GCD 3022 Lecture Notes - Lecture 5: Lethal Allele, Overdominance, Pseudoautosomal Region

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9 Mar 2018

School

UMN

Department

Genetics, Cell Biol/Development

Course

GCD 3022

Professor

Naoka Shima

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Document Summary

Several inheritance patterns involving single genes differ from those observed by mendel. Wild-type alleles are defined as those that are prevalent in a population. A gene that exists in two or more wild-type alleles is an example of genetic polymorphism. Recessive alleles are often due to mutations that result in a reduction or loss of function of the encoded protein. Dominant mutant alleles are most commonly caused by gain-of-function mutations, dominant negative mutations, or haploinsufficiency. Incomplete penetrance is a situation in which an allele that is expected to be expressed is not expressed. The outcome of traits is influenced by the environment. Incomplete dominance is an inheritance pattern in which the heterozygote has an intermediate phenotype. Whether we judge an allele to be dominant or incompletely dominant may depend on how closely we examine the phenotype. Overdominance is an inheritance pattern in which the heterozygote has greater reproductive success. Most genes exist in multiple alleles in a population.

Related Questions

QUESTION 1

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.

QUESTION 3

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

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

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

genotype

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?

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

polygenic inheritance

QUESTION 9

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

polygenic inheritance

QUESTION 10

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

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.

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?

codominance

polygenic inheritance

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.

Are the following genetic mutation positive for the 3 characteristics listed below - Phenylketonuria (PKU), Smith-Lemli-Opitz syndrome (SLOS), Alzheimerâs disease, Sickle cell anemia?

1. It is inherited (at least in some individuals or families) as a single-gene disorder (this means that a disorder where many cases are due to a mix of multiple contributing genes and environmental factors, such as heart disease or Alzheimerâs, could still be chosen if you focus on those instances with a single-gene cause)

2. It demonstrates at least one non-Mendelian characteristic (incomplete penetrance, variable expressivity, sex inflence, sex limited multiple alleles, or incomplete dominance) in its inheritance pattern

3. It is caused by mutations in a gene that has been identified and characterized.

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GCD 3022 Lecture Notes - Lecture 5: Lethal Allele, Overdominance, Pseudoautosomal Region

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