Genetics Chapter 4: Extensions of mendelian inheritence

Exam 1

Explain simple mendelian inheritence

involves a single gene w two diff alleles, the alleles display a dominant/recessive relationship

What are extensions of mendelian inheritance? How are they different from simple?

codominance, incomplete dominance, overdominance

Do extensions follow the law of segregation?

yes, all genes still segregate

Do extensions follow the law of independent assortment for two genes on diff, non-homologous chromosomes?

yes, bc genes are still seperated the same during meiosis

Incomplete dominance (molecular explanation)

heterozygote exhibits phenotype that is intermediate between the corresponding homozygotes (1:2:1) phenotypic ratio

Codominance(molecular explanation)

both expressed in a heterozygous individual

How can complete dominance at a gross level actually represent incomplete dominance?

A heterozygote may look identical to the a homozygous dominant at the individual level, however differences can be seen in composition at the cellular level

Over-dominance

heterozygote has greater reproductive success compared to corresponding homozygotes due to two alleles producing slighty different proteins

Heterozygote advantage

over-dominance

explain over-dominance with repect to sickle cell/malarian resistance

Sickle cell heterozygotes have an advantage over either homo, they have protection against sickle cell and malaria and a longer life span (Hba and Hbs alleles)

Name mechanisms that may make a heterozygote more fit than a homozygote

disease resistance, homodimer formation, and variation in functional activty

Describe the ABO blood system

blood type is determined by the type of antigen present on the surface of red blood cells (IA, IB, or i)

Type B blood (antibodies)

iB, B antigens, A antibodies

Type O blood

iI, no antigens, A and B antibodies

Type A blood (include antibodies)

IA, A antigens with B antibodies

Which two blood groups represent codominance

AB

Which blood group represents complete dominance?

A and B

Multiallelism

3 or more different alleles within a population that can affect phenotype

why is the ABO system multiallelic

the three different alleles include IA, IB and i which produce A, B and no antigen respectively

What is the molecular basis for A and B antigens?

antigen a contains N-acetyl galactosamine and antigen B just has another galactose

What happens if an individual only possesses the i allele

no antigens (type O)

Complete H antigen

antigen produced by type O individuals

What happens to a person with the bombay “hh” blood group?

the have no H, A, or B antigens

Which of the three antigens/antibodies does a person with bombay normally produce?

All of them (A,B and H)

why it would be dangerous for a bombay blooded person to receive blood from a type O?

The their body would reject the blood bc it has H antibodies that would interact with type O antigens

Lethal Allele

has the potential to cause death of an organism

Essential Gene

genes absolutely required for survival

dominant lethal allel vs recessive lethal allele

Dom lethal kills w one copy, recessive kills with two copies.

Why do recessive lethal alleles such as in the case of Manx cats, give a ratio of 2:1 (phenotype: normal) for a second trait (eg defective spine and tail) despite heterozygotes being crossed to one another?

the homozygous dominant genotype dies early in development

conditional lethal alleles vs semi-lethal alleles.

conditional only kills in certain environments, semi kills only some regardless of environment

Explain the dominant lethal nature of the Huntington allele

In this case of heterozygote, the individual is
able to be born and enter adulthood, however thereafter he or she begins to
develop neurodegeneration that is 100% fatal by 65 years and therefore it is
categorized as a lethal allele)

What is the nature of the mutation carried in the disease allele for HD and what is the consequence on the Huntingtin protein?

overexpression of glutamine leads to instability and misfolding + aggregation. Presents as progressive degeneration of nervous system

Be able to explain how HD’s lethal mutation continues to be maintained in the human population.

doesn’t appear until after the affected individual has children

Sex-limited inheritence

one phenotype is exclusively seen in one sex whereas the second phenotype is present in both sexes depending upon the genotypes.

Pleiotropy

one gene has multiple effects on the phenotype of an organism

List three possible reasons why pleiotropy may happen and two examples we have discussed in class.

Gene production may affect cell function in more than one way, may be expressed in different cell types, or different stages of development. Cystic fibrosis and sickle cell

What is the importance of understanding gene interactions?

all traits are affected by the contributions of many genes.

What are the 4 different kinds of gene interactions we have discussed in this topic?

Epistasis, complementation, gene, modifier effect, gene redundancy

Epistasis

alleles of one gene masks the phenotypic effects of another gene

Complementation

two parents with similar recessive phenotype create offspring with a wild type phenotype

sex-influenced inheritance

autosomal traits where one allele is domiannt in one sex but recessive in another

Incomplete penetrance

In some instances, a dominant allele does not influence the outcome of a trait in a heterozygote individual

True or flase: If 60% of heterozygotes carrying a dominant allele exhibit
the trait, the trait is 60% penetrant

True

Expressivity

degree to which a trait is expressed

Incomplete dominance

heterozygous exhibits phenotype that is intermediate between corresponding homozygotes in F1 50/50 in F2 1:2:1 phenotypic ratio

Disease resistance

microorganism will infect a cell if certain cellular proteins function optimally, heterozygotes have an abornormal copy not bad enough to cause issues but enough to avoid disease

Homor dimer formation

can make three forms of homo dimer

Variation in functional activity

combining two genes allow greater ability to adapt range

modifier effect

allele of one gene modifies the phenotypic outcome of the alleles of another

gene redundancy

loss of function in a single gene has no effect, loss of function in two has an effect (only 1 is actually neccessary)

sexual dimorphism

sexes in a species have diff morphological traits