In This Section, We Ll Define Terms You Ll Be Seeing a Lot Of

In This Section, We Ll Define Terms You Ll Be Seeing a Lot Of

Mendelian genetics and crosses.
Supplemental Instruction
IowaStateUniversity / Leader: / Matt C.
Course: / Biol/Gen 313
Instructor: / Dr. Rodermel
Date: / 12/04/2017

Introduction: This worksheet discusses material covered in the thirty-sixth and thirty-seventh lectures(12/01/2017 and 12/06/17). Chapter 3 examines these topics. We will not get through all of this worksheet in the session.

Concepts

  1. Terms to know.
  2. Monohybrid crosses.
  3. Multihybrid crosses.

Material

  1. Terms to know.

In this section, we’ll define terms you’ll be seeing a lot of.

  1. Describe the difference between a phenotype and a genotype.
  1. An organism has two codominant alleles for a certain trait. Is the organism considered homozygous or heterozygous for this trait?
  1. An organism’s parents were each homozygous for a certain trait. However, while passing on their genetic info to their offspring, a mutation occurred in one of the genes from the parents that had an effect on gene function. Is the offspring considered homozygous or heterozygous?
  1. Describe the difference between the terms “gene,” “allele,” and “characteristic/trait.”
  1. What does the Principle of Segregation say? Why is this helpful when predicting the results of certain crosses?
  1. What is a reciprocal cross? What is a testcross?
  1. Monohybrid crosses.

Here we’ll practice working with crosses.

For all of the following questions, we’ll use Drosophila melanogaster as our model organism. We’ll discuss four traits with two alleles each.

Wing Size
Normal Wings (W) / Short Wings (w)
Body Color
Normal Color (A) / Albino (a)
Eye Color
Red (R) / Orange (r)
Antennapedia
Antennapedia (L) / Normal antennae (l)
  1. You cross a true-breeding, normal-winged male with a true breeding, short-winged female. What will be the ratios for the genotype(s) and phenotype(s) of the first filial generation (F1)?
  1. You cross members of the F1 generation described above. What will be the ratios for the genotype(s) and phenotype(s) of the second filial generation (F2)?
  1. You cross a female that’s homozygous for red eye color with a male that is heterozygous for red eye color. What will be the ratios for the genotype(s) and phenotype(s) of the F1 generation?
  1. From the previous cross, you now cross only the heterozygotes from the F1 generation. What will be the ratios for the genotype(s) and phenotype(s) for the F2?
  1. You have a female of unknown genotype that exhibits antennapedia. You cross this female with a wild-type male. What will be the expected genotypic and phenotypic ratios in the offspring if the female is a heterozygote?
  1. After crossing two fruit flies and counting the number of offspring with each eye color as described below, what would you conclude about the genotypes and phenotypes of the parents?

Red Eyes / Orange Eyes
124 / 118
  1. Similar to the previous case, you conduct another cross, but look at the occurrence of albinism. What would you conclude about the likely genotypes and phenotypes of the parents?

Normal Body Color / Albino
107 / 37
  1. Multihybrid Crosses

In this section, we’ll work on some more complex crosses. We’ll be using the same fly alleles as described in the previous section.

  1. What are the expected genotypic and phenotypic ratios of crossing a true-breeding female with orange eyes and normal wings with a true-breeding male with red eyes and short wings?
  1. What are the expected genotypic and phenotypic ratios of the F2 generation after allowing the F1 generation to mate?
  1. You cross two flies and observe the wing size and body color of the offspring. What are the likely genotypes and phenotypes of the parents?

Normal body; Normal wings / Normal body;
Short wings / Albino;
Normal wings / Albino;
Short wings
62 / 19 / 20 / 7
  1. You again cross two flies and observe the eye color and possible development of antennapedia in the offspring. What are the likely genotypes and phenotypes of the parents?

Red eyes;
Antennapedia / Red eyes;
Normal antennae / Orange eyes;
Antennapedia / Orange eyes;
Normal antennae
179 / 176 / 0 / 0
  1. You cross the following two flies.

WWAaRr x WwAarr

  1. What is the probability that a random member of the F1 has normal wings?
  1. What is the probability that a random member of the F1 has orange eyes?
  1. What is the probability that a random member of the F1 has normal body color and red eyes?
  1. What is the probability that a random member of the F1 has normal wings, albinism, and red eyes?
  1. What is the probability that a random member of the F1 has short wings, normal body color, and red eyes?