Biology Exam Review Weeks 14
Genetics & Evolution
Traits: Distinguishing characteristics which make up a living being
Inherited: A trait that is given to you genetically, and biologically from a parent
Genetics: The branch of biology dealing with the principles of variation and inheritance in
animals and plants.
• A theory of Charles Darwin that came to be known as Darwin’s theory of evolution,
though Darwin never actually used the word evolution in any of his studies.
• He believed that species changed to become what they are by the natural selection
process in mating.
• An organism is considered successful if it can produce a lot of offspring
• Natural selection is when the males have a random genetic mutation which can help
them; they end up with more females wanting to mate with them in hopes that their
offspring will also have this trait.
• An example of natural selection is Darwin’s finches. He studied them on an island and
watched as the natural selection took place based on the food source and seed size.
Gregor Mendel and his Discoveries
• Mendel discovered the basis of inheritance, doing research with the common pea plant
• He controlled with plants were bred together, looking for variation in certain different
traits, breeding only plants that had two possible different outcomes.
• Used pure bred plants crossed with mixed bred plants and noted all differences and the
percentages of each.
• He made a cross between two different purebred plants to look for the characteristics of
one trait. This is called a monohybrid cross.
• He took a pure bread short plant and crossed it with a pure bred tall plant, and ended up
with a result of all tall plants. He then crossed the F1 pairs and got 75% tall plants and
25% short plants in the F2 generation. This lead to the discovery of dominant and
recessive traits and, in effect, the use of punnett squares for research.
• A dominant trait is a characteristic that is always expressed, where as a recessive trait
is latent, and only appears in the absence of a dominant trait.
Genes: The part of the chromosome that governs the expression of a specific trait
Allele: A gene can occur in alternate forms called alleles. When two alleles are present, a
dominant allele may stop a recessive allele from being expressed. However it does not
physically alter the recessive allele and it will be passed on to the next generation where it may
or may not be expressed.
Homozygous: The two alleles are the same
Heterozygous: The two alleles are different.
Punnett Square: A square used to calculate the probability of a certain outcome based on the
traits of the parent generation. All possible gametes for one parent are copied across the top,
and all possible gametes for the other parent are copied across the side. Then your cross the alleles (represented by different letters) to see what are all the possible outcomes for the
genotypes of the offspring.
Genotype: The genetic make-up of an organism and the alleles it carries for specific traits.
Phenotype: The appearance of a trait in an organism
Test Cross: used for determining if a trait is recessive or dominant. Done by crossing an animal
or plant you know is pure bred with one you are unsure of. If all offspring appear dominant then
it is also a pure bred and offspring are also pure bred. Not fool proof.
The law of Independent Assortment: What Mendel discovered about how different alleles
have no affect on each other he discovered this using a dihybrid cross.
Incomplete Dominance: When neither allele is dominant a blending of the two traits can occur.
For example when crossing a red and white flower. If neither the red nor white is dominant then
all offspring should be pink and the f2 generation should be 50% pink and 25% red and 25%
Co-dominance: If both alleles are dominant then both traits show up equally. If a dominantly
white coloured cat and a dominant black coated cat had a kitten, that kitten would have black
AND white fur rather than one or the other.
Multiple Alleles: mainly used for human blood type. There are three alleles involved, and each
person has 2 of the three. Type A blood, and type B bloods are dominant over type O blood,
however they are co-dominant with each other.
The Cell Cycle:
The Cell Cycle: The continuous cycle of growth and division of cells.
Mitosis: The division of cells, and the cell’s nucleus
• It is through mitosis that cells can regenerate damaged tissues, and heal
• Also helps maintain body be replacing old, dead cells
• The function of mitosis is to maintain the same number of chromosomes from cell to cell
Chromosomes: Hold the genetic information within a cell need to maintain and make copies of
that cell. It is made up of two genetically identical sister chromatids held together with a
Parent Cell: The original cell, which is then divided into two new daughter cells.
• Interphase: The longest stage. Every cell spends the majority of its life in interphase. It
is the stage of growth and development
• Prophase: nuclear membrane and nucleolus disappear. Centrioles migrate to opposite
sides of the cell, and spindle fibres begin to form between the two centrioles.
• Metaphase: The chromatids are guided by spindle fibres to middle of the cell. Each
chomatid is attached to its own spindle fibre ensuring at each new daughter cell will have
one of the identical chromatids, and therefore the same genetic information.
• Anaphase: The centromere splits and chromatids are pulled to opposite sides f the cell
by spindle fibres
• Telophase: each chromatid upon reaching the opposite poles of the cell is now called a
single,, unreplicated chromosome. They begin to unwind and become less visible.
• Cytokinesis: Not actually a part of mitosis, but it always follows it. This is the actually
cell division. Spindle fibres disappear Nuclear membra