Genetics Exam 1 Study Guide Tutorial Workbook With Questions And Answers PDF

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Genetics Exam 1 Study Guide Chapter 1 Why are model organisms so important? The natural course of a disease in a human may take dozens of years. Simple organisms that can develop a disease or some of its symptoms make it possible for researchers to learn about the disease faster—in a period of months to a few years. That would be nearly impossible, and often unethical, to do in humans. When scientists discover that a particular gene is associated with a disease in humans, one of the first things they typically do is find out what that gene does in a model organism. This often provides important clues for understanding the cause of a disease and for developing potential diagnostic tests and treatments.

Discuss the early theories of hereditary transmission. 

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Pangenesis – specific particles (gemmules) carry information from body to reproductive organs, which are passed to embryo at conception (very early concept) o A gemmule from specific parts of the body are all carried to reproductive organs (gemmules from the brain say “this is how to make a brain”, gemmules from the heart say, “this is how to make a heart”) Inheritance of acquired characteristics – Greeks proposed traits acquired in life incorporated into hereditary information and passed on (example: artist would pass on art skills to offspring

These two ideas were both found to be incorrect – these theologies stuck around for a very long time. The word “gene” comes from the word pangenesis, even though the idea of a gene completely disproves the idea of pangenesis.

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Preformationism – inside egg or sperm is a tiny version of an adult (homunculus) o People began to move away from pangenesis and come up with new ideas, such as preformationism (they thought that the homunculus already existed) o People first thought the homunculus was inside the sperm, but then they thought it was in the egg because the egg is slightly larger – eventually people realized it was more of a blend Blending inheritance – offspring are a blend of parents

Important people and their contributions. Scientist Schwann and Schleiden

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Darwin

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Mendel

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Flemming

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Contribution(s) Proposed the cell theory (1839) Cells are the basic unit of all living things Cells arise from preexisting cells Identifying the cell, monitoring and watching was going on allowed them to identify the cell theory Theory of evolution through natural selection Heredity was the fundamental of evolution Many holes were left in Darwin’s theory because people didn’t understand what was going on – Darwin’s work was very heavily debated Discovered basic principles of heredity (1866) Crossed pea plants and analyzed patterns of transmission Known as the “father of genetics” and founded the principles/how it works and how things are inherited although he could not thoroughly explain it Observed division of chromosomes Hereditary information contained in the nucleus Actually saw chromosomes dividing – visualized this by the microscope and said that the hereditary information is specifically located in the nucleus and it is very important for how

Weismann

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hereditary works Tested the theory and experimented against the idea of pangenesis – so he proposed the germ plasma theory His idea was that cells of the reproductive system carry complete set of information and no other cells contribute or are necessary to create the next generation Cut off the tails of mice for 22 generations, tail length of descendants did not change Proposed genes are on chromosomes

Chapter 2 Describe the difference between prokaryotes and eukaryotes.

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In general, prokaryotes have less DNA than eukaryotes – however, the amount of DNA does not tell you the complexity of an organism. Prokaryotes have single strand DNA and eukaryotes have double stranded DNA o Most of the time the DNA in the prokaryote is relaxed, whereas the DNA in the eukaryote is always interacting with histone proteins A eukaryote has a lot more structure than a prokaryote.

Define ploidy.  

Ploidy refers to the number of sets of chromosomes in a cell, or in the cells of an organism Ploidy tells you how many copies of the genome you have o With haploid cells (reproductive cells) only one set is passed to the next generation

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o The majority of human cells are diploid, meaning we have two copies of each chromosome with the same genetic information – however, between chromosomes from different people, they can have different alleles.  For example, both genes are contributing to pigment of hair color, but the different alleles can alter the actual color although overall, the chromosomes look the same. Eukaryotes typically have two sets of chromosomes per cell (a result of sexual reproduction, one set from the mother, one from the father – called homologous pairs). o 2 sets of genetic information = diploid (2n, example: most eukaryotic cells) o 1 set of genetic information = haploid (1n, example: reproductive cells) Humans are diploid (aka we have two copies of our genome) o In somatic cells, we have two copies of the genome (one set from mom, one set from dad)

Explain the structure of chromosomes.

