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BIOL 142 Lecture Notes - Lecture 7: Wild Type, Phenylketonuria, Quantitative Trait Locus

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3 Jul 2018

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Thursday, March 1, 2018

BIOL 142

•Most traits are inherited in ways that are more complex than simple Mendelian

inheritance - they are not exceptions, just extensions of Mendel’s principles"

•Incomplete dominance occurs when the zygotes have an intermediate phenotype"

•A heterozygous organism that displays both alleles is said to have codominance"

•Blood groups - codominance"

•Penetrance I the proportion of individuals that carry a particular variant (or allele) of a

gene that also express an associated trait - the penetrance is 100%"

•Polymorphic traits - when more than two distinct phenotypes are present in a

population"

•Multiple allelism - when there are more than two alleles for a given trait - contributes

to polymorphism"

•The expression of many genes depends on the presence or absence of other genes"

•When these gene-by-gene interactions occur - the phenotype produced by an allele

depends on the action of alleles of other genes"

•Epistasis - some genes alter the eﬀect of other genes (ex mouse coloration)"

•The alleles Mendel analyzed aﬀected only a single trait"

•Some genes inﬂuence many traits - these genes are said to be pleiotropic"

•This explains why mutations in one end can lead to disease that aﬀect multiple

pathways"

•Mendel worked with discrete traits - characteristics that are qualitatively diﬀerent"

•In garden peas, seed color is either yellow or green - no intermediates"

•Traits that are not discrete but fall into a continuum - are called quantitative traits"

•Transmission of quantitative traits results from polygenic inheritance - each gene

adds a small amount to the value of the phenotype"

•Nilsson - Ehle proposed that many genes each contribute a small amount to the

value of quantitative traits, the population usually exhibits a bell-shaped curve for the

trait"

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Related Questions

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.

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

Canaries: Green (wild-type) Pied phenotype Yellow type

Canaries are popular pets and easy to breed in captivity. Additionally, they display great phenotypic diversity, which allows you to do some interesting genetic investigations with them.

When you take a canary from a true-breeding green strain and cross it with a canary from a true-breeding yellow strain, all offspring display the pied phenotype. Based on this you suspect that this color variation is inherited by a gene with a co-dominant inheritance pattern (showing both phenotypic traits in hybrid phenotypes).

You decide to test this hypothesis. To do so, you take pairs of your hybrid F1 individuals (of pied phenotype), and cross them to produce an F2 generation.

After many dozens of crosses and hundreds of offspring, you arrive at the peculiar ratio of:

3/16 green : 6/16 pied : 7/16 yellow

Which of the following hypotheses are consistent with these data? (Note that not all of these hypotheses are mutually exclusive. Assume that the two genes are independently assorting)

Hint: This problem is very hard to work from the given ratios to what is happening genetically. It is easier to "work backwards" and start with each choice below, and see if you can obtain all or important aspects of the results of your cross when making the assumption that the answer choice is correct.

Select all that apply:

Select one or more:

a. At least one of the genes involved is sex linked.

b. One gene controls production of darker pigment (melanin which appears green when mixed with yellow). A second gene acts as a patterning gene with one allele causing expression and the other non-expression of melanin and when in the heterozygous condition each allele controls melanin expression on different parts of the body so long as the bird's genotype of the first gene allows for the production of melanin.

c. this is a single-gene trait with co-dominance

d. one of the two genes involved displays complete dominance, while the other displays co-dominance.

e. the genes involved are epistatically interacting

f. more than one gene is involved