Biology Exam 3 Review Guide
Cells/ Cell division
 Telomeres
o Protective cap for DNA
o Gets shorter with each cell division
 Cell division is an ongoing process in most organisms and their tissues; disruptions to
normal cell division can have serious consequences.
 In bacteria and arche genetic information is carried in one circular chromosome
 Bacteria: Binary fission
o Asexual reproduction
circular chromosome duplicates itself
o Parent cell splits into two new genetically identical daughter cells
 Somatic cells: cells forming the body of the organism
 Reproductive cells: sex cells
o With each cell division the cell duplicates itself so both daughter cells has all of
the genetic material from the parent cell
 Even with enzymes proof reading and repairing DNA during and after replication, error
still takes place
 Mitosis:
o Enables existing cells to generate new genetically identically cells
o Makes cell growth and replacement possible
o Leads to duplicate cells
o Follows chromosome replication leads to two daughter cells from one parent cell
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 Cancer
o Unrestrained cell growth and cell division which can lead to large cell duplication
resulting in large-scale health problems
o Results form mutations in the genes, weakening the effectiveness of checkpoints
o Treatment: kills or slows down the fast-growing cells, chemotherapy or radiation
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Genetics
 Meiosis:
o Generates sperm and egg in a great deal of variation
o
2 outcomes:

Reduces genetic material in gametes

Produces gametes that are all different from each other with
respect to the combinations of alleles each carry.
o Starts with a diploid cell

Homologous pair or homologues

Maternal and paternal copies of the chromosome

In animals meiosis only takes place in gamete producing cells

Final product of meiosis in a diploid organism is four haploid gametes

Regardless of the gender of the gametes being produces each only ends up
with one copy of each chromosome

Females make a larger gamete while males create smaller gametes
 Crossing over:
o Crossing over can create gametes with combinations of traits that may never have
existed before
o This variation is important for evolution
 Reproduction:
o Asexual is fast and effect however it creates identical genes that carry all of the
genes their parent carries, disadvantageous to a changing environment
o Sexual: offspring that are genetically different from one another and from either
parent, takes more time and energy also carries higher risks
 Sex chromosomes:
o Sex chromosomes carry information for the developing fetus in regards to gender
o Male if Y is present
o Female if X is present
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o Sex depends on the sex chromosome inherited from the father
 Nondisjunction:
o Unequal distribution of chromosomes during meiosis
o Error in cell division that creates a gamete with zero copies of a chromosome
rather than a single copy
 Karyotype:
o Visual display of a complete set of chromosomes
o Diagnostic tool which can be seen in fetal development to assess whether there is
abnormality in chromosome structure
o Down syndrome = extra copy of chromosome 21
 People with too few or too many sex chromosomes can survive while encountering many
physical./mental problems
 Genes are instruction sets for biochemical, physical, and behavioral traits
 Single-gene traits: some traits are determined by instructions an organism carries on one
gene
 Mendel- heredity: categorized traits in garden peas to experiment on how traits are
inherited.
 Segregation: two copies of each gene but put only one in each egg/sperm
 dominant > recessive
 Genes:
o Each parent puts a set of instruction for building a particular trait into every
sperm/ egg she /she makes
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o The trait observed in an individual depends on the two alleles inherited from the
parents
 Phenotype: the physical trait
 Genotype: the gene itself, which lies under the phenotype
 Observation of a phenotype is not sufficient for determining ones genotype
 Particular traits can be masked by a dominant allele and the person becomes a carrier
 Probability:
o Consequence of segregation: each gamete that is produced receives only one of
the two copies of each gene the individual carries
o Fertilization
o Holds a central role in genetics
o Impossible to know which allele goes into the gamete
 Pedigree: a type of family tree
o Useful for documenting traits of interest throughout generations
o The use of these decipher and predict the inheritance of genes
 Colorblindness
o More men than women are colorblind
o Sex linked traits differ in their patterns of expression in males and females
o Most traits do not differ when it comes to inheritance
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Evolution and Natural selection
 Environmental effects: identical twins are not identical
o Genotypes are not blueprints that specify phenotypes
o Phenotypes+ product of genotype, environment
 Evolution and natural selection:
o Characteristics of individuals present in a population changes over time
o We can observe the change or cause it to occur
o Darwin noted unexpected changes/patterns among fossils and living organisms.
o Fossils resembled however were not identical to living organisms in the same
areas
o These theories with finch’s helped Darwin develop his theory of how species
change overtime

Finch’s in each Galapagos islands are all different in small ways
o Evolution occurs when the allele frequencies change in a population: mutation,
genetic drift, migration, and natural selection
 Natural selection:
o
An efficient mechanism of evolution as well as a powerful force in adapting
populations to their environment
o Elimination of alleles that reduce the reproductive rate of individuals carrying
those alleles vs. the ones who do not
o Issues:

Environments can change more quickly than natural selection can adapt
organisms

Mutation doesn’t produce all possible alleles

Not always a single adaption for a specific environment
o Sometimes a trait with the purpose to serve one function will adapt and serve a
completely different one
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 Artificial selection:
o Farmers/ breeders are manipulating natural selection by breeding the supply they
modify
 Mutation
o direct change in an individual, and it is the ultimate source of all genetic variation.
o Can be caused by high energy radiation, chemicals in the environment,
spontaneously
o The only way new alleles can be created within a population, generates variation
causing natural selection to erupt
 Evolution by natural selection
o Must be a variation within the populations trait
o Variation must be inheritable
o Individuals with one version of the trait must produce more offspring than those
with a different version of the trait
 Reproductive stress:
o Fitness: alleles carried by those with high fitness will increase their market chare
in a population and will help it evolve overtime
 Homoeologous structures:
o Similarity between mammal bone structure shows apparent ancestry
o Convergent evolution: Analogous structures all developed from original structures
 Molecular biology:
o Common genetic sequences link all life forms
o Genetic code provides our fourth line of evidence that evolution occurs
o
Fifth line evidence: multigeneration experiments and observations