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QuestionMendelian traits are those that are inherited simply and are…   Mendelian traits are those that are inherited simply and are expressed based on the presence or absence of dominant and recessive alleles. The genotype of a trait is the combination of two inherited alleles at one locus (both of these alleles can either be dominant or recessive). The genotype determines phenotype, or how the trait is expressed. If one dominant allele is present in the genotype, either as homozygous (both the same) or heterozygous (one each of dominant and recessive alleles), the dominant phenotype will be expressed. If the alleles are homozygous recessive, or both recessive, then the recessive phenotype will be expressed.   A. Below is a list of traits that are inherited in this way. Record which phenotype you display for each trait by marking the appropriate column with an X (for these traits this will be presence or absence of the trait). The photographs supplied will help you determine whether you do or do not exhibit the trait. (9 pts) Trait Descriptions: 1.   Widow’s peak:  A distinct downward point of the hairline at the center of the forehead is called a widow’s peak (if you are a lady and have this trait you are supposed to outlive your husband). A receding hairline due to baldness will mask this trait, so try to remember what you may have looked like in your younger days. The dominant phenotype for this trait is to have a widow’s peak, while a straight hairline is recessive.  2.   Attached earlobes: The inheritance of a dominant allele results in earlobes that hang free rather than attaching directly to the side of the head. Those with attached earlobes are homozygous recessive for the trait.   3.   Darwin’s tubercle: A projection or thickening of cartilage on the outer rim of the ear about halfway up is called a Darwin’s tubercle. The size of the projection is variable and may be seen on only one ear, but the presence of a tubercle is due to a dominant allele. Absence of the trait is recessive. 4.   Hitchhiker’s thumb: Hold your hand up like you’re trying to hitch a ride. If the end of your thumb bends backwards more than 45 degrees, you have “hitchhiker’s thumb.” If your thumb is straight, start thinking of another way to get a ride. Straight thumbs are dominant, while expression of the hitchhiker’s thumb is recessive. 5.   Bent little finger:  Lay your hands palm down on the table and relax your muscles. If the last joint of your little finger angles slightly towards your ring finger, your little finger is “bent.” This is the result of a dominant allele causing in shortening of the middle bone of your little finger so that it has a triangular shape. Those with straight little fingers are homozygous recessive.  6.   Mid-digital hair: The presence of hair on the middle segment of the fingers is due to the presence of a dominant allele. Make fists with both hands. Examine the surface of the middle finger segments for the presence of any hair. Those with no hair are homozygous recessive. 7.   Short hallux: Compare the length of your big toe (hallux) to your second toe. If your big toe is shorter than your second toe, you have inherited a dominant allele. If your big toe is equal to or longer than your second toe, you are homozygous recessive for this trait. 8.   Left thumb hand clasping: Fold your hands together by interlacing your fingers. Which thumb is on top? Try interlacing your fingers the opposite way. It will feel awkward and may require some thought to accomplish. Those who place the left thumb over the right have inherited a dominant allele, while those who place the right thumb over the left are homozygous recessive. 9.   Short index finger: This trait is sex-linked, so is inherited a little bit differently than the previous traits. Having a short index finger is the recessive state, but since the alleles are located on the X chromosome, you need two recessive alleles to be a short index-fingered lady (since you have two X chromosomes), and only one recessive allele to be a short index-fingered man (you and your embarrassing Y chromosome!). To find out the state of your fingers, lay your hands palm down on the table. Look to see whether your second (index) finger is shorter than your fourth (ring) finger. If so, then you have a short index finger!   TRAIT                                         PRESENT     ABSENT    Dominant State1. Widow’s peak                     ________     ________             Present2. Attached earlobe                ________     ________             Absent3. Darwin’s tubercle              ________     ________   Present4. Hitchhiker’s thumb            ________     ________   Absent5. Bent little finger                 ________     ________   Present6. Mid-digital hair                  ________     ________   Present7. Short hallux                      ________     ________   Present8. Left thumb hand clasping  ________    ________   Present9.  Short index finger              ________     ________   Absent1.   Do you more often express dominant traits out of the traits above? (1 pt)2.   Do you think any of these traits provides an “advantage” in the human environment (i.e., natural selection)? (1 pt)3.   Why is variation in traits, phenotypes and genotypes important for natural selection? (2 pts) Part 2: Mendelian Inheritance Mendel came to some amazing conclusions about heredity through observation and some very simple cross-breeding experiments with pea plants. For instance, he was able to identify that genes are passed down from both parents, can be expressed in different ways, and act as discrete units.  