BIOL100 Laboratory Assignment 5: Genetics. Name: Part A:

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1 BIOL100 Laboratory Assignment 5: Genetics Name: Part A: Genes are regions o chromosomes that code or a speciic product, usually a protein. In diploid organisms, each cell contains two copies o each chromosome (except or in the case o the sex chromosomes) and thereore two copies o each gene. Not all genes are the same and types o the same gene that are slightly dierent are termed alleles. Dierent alleles are usually written short hand using a system o lower and upper case letters. For instance, the dierent alleles o the gene or inger hair might be written as an H or the allele that leads to inger hair and as an h or the no inger hair allele. Capital letters are usually assigned to an allele that is dominant. Being a dominant allele means that i a person carries that allele then they will display the trait that is coded or by that allele. Alternatively, lower case letters are assigned to traits that are recessive. Recessive traits are only displayed by an organism i that organism does not carry any copies o the dominant allele. Using the example above, we can write out potential allele combinations that a person might carry or the inger hair gene. Remember, a person will carry two copies (alleles) o each gene because we have two copies o each o our chromosomes. Genotype HH Homozygous dominant Heterozygous Homozygous recessive Above, the potential allele combinations or the inger hair gene are written. These are termed genotypes, because they indicate the type o gene alleles that a person could be carrying. I both o the alleles that a person carries are the same, that genotype is reerred to as homozygous (i.e. HH and hh are both homozygous genotypes). I the two alleles are dierent than an individual would be heterozygous or that gene (i.e. ). Using the inormation rom above on which trait is dominant and which trait is recessive, we could also assign to each o these genotypes a phenotype. A phenotype is the trait that an organism with a given genotype would display. In the above example we would have the ollowing phenotypes. Note that i a person displays the recessive phenotype, you also know that they are homozygous recessive in their genotype, but that i they display the dominant genotypes you cannot determine whether they are homozygous dominant or heterozygous without getting additional inormation. Genotype HH Phenotype Finger hair Finger hair No inger hair 1

2 Go through the ollowing list and determine what your phenotype is or each trait. Do you display the dominant or the recessive phenotype? Trait 1. Finger hair The presence o inger hair on the middle segment o your ingers is determined by a single dominant gene. 2. Tongue rolling The ability to roll your tongue into a U shape is controlled by a single dominant gene. 3. Tasting Phenyl thio carbamide (PTC) The ability to taste PTC is controlled by a single dominant gene. There is PTC paper available at your tables. Touch a small piece o the paper to your tongue (it is harmless); i you can taste PTC you will be able to taste a strong bitter taste. I you are unable to taste PTC you will not taste anything. Approximately 70% o the population can taste PTC. 4. Widow s Peak This reers to the ormation o a point in your hairline at the center o your orehead. Widow s peak (i.e. having a point) is determined by a single dominant gene. 5. Free Ear Lobe Free ear lobes are dominant over attached ear lobes. 6. Darwin s Ear Point Feel along the upper curved part o your ear. I you can eel a thickening in the cartilage there, then you have Darwin s ear point (it can be present in just one ear). This is a dominant trait. 7. Clet Chin Having a clet chin (a distinct indentation in the center o the chin) is a dominant trait. 8. Hitchhiker s thumb Bend your thumb back as ar as you can (without pulling on it or causing any pain). I your thumb can naturally bend backward urther than vertical (hyper extensibility), then you have a hitchhiker s thumb. This is a recessive trait. 9. Interlocking ingers Shake your hands and then, without over thinking, clasp your hands together interlocking your ingers. Which o your thumbs is on top? Having the let thumb on top when your hands are clasped is controlled by a single dominant gene. Part B: Your Phenotype Dominant or Recessive? Traits such as those listed above are oten used to reconstruct amily trees, determine amilial relationships, or determine genotypes. In animals and plants, traits such as these can be used to determine genotype so that breeding can be selectively carried out, or instance to create dogs with a desired type o ur or lowers with a speciic color. Oten, genetics problems can be most easily solved through the use o a Punnett Square. A Punnett Square is a way o graphically depicting the separation o alleles rom each parent (remember, only one copy o each chromosome is contained within a sperm or egg and so each parent is only giving one copy to their ospring). By completing the Punnett square, you are depicting the potential genotypes o zygotes and also gaining inormation about the likelihood o dierent potential ospring genotypes and phenotypes. 2

