible, individualistic, optimistic and passionate. Type O is supposed to be arrogant, insensitive, vain, ambitious, self-confident and robust. My dad is type O, his personality is only 33% correct. My best friend is also O, his personality is only 50% correct. Type AB is supposed to be critical, indecisive, unforgiving, aloof, cool, controlled, introverted and rational. 11%, 33%, 44%, 50% -> F, F, F and F+. Overall it doesn't seem like the system is accurate, based on people I know. I'm calling bullshit, on blood type affecting personality.
My Family Blood-Type Pedigree
5. Homozygosity and Heterozygosity Homozygous: having the same alleles for a gene (ii) Heterozygous: having differing alleles for a gene (i andIB)
6. Wild Type The most common type of allele for an organism. Cows are usually colored, white cows are rare. Color is the wild type for cows. The wild type, for humans in Asia, is black hair and brown eyes.
7. Recessiveness Genes that are not shown unless they are both the same, these genes are overpowered when other genes are present. Blond and red hair are recessive. Black hair is dominant to blond, but recessive to brown.
8. Complete Dominance Complete dominance means that a recessive trait is not used at all when a dominant allele is present, and the dominant trait is expressed completely.
9. Codominance Codominance describes two alleles that are equally dominant, both will be used like AB blood type producing A and B antigens.
Incomplete dominance is shown in the pink flowers that are offspring of red and white flowers. Even though the red allele is dominant, it is not dominant enough to totally suppress the white allele.
Leakage refers to gene flow from one species to another.
Penetrace is the strength of expression in a gene. If you have a cancer gene, it does not mean you will develop cancer. The amount that a gene really does what it is supposed to is penetrance.
Expressivity is the amount that a gene is expressed. I have 0% expressivity for red hair, red haired people have <0%. Genes can be expressed to varying degrees.
11. Gene Pool The gene pool refers to all the possible alleles in a population. A large gene pool is healthy. Small gene pools begin to develop recessive diseases.
B. Meiosis and Genetic Variability
Mitosis creates two identical daughter cells, but meiosis creates a multitude of different daughter cells.
Meiosis Video [6]
1. Significance of Meiosis The process of meiosis allows crossing-over and independent assortment, which lead to variety in daughter cells. Without meiosis all offspring would be the same, evolution would be limited, the species would be more likely to become extinct.
2. Important Differences Between Meiosis and Mitosis Meiosis forms tetrads (the matching chromosomes pair up and swap genes, called crossing over). In meiosis the resulting cells are different then the parent cell, and contain half the normal amount of DNA (one allele for each gene, instead of two). Meiosis has two divisions and produces 4 sperm or 1 egg and 3 polar bodies.
3. Segregation of Genes Genes are given opportunities to swap locations (ending up in different cells), genes from each parent are separated randomly into different daughter cells.
A. Independent Assortment Depending on if each gene is on the left or right side of the cell during metaphase I, the gene will be pulled into the left or right daughter cell.
B. Linkage Another factor that complicated genetics even more (that Mendel was unaware of) is that genes on the same chromosome are linked (usual stay and occur together). Red hair and freckles seem to be linked. The closer in physical proximity on the chromosome, the less crossing over effects linkage. The genes furthest away from each other are the most likely to end up on opposite chromosomes, genes right next to each other will more then likely remain next to one another.
C. Recombination Recombination means changing up the genes in new combinations, which refers to both independent assortment and crossing over.
D. Single Crossovers Crossing over happens during prophase I, when a synapsis forms a tetrad out of homologous chromosomes, which form a chiasma (the site of crossing over). Independent assortment is the sorting of one chromosome each into the two daughter cells.[7]
E. Double Crossovers If chromatids exchange exactly the same genes twice no genetic recombination has occurred. If chromatids exchange and then one of them exchanges with a different chromatids (3-strand double crossover) recombination occurs. If chromatids exchange and then both of them exchange with different chromatids (4-strand double crossover) double the recombination occurs.[7]
4. Sex-Linked Characteristics Human females have two X chromosomes, males have one X and one y. The genes below would belong to a male.
Human X and Y Chromosome [8]
A. Very Few Genes on Y Chromosome The y chromosome is too small to fit much. The vital genes are usually put on the X chromosome.
B. Sex Determination XX -> Female Xy -> Male
C. Cytoplasmic Inheritance, Mitochondrial Inheritance All cytoplasmic contents such as mitochondria and organelles are inherited from the mother (because they fit in the egg, but not the sperm). Therefore, any mitochondrian defects are from the mother's side.
