Genetics Lecture Notes Week 2
Genetics Lecture Notes Week 2 85033 - GEN 3000 - 002
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85033 - GEN 3000 - 002
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This 16 page Class Notes was uploaded by Toni Franken on Tuesday January 12, 2016. The Class Notes belongs to 85033 - GEN 3000 - 002 at Clemson University taught by Kate Leanne Willingha Tsai in Summer 2015. Since its upload, it has received 42 views. For similar materials see Fundamental Genetics in Biomedical Sciences at Clemson University.
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GEN 3000 – Notes Set 2, 01/11/2016 Dr. Tsai, Clemson University Chapter 2 Continued Mitosis/Meiosis: Mitosis – the duplication of cells: Produces Diploid Cells Mitosis occurs regularly in the body, such as in bone marrow and blood production, or inside the lining of the gut. New cells are created through mitosis. There are some exceptions, such as mature neurons, which don’t usually undergo a full cell cycle. Before Mitosis occurs, a cell is in Interphase, which is composed of G1, S (DNA replication), and G2. During interphase, you cannot see chromosomes with light microscope. It’s a jumbled up mess inside the nucleus. During the M phase, or mitosis, we’re focusing on replication, and the chromosomes condense to the point that they can be seen with a light microscope. DNA is ALREADY REPLICATED AT THIS POINT. Note: Mitosis is dynamic and fluid, sometimes making it difficult to determine exact beginning and ending points of phases. Other sources may list them differently. For this class, study according to the information listed below. Stages of Mitosis: 1.) Prophase: The already replicated chromosomes condense, and the mitotic spindle forms from the centrosomes. These centrosomes are only present in animal cells, and will not be found in plants. During this phase, we’re looking at diploid cells – each chromosome consists of 2 sister chromatids. We’ll see the centrosomes start to move to opposite ends of the cell, and they organize the spindle fibers, which are also called microtubules or microtubular filaments. The nuclear membrane, also called the nuclear envelope, begins to break down. 2.) Prometaphase: The nuclear envelope disappears completely, and microtubules contact the chromatids. They will attach at the centromere of each chromosome, and then will be able to move them. Once contact is established, they will either lengthen or shorten to move the chromosomes to the metaphase plate. 3.) Metaphase: Trigger word – Middle. Spindle fibers arrange the chromosomes in a single plane called the metaphase plate. Unlike in Meiosis, which we’ll look at later, the chromosomes don’t care what the other chromosomes are doing. 4.) Anaphase: Trigger word – Apart. Sister chromatids are separated, and they move toward the opposite poles creating separate chromosomes. This separation is called disjunction. If they do not separate, this is called nondisjunction. 5.) Telophase: Trigger word – Twins. Chromosomes arrive at spindle poles, and the nuclear membrane reforms to form 2 nuclei. The chromosomes begin to disappear from view. If everything has gone properly, they will be exact copies. Cytokinesis: The division of the plasma membrane and organelles – considered to happen at the same time as telophase, and some consider it part of telophase, while others say it is a separate phase itself. Most important factors of each phase: Interphase: nondistinct, mushy chromosomes and growth, DNA replication Prophase: Condesnation of chromosomes Prometaphase: Spindles form Metaphase: Middle line/metaphase plate Anaphase: Separation of Sister chromatids Early Telophase: Separation into two identical cells Late Telophase: Formation of new nuclei How do chromosomes move? Spindle fibers are going to connect to the centromere to form the kinetochore. Spindle fibers are made up of tubulin subunits that can be added or removed according to which direction they need to move. There are molecular motors that help with this. They’ll lengthen by adding subunits, and shorten the tubules by removing subunits. This process is ESSENTIAL. If the spindle fibers cannot change length, the process will halt and kill the cell. Some drugs specifically target spindle fibers to freeze them, or prevent the molecular motors from working, which forces the cell to shut down. This is used commonly in cancer treatments. If something happens and a single fiber breaks, the process of disjunction won’t work properly. You can end up with something like Turner syndrome (lacking a Y chromosome, or a second half to the X chromosome). Has consequences on the cell, and is usually fatal. When we classify chromosome types by centromere location, we’re looking at metaphase chromosomes that have been through the S phase, and are arranged with their homologous pair. Both sister chromatids are present (or should be). Counting Chromosomes: The cell is diploid during almost the entire process of Mitosis. Say a cell starts out in G1 with 4 chromosomes. During the S phase, all of those chromosomes are going to be replicated to result in sister