3 As an example: Two individuals, a emale with inger hair and a male without inger hair are trying to have a child. What is the likelihood that they have a child with inger hair? Note, the emale had a ather who did not have inger hair. The irst step is to determine the genotypes o the male and emale: Because igure hair is dominant and the male doesn t have inger hair, he must be homozygous recessive with a genotype o. The emale has inger hair, so she must have at least one F but her ather was homozygous recessive () and she had to get one o her alleles rom her ather so she must also have an. This means that she is heterozygous or inger hair (F). The second step is to set up a Punnett Square: Female potential gamete alleles: F Male potential gamete alleles: Complete the Punnett Square by illing in the alleles rom the emale and male down and across, respectively, to indicate the potential zygote genotypes. Female potential gamete alleles: F F Male potential gamete alleles: F The inal step is to determine the ratios o these dierent genotypes and their respective phenotypes. This couple has a 50% chance o having a child with an F genotypes and 50% chance o having a child with an genotype. The phenotype o F is inger hair and the phenotype o is no inger hair. Thereore, the couple has a 50% chance o having a child with inger hair. 3

4 Complete the ollowing genetics problems. These problems will help you develop your skills in the process o solving these types o problems. Some new terms will also be introduced as you work through several o the problems below. Make sure that you show the work that you do to solve each problem. This will usually involve making a Punnett Square. 1. In corn, the gene or high sugar production (s) is recessive to starch production (S). What are the phenotypes or the ollowing individuals: a) ss b) Ss c) SS 2. I a high sugar corn plant is crossed with a heterozygous starchy plant, what is the likelihood that the seeds produced with be or a high sugar plant? 3. In dogs, long ur () is recessive to short ur (F). I a long urred emale is crossed with a homozygous short urred male, a) what are the potential genotypes o their puppies? b) what are the potential phenotypes o their puppies? 4. In cats, having six toes is controlled by a single dominant gene. A six toed heterozygous cat is crossed with a normal toed cat. What is the likelihood that their kittens will be born with 6 toes? 4

5 5. Sickle cell anemia is a recessive trait. I two individuals who carry the allele or sickle cell anemia have children, a) what is the likelihood that the child will have sickle cell anemia? b) what is the likelihood that their child will be a carrier or sickle cell anemia? 6. In some lowers, pigments show incomplete dominance. In a trait that has incomplete dominance, the homozygous dominant o a trait will show a strong phenotype (red lowers), the homozygous recessive will have a weak trait phenotype (white lowers), and the heterozygote will display an trait phenotype that is intermediate (pink lowers). a) I you cross two pink lowers (Rr x Rr), what are the likely genotypic ratios o the ospring? b) I you cross two pink lowers, what are the likely phenotypic ratios o the ospring? c) What are the likely ratios in phenotypes produced when a red lower and a white lowered individual are crossed? 5

6 7. Some alleles are co dominant. In co dominant alleles, the phenotype o both alleles are expressed. A common example o co dominance is blood type. The alleles or blood type are as ollows: I A, I B, and i. An individual with type A blood (a phenotype) could have a genotype o either I A I A or I A i. An individual with type B blood could have a genotype o either I B I B or I B i. An individual with type AB blood has the genotype I A I B and an individual with type O blood has the genotype ii. a) I a male with type AB blood marries a woman with type A blood (and her ather had type O blood), what are the possible blood types o their children? b) I two people, both with type AB blood have children, what are the possible blood types o their children? c) I two people, both with type AB blood have children, what is the possibility that they have a child with type O blood? 8. Some alleles are sex linked. Sex linked alleles occur on the X chromosome only, so human males (XY) only have one copy o these alleles. This means that they will display the dominant phenotype i their one copy o the allele is the dominant allele and they will display the recessive trait i their one copy o the allele is the recessive allele. Hemophilia is a sex linked recessive phenotype. I a woman who is a carrier or hemophilia (this means that she "carries" a copy o the allele but that she doesn't display the phenotype) marries a man who does not have hemophilia, a) what are the chances that, i they have a male child, that the child will have hemophilia? 6

7 b) what is that likelihood that a child o theirs o any sex will have hemophilia? 9. All o the Punnett Square crosses that you have completed above have been monohybrid crosses (only dealing with a single gene). O course, with sexual reproduction there are many many genes that are "crossing" with any breeding event. The ollowing example will involve two genes and is called a dihybrid cross. Remember, the chromosomes independently sort in Metaphase 1, so with two genes you will have our possible allele combinations or each parent (a 4 x 4 Punnett Square). In rabbits, there is a gene or short hair (H) that is dominant over the gene or long hair (h). There is also a gene or a Brown coat color (B) that is dominant over black coat color (b). a) Complete a dihybrid Punnett Square or the crossing o two heterozygous short haired, brown coated rabbits. b) What is the likelihood that the cross will result in a long haired, black coated rabbit? c) What is the likelihood that a rabbit will be born that has the same genotype as the parents? 7