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For linear chromosomes, caps (called teleomeres) are put on the ends and these are essential for the chromosome for they ensure that the body’s chromosomes will not be attacked The centromere is another essential part of the chromosome – it is necessary during cellular division because where the centromere is, the kinetochore forms around it and spindle microtubules attach there. o Centromeres are also used to count chromosomes, whenever we divide genetic material a step of replication is required so for a short amount of time the chromosome will stay attached to it’s copy  Without the centromere, chromosomes are lost

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There are four major types of chromosomes o Metacentric  Centromere in the middle o Submetacentric  Centromere slightly further away from the middle o Acrocentric  Centromere almost to the end o Telocentric  Centromere all the way at the end of the chromosome

Discuss the phases of the cell cycle.

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G0 – the cell does not G1 – cells begins growing G1s – checkpoint – cell commits to dividing at this checkpoint (checks for environmental issues, DNA damage, etc) S phase – DNA synthesis phase G2 – the cells begin growing, checking (is replication of DNA finished? Is DNA damaged? Is there enough space to grow and divide) at this point we have replicated DNA, but have not divided yet Mitosis – undergo division of the genetic material in the nucleus Cytokinesis – divides us everything else in the cell – “cytoplasmic division”

Discuss the phases and important events that occur during mitosis. 

Interphase o DNA synthesis o G1, S, G2 occur o Cannot see chromosomes with light microscope

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Prophase o Chromosomes condense and become distinguishable from other chromosomes o DNA is already replicated **** o Mitotic spindle forms from centrosomes (animals only!) Prometaphase o Nuclear envelope disappears and allows the spindle fibers to attach to kinetochores and latch onto chromosomes o Microtubules contact chromatids Metaphase o Chromosomes arrange in single plane – metaphase plate o Chromatids line up independently down the middle o Four chromosomes Anaphase o Sister chromatids move toward opposite poles (after separation of chromatids they are chromosomes) o Eight chromosomes Telophase o Chromosomes arrive at spindle poles o Nuclear membrane reforms = 2 nuclei o Chromosomes disappear from view

At the end of mitosis, we should have two genetically identical cells. What role do spindle fibers play in mitosis? Spindle fibers are essential to the process of mitosis.

Compare mitosis and meiosis. Mitosis:  Single nuclear division  Results in the same number of chromosomes  Yields genetically identical cells  CHROMATID is what is pulling apart Meiosis:  Two divisions o Dividing nuclear information  Newly formed cells has half of starting chromosomes o Takes place in humans germ line (it becomes gametes (the sperm and the egg), which need to be haploid because we only need one copy to pass onto the next generation) o Reduces the number of chromosomes

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o After one round of division, the diploid is reduced to haploid – and then another division is necessary to split chromatid Genetically variable cells Pulling apart HOMOLOGOUS PAIRS in the first part and then CHROMATID in the second

Discuss the phases and important events of meiosis. 

Meiosis I o Prophase  Middle prophase I  Chromosomes begin to condense  Spindle forms  Late prophase I  Homologous chromosomes pair  Synapsis (very close association)  Bivalent/tetrad (or a pair of homologs)  CROSSING OVER TAKES PLACE  Chiasma – area of crossing over  Nuclear membrane break down o Metaphase I  Homologous pairs of chromosomes align along metaphase plate  Microtubules attach to one pair from each pole o Anaphase I  Homologous pairs of chromosomes are separated

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 Pulls apart homologous pairs o Interkinesis – nuclear membrane reforms, DNA relaxes o Telophase I  Cytoplasm divides after chromosomes in each cell and is where we see the reduction and go from diploid to haploid Meiosis II o Prophase II  Chromosomes re-condense  Nuclear envelope breaks down o Metaphase II  Like metaphase of mitosis  Chromosomes align on metaphase plate o Anaphase II  Sister chromatid are pulled apart (now = chromosome) o Telophase II  Chromosomes arrive at spindle pole  Nuclear envelope reforms  Cytoplasm divides

What is “crossing over” in meiosis? Crossing over during meiosis allows recombination of genes between homolgous chromosomes. This alters the linkage between genes on the same chromosome.