chromatids, but each pair is still considered one chromosome. This continues through G2, Prophase, Prometaphase, and Metaphase. Only once we get to anaphase, where the sister chromatids separate, does the number temporarily change to 8. In telophase, the separation of cells returns chromosomes numbers to 4. Controlling the Cell Cycle: The cell cycle is virtually the same in all eukaryotic/diploid organisms. The cycle requires proteins with specific patters, which has helped us understand the “checkpoints” of the cell cycle. The two proteins we focus on are Cyclin B, and Cyclin Dependent Kinase (CDK). Cyclin B gradually builds from interphase to the end of mitosis, where it suddenly drops to start over again in the next interphase. CDK maintains a steady level throughout the process. The cooperation of the two cycles results in a curved pattern. If the proteins do not follow their patterns, the cell cycle cannot continue properly. If a protein stays present when it should decrease in amount, it may lead to a particular type of cancer. However, this also allows us to use targeted treatment for the illness. Meiosis – the production of gametes: Produces haploid gametes. Has two round of Prophase, Metaphase, Anaphase, and Telophase The first round of meiosis is considered the reduction division, where the cells are reduced from diploid to haploid, and stay as such through the second round. The second round of meiosis is more like mitosis with sister chromatid separation. Stages of Meiosis: 1.) Prophase 1: Starts a lot like mitosis where the chromatin condenses, and the nuclear envelope begins to break down. Unlike in mitosis, homologous chromosomes from mom and dad line up together to create a synapsis (very close association). These two sets of chromosomes are also called a tetrad, or bivalent. There are 4 chromatids total in this junction, two sets of sister chromatids. CROSSING OVER TAKES PLACE IN PROPHASE 1! Crossing over is where, at a chiasma (direct contact of chromatids), genetic material is physically broken and swapped as the homologous, nonsister chromatids entangle. The chromatids will then have pieces from both parents, creating four unique chromatids Crossing over, as far as we’re concerned, is between nonsister chromatids. Nonsister chromatids are the same in overall genetic information, but their alleles may contain different characteristics. Even if sister chromatids swap information, we would be unable to tell genetically due to identical genes. Can take place many places along the length of chromosome 2.) Metaphase I: The homologous pairs of male and female chromosomes are still attached. They line up together in the middle via microtubules along metaphase plate. Every time the homologous pairs of chromosomes line up to divide for a meiosis, the chromosomes can line up in a different order, with different parent chromosomes on either side of the metaphase plate. This results in a multitude of genetic possibilities. The number can be calculated with 2^n, where n = number of homologous pairs. Humans have 23 sets of chromosomes, which results in over 8 million different combos. 3.) Anaphase I: Homologous pairs of chromosomes are separated, causing a reduction in the number of chromosomes. THIS IS WHERE THE CELLS BECOME HAPLOID. 4.) Telophase I: This phase is not the same across every organism and species. The chromosomes will be at opposite poles in separate cells, but not all form a complete nuclear envelope. Some will form partially, others completely. 5.) Prophase II: Chromosomes recondense, and the nuclear envelope breaks down. 6.) Metaphase II: Like metaphase of mitosis, chromosomes align in no particular order on the metaphase plate. 7.) Anaphase II: Sister chromatids separate, each forming a separate chromosome. 8.) Telophase II: Chromosomes arrive at spindle poles, nuclear envelope reforms, and cytoplasm divides. Should result in four genetically distinct cells. Consequences of Meiosis: 1 parent cell usually creates 4 new cells with a chromosome number reduced by ½. Cells produced from meiosis are genetically distinct due to crossing over (creating sister chromatids that are not identical), as well as random distribution of chromosomes in Anaphase I due to random line up in Metaphase I. With meiosis, you usually end up with 4 genetically different cells. Human females are an exception to this rule. o Both a male and female start with a diploid cell (arise from spermatogonium or oogonium). Sperm goes through process of meiosis without any deviation. However, on the female side, there is a difference. o On the nuclear level, meiosis occurs as expected. But, at the end of meiosis I, there is unequal cytokinesis. All the possible extra cytoplasm that can be deviated to once cell will be to create the secondary oocyte. The smaller half is called the first polar body, and will not become an actual gamete. o The secondary oocyte will then undergo meiosis II, and once again has unequal cytokinesis, creating 1 viable 1n ovum, and a second polar body. o Fertilization of an egg by a sperm will create a diploid zygote. One hypothesized reason for the unequal