Lectures Notes New Material Exam 2

Feb 9, 2010
Mendelian genetics

Mendel – did experiments with peas in his gardens. Had no idea what DNA was. Messed with genetics of his peas
Character – Mendel’s word. Observable physical characteristic of an organism Ex Human eye color
Doesn’t really exist anymore
Trait – refers to one particular version of a character Ex having blue eyes
Gene – sequence of nucleotides that codes for a particular protein. Ex humans have gene for eye color
Allele – particular version of a gene Ex blue eye allele
Heritable trait – trait that can be passed on from parents to offspring
Homozygous (homo – same) – only applies to diploid organisms (have 2 sets of chromosomes)
Defin: having 2 copies for the same allele
Ex 2 blue eye alleles (recessive bb)
Heterozygous (hetero – different; zygous looks similar to zygote)- only applies to diploid organisms (have 2 sets of chromosomes)
Defin: having 1 of one allele and 1 of another allele for the same gene (having 2 different alleles)
Ex 1 blue allele and 1 brown allele (brown dominant Bb)
Haploid – possessing 1 set of chromosomes
Ex: bacteria, people born with genetic disorder – don’t possess 2 sex chromosomes. Guys are born haploid with respect to Y chromosome.
Diploid – having 2 sets of chromosomes
Dominant – allele version which overrides recessive trait; it’s the trait that shows. Only applies to diploid organisms
Usually codes for a protein (brown eyes are dominant over blue eyes since it’s better to code for a pigment protein than for nothing)
Recessive – allele version that is overridden. Only applies to diploid organisms
Codes for nothing/nonfunctional/protein unlike a dominant trait
Autosomal chromosomes– non-sex chromosomes; everybody has two copies of these
Are diploid, not haploid
Sex-chromosomes – females have 2 x chromosomes, males have one x & one y
Wild-type trait- common trait/allele as it exists in nature
Mutant trait – new/newly discovered trait /allele/gene
Wild type E. coli are killed by T4 phages
Wanted to see if mutant E. coli could resist T4 phages.

Probability of an event occurring, given that there is more than one way for that event to happen calculated by: Sum of all probabilities
Probability of multiple independent events occurring simultaneously: multiply different probabilities
Ex ½ probability of it snowing tomorrow. 1/8 probability of chicken nuggets in cafeteria. What is probability of it snowing and chicken nuggets? Multiply
EX ½ probability blue eyes, ½ probability boy = ¼ blue-eyed boy
Mendel’s “laws”
Segregation: traits cluster into organisms with and without traits (no intermediate categories)
Exceptions: hair color, skin color, eye color, etc
Independent assortment: traits inherited independently (inheriting 1 trait doesn’t predict for inheriting separate trait)
EX: just because plants were tall, it didn’t mean all of the flowers were the same color
Caused by meiosis – mom and dad chromosomes go to either cell – ½ complement on either side of cell – before crossing over- chromosomes are divided randomly
Chromosomes have more than one trait/gene per chromosome – so independent assortment doesn’t always hold up
Meiosis and Mendelian genetics
Because of crossing over of large sections of chromosomes in meiosis, genes that are close to each other on same chromosome are likely to be inherited together
This disproves independent assortment
Look over figure 10.18 – will be test question similar to this

Codominance
Both alleles result in expression of a functional protein, so neither one “outweighs” the other
Ex: Sickle cell trait
Have 1 sickle cell allele makes alternate hemoglobin – changes shape of blood cell
Wild type allele creates normal hemoglobin
Two types of wild alleles, you’re susceptible to malaria but you don’t have sickle cell
Heterozygote – codominance. Resistant to malaria. Suffer from sickle cell anemia.

Incomplete dominance
One allele produces functional protein, one doesn’t
Can’t have dominant phenotype with one allele producing functional protein
EX red, white, and pink flowers

There is NO relationship between dominant traits and good/ common traits/ advantageous traits
There are a lot of dominant traits which are bad – Huntington’s disease

Thank you very much, this will all come in handy during the test.

When is the test?

Thursday the 25th (before Spring Break)

And we don't have class the next day!

I suspected that! I should check the syllabus, though…

True…

I checked the syllabus; class is canceled on the 26th!!

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