Mcat: Linkage, Recombination, Inheritance, Genetics, Hardy-Weinberg, Natural Selection, Evolution

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RF = Recombination Frequency equation

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# Recombinant phenotypes / # Offspring

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The frequency of recombination is determined by

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How far apart genes are located on a chromosome

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Genetic variation on the autosomes are traits collectively called

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Autosomal Traits

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What are the two types of Autosomal traits?

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Autosomal Dominant: A single copy of the allele will confer the trait or disease phenotype.

Autosomal Recessive: Two copies of the allele are required for the affected phenotype.

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Autosomal traits affect males or females?

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Both equally

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How does the autosomal inheritance differ by location:

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Mitochondria: Maternal (rare)
Nuclear Chromosomes: Sperm

All other organelles: Maternal from Ovum

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Mitochondrial Inheritance

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Rare
Maternal
Easy to spot because affected females have all affected offspring.

Any affected males cannot have affected offspring.

Mitochondrial traits are an example of hemizygosity.

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Hemizygosity

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The individual only has one copy of the chromosome in a diploid organism.
Seen in MItochondrial inheritance.

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Traits that are determined by genes on the X or Y chromosome

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Sex-Linked traits

Usually display unusual patterns of inheritance.

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X linked traits

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Can appear on males and females. Observed frequently.

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X-Linked Dominant:

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Harder to identify.
A female will display x-linked dominant phenotype if she has one or two copies of the allele on her X chromosomes.
A male will express the phenotype if inherits the affected allele from his mother.

Less obvious than x-linked recessive traits.

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X-Linked Recessive: Common disorder

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Hemophilia

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X-Linked Recessive:

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Women will only express X-Linked Recessive phenotypes when they are homozygous. Often women are carriers but only on one chromosome.

Males always express x-linked recessive traits as they are Hemizygous for the X chromosome anyway.

Tend to affect males more than females.

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An allele that encodes inactive protein or no protein is generally considered:

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Recessive

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X-Linked Recessive: Common disorder

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Red-Green colorblindness

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Inheritance pattern:
- Can skip generations.
- Number of affected males is usually equal to the number of affected females.

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Autosomal Recessive

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Inheritance pattern:
- Does not skip generations
- Number of affected males is usually equal to number of affected females.
- An affected parent passes the trait to either all or half the offspring.

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Autosomal Dominant

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Inheritance pattern:
- Maternal inheritance
- Affected female has all affected children.
- Affected ale cannot pass the trait to his children
- Unaffected female cannot have affected children.

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Mitochondrial

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Inheritance pattern:
- Affects male only
- Affected father has all affected sons
- Unaffected father cannot have an affected son.

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Y-Linked

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Inheritance pattern:
- Can skip generations
- Tend to affect males more than females
- Unaffected females can have affected sons
- Affected female has all affected sons, but can have both affected and unaffected daughters.

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X-Linked Recessive

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Inheritance pattern:
- Hardest to identify
- Does not skip generations
- Usually affects males more than females
- Affected fathers have all affected daughters
- Affected mothers can have unaffected sons, and pass the trait equally to sons and daughters.

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X-Linked Dominant

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Affected Genotype:

aa

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Autosomal Recessive

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Affected Genotype:

AA
Aa

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Autosomal Dominant

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Affected Genotype:

A

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Mitochondrial

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Affected Genotype:

XY ^A

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X-Linked

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Affected Genotype:

X^a X^a
X^a Y

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X-Linked Recessive

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Affected Genotype:

X^A X^A
X^A X^a
X^A Y

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X-Linked Dominant

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Charts that depict inheritance of a trait are called

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Pedigrees

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Pedigrees allow researchers to identify:

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1) A pattern of inheritance
2) Linked to other genes or not
3) Likely to be passed onto the offspring

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Which type of inherited trait commonly skips a generation?

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Recessive traits, dominant traits do not.

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When affected females have all affected children, but affected males do not pass it on, this is characteristic of which inheritance pattern?

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Maternal

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If there is unequal distribution of affected males vs. less females it is more likely to be inherited:

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Sex linked

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If the numbers of affected males and females is approximately equal, this is inherited most likely by:

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Autosomal inheritance

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What does Hardy-Weinberg law state about frequencies of alleles in the gene pool of a population?

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They do not change over time.

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5 Assumptions of Hardy-Weinberg

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1) No Mutation
2) No Migration
3) No Natural Selection
4) Random Mating
5) Large enough population to prevent random drift in allele frequencies

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Hardy-Weinberg at molecular level states:

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Segregation of alleles, independent assortment, and recombination during meiosis can alter the combinations of alleles in gametes but cannot increase or decrease the frequency of an allele in the gametes of one individual or the gametes of the population as a whole.

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Is Independent assortment a requirement for Hardy-Weinberg?

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No. Genes are allowed to be closely located to each other on the same chromosome.

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Does Hardy-Weinberg apply to linked genes?

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Yes

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Assuming that there are two alleles of a gene in a population:
p =
q =

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p = Frequency of the dominant allele
q = frequency of the recessive allele

p + q = 1

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How to calculate the proportion of genotypes in a population: Equation

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(p + q)^2 = 1

p^2 + 2pq + q^2 = 1

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p^2 + 2pq + q^2 = 1

What is this a calculation of ?

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Based on allele frequency, it is used to calculate the proportion of genotypes in a population.

p^2 = frequency of AA
2pq = frequency of Aa
q^2 = frequency of aa

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What is Hardy-Weinberg equilibrium?