How does meiosis provide genetic variability? Cells produced from meiosis are genetically distinct because crossing over yields siter chromatids that are not identical, and there is a random distribution of chromosomes in Anaphase I. The random alignment in metaphase and random splitting in anaphase results

in variability (Number of possible combinations – 2n (n=number of homologous pairs) humans have 23 chromosomes = 8388608 combinations) We get variability because mom and dad’s chromosomes have the same gene but have different alleles. Chromosome splitting results in four different chromosomes, and it can happen to many genes along the chromosome. Discuss unequal division that occurs in meiosis. Usually you get four cells but sometimes you do not. If we look at gamete formation in male vs. female in humans – In males, meiosis proceeds pretty normally. In females, meiosis does not follow the same rule. Meiosis 1 takes place and it does all of the same nuclear division but cytokinesis is different and there is “unequal cytokinesis” and we end up with the first polar body. After meiosis one, the first polar body is done and does not continue to become a gamete. In meiosis two, we have another round of unequal cytokinesis and all of the cytoplasm goes to only one cell so you get the second polar body and what will become the egg. What happens in the nucleus stays the same, but the consequences are much different. This is why the egg is so much bigger. Once a male hit puberty, they undergo this process continuously. In females, this is a very disjointed process.

Chapter 3 Johann Gregor Mendel. Between 1856 and 1863 Mendel performed breeding experiments to study genetics. In 1865, he presented the results at a meeting and in 1866 he published a paper that went largely unnoticed. Finally, in the 1900s Mendel’s work was recognized. Definitions to know. Term Gene Allele Locus Genotype

Definition A genetic factor (region of DNA) that helps determine a characteristic One of two or more alternate forms of a gene Specific place on a chromosome occupied by an allele Set of alleles that an individual possesses **Only genotype is inherited**

Heterozygote Homozygote Phenotype or trait Character or characteristic

An individual possessing two different alleles at a locus An individual possessing two of the same alleles at a locus The appearance or manifestation of a character (genotype + environment) An attribute or feature

With genotype, we are looking at what combination of alleles does an individual have? If the alleles are different, we consider that heterozygote (if you have two different alleles at one locus). The genotype helps determine what the phenotype will be. Mendel’s experiments. 

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Monohybrid cross – parents differ in a single characteristic o If you cross the other direction this is called a reciprocal cross:  Mendel crossed yellow male pea plant with green female pea plant and also crossed green male with yellow female to show that sex is not involved.  Reciprocal crosses allowed them to eliminate some ideas/theories o Mendel concluded:  Unit factors in pairs – each trait has two different “unit factors” that result in different traits; which gives three possible combinations  Dominance/recessiveness – traits that were observed in F1 = dominant. Those that disappeared = recessive  Segregation – two alleles separate when gametes are formed – one allele to each gamete (upon fusion at fertilization, zygote gets on allele from both male and female parent; separate with equal probability into gametes. Backcross o Backcross = either parent

Test cross o With a test cross, you always cross back with a homozygous recessive parent ALWAYS. o Cross individual of unknown genotype with Tall pea plant – either Tt or TT – how can we figure out which one it is? (When you self cross, you should get the 3:1 ratio)

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Dihybrid cross o Crosses of organisms that differ in two characteristics

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Principle of segregation (Mendel’s First Law) o Each individual diploid organism possesses two alleles for any particular characteristic. Two alleles segregate into gametes, and this occurs randomly and in equal proportions. Principle of independent assortment (Mendel’s Second Law) o Allele’s at different loci separate independently of one another o NOTE: the characters must be located on different chromosomes (as assortment is related to chromosome separation at Anaphase I)

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Describe phenotypic and genotypic ratios.