Two principles were illustrated: The Law of Segregation simply states that the two alleles of a gene pair segregate (separate) from each other in the formation of gametes. Half the gametes carry one allele, and the other half of the gametes carries the other allele.The Law of Independent Assortment tells us that genes for different traits assort independently of one another in the formation of gametes. Punnett Squares To help understand Mendel’s laws, we can use a Punnett Square. Punnett Squares are designed to illustrate how alleles for a gene can be passed on from parents and combined and inherited in offspring.  A. Punnett Squares crossing one geneIn the example below, the letters H and h represent the two alleles found for the gene expressing mid-digital hair. Remember from earlier that having hair on your knuckles is the dominant state, and is represented here by H. A Punnett Square is organized with the potential gametes produced by parents (the F0 generation) in the first column and row. Only one allele will be passed on in each gamete, as described in Mendel’s Law of Segregation.  The interior of the Punnett Square, which is shaded gray here, is where you find the possible combinations of alleles that could occur in the offspring (the F1 generation) once the gametes from both parents find themselves together. Each potential offspring genotype is equally likely to occur.      Parent 1 (Hh)   Parent 2 (Hh)    H h H HH Hh h Hh hh There are three possible genotypes in the offspring from this mating: HH, Hh and hh. The ratio of these genotypes is 1:2:1.  From these genotypes only two phenotypes are possible: those who have hairy knuckles and those who do not. Because H, hairy knuckles, is dominant, both the HH and Hh genotypes express a hairy-knuckled phenotype.  Read the explanations and answer the questions below based on what you have learned from the Punnett Square above. Make sure you understand the basics, because more complex squares are next.4. Mendel discovered that one of his pea plants could have either green pea pods or yellow pea pods. G represents the dominant green color, and g represents the recessive yellow color. Mendel found that one of his favorite plants was heterozygous for pod color. a.   What is this plant’s genotype for pod color? (1 pt)b.   What is this plant’s phenotype for pod color? (1 pt)c.   In order for the plant to have the recessive pod color, what would the genotype have to be? (1 pt)   5. You decide you want to find out which pea pod color looks better with your garden. You begin your experiment with the seeds from a homozygous green plant and a homozygous yellow plant. These parents are the F0 generation of your experiment.  a.   What are the genotypes for each plant? (1 pt)b.   Fill in the Punnett Square below to illustrate a cross between the two plants (4pts)  Parent 1 (    )   Parent 2 (    )    c.   What is/are the possible genotype(s) for the offspring produced by crossing the plants? This group of offspring is the F1 generation. (1pts)d.   What is/are the possible phenotype(s) for the F1 generation? (1 pts)6. You discover that the F1 generation does not provide you with both color pea pods to compare in your garden.  You decide you may as well not let all these pea pods go to waste, so you make a cross between two of the F1 generation to discover what might happen next. The product of this second cross is called the F2 generation.   a.   Fill in the Punnett Square below to illustrate a cross between two members of the F1 generation (4 pts):  Parent 1 (  )   Parent 2 (  )    b.   What is/are the possible genotype(s) for the F2 generation? (1 pt)c.   Can this second generation help you decide which pea-pod color looks best in your garden? (1 pt)7. In your own words, explain how the Law of Segregation works when gametes are created (2 pts):B. CodominanceThe ABO blood system is responsible for blood type. The gene for blood type works in the same way as all of the above examples, but has three possible alleles (A, B, and O) instead of two. The A and B alleles are codominant, meaning that whenever they are present they are expressed, including when they are both present in the same individual. The O allele, on the other hand, is always recessive.           Blood Type (phenotype)             Possible Alleles (genotype)                       AB                                                      AB                       A                                                        AA or AO                       B                                                        BB or BO                       O                                                        OOScenario: A daytime talk show is doing a spot about a child, his ‘forgetful’ mother, and the kid’s two potential fathers. The talk show had enough money to find out the blood types of all of the characters involved, but doesn’t know where to go from there to determine who the father of the child is. They have asked for your help, and provide you with these blood types: Mother: Type A Potential Father 1: Type A Potential Father 2: Type O Child: Type O 8. List the possible genotypes for each individual. (2 pts) Mother:                                      Potential Father 1: Child:                                          Potential Father 2: 9. Write down the gametes that mom must have made, and also those that could have been produced by each potential father. Mother:                      Potential Father 1:              Potential Father 2    10. With this information, is it possible to exclude either of them as the father      of the child? Why or why not? (4 pts)11. In classic daytime style, a surprise twin of the child is produced (yes, he has the same father as the first child). He is revealed to be blood type A. Does this information help you exclude either of the potential fathers? Why? (2 pts)12. How is the inheritance of the ABO blood system different from the other examples you’ve worked with in this lab? Give at least 2 reasons. (2 pts)  ScienceBiologyBIO 101Share Question