Download Biology 345 Organic Evolution

Overview/Review of Basic Genetics
Genetic material (DNA) is stored within structures called
chromosomes.
In sexually reproducing organisms (e.g. mammals and birds),
an individual has two copies of each type of chromosome.
Every species has a specific number of chromosomes (in
humans there are 23 pairs of chromosomes = 46 total).
Overview/Review of Basic Genetics
Genes (sequences of DNA which encode proteins) are found
on chromosomes.
Each chromosome
in a pair has the
same genes in the
same order.
However, specific
genes can be
variable and the
two chromsomes
may not have the
same gene variant.
Different
Genes
Overview/Review of Basic Genetics
Variants of a specific gene are known as alleles.
Example: There is a gene in humans that controls basic eye
color. There are two alleles: Blue (b) and Brown (B).
The genotype of an individual is the set of alleles the
individual has.
Question: What are the possible genotypes for eye color?
Answer:
BB or Bb or bb
Overview/Review of Basic Genetics
The phenotype of an individual is the physical characteristic
formed by their specific alleles.
Example: An individual with the brown alleles (BB) has a
brown eyed phenotype. An individual with two blue alleles
(bb) has a blue eyed phenotype.
Question: Does an individual with 1 brown and 1 blue allele
(Bb) have one brown eye and one blue eye?
Answer: No. The brown allele is dominant over the blue
allele (which is recessive). An individual with both alleles
(heterozygous) has the phenotype of the dominant allele. Thus
the Bb genotype = Brown phenotype.
Overview/Review of Basic Genetics
Another example: Many plants can have flowers of different
colors.
Bougainvillea
Snap Dragons
Bougainvillea on Campus
Overview/Review of Basic Genetics
In many plants, flower color is controlled by a single gene.
There are alleles for Red (R) and White (W) and sometimes
other colors (e.g., yellow).
A plant with an RR genotype has a red phenotype.
A plant with a WW genotype has a white phenotype.
A plant with an RW genotype has a pink phenotype.
Neither R nor W are dominant. They are called incompletely
or partially dominant alleles and the observed phenotype of a
heterozygote is in between the phenotype of either
homozygote ( a blend).
Overview/Review of Basic Genetics
Question: Can you predict phenotype from genotype?
Answer: Yes. For eye color we know that BB and Bb are
always brown and bb is always blue.
Question: Can you predict genotype from phenotype?
Answer: No. While we know a blue eyed person must have a
bb genotype, a brown eyed person could have either Bb or BB.
All we know for sure is they have at least 1 B.
What does any of this have to do with math?
An individual’s chromosomes are inherited from their parents.
One from the father and one from the mother.
When an individual has children, half of its chromosomes (one
from each chromosome pair) will go into the child.
The process by which a specific chromosome (and therefore
specific alleles) goes into a child is random.
What does any of this have to do with math?
Pretend you are going to breed a pair of plants with pink
flowers.
Question: What are the phenotypes of these plants? What are
the genotypes?
Answer: Phenotypes are both pink. Genotypes are both RW.
Questions: What are the possible genotypes and phenotypes of
the offspring? What is the probability of getting these
genotypes and phenotypes?
You may know the answer, but do you know the mathematics
behind it…