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BIO SCI 97 Chapter Notes -Dihybrid Cross, Phenylalanine, Phenylketonuria

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30 Jan 2014

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Incomplete dominance: heterozygotes have a phenotype intermediate to the two alleles. More than one phenotype at the same time. If you have a and b, then you will have both of the alleles and not just one that is dominant over the other. A and b are codominant of each other. The phenotype of both alleles is fully expressed in heterozygotes. Penetrance: the probability that a mutation will manifest its phenotype. Waardenburg syndrome dominant trait variable expressivity. Multiple symptoms only some manifest in each individual. Epistasis - two different gene loci that control the same trait. Epistasis occurs when there is phenotypic interaction of non-allelic genes: one gene can mask another. For epistatic genes, a dihybrid cross produces a modified 9:3:3:1 ratio of phenotypes. Genotypic ratios do not change, just the phenotypes produced. Genes alone are not responsible for all the variation seen between organisms.

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Related Questions

Jim is blood type A, his brother John is type O and his sister Jane is type AB. What are the genotypes of their parents?

Which of the following is true for alleles that show incomplete dominance?

Heterozygotes have a genotype like the dominant allele.

Homozygotes have a genotype like the recessive allele.

Heterozygotes have a phenotype intermediate between the dominant and recessive alleles.

Homozygotes have the same phenotype as the heterozygotes.

Which principle of inheritance concluded that when games are formed in meiosis, the two alleles of each gene separate from one another, and each gamete receives only one allele?

independent assortment

Which term best describes a condition in which alleles at one locus can alter the expression of alleles at another locus?

polygenic inheritance

multiple alleles

A single unit of genetic information located on a chromosome defines:

The physical expression (appearance or function) of an organism's genes defines:

a single characteristic

Palomino horses (golden color with a blond mane) are an incompletely dominant trait produced by the combination of the chestnut color allele and the cream color allele. If you wanted to produce as many palominos as possible, which mating strategy below would be the best choice?

Chestnut x Cream

Palomino x Cream

Palomino x Chestnut

Palomino x Palomino

Which term best describes the effect of a single gene on multiple aspects of the phenotype?

multiple alleles

polygenic inheritance

Which term best describes the separate expression of both alleles for a single trait in the same cell?

multiple alleles

polygenic inheritance

One form of a gene found on a single chromosome defines:

A chocolate lab (whose mother was a yellow lab) is mated with a black lab whose genotype is BbEe. What fraction of the offspring would be expected to be yellow labs?

What type of allele is always expressed regardless of whether the individual is homozygous or heterozygous for it?

Both the dominant and recessive alleles

Recessive allele

Allosteric allele

Dominant allele

Given the parents AABBGgHhrr Ã AabbGgHhRr, assume simple dominance and independent assortment. What proportion of the progeny will be expected to have the genotype AaBbggHHrr?

___________________ is defined as having two of the same type of allele for a particular trait.

Incomplete dominance

The physical position of an allele on a single chromosome defines:

Which term best describes two or more genes affecting the phenotype in an additive fashion?

polygenic inheritance

multiple alleles

coppersea-lion534

These all relate to exceptions to the inheritance patterns encountered by Mendel.â

Why do multiple and lethal alleles often result in modifications of the classic Mendelian monohybrid and dihybrid ratios?

Select the four correct statements.

-When an essential gene is mutated, it can result in a lethal phenotype. There are no classic Mendelian monohybrid and dihybrid ratios.

-In the case of codominance, heterozygotes produce gene products from both alleles of a gene. Classic Mendelian monohybrid and dihybrid ratios are modified by codominance.

-In the case of incomplete dominance, the phenotype of the heterozygote is distinct from and often intermediate to the phenotypes of homozygous individuals. Classic Mendelian monohybrid and dihybrid ratios are modified by incomplete dominance.

-Genes exist in a large number of allelic versions and a diploid organism has two homologous gene loci that may be occupied by different alleles of the same gene. This can result in many different phenotypes for traits, which may not follow typical Mendelian ratios.

-When an essential gene is mutated, it can result in a lethal phenotype. This results in a modification of classic Mendelian ratios.

-The phenotype of the heterozygous genotype is distinct from and often intermediate to the phenotypes of the homozygous genotypes. The joint expression of both alleles in a heterozygote is called codominance. There are no classic Mendelian monohybrid and dihybrid ratios.

-Genes exist in a large number of allelic versions, but in a diploid organism, only one allele of the gene can occupy one homologous gene loci. Classic Mendelian inheritance cannot explain this phenomenon.

-Each gene produces a unique gene product. The effect of one allele in a heterozygote completely masks the effect of the other. Classic Mendelian genetics cannot explain this phenomenon.

answer to: matching:

Complete Dominance________

Genomic Imprinting_________

Incomplete Dominance________

Co-dominance __________

Polygenic trait___________

Lethal allele______________

Pleiotropy_____________

Penetrance___________

Sex-limited trait_________

Sex-influenced trait________

Anticipation ____________

Expressivity ____________

A. Heterozygotes have phenotypes intermediate between the phenotypes of the two homozygotes.

B. The heterozygote simultaneously expresses the phenotypes of both homozygotes.

C. Causes death at an early stage of development so that some genotypes do not appear among the progeny.

D. The percentage of individuals having a particular phenotype that exhibit the expected phenotype.

E. The phenotype of the heterozygote is the same as the phenotype of one of the homozygotes.

F. A trait determined by an autosomal gene that is more easily expressed in one sex

G. A trait determined by an autosomal gene that is expressed in only one sex

H. A trait determined by genes at many loci

I. The expression of a trait is affected by the sex of the parent that transmits the gene to the offspring

J. The trait appears earlier or more severely in succeeding generations

K. Degree to which a trait is expressed

L. A gene affects more than one phenotype