BIOL 2500 Lecture Notes - Lecture 5: Null Allele, Hbb, Wild Type

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grayrabbit360

2 Feb 2017

School

University of Manitoba

Department

Biological Sciences

Course

BIOL 2500

Professor

Roman Gietz

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Document Summary

Inheritance patterns of single genes and gene interaction. The phrase gene interactions refers to the ways genes collaborate or interact to influence a phenotype. There are several important types of interactions. There may be more than two alleles for a given locus within a population: the beta globin locus has many different alleles. Dominance of one allele over another may not be complete. Two or more genes may affect a single trait. The expression of a trait may depend on the interaction of more than one gene and/or the interaction of genes with nongenic factors (environment) Mendel chose to examine traits with just two alternative forms. In each case one form was completely dominant over the other, such that individuals heterozygous for the two alleles showed the dominant phenotype. Research in the early and mid-20th century was aimed at better understanding the molecular nature of dominance. The terms dominant and recessive have a phenotypic basis.

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?

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Differentiate amongcomplete dominance, incomplete dominance andco-dominance.

3. Understand an allelicseries -How many possible alleles are there for any given gene? Isthere only one recessive allele for a gene? Is there only onedominant allele for a gene? Is an allele always recessive ordominant with respect to other alleles of the gene?

4. What is a lethalallele? Are lethal alleles usually dominant or recessive? Are thereany exceptions? (Hint: Huntington disease in humans). How do wemaintain stocks with lethal alleles?

5. How can you tell if anallele is lethal? If one of the parents has a lethal allele, wouldall the possible genotypes be present in the progeny? What wouldhappen to the phenotypic ratios of the progeny?

6. What ispleiotropy?

7. How can you tell if atrait is determined by more than one gene? What ratios ofphenotypes in the F2 generation would you expect if a trait isdetermined by a single gene?

8. What is epistasis? Howcan the genotype at a locus affect the phenotype determined by thegenotype at another locus? What are complementary gene action,duplicate gene action, dominant suppression, dominant epistasis,and recessive epistasis?