cytokinesis is giving as much nourishment to a developing offspring as possible. The overall process is, however, the same. GEN 3000 – Notes Set 3, 01/13/2016 Dr. Tsai, Clemson University Chapter 2 Continued, Beginning of Chapter 3 Meiosis Continued: Meiosis is a longer process in females. It starts in the embryonic ovary, and freezes in meiosis I. Then, upon ovulation in a young adult female, it restarts, and freezes in Meiosis II, and only completes if fertilization occurs. Keep in mind that plants also have this cycle. They go between diploid and haploid, also called the sporophyte and megaspore (female side of plants), respectively. Chapter 3: Mendelian Genetics About Johann Gregor Mendel: Mendel’s work is the basis of what we know about genetics. He was carrying out his work in the 1850s – 1860’s. He may have read some of Darwin’s work during this time, but it isn’t certain. He was a monk, and after he carried out his work and published his findings, he was called to other duties. He did not return to genetics. At the time of publishing, his work wasn’t really recognized. In the early 1900s, as other scientists began doing similar experiments and achieve similar results, Mendel’s work begins to get recognized and built off of. Mendel’s scientific and experimental approach were very detailed, and allowed little room for error. Mendel used the garden pea plant, which was a perfect model for studying genetics and heredity due to the following characteristics: o Grow rapidly o Produce many offspring o Had genetically pure strains to start with o Stem characteristics, color, seed shape, and seed coat color allowed him to study genetic variation and heredity. o Mendel avoided base plants with a lot of variation Vocab: Gene: A genetic factor that is responsible for determining characteristics – Johannsen established the term “gene” from the original term of pangenesis. Allele: One of the possible forms of a gene. In Mendel’s experiments, the same gene with a different allele was what produced the two different colors of pods, or wrinkled versus round, as well as the other varied characteristics. Locus/Loci: A location on a chromosome where an allele is located. Genotype: The set of alleles than an individual possesses. Can be heterozygous or homozygous. This is the ONLY thing that is inherited. Phenotype is not (see below). Heterozygote: An Individual with two different alleles at a locus. Homozygote: An individual with two of the same allele at a locus. Phenotype or Trait: The appearance or manifestation of a character – this is equal to the genotype combined with the environmental factors that contribute. Character or characteristic: An attribute or feature. Blue or green eye color, etc. Homologous chromosomes can have alleles that occupy the same locus, but may have different characteristic exhibition. This is true across species. Mendel’s work: Started with a monohybrid cross, or two pure parents that had one characteristic opposite of each other, such as two tall plants with green pods and seed coats, but one plant had a smooth seed coat, the other wrinkled seed coats. He did this to look at one characteristic at a time. Pea plants prefer to selffertilize, so Mendel cut off the anthers (pollen provider) of the flower so the plants could not fertilize themselves. This way he could control phenotypic variables. He did crosses in both directions, such as where first the female plant would have the wrinkled seeds, then the second time the male plant would have the wrinkled seeds This was called a reciprocal cross. By doing this, he showed that all inheritance was independent of the sex of the parent. 1.) The Experiment began with the Parent generation abbreviated P, that were homozygous for round seeds or wrinkled seeds. He cross pollinated the plants to produce the F1 generation (filial 1). 2.) Within the F1 generation, he noticed that one of those phenotypes (wrinkled seeds) disappeared from the offspring characteristics. He then allowed the plants to selffertilize, to produce the F2 (filial 2) generation. 3.) This second set of offspring would exhibit the wrinkled seeds again, but in a 3:1 ratio of round to wrinkled seeds. He did this for all of the characteristics. Mendel’s conclusions: Through this process, performed hundreds of times, Mendel discovered that the unit factors came in pairs (what we now call alleles), so that each trait has 2 different unit factors that result in different traits, and gives 3 possible combinations. This experiment also showed that Dominant and Recessive traits existed, and that those that disappeared were recessive and required 2 of them to show in the phenotype. That’s why it returns in F2. He determined that the alleles had equal genetic opportunity in hybrid, or heterozygous, individuals, and are separated into the gametes (each parent only contributes o This led to the Principle of Segregation, Mendel’s first law. He concluded that plants that produced purely round seeds contained only dominant alleles (RR), and wrinkled seeds alone were recessive only seeds (rr). When those alleles were separated and combined by fertilization, they