Mod 5 Activity 1 PDF

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Genetics Problems: Monohybrids Name:__Aspen Greser TERMINOLOGY These are the standard terms used in problems about gene interactions, presented here in matched pairs of opposites: *Dominant – the gene is always able to show itself if present *Recessive – the gene can be hidden by its dominant partner, if one is present

*Pure (or homozygous) – indicates that the genes in a pair are alike *Hybrid (or heterozygous) – indicates that the genes in a pair are not alike

*Genotype – the set of genes present in the organism *Phenotype – the appearance of the organism

PROBLEM-SOLVING APPROACH In most cases, these steps are appropriate: 1. After reading the problem, represent genes with letters. Typically capital letters are used for dominant genes and small letters for recessive genes. 2. Write the gene pairs for each individual. Organize the parent/offspring information in a table or diagram format like that shown below. 3. Write all possible sex cells produced by each parent. 4. Write all possible fertilizations, that is, account for all possible offspring. 5. Check to see that you have answered the question posed in the problem. The following problems involve monohybrid crosses. Monohybrid crosses look at one gene that has two alleles. All the problems below follow the Mendelian pattern of one allele being completely dominant to the other allele. Hybrid refers to individuals that are heterozygous. Solve these problems using the information you have learned about Mendelian genetics.

1. In squash, white fruit is dominant over yellow fruit. If a hybrid white-fruited plant pollinates a yellow-fruited one, what ratio of fruit colors can be predicted among the offspring? 3:1, white:yellow % white – 75% % yellow – 25%

2. Human ear lobes hang freely due to a dominant gene, while attached lobes are due to recessive genes. A child whose ear lobes are free-hanging has one parent with ears like his, one parent with attached lobes, and one sibling with attached lobes. Write the genotype of all 4 people. Could other genotypes exist in other children in this family?

Child – Ha

First Parent - Ha

Second Parent - aa

Sibling - aa

No, each child has each possible genotype

3. Suppose a large-nosed man married a small-nosed woman, large nose being the dominant trait. One parent of both is known to be small-nosed. What proportion of their children is likely to be small-nosed? 50%

4. Dimples are dominant. A dimpled man and a non-dimpled woman have 10 children, all dimpled. We might be tempted to assume that the father homozygous for the dimpled trait. Do we know this? What must child #11 be to determine the father's genotype with certainty? Explain. The last child would have to be dimpled for us to be sure that the father is homozygous. Because he has two dominant alleles and the mother has two recessive alleles, his dominant genes would always trump her recessive genes.

5. Freckles are dominant. A freckled man whose father was freckled and whose mother was not freckled, married a non-freckled woman whose father and mother were both freckled. This couple has a non-freckled son. Identify the genotypes of all 7 individuals. Can all these be determined with certainty? What can we expect in terms of freckles in their future offspring. [Suggestion: make a family tree diagram.] Man: Fn Woman: nn Man’s mom: nn Man’s dad: Fn Woman’s mom: Fn Woman’s dad: Fn Son: nn I don’t believe all of these can be determined with certainty, especially the woman’s parents considering both of her parents are freckled, but she isn’t. I think I would have to see her grandparents for it to be more accurate. I think that their future son has a 50/50 chance on being freckled or not freckled....