5. Mutation Errors occur in DNA. Turtles become ninja turtles...
A. General Concept of Mutation Mutation can be a good thing, because it leads to variety in small populations. Or it can be a bad thing that causes disease or death.
B. Types of Mutations (Random, Translation Error, Transcription Error, Base Substitution, Insertion, Deletion, Frameshift)
Random Mutations: UV radiation, chemicals and replication errors cause mutation.
Translation Error Mutations: Errors can occur during the translation into protein.
Transcriptional Error Mutations: Errors can occur during transcription into mRNA.
Base Substitutions Mutations: A base pair is switched on accident.
Insertion Mutations: A base pair is accidentally added, lengthening the sequence.
Deletion Mutations: A base pair is accidentally removed, shortening the sequence.
Frameshift Mutations: Three bases are messed up, therefore different amino acids are coded.
C. Chromosomal Rearrangements (Inversion, Translocation) The chromosomes can break and rearrange itself end to end (inversion) or can move and reattach in another location (translocation).
D. Advantageous Versus Deleterious Mutation Advantageous Mutation -> Improvement Deleterious Mutation -> Harmful
E. Inborn Errors of Metabolism Errors of metabolism caused by genes.
F. Relationship of Mutagens to Carcinogens A mutagen causes mutation, a carcinogen causes cancer. Carcinogens are often mutagens. Mutagens may or may not by carcinogens.
C. Analytic Methods
The method for determining genetic shift is by measuring the amount of alleles within a population and seeing if they change or remain the same.
1. Hardy–Weinberg Principle Mendelian genetics shows a normal ration of dominant and recessive alleles are passed down to future generations. A dihybrid cross produces offspring with the ratio 9:3:3:1. That concept developed into the Hardy-Weinberg Principle:
p2 + 2pq + q2 = 1 and p + q = 1
P: the Dominant Allele
q: the Recessive Allele
p2 = percentage of homozygous dominant individuals
q2 = percentage of homozygous recessive individuals
2pq = percentage of heterozygous individuals
There are five rules to using the Hardy-Weinberg Principle:
1. No mutations must occur so that new alleles do not enter the population.
2. No gene flow can occur (migration).
3. Random mating must occur (individuals must pair by chance).
4. The population must be large so that no genetic drift (random chance) can cause the allele frequencies to change.
5. No selection can occur so that certain alleles are not selected for, or against.
[7]
2. Testcross (Backcross; Concepts of Parental, F1, and F2 Generations)
The testcross is the way to tell what hidden genes are carried, but not expressed. By breeding a dominant phenotype with a recessive phenotype and observing the offspring (half recessive or all dominant), it is possible to tell if the dominant subject was double dominant or only single dominant.
Ex. I have brown hair, if I have children with someone with black hair, and the children have black hair, then I am heterozygous dominant.
Backcross is mating between offspring and parent.
P represents parent, F1 (filial 1) represents the children and F2 represents the grandchildren.
The human reproductive system is responsible for a great variety of people, because each person has possible genes for everything (one from each parent). One gene is expressed and the other is not, but both can be passed down to children. I have brown eyes, but I probably have my parents green eye gene also. The reproductive system takes all the genetic information and puts only half in eggs and sperm (gametogenesis, using meiosis I and II), so that when the egg and sperm combine, they have exactly enough genes. Which half is used for each egg and sperm is random, so many possibilities are possible for humans (unlike cheetahs which are almost identical clones).
1. Male and Female Reproductive Structures and Their Functions
Both reproductive structures must produce gametes with half the normal DNA. The female reproductive structures must also facilitate the growth of a zygote into a baby, and allow the baby to leave the body during birth. The male reproductive structures must allow sperm to exit the body near enough to the cervix for fertilization to occur and also produce a buffer to keep sperm from being killed by the acid of the female reproductive system.
Male Reproductive Structures [2]
Prostate Cancer is the 4th most lethal cancer for men, drinking tea and eating soy help:
"I think the most important finding is that consumption of both soy and tea has a synergistic effect," says study author Jin-Rong Zhou, adding that each appears to reinforce the power of the other to fight cancer... statistical data showed that China had one of the lowest prostate cancer risk profiles in the world... Ultimately, both tea-soy combinations inhibited angiogenesis, a process in which tumors grow blood vessels to stay alive. [3]Read more.
A. Gonads
Female Gonads: Ovaries (hold eggs which are made before birth, releasing them monthly after puberty and produces estrogen).
Male Gonads: Testes (make spermin the seminiferous tubules and produces testosterone in the interstitial cells).
B. Genitalia
Female: The ovaries store eggs, which pass through the fallopian tubes, into the uterus, through the cervix and out the vagina.
