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

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

yes

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?

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

iA and iB, A and B antigens, no 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

why is the ABO system multiallelic

What is the molecular basis for A and B antigens?

What happens if an individual only possesses the i allele

Complete H antigen

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

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

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

Lethal Allele

Essential Gene

dominant lethal allel vs recessive lethal allele

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? For this second trait the allele behaves in a dominant manner.

conditional lethal alleles vs semi-lethal alleles.

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?

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

Do epistasis and other observations of gene interactions results suggest the violation of Mendel’s laws of segregation and independent assortment? Justify your answer.

In two gene interactions what property of the phenotypic ratios suggest that two genes are involved (hint: denominator of the ratios?).

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

Given an example, be able to identify it as sex-influenced inheritance. In this
case suppose the allelic combinations of a gene has two possible phenotypes
and both these phenotypes are possible in both sexes for the appropriate
genotypes. However for one sex, one allele behaves as a dominant allele
whereas in the other sex the second allele behaves as a dominant allele.
Therefore the heterozygote shows two different phenotypes in the two sexes.
Explain what mechanisms may account for this difference?

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