would separate equally, and produce only Heterozygous individuals with round seeds (Rr). Then, in the F2 generation, there are even greater possibilities of combinations (RR, Rr, rR, rr). Mendel did continue onto the F3 generation, and it further supported his theories. Punnett Square: Developed by R.C. Punnett in 1917 Allows us to quickly determine the possible genotypic and phenotypic ratios based on parental allele contribution. For the above example, a simple Punnett Square would look as follows: Both parents heterozygous R (round) r (wrinkled) (phenotypically round seeds) R (round) RR (homozygous dominant/round) rR (heterozygous/round) r (wrinkled) Rr (heterozygous/round) rr (homozygous recessive/wrinkled) Types of Genetic Crosses Mendel Used: Backcross: Experimental action where an offspring is fertilized back to a parent individual. Can be done with either parent. Test cross: Cross of a dominant expressing individual of unknown genotypic makeup (R_) to a heterozygous recessive individual (rr) to see what offspring are produced. This allows us to determine the second allele in the individual with a dominant trait. A test cross MUST be done with a homozygous recessive individual. o If there is a 50/50 split of offspring with dominant and recessive traits, a test cross shows there is a recessive allele with the dominant in the test plant (Rr). o If there are only dominant traits in the offspring, the test plant is homozygous dominant (RR). Genotypic and Phenotypic Ratios of Single Characteristics from Specific Parent Crosses: Two heterozygous parents (Rr x Rr): 1:2:1 Genotypic ratio, (1RR, 2Rr, 1rr), but a phenotypic ratio of 3:1 (3 dominant, 1 recessive). Heterozygous parent crossed to a homozygous parent (Rr x rr): 1:1 Genotypic ratio (2Rr, 2rr), with a phenotypic ratio of 1:1 (2 dominant, 2 recessive). Two homozygous parents crossed (RRxrr;RRxRR,rrxrr): Uniform progeny result, phenotypically and genotypically. In other words, all offspring will be dominant in (RRxrr or RRxRR) or all recessive in (rrxrr). If the genotype in such a cross cannot be determined, it is shown with an underscore as the second allele (R_). Experiments with Heredity of Two Characteristics: After determining the heredity of a certain characteristic, Mendel started comparing the heredity of two different phenotypes at once. He did so using dihybrid crosses. The genotype for one parent would be RRYY, dominant homozygous dominant for two characteristics, and the other parent would be rryy, homozygous recessive for two characteristics. o The F1 generation, once again, shows that all are heterozygous for all traits (All RrYy). o The F2 generation, when crossed with various possibilities, he figured out for all different dihybrid characteristic crosses, produced a 9:3:3:1 phenotypic ratio. (9 with 2 dominant traits; 3 with the first dominant, and second recessive trait; 3 with the first recessive, and the second dominant trait; and 1 with only recessive traits). This developed Mendel’s Principle of Independent Assortment , which states that different alleles do not impact each other. This occurs when alleles are on different chromosomes. Probability in Genetics: It is still possible to use the Punnett Square with dihybrid crosses, but it gets harder the more loci you look at. Instead, you can use probability. o The multiplication/product rule is used any time you are asking AND, where you have independent events, and you want to figure out the probability of these events happening one after the other. The events MUST BE INDEPENDENT OF EACH OTHER. You then multiply the probability of each individual event to the other. AND = MULTIPLICATION o Example: In a coin toss, there is a ½ chance of getting heads the first time, and ½ chance of getting heads the second time. If you want to know how probably it is to get heads the first AND second time, you multiply ½ x ½ to get ¼, or 25% chance of getting heads both times. This can be used in genetics with alleles. What is the probability of getting a certain allele from one parent, and the probability of getting a second allele, from each parent to give a certain genotype in the offspring? o Example: RR x Rr – What is the probability of getting an Rr offspring? 2/2 chance to get R from parent 1, and ½ chance to get r from parent 2. 1 x ½ = ½, or a 50% chance to get Rr. Another method to determine heredity in a dihybrid cross is the use of a branch diagram, also called a fork diagram. You need to know within each gene what you’re expecting. You start with one characteristic (such as seed coat color) and split them into their dominant and recessive ratios. Within each of those ratios, you split them further into the ratios of the dominant and recessive expressions of the second characteristic. This shows, out of that group, how many of them have the other phenotype you’re looking at – much easier to see on paper. GEN 3000 – Notes Set 5, 01/152016 Dr. Tsai, Clemson University Chapter 3 Continued Reminder: The multiplication/product rule is used any time you are asking AND, where you have independent events, and you want to figure out the probability of