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Genetic Variation and Change Study Notes
1. Write the definition for the following words:
a. Genetic variation: Diversity in gene frequencies, or the differences between
individuals in a population.
b. Chromosome: A thread like structure in the nucleus that carries genetic information
(DNA)
c. Gene: A unit of heredity, composed of a series of nucleotides forming part of a
chromosome.
d. Gamete: Sex cell (sperm and egg in humans)
e. Diploid: A cell containing two sets of chromosomes, one from each parent
f. Haploid: A cell contain one set of chromosomes, half the usual amount
g. Meiosis: Sexual reproduction, a process that creates 4 daughter (haploid) cells with
half the usual number of chromosomes (ie. 1 set)
h. Crossing over: the interchange of various genes (sections of chromosomes) during
meiosis.
i. Law of independent assortment: That when characteristics are inherited, allele pairs
separate. So traits are transmitted to offspring independently to one another.
j. Recombination: Where DNA is broken down and recombined to create new
combinations of alleles.
k. Mutation: A permanent change of the nucleotide sequence of a gene, producing new
proteins and therefore different traits.
l. Homologous Chromosomes: A set of one maternal chromosome and one paternal
chromosome that pairs up inside the cell during meiosis.
m. Chiasma: A point where paired chromosomes remain in contact during the first
metaphase of meiosis, where crossing over occurs.
n. Chromatids: A ‘side of the chromosome’, so one copy of the newly replicated
chromosome.
o. Alleles: A possible resulting trait of a certain gene.
p. Paternal: From father.
q. Maternal: From mother.
2. Why genetic variation important in any population of living things: Genetically different
populations are very important. For one, natural selection weeds out the bad genes, so strong
genes are also needed. Without variation, disease would spread fast due to similar genes.
Essentially genetic variation is important so organisms can adapt to changes in environment.
3. Name 3 processes that cause genetic variation in the whole process of sexual reproduction
(this includes formation of gametes): Crossing over, meiosis (halves and duplicates
chromosomes, does a bunch of crazy stuff), gene flow (where genes transfer from one
population to another)
4. Name one other source of variation which causes a change in the order of bases in the genetic
code: Mutations
5. Draw a diagram showing how 3 pairs of homologous chromosomes (use colour coding) line
up at the equator during the first stage of meiosis. Show where crossing over may occur and
use the law of independent assortment when drawing them:
6. In terms of the genetic make-up of the gametes formed, why are these two processes
important: Crossing over swaps various alleles for each other. So a gene from one parent will
end up with a gene from the other parent, making the new gamete genetically different from
either parent. The law of independent assortment means that crossing over is independent so
each gene has an equal chance of occurring together
7. Why do sex cells only have half the number of chromosomes? Explain: Because they will pair
up with another gamete (either a sperm or egg) to produce the full amount.
8. What are the two main types of mutations? Gene (where there are changes within the base
(ATCG) code of the DNA so they occur within a gene) and chromosomal (where whole parts
of chromosomes including whole genes are deleted, repeated or relocated to other
chromosomes)
9. List and give examples of each of the types of these two mutations: Down Syndrome where
there is 3 chromosomes in the 21st ‘pair’ instead of two, and Turner Syndrome, where the
individual only has one X sex chromosome (thus making the individual a female) are
examples of chromosomal mutation as a chromosome has been added or deleted. Albinism is
an example of gene mutation as the faulty gene makes the enzyme that produces melanin not
work.
10. How do mutations lead to genetic variation in a population: If a mutation occurs in sex cells,
the mutation enters the gene pool and becomes subject to natural selection. If this mutation is
beneficial to the survival of the species, the mutation thrives
11. Write the definition for the following words:
a. Population: A group of organisms (same species) in an area.
b. Gene pool: All the genes in a population.
c. Species: A group of animals which are similar and can produce fertile offspring.
d. Gene flow: Transfer of genes/alleles from one population to another, due to
migration etc.
e. Allele frequency: The proportion of a particular allele compared to the total amount
of alleles (ie. 3/5 have red eyes out of total population)
f. Genetic drift: Variance in the allele frequency over time, due to disease etc.
g. Founder effect: Loss of variation when a population is all descended from a small
group of individuals (ie. Adam and Eve, you’d think everyone would be white)
h. Bottleneck: Sharp reduction in the size of the population due to environmental or
human activities
i. Genetic equilibrium: Where allele frequency doesn’t change over the generations.
j. Selection pressures: Effects that cause natural selection (ie. environmental effects)
k. Biodiversity: Genetic diversity among an environment.
l. Adaptation: A evolutionary change where an organism becomes better suited to its
environment.
m. Evolution: The processes where organism have adapted over time.
12. Describe how the founder effect, affects genetic biodiversity of that species: Because no new
alleles are added in, the only possible alleles will be the ones that the founders have. So
biodiversity is very low.
13. List all the factors (at least 6) that lead to genetic change in a gene pool. That is, things that
add and remove alleles from a gene pool: Migration, environmental selection pressures,
mutation, a bottleneck (like an earthquake randomly wiping out only one allele), reproduction
(like donkey/horse/zebra).
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17. Write a paragraph to explain what natural selection is. You should use the following words
in your discussion: variation, adaptation, different alleles, selection pressure, survival of the
fittest, death, reproductive age, inherit good alleles, allele frequency, evolution (genetic
change). Give some examples: Natural selection is where the organisms with a certain trait
die off (decreasing that allele frequency) over time, leaving other traits that are more
adaptable and allow the organism to survive. For example, a deer with ‘fast’ genes will
survive, whilst a deer with ‘slow’ genes will die. This is called survival of the fittest. Their
offspring will inherit the fast genes and the slow gene will die off. This is one of the benefits
to evolution, as it allows the species to adapt to environmental changes.
18. What are the 3 types of natural selection? Describe each:
a. Stabilizing selection: Where genetic diversity decreases as the population stabilizes
on a particular trait.
b. Directional selection: Where a single phenotype is favoured, causing the allele
frequency to continuously shift in one direction.
c. Disruptive selection: Where extreme trait values are favoured over intermediate
ones.
19. Read the following scenario and answer the question at the bottom:
a. One species of ground finch (flightless bird) thrived on Island Alpha for thousands of
years. It had small beaks and ate the soft, succulent seeds that were produced by the
plants on the island. One day there was a huge volcanic eruption which killed many,
but not all of the birds on the island. A huge mountain formed which caused one side
of the island to turn into a desert, with very little rainfall. Only the hardiest of plants
survived and they only produced hard seeds. The two sides of the island were cut off
from one another and the birds couldn’t fly. Thousands of years later, on the side of
the island that remained normal, finches with small beaks still flourished, eating the
soft succulent seeds still made by the plants. However, on the desert side, a new
species of Finch with large, stronger beaks existed which feeds on the tough seeds.
No smaller beaked finches exist here. No new birds were brought to the island and
the two populations are geographically isolated.
b. Explain, using all of your knowledge of genetic variation and how a species changes
over time (genetically), how a new type of Finch came about on the desert side of the
island after the eruption. The key starting question is “was there genetic variation in
the original population of Finches to begin with and if so, how did this occur. Then,
how did it change over time?
c. Well no, there wasn’t any variation to begin with, because no tough seeds existed. It
changed when the volcano happened. The birds on the desert side were faced with
two choices, die or eat the tough seeds. Those who had adapted to eat the tough seeds
died, so that allele was removed from the desert population, and left only those who
could eat them. So two distinct finch populations formed. (NOT REALLY SURE
WHAT ELESE TO PUT…)