Biology 345 Organic Evolution

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Module II Mendelian Genetics Probability Theory
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GENETICS

• Genetics is the study of heredity and variation
  in organisms
• Genes are the hereditary units transmitted from
  generation to the next
• Genes reside in the long molecules of
  deoxyribonucleic acid (DNA) that exists within
  the cell
• DNA, in conjunction with a protein matrix forms
  nucleoprotein and becomes organized into
  structures called chromosomes that are found in
  the nucleus of the cell

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ALLELES

• Mutation is a change in some part of the DNA
• The result of a mutation is a change a character
  or trait of the individual
• Through a mutation, a gene may be changed into
  two or more alternative forms called alleles
• Homologous chromosomes are genetically similar

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MENDELS LAWS

• Law of segregation If a parent contains 2
  alleles of a trait, only 1 is transmitted through
  a gamete to the offspring
• Law of independent assortment Segregation of one
  gene pair occurs independently of any other gene
  pair

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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).
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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
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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
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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.
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Overview/Review of Basic Genetics
Another example Many plants can have flowers of
different colors.
Bougainvillea
Snap Dragons
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Bougainvillea on Campus
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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. The
are called co-dominant and the observed phenotype
of a heterozygote is in between the phenotype of
either homozygote.
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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.
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What does any of this have to do with math?
An individuals 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.
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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? Answer You
may know the answer, but do you know the
mathematics behind it