these events happening one after the other. Probability: Can be applied to hybrid, dihybrid, or even greater crosses. The easiest way to work with probability in larger crosses is by looking 1 loci at a time (In other words, when looking at RrYy x RrYy, only look at the R’s first, then the Y’s). o How likely is it the offspring will have the genotype rryy? First, we look at the R loci. In parent 1, there is a ½ chance to get the r, which is the same as parent two. Since we’re looking for r AND r, we must multiply the two probabilities together. ½ x ½ = ¼ chance of getting an rr. o If we look at the Y loci, there is a ½ chance to get the y out of both parents, allowing us to do the same process of ½ x ½ = ¼ chance of getting y AND y. o However, we need to get rr AND yy. Since we need both of these combinations, we must multiply the probability of each loci occurring (which we just found) as follows: ¼ x ¼ = 1/16 chance to get the genotype of rryy. o What about this example? Probability of crossing RRYy x RrYy to get RrYy. Answer and work is below in white – highlight and change color to see. Probability of R’s: Parent 1 = 2/2 (or 1) chance of an R. Parent 2 = ½ chance of an r. 1 x ½ = ½. Probability of Y’s: Parent 1 = ½ chance of a Y. Parent 2 = ½ chance of a y. ½ x ½ = ¼ chance of a Yy. Probability of genome in question: ½ chance of Rr. ¼ chance of Yy. We need both, so ½ x ¼ = 1/8 chance of RrYy. o NOTE: This is probability of genotypes. When looking at the probability of phenotypes, we will take other factors into account. This is easier to understand once you know how to use the addition rule, which can be found below. We can relate Mendel’s pea plants to chromosomes, and the overall idea of independent inheritance. Walter Sutton (1900s): Studied insects, and discovered that chromosome sets contain one chromosome from the maternal side, and one from the paternal side. He also found that these chromosome sets segregate independently at meiosis. He developed the Chromosome Theory of Heredity from this – the idea that genetic material in all living organisms is contained in chromosomes. Each homologous chromosome has corresponding alleles. The two alleles segregate during either anaphase I or anaphase II, depending on whether or not crossing over has occurred. The addition Rule of probability: When two mutually exclusive events are connect by an “either” or an “or,” we must use the addition rule. In other words, if two evens can happen separately, and do not rely on each other, we must add the probability of each individual event happening together. If we are wondering what the probability of getting heads OR tails of a coin flip, we would take ½ + ½ = 1, or 100%. If we look at a die, and we want to see what the probability of rolling a EITHER a two OR a three is, we look at each one. We know, with 6 sides, the probability of rolling a two is a 1/6, as is the probability of rolling a three a 1/6. Since we’re using the addition rule, we must add them together to get 1/6 + 1/6 = 2/6. NOTE: 2/6 can then be simplified to 1/3. ALL FRACTIONS SHOULD BE SIMPLIFIED. We can apply the addition rule to genetics very easily! If we look at a cross of Tt x Tt, and we want to know how likely it is to get the dominant gene expressed, we can use probability to figure that out. o We know if a dominant gene is expressed, it has to have at least 1 dominant allele, but can also have a recessive allele. That means we might have TT, tT, or Tt genotype to get an offspring expressing the dominant trait. We know from a Punnett square that there is a ¼ chance of a TT, a ¼ chance of tT, a ¼ chance of Tt, and (even though we won’t be using it in this case) a ¼ chance of a tt. o To see how probable it is for a dominant expressive offspring, in other words, to have TT OR tT OR Tt, we add their individual probabilities together! ¼ + ¼ + ¼ = ¾ chance of having a dominant expressing offspring. This can also be done with more loci, as well. o What about this example? Tt x Tt – what is the probability of the offspring having either a Homozygous dominant, or a homozygous recessive offspring (without using the Punnett square)? Answer and work below in white – highlight and change color to see: Chance of getting T from both parents: ½ chance from parent 1, and ½ chance from parent 2 – so, ½ x ½ = ¼ chance of a dominant T from both parents to get a TT offspring. Chance of getting t from both parents: ½ chance from parent 1, and ½ chance from parents 2 – so ½ x ½ = ¼ chance of a recessive t from both parents to get a tt offspring. Chance of TT OR tt: The OR indicates we must use addition. ¼ + ¼ = ½ chance of getting a TT OR tt. We can use both the multiplication and addition rule within the same probability to determine the chances of a certain phenotype or genotype occurring, as can be seen in the extra example above. Harder example using both the addition and multiplication rules: What is the probability that AaBbCC x aaBbCc will give us an offspring recessive for a OR an offspring recessive for b? Remember, in order for a trait to be recessive, it HAS to have TWO recessive alleles. In other words, the offspring