Menstruation/Fertilization: The lining of the uterus thickens every month (normally), growing more blood vessels. The egg (oocyte), becomes a secondary oocyte and enters the uterus. If fertilization occurs, the embryo releases human Chorionic Gonadotropin (hCG)(testable by pregnancy tests, cause of nausea), which releases hormones preventing menstruation and triggering the placenta to create progesterone and estrogen.
GonadotropinReleasing Hormone (GnRH) made in the hypothalamus releases the gonadotropins: Folicle Stimulating Hormone (FSH) and Luteinizing Hormone (LH) from the anterior pituitary, these stimulate the growth of the oocyte/follicle and trigger maturation/ovulation (respectively).[4]Further Details.
Estrogen made in the ovaries normally inhibits luteinizing hormone and folicle stimulating hormone, but once it reaches a threshold it causes a surge of luteinizing hormone that triggers ovulation.
[5]
The corpus luteum, which remains in the ovary after expelling the oocyte into the Fallopian tube, prevents the endometrium from shedding by secreting estrogen and progesterone.If fertilization does not occur the corpus luteum dies, estrogen and progesterone levels drop, the endometrium dies and sheds, and the menstrual cycle restarts.[6]Further Details.
Male: Inside the testes sperm is made (in the seminiferous tubules, inside the testicle) and stored (inside the epididymis, on top of the testicle). The sperm travels through the vas deferens, the ejaculatory duct, and exits the body via the urethra.
Male Accessory Structures:The prostate secretes alkaline fluid to protect the sperm from female acidity, citric acid, fibrinolysin (to liquefy the semen) and acid phosphate. The seminal vesicles secrete fructose to provide energy for the sperm, prostaglandins, flavins (florescent). Bulbourethral glands (Cowper's glands) produce a lubricant to help sperm swim. The interstitial cells of the testis produce testosterone. [8]
C. Differences Between Male and Female Structures
Male reproductive organs develop from female structures. Ovaries drop into the scrotum in males. Erectile clitoris tissue become the penis in males. The skin of the vagina forms the skin of the scrotum in males. Testicles need to be away from the body, because too much heat kills sperm. The male reproductive system is connected to the urinary tract, the female reproductive system in separate. All the eggs of a female are created before birth. Males do not produce sperm until around age 12. Thus, females are about 12 year more mature then males, not surprisingly.
2. Gametogenesis by Meiosis
Female Gametogeneis: Making eggs with half the DNA for a child, at birth females have all the eggs they will ever have stored in their ovaries.
Eggs are frozen in Meiosis I (at prophase) until puberty (when meiosis I begins to reach completion monthly), there is too much DNA (diplotene) in the eggs until ovulation occurs, allowing meiosis II (meiosis II pauses in metaphase II and continues when the egg nucleus contacts sperm) to occur, reducing the DNA in half.[5]
Male spermatogenesis occurs in the seminiferous tubules. The names of the sperm keep changing. Spermatogonium until mitosis, then primary spermatocyte (required puberty), until meiosis I, then secondary spermatocyte, until meiosis II, then spermatid (having the correct amount of DNA, half a normal cell), then sperm (after maturing) or spermatozoa (same thing as sperm).[5]
Sperm is made at about 70,000/minute, each sperm takes 70-74 days to develop.[9]
3. Ovum and Sperm
Ovum and sperm have half the normal DNA each, they combine to form a complete set of DNA that grows into a complete individual about 25% of the time, miscarriage occurs nearly 75% of the time in humans (counting early miscarriage of zygotes ext.).
A. Differences in Formation
Male VA Female (Gametogenesis) [5]
Male
Female
Difference
Spermatogonium (2n)
Oogonium (2n)
Spermatogonium made fresh. Oogonium all done before birth.
Primary spermatocyte
Primary oocyte
Primary oocye pauses at prophase I
Secondary spermatocyte
Secondary oocyte
Secondary oocyte pauses at metaphase II
Sperm
Ovum
Between the secondary spermatocyte and the sperm, there's the spermatid.
B. Differences in Morphology
Sperm are small and move with a flagella, using sugar for energy. Eggs are very large spheres that don't move.
C. Relative Contribution to Next Generation
Sperm contributes only half the DNA; eggs contribute half the DNA, mitochondria, organelles and epigenetics).[5]
Fertilization: the sperm and egg meet, then combine nucleus and DNA (forming a zygote).
Implantation: the zygote then grows into a morula (by dividing via mitosis), keeps dividing into a blastocyst and sticks to the wall of the uterus.
Development: gastrulation (development of3 layers: mesoderm, ectoderm, endoderm and a pore) and organogenesis (organ development) occur.
