BIOL 1020 Lecture 24: Lecture 24

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erinchimpanzee657

12 May 2017

School

University of Manitoba

Department

Biological Sciences

Course

BIOL 1020

Professor

Joy Stacey

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Mendel developed a hypothesis to explain the 3:1 inheritance pattern he observed in f2 offspring. Each gene resides at a specific locus on a specific chromosome. Homologous pair of chromosomes- different alleles but same locus: for each characteristic, an organism inherits two alleles, one from each parent. Mendel made this deduction without knowing about role of chromosomes. Two alleles at a locus on a chromosomes may be identical, as in the true breeding plants of mendel"s p generation. Alternatively, the two alleles at a locus may differ, as in the f1 hybrids. The third concept is that is the two alleles at a locus differ, then one (the dominant allele) determines the appearance, and the other (the recessive allele) has no effect on appearance. In the flower-color example, the f1 plants had purple flowers because the allele for that trait is dominant.

Related Questions

A strong understanding of the difference between gene and allele is needed now. We covered allele interactions in the lesson before this one. Allele interactions deal with a single gene and its alleles. Alleles, versions of a gene, can interact when placed together in a heterozygote.

We are now looking at two genes and how they interact. To more easily understand how two genes interact, we will only be considering the normal alleles and null alleles of both genes. Normal alleles will be dominant, null alleles will be recessive. In addition, the two genes are UNLINKED. The various interactions are made evident in standard F2 generations: Two purebred parents are crossed, a dihybrid F1 is formed, the dihybrid F1 is selfed, and F2 generation is examined. One must remember, the progeny of dihybrid selfs are always in a fixed genotype distribution: 9 A _ B_ : 3 A _ bb : 3: aa B _ : 1 aa bb. BUT, with genes interacting the phenotypic ratios are changed.

Please focus on how genes interact. You do not need to know specific pathways or organisms.

Answer the following questions.

2. There is a hypothetical plant called rat-ear. Red and pink varieties flourish in Hawaii and Long Island, NY. All the red and pink varieties can be bred true. Surprisingly, when the Hawaiian pink is bred with the Long Island pink, all the resulting progeny are red. When these red progeny are selfed the next generation has 333 red flowered and 259 pink flowered plants. The breeders breathe a sigh of relief. What do the breeders understand about the petal pigmentation of rat-ear plants?

turquoiseeel573

1.) In tomato plants, spines (s) are recessive to nospines (S), and white fruit color (w) isrecessive to red fruit color (W). The genes for spines andfruit color are located on the same chromosome; findings frommapping experiments indicate that they are 13.2 m.u. apart. Atomato plant having spines and white fruit color is crossed with aplant that is homozygous for no spines and red fruit color. The F1are crossed with plants that have spines and white fruit color.Which of the following phenotypes and proportions are expected inthe progeny of this cross? Check all that apply.

a) Red, no spines = 43.4%; white, spines = 43.4%

b) White, no spines = 43.4%; red, spines = 43.4%

c) Red, no spines = 6.6%; red, spines = 6.6%

d) White, no spines = 6.6%; white, spines = 6.6%

e) White, no spines = 6.6%; red, spines = 6.6%

f) Red, no spines = 43.4%; red, spines = 43.4%

g) Red, no spines = 6.6%; white, spines = 6.6%

h) White, no spines = 43.4%; white, spines = 43.4%

2.) In Drosophila, the map positions of genes are givenin map units numbering from one end of a chromosome to the other.The X chromosome of Drosophila is 66 m.u. long.The X-linked gene for body color-with two alleles,y ⁺for gray body and y foryellow body-resides at one end of the chromosome at map position0.0. A nearby locus controlling bristle form, withf ⁺for normal bristles and ffor forked bristles is located at map position 1.5. A thirdX-linked gene for eye color, with alleles w⁺for red eye and w for white eye, islocated at map position 56.7. Each gene resides on the Xchromosome, and at each locus the wild-type allele is dominant overthe mutant allele. Do you expect any of these gene pair(s) toassort independently?

a) Yes, y and w are each expected to assortindependently of f

b) Yes, all the genes are expected to assort independently

c) Yes, y and f are each expected to assortindependently of w

d) No, there are no genes expected to assortindependently

rubywallaby524

Which of these statements is incorrect?

Syntenic genes are located on the same chromosome.

Independent assortment results in recombinant chromosomes.

You can reliably predict the relative genetic distance fromgenesâ physical distance on a chromosome.

Linked genes are always syntenic.

What is the relative genetic distance between two linked genesif the recombination frequency is 0.49?

0.49 cM

4.9 cM

49 cM

490 cM

What statement best explains the distortion in Mendelian ratiosobserved by Bateson & Punnett in 1905? (Reminder: they found anoverrepresentation of F2 offspring showing both dominant orrecessive phenotypes, and an underrepresentation of offspringdisplaying one dominant and one recessive phenotype)

Human error: they should have been more careful about theirexperimental setup.

Gene linkage: Genes for flower color and pollen shape arephysically close on the same chromosome, leading to a breakdown inthe independent assortment of the alleles for these traits.

Chromosome crossover: Homologous recombination of twochromatids during meiosis caused the alleles to shuffle, resultingin a breakdown of the independent assortment of the alleles forthose genes.

Random variation: No two situations are alike. In finitepopulations, you are going to get some variation across a mean.

When determining the relative genetic distance between twogenes, why is dihybrid back-cross preferable over traditionaldihybrid cross?

9:3:3:1 phenotypic ratio is easier to work with than 1:1:1:1ratio.

Genotypes of the offspring can be determined based on theirphenotype.

If the genes are independently assorted, the dihybrid back-crosswould result in only 2 genotypes in the F1 generation.

B and C

Why do we map genes?

To understand how genes interact with each other

Comparative genomics analysis

To determine the genotype of an organism

All of the above

coralox210

BIOL 1020 Lecture 24: Lecture 24

BIOL 1020 Full Course Notes

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