BIOL 2500 - Topic 5 (part 5)

Family studies

It tracks the precedence and prevalence of traits within a family

Family studies on asthama

There is more of a chance of having asthma if one or both of your parents have it, but it is not guaranteed for you to have it if they do

Twins on allergies

Identical (monozygotic) twins are more likely to share allergies than non-identical (dizygotic) twins

Immune system mutations

Mutations in T-helper cells increases allergy risk

Identical twins having the same allergy

They may be allergic to the same thing, but they will most likely display different symptoms (i.e. rash vs. anaphylactic shock)

Incidence of allergies are higher in…

1.) Developed countries

2.) First born kids

Incidence of allergies are lower in…

1.) Large families

2.) Kids attending daycares

3.) Kids from rural families

Hygiene hypothesis

The theory that exposure to more diseases leads to a better immune system

Why are allergies so common?

1.) Allergies are hypothesized to reflect immune systems that have not been exposed to the allergen, combined with the effects of past selection for parasite resistance

2.) Some also believe that it is inherited

Resistance to parasitic worms

It causes huge health problems in developing countries, but resistance increases with age, as the immune system matures and learns to recognize the parasite

Alleles regarding parasitic worms

1.) In rural China and Mali, specific alleles are associated with decreased parasitic worm load

2.) However, in British populations, the same alleles increase susceptibility to allergies

Epidemiological risks for food allergy (pattern)

Patterns support the idea that undereducated immune systems are more likely to develop allergies

Current Canadian guidelines

For the first six months, it is required for mothers to only breastfeed or use formula to feed the baby

How have Canadian guidelines changed?

1.) There are no more restrictions to what the mother can eat during pregnancy and breastfeeding, as they were instructed to avoid it before

2.) Allergenic foods can be introduced to the baby after six months, but it used to be 3 years.

What influences phenotypes

1.) The genotype

2.) Environmental influences and other random events

2.) Actions of other genes and their products (i.e. genetic interactions)

Who came up with the one-gene-one-polypeptide hypothesis

Beadle and Tatum, using forward genetics to investigate the biosynthetic pathways of the Neurospora crassa fungi

Why did they use Neurospora crassa?

1.) Fast growing

2.) Haploid

3.) Can show various phenotypes depending on the medium

How did Beadle and Tatum’s experiment work?

1.) They generated single-gene mutants to infer the function of the genes, by observing how the mutation affected the phenotype

2.) They would observe that the fungus couldn’t grow on certain media due to the change in the enzyme function from the mutation

Results of Beadle and Tatum’s experiment

They found that one gene produces a single enzyme, which has a specialized functional role in metabolism

Prototrophic/prototroph

Refers to the wildtype

Auxotrophic/auxotroph

“Auxo” means lacking, which refers to the mutant

How did they identify auxotrophs?

If the N. crassa could not grow on a certain medium, this meant that they lack the gene to be able to metabolize it

What we know about genes now

1.) Certain genes can produce multiple proteins, via alternative splicing

2.) Some genes produce various RNAs

3.) Others produce peptides that will make quarternary proteins