B. Embryogenesis
The process of making an embryo.
Embryogenesis [10]
1. Stages of Early Development (Order and General Features of Each)
Zygote 1-15 cells.
Morula 16-127 cells/4 divisions (solid ball).
Blastocyst 128 cells/7 divisions (hollow ball).
Gastrula many cells (3 layers, pore/blastopore).
Then embryo... [11]
A. Fertilization
Sperm + Egg -> Zygote
The sperms release hormones to weaken the egg membrane as a team, then one sperm causes a acrosomal reaction allowing it to penetrate the membrane and enter the egg, the egg goes through a cortical reaction preventing more sperm from entering, meiosis II occurs and the sperm and egg nuclei fuse).[5]
B. Cleavage
Zygote -> Morula (solid ball, produced by repeated mitotic divisions)
C. Blastula Formation
Morula -> Blastocyst (hollow ball, implants on the uterus)
D. Gastrulation
The trilaminar (three layers) ball of cells that goes on to form organs. The blastopore become the mouth (protosomes) or the anus (in humans/deutrostomes). [12]
Gastrulation [13]
I. First Cell Movements
The surface cells (blue in the above picture) migrate inwards forming a blastopore.
II. Formation of Primary Germ Layers (Endoderm, Mesoderm, Ectoderm)
The three cell layers are the endoderm (cells migrate inwards), the mesoderm (cells the the middle, the Oreo filling cells if you will) and the ectoderm (cells that remain outside).
E. Neurulation
The ectoderm becomes a tube that forms the brain and spinal cord, as well as the skin and all nerves.
2. Major Structures Arising out of Primary Germ Layers
Mesoderm makes: muscle, blood, bone, internal organs (kidney and gonads).
Ectoderm makes: skin and nerves (including the brain). This means skin is exposed neural tissue, that concept is where the term neuromuscular therapist (for massage therapist) has its basis. The Color of Distance, by Amy Thomson is a great book (fiction) about creatures that display their emotion, heal themselves, communicate and experience the world mostly with their skin. In reality, we as humans are very much like those creatures. Our skins are the boundary and contact, with each other and the world in which we live.
Day 23:
C. Developmental Mechanisms
The cells of the body have a destiny (specialization) to become a certain type of cell, based on the way we use our body we change some cells to do different things, when the cell is at a certain point (determination) they can no longer change (can't teach an old dog new tricks), the point when the cell starts to preform its function (differentiation) is the end of development.
Long Overview of Development (14 Minutes) [14]
1. Cell Specialization
The destiny of each individual cell to become a specific type of cell as it grows. The cell starts to develop a certain way, but can change still.
A. Determination
The point of no return for a growing cell.
B. Differentiation
The concept that stem cells can become other types of cells, adopting different shapes, sizes, contents and functions.
C. Tissue Types
The tissue types are explained in detail in this post.
They are epithelial (skin and linings), connective (blood, bone, tendons, ligaments, fat, cartilage and basement membranes), nervous (neurons and supporting cells) and muscle (skeletal, smooth and cardiac).
2. Cell Communication in Development
The body communicates on all levels. On the level of tissues, cells speak to each other. Inducer (the cell talking) tells the responder (the cell listening) to change.
3. Gene Regulation in Development
Differential Gene Transcription: genes are limited by transcription factors, histones proteins are modified (methylations, acetylations) to wrap around DNA turning genes off or on, DNA is modified (methylations), to turn genes on and off, as well.
Differential RNA Processing: RNA may not be transcribed if it doesn't leave the nucleus, RNA can be spliced in different ways to regulate genes.
Translation Regulation: mRNA are used to different extents, selective inhibition of translation of stored RNA occurs in the oocyte (translation occurs as needed after fertilization).
Post-Transnational Regulation: some proteins are inactive without modifications, proteins can be marked for ubiquitin degradation.[5]
4. Programmed Cell Death
The name of intensional cell death is apoptosis. Capases are the proteases that digest the cell. This type of cell death can be used for remodeling the shape of the body as it grows.
Today, I am starting to use the American Chemical Society Citation Style to cite my sources. I will have to go back and cite my sources in earlier posts soon...
Footnotes:
1. Brenda. [Untitled Diagram of Female Reproductive System]. Brenda's A & P Eportfolio. [Online]. Apr 14, 2011. http://blm1128.blogspot.com/2011/04/objective-79-locate-structures-of-male.htm (retrievedJul 01, 2012). 2. [Untitled Diagram of Male Reproductive System]. The Health Success Site. [Online]. http://www.thehealthsuccesssite.com/what-is-prostate-cancer.html (retrieved Jul 2, 2012).
