Ch. 8 LO

Define Pleiotrophy. Give an example.

A gene or mutation in a gene can have multiple effects or phenotypes. When this occurs, the gene or mutation is referred to as being pleiotropic. white-eyed flies also lack pigmentation in some other organs having sickle cell anemia cascades down to other organs=it can causes breakdown of RBCs, which leads to physical weakness, spleen damage etc.

What is a polymorphic gene? Answers: A gene that has accumulated more than the usual number of mutations. A gene that has more than one common variant A gene that is always heterozygous A gene that has multiple functions

A gene that has more than one common variant

Compare and contrast complete, incomplete dominance, and co-dominance.

Co-dominance, the phenotype reflects both alleles. (usually seen at the molecular level only with ABO blood types) Incomplete dominance, the phenotype lies between the phenotypes of the parent alleles. Phenotype of the heterozygote is intermediate (falls within the range) between the phenotypes of the two homozygotes. complete dominance: a form of dominance in heterozygous condition wherein the allele that is regarded as dominant completely masks the effect of the allele that is recessive. Phenotype of the heterozygote is the same as the phenotype of one of the homozygotes.

Describe dihybrid crosses, what genotypes and phenotypes are produced and in which ratios?

Dihybrid crosses (AaBb X AaBb) will yield phenotypes in the 9:3:3:1 ratio

True or false? Coat color in Labrador retrievers is usually yellow, black, or chocolate brown. This is determined by alleles of the E gene and the B gene. Dogs with recessive e alleles (ee) are yellow, even when the B locus is functional. This means that the B gene is epistatic to the E gene. Answers: True False

F, the E gene is epistatic to the B gene. the genotype at the E gene affects the phenotype controlled by the B locus

Dihybrid crosses (AaBb X AaBb) will yield 64 different phenotypes Answers: True False

F, they yield 4 different phenotypes in the 9:3:3:1 ratio

What is the difference between co-dominance and incomplete dominance? Answers: In co-dominance, neither allele produces sufficient protein. In incomplete dominance, both alleles make sufficient protein. In co-dominance, both alleles produce sufficient protein. In incomplete dominance, neither allele makes sufficient protein. In co-dominance, the phenotype lies between the phenotypes of the parent alleles. For incomplete dominance, the phenotype of both alleles is seen. In co-dominance, the phenotype reflects both alleles. For incomplete dominance, the phenotype lies between the phenotypes of the parent alleles.

In co-dominance, the phenotype reflects both alleles. For incomplete dominance, the phenotype lies between the phenotypes of the parent alleles.

Compare and Contrast Mendel's principles (laws) of segregation and independent assortment.

Mendel's law of independent assortment suggests that the inheritance of one gene or trait does not influence the inheritance of a separate unlinked trait. Mendel's law of segregation states that allele pairs separate during gamete formation, and randomly unite at fertilization. both transmission of traits and segregation of allels happen in both cases

What term is used for a gene that contributes to more than one phenotype? Answers: Epistatic Dominant Pleiotropic Complex

Pleiotropic

Discuss the effects of lethal alleles. Why are they usually recessive

Recessive lethal alleles can be passed from generation to generation but dominant lethal alleles are not inherited because they dead. When two heterozygotes for a lethal allele (let) are mated, one-fourth of their offspring will die. Since the phenotypes and genotypes ratios are based on surviving offspring, these ratios are based on thirds.

Why are lethal alleles usually recessive? Answers: Lethal alleles have a higher fitness Lethal alleles prevent an organism from reproducing Lethal alleles are usually dominant rather than recessive Recessive lethal alleles can be passed from generation to generation but dominant lethal alleles are not inherited.

Recessive lethal alleles can be passed from generation to generation but dominant lethal alleles are not inherited.

True or false? Mendel's law of independent assortment suggests that the inheritance of one gene or trait does not influence the inheritance of a separate unlinked trait. Answers: True False

T

When are there exceptions to the dihybrid 9:3:3:1 dihybrid ratios.

The standard 9:3:3:1 ratio for phenotypes is altered if the genes interact with each other or exhibit a form of epistasis. Example: since the activities of both genes are needed, only A-B- individuals are dark blue, and all other genotypes fail to carry out one of both steps. This results in a 9:7 phenotype ratio if only aabb lacks the activity but all other genotypes produce the same phenotype, it results in a 15:1 ratio. still the phenotypic ratio will be based on 16ths but the genotypic combinations are altered

What is the purpose of a complementation test? Answers: To determine whether an organism is homozygous or recessive at a particular locus. To determine whether an allele is dominant or recessive To determine whether lethal alleles are present To determine whether two mutants with the same phenotype have defects in the same gene

To determine whether two mutants with the same phenotype have defects in the same gene

Phenotypes are not always inherited in a predictable Mendelian manner. Which of the following are possible reasons for this? Please select all that apply. Answers: A trait may be affected by the environment Traits may be influenced by multiple genes There may be differences in penetrance or expressivity Alleles may not be completely dominant

all are correct

What is a complementation test?

can be used to determine whether two different mutations are in the same gene or in two different genes. two individuals that share the same phenotype, but are each homozygous for a different recessive mutation are crossed together. if the offspring all show the same recessive phenotype as the parents, we deduce that the mutations were in the same gene and do not complement. if the offspring show the wild type, the two mutations are defined as complementing each other and represent two different genes.

Describe Epistasis. Give a specific example.

epistasis involves two or more genes whereby the phenotype of one gene masks the phenotype of the other. the gene that masks the phenotype of the other is referred to as the epistatic gene. similar to dominance, but not. epistasis occurs between two or more different genes and could involve either dominant or recessive alleles of these genes. Coat color in Labrador retrievers is usually yellow, black, or chocolate brown. This is determined by alleles of the E gene and the B gene. Dogs with recessive e alleles (ee) are yellow, even when the B locus is functional. This means that the E gene is epistatic to the B gene.

Define Penetrance. Give a specific example.

if all of the individuals who are genotypically mutant are also phenotypically mutant, then the mutation is said to be 100% penetrant. every individual whose genotype at the ABO locus is ii has type O blood because phenotypes at the ABO locus are 100% penetrant. reduced penetrance means that not every individual with the mutant genotype displays a mutant phenotype. An example is the bli-5 gene in C. elegans. recessive mutations in this gene result in the formation of blister on the head. although all worms in the photo are homozygous for the bli-5 mutant allele, but not all of them exhibit the blister, and shown by the non-blistered worms. 72% penetrance.

Define Expressivity. Give a specific example.

individuals who share the same genotype for an allele may differ in the severity or strength of the associated phenotype. such alleles are said to show variable expressivity. BRCA1-a particular mutation in this gene elevates the risk of breast or ovarian cancer by as much as 8-fold over the risk for women who do not have the mutation. some women develop breast cancer, while their sister develops ovarian cancer, so different tissues can be affected. to what extent to this trait expressed, its a spectrum

True or false? Mendel's law of segregation states that allele pairs separate during gamete formation, and randomly unite at fertilization. Answers: True False

true