must have two a’s, or two b’s. Chance of getting an a from BOTH parents: parent 1 has ½ chance of an a. parent 2 has 2/2 chance (or 1) for an a. So, to get a AND a, we take ½ x 1 = ½ chance of an aa genotype. Chance of getting a b from BOTH parents: Parent 1 has ½ chance of a b. Parent 2 has ½ chance of a b as well. So, to get b AND b, we take ½ x ½ = ¼ chance of a bb genotype. Chance of getting aa OR bb: Because the example is asking for the likelihood of either recessive a or recessive b, we must use addition. We have ½ chance of an aa genotype, and ¼ chance of a bb genotype. ½ + ¼ = 3/8 chance of a recessive expression in a or b alleles. What if it was the chance of getting recessive a and recessive b expression? Answer to the right in white – highlight and change color to see: ½ x ¼ = 1/8 chance of both aa and bb genotypes. Chance: In the real world, things do not always happen according to probability. There is always a measure of chance involved. For instance, if you flip a coin twice, the probability would suggest that you will get 1 heads, and 1 tails, or ½ and ½. However, chance comes into play, and that may not happen. To rule out errors as a cause of variation from probability when conducting experiments, we use the chisquare test. It won’t tell you where you went wrong, only the likelihood that the difference between what was expected (probability) to what actually happened was due to chance. o What the Chisquare test DOES: Uses found values to determine the probability that a number different than what was expected is due to chance. o What it DOESN’T do: Tell you where the problem is. Tell you if the cross has been done correctly. Tell you if your results are correct 2 2 ∑ (¿observed−¿expected) The formula for the Chisquare test is x = ¿expected We will then cross reference what is found using the chisquare test with the degrees of freedom (n1) on the chart of critical values for the chisquared test. The degrees of freedom requires us to know the number of possible outcomes, and subtracting that number by 1. For instance, in a single allele cross (TtxTt), there is a ratio phenotypic ratio of 3:1 dominant to recessive. Therefore, there are only two possible outcomes. Our degrees of freedom will be 21 = 1. This is on the left side of the chart we reference. Once we have our value and our degrees of freedom, we go to the left, and look at the row for degrees of freedom to see where the value from our chi square calculation falls according to the numbers (P) along the top of the chart. If our P value falls above .05, or 5%, there is a greater than 5% probability that variation from expected outcomes is due to chance. If our P value falls below .05, there is less than a 5% chance that variation from expected outcomes is due to chance, and we must go back and see where our experiment went wrong. In an experiment, we start with something called the null hypothesis (H0). This hypothesis cannot be proved as correct, but can either be rejected by showing data to be faulty (variable due to something other than chance), or fail to be rejected. o If the P≥.05, we fail to reject the null hypothesis, because the experiment variation was probably due to chance. o If the P≤.05, we reject the null hypothesis, because something went wrong, and our values vary from the expected outcome due to something other than chance. Possible errors in experimentation, resulting in P≤.05, may be attributed to: Errors in counting Crossing the wrong set of parents Deaths of experimental subjects before counting could occur An unknown variable playing a role Many other possibilities Pedigree Charts: The legend is incredibly important for pedigree charts! For the purposes of this class, we must know only the general, basic rules of pedigree charts, which can be found below. Unknown/Unspecifie Male Female d Sex Unaffected individuals Affected individuals Obligate carrier: not affected, carries trait Asymptomatic carrier: Has trait, but is unaffected for now. Multiple individuals 3 3 3 represented (3) Deceased Individual Proband: The first affected family member coming to P P attention of genetics P P P Family history of individual is ? ? ? unknown Family: In this case, a father, mother, and four children (in I order of birth from left to right). Note: the roman II numerals on the left represent generation numbers. Adoption: If an offspring is I adopted, it is shown in brackets. A dotted line goes from its adoptive parents, and aII solid line from its biological parents in a separate family line. ? Twins: From Right to left: Identical, nonidentical, and unkown if identical or nonidentical. Consanguinity: Mating between related individuals. Represented by a double line I connection. II Note: In dogs, the double line isn’t always shown for consanguinity due to individuals being from the same litter. III Note: If there are offspring from DIFFERENT families within the same generation, the offspring may not be in birth order from left to right. They are in birth order within immediate families, but not necessarily across different families.
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