Why are branch diagrams useful? They can obtain both genotypic and phenotypic ratios. By setting out the proportions of genotypes or phenotypes for each allele pair and connecting these to proportions of the other allele pairs, a branch or web of genotypes or phenotypes can be constructed. Example: How can probability make genetics easier? The product rule of probability can be used in genetics as long as the events are independent, such that one does not have an influence over the other. For example, what is the probability of rolling the die twice and getting “4” both times? 1 in 6 (1/6) and 1 in 6 or (1/6) so 1/6 x 1/6 = 1/36 The addition rule of probability is the probability of one of two or more mutually exclusive events by adding the probabilities of two events. Role dice once, what is the probability of getting either a 5 or a 6? 1/6 of getting 5 1/6 of getting 6 1/6 + 1/6 = 1/3

Chi-Square Test.

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Used to determine the probability that the difference between the observed and the expected values is due to chance. If P is greater than or equal to 0.05 – difference is likely caused by chance (random) If P is less than 0.05 – assume chance is NOT responsible and a significant difference exists

Chi Square Analysis =

X2 = ∑

(#Obs. - #Exp.)2 #Expected

for all classes

Pedigree Analysis. 

Pictorial representation of a family history

Chapter 4 Definitions to know.       

Allele – wild type allele (the allele that is most popular within a population) o Anything that changes the wild type allele is often known as a mutant Loss-of-function mutation – decreases the function of an allele Null allele – complete loss of the function of an allele Gain-of-function mutation – gained a function at a specific time point and ultimately produces more than it should Neutral mutation – does not have an impact on the phenotype, but can be distinguished in the genotype Gene interaction X-linkage

Identification of symbols.  

Capital vs. lowercase Wild-type vs. mutant (+ vs -) o We are just saying that this is different, not necessarily a bad thing

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o The + indicates wild-type and – indicates mutant Superscripts

Discuss incomplete dominance. Genetically, the same exact thing is happening but the phenotype changes slightly. With incomplete dominance, we see a blending in the heterozygous state.

Define Codominance.  

Phenotype of the heterozygote includes the phenotypes of both homozygotes MN blood types – antigen on red blood cells o No blending, you see M and you see N o Both exist in the heterozygotes but can be distinguished o Two alleles: LM and LN o Possible Genotypes: LMLM, LMLN, LNLN o Phenotypes: o LMLM – Only produce M antigen o LNLN – Only produce N antigen o LMLN – Produce BOTH M and N antigen o Sickle Cell Anemia is an example of Codominance

Multiple alleles. There can be many different alleles for one gene in the general population. ABO blood group: IA = codes for A antigen

IB = codes for B antigen i = codes for no antigen IA > i IB > i I A = IB *A and B are both dominant to I but are codominant to each other* Genotypically, the same thing could be happening – but phenotypically, the results are different. Lethal alleles. A dominant lethal allele means that one copy immediately causes death (example: Huntington’s disease). But a recessive lethal allele means that there must be two copies to die, even though the lethal allele is dominant to another allele (such as color). This is known as Pleiotropy. Pleiotropy  

One gene that impacts several aspects of the overall phenotype Example: o ML/M hets do not have a tail (deformed spinal development (so dominant allele for spine development) o ML/ML fail to complete embryonic development (so recessive for death!)

Describe epistasis.  

The interaction of genes that are not alleles, in particular the suppression of the effect of one such gene by another. For example, in black, chocolate and yellow labs B is dominant for black and b is recessive for chocolate. o ee completely masks what is happening on the Bb gene – resulting in a yellow lab o The E takes pigment and sticks it to hair where as the “e” does not do that and results in a yellow coat with no pigment stuck on it o Hypostatic gene - hidden by the epistatic gene o Epistatic gene – does the hiding  Note: the E gene is responsible for putting pigment on hair, so ee puts no pigment on hair  Notice the nose is black, and can have yellow labs with brown noses since E gene is specific to hair pigment

Complementation. A complementation test is used to determine if mutations are in the same or different loci

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The test can be done when showing that all mustations are recessive wild-type Complement each other = different gene Don’t complement each other = same gene Recessive mutants complementing each other leads to wild-type phenotype

Discuss penetrance and expressivity. 

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Penetrance – the percentage of individuals ha...