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Lecture

BIOL 121 Lecture Notes - Model Organism, Pisum, Membrane Protein


Department
Biology
Course Code
BIOL 121
Professor
Carol Pollock

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Biol 121 225
Freeman 265-276 (Ch. 13) Feb. 5, 10
Hereditary
-inheritance, or transmission of traits from parents to offspring
Trait
-any characteristic of an individual, ranging from overall height to primary
structure of a particular membrane protein
Model organism
-desired characteristics?
-an appropriate model organism in order to study hereditary (transmission of
traits)
-for Mendel, it was Pisum sativum (pea plant)
-model organism is a species where individuals are:
Small
short-lived
inexpensive to care for
able to produce large numbers of offspring
easy to manipulate experimentally
-therefore, can continue experiments over several generations and to collect data
from a large number of individuals
-experimental results from using model organisms applied to other spp
Two additional features of the pea
that are good for experiments
1) Can control which parents are involved in mating
2) Can arrange matings between individuals that differed in easily recognizable
traits such as flower colour/seed shape
Genetics
-branch of biology that focuses on the inheritance of traits
Phenotype
-observable features of an individual
Pure line
-a pure line consists of individuals that produce offspring identical to themselves
when self-pollinated or crossed to another member of the pure-line population
Hybridd
-offspring from matings b/t true-breeding parents that differ in 1+ traits
Parental generation
-adults used in an initial experimental cross
F1 and F2 generations
-F1 is the progeny of the parental generation (or offspring), F2 is progeny of F1
Dominance and recessiveness
-these terms identify only which phenotype is observed in individuals carrying two
different genetic determinants (alleles)
Gene
-the hereditary determinant for a trait (e.g. gene for seed shape)
Allele
-a version of a particular gene (may be dominant or recessive)
-different alleles are responsible for the variation in the traits Mendel studied
Genotype
-alleles found in a particular individual
Phenotype
-physical traits, affected by the individual’s genotype
Principle of segregation
-to explain 3:1 ratio of phenotypes in F2, Mendel reasoned that the two alleles of
each gene must segregate/separate into different gamete cells during the
formation of eggs and sperm in the parents
-as a result, each gamete contains one allele of each gene
Homozygous
-individuals that have two copies of the same allele (pure-line individuals will be
homozygous for the gene of interest)
Heterozygous
-individuals with two different alleles for the same gene are heterozygous
Monohybrid cross
Punnett square
-Mating b/t parents that are both heterozygous at the gene in question:
R = dominant (round), r = recessive (wrinkled)
Rr x Rr
Offspring genotypes: ¼ RR : ½ Rr : ¼ rr
Offspring phenotypes: ¾ round : ¼ wrinkled
R
r
R
RR
Rr
r
Rr
rr
Steps on which the Punnett square
is based
1) Write each unique gamete genotype produced by one parent to make a new
row
2) Write each unique gamete genotype produced by the other parent in a column
3) Create boxes in the square/rectangle composed of the rows and columns
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