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The point at which after one generation the allele frequencies no longer change.. Then genotype frequencies can be calculated.

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When does a population reach Hardy-Weinberg equilibrium?

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After one generation with the 5 assumptions included.

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Is it possible in reality for a population to meet Hardy-Weinberg criteria?

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No way Jose!

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How is the Hardy-Weinberg assumption of: No Mutation unrealistic?

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Mutation: Inevitable even by inherent errors by DNA Polymerase over time.
Also what about radiation and chemical mutagens!

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How is the Hardy-Weinberg assumption of: No Migration unrealistic?

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Migration: Animals leaving or entering a population would bring new alleles and disturb the H-W equilibrium.

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How is the Hardy-Weinberg assumption of: No Natural Selection unrealistic?

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Natural Selection: For there to be no natural selection, there would also have to be unlimited resources, no predation, no disease, etc. Unrealistic.

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How is the Hardy-Weinberg assumption of: Random Mating unrealistic?

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Non-Random Mating: If individuals pick their mates preferentially based on one or more traits, alleles that cause those traits will be passed on preferentially from one generation to another.

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How is the Hardy-Weinberg assumption of: No Random Drift in a large enough population unrealistic?

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Random Drift: If a population becomes very small, it cannot contain as great a variety of alleles. In a very small population, random events can alter allele frequencies significantly and have a large influence on future generations.

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Fitness

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How well an organism is physically adapted to pass on its alleles to future generations.

How well an organism is adapted to it's niche or how well it can feed itself.

Not taken into account: how it protects and nurtures it's young to maturity.

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How is the fitness of an organism affected by new alleles caused by mutation?

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Generally rendering gene products to be less active or even inactive. Mutations are generally harmful.

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What happens if a mutation occurs in a muscle cell of an individual who then reproduces, that the mutation increase genetic variation ?

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No, somatic cell mutations are not passed to the next generation. Only germ cells.

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Can non-random mating create new alleles in a population?

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No, but it will alter allele frequencies.

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Can Random Drift create new alleles in a population?

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No, but it can alter allele frequencies.

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Can Recombination create new alleles in a population?

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No, but it can create new combinations of alleles.

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Can Deletion create new alleles in a population?

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Yes, only mutation of a genome can create new alleles. A deletion can create a new allele even if the new allele is a truncated gene product or does not express any gene product at all.

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Directional, Divergent, Stabilizing, Artificial, Sexual, Kin Selections are all modes of what overall Selection?

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Natural Selection

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When Polygenic traits follow a bell-shaped curve of expression, with most clustered around the average and some trailing in either direction.

If natural selection removes those at one extreme, the population average over time will shift to the other direction.
Give an example of this.

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Directional Selection.

Example:
Giraffes get taller as all short giraffes die for lack of food.

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Mode of Natural Selection: Giraffes get taller as all short giraffes die for lack of food.

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Directional Selection

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Mode of Natural Selection: Small deer are selected for because they can hide, large deer are selected for because they can fight, but mid-sized deer are a yummy snack for deer munchers.

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Divergent Selection

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Mode of Natural Selection:
Birds that are too large or too small are eliminated from a population because they cannot mate.

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Stabilizing Selection

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Mode of Natural Selection:
THe pets and crop plants we have are the result of many generations of _________ selection.
(Breeders and shit)

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Artificial Selection

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Mode of Natural Selection:
Some birds have bright plumage to attract a mate, even at the cost of increased predation (peacocks bitches!)

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Sexual Selection

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Mode of Natural Selection:
A female lion sacrifices herself to save her sister's children.

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Kin Selection

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Mode of Natural Selection:
Animals that live socially often share alleles with other individuals and will sacrifice themselves for the sake of the alleles they share with another individual.

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Kin Selection

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Mode of Natural Selection:
Animals often do not choose mates randomly but have evolved elaborate rituals and physical displays that play a key role in attracting and choosing a mate.

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Sexual Selection

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Mode of Natural Selection:
Humans intervene in the mating of many animals and plants, using artificial selection to achieve desired traits through controlled mating.

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Artificial Selection

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Mode of Natural Selection:
Both extremes of a trait are selected against, driving the population closer to the average.

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Stabilizing Selection

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Mode of Natural Selection:
Removes the members near the average leave those at either end.
Over time it will split the population in two and perhaps lead to a new species!

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Divergent Selection

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A group of organisms which are capable of reproducing with each other sexually

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Species

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What keeps existing species separate?

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Reproductive Isolation.

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Prezygotic and Postzygotic are two types of:

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Reproductive Isolation

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Barriers that prevent the formation of a hybrid zygote:

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Prezygotic

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Ecological
Temporal
Mechanical
Behavioral
Gametic

Are all types of what Reproductive barrier?

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Prezygotic

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Barrier that prevents the development, survival, or reproduction of hybrid individuals.
Eg. Mule

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Postzygotic

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A mule is an example of which type of reproductive isolation barrier?

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Postzygotic

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The creation of a new species.

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Speciation

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Cladogenesis
- Allopatric Isolation
Anagenesis
Sympatric

Types of what?

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Speciation. All species come from pre-existing species.

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One biological species simply becomes another by changing so much that if an individual were to go backin time it would be unable to reproduce sexually with it's ancestors.

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Anagenesis

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Initiated by geographical isolation.

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Allopatric Isolation

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Branching where one species diversifies and becomes two or more new species.

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Cladogenesis

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When a species gives rise to a new species in the same geographical area, such as through divergent selection.

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Sympatric Speciation

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Over time, geographical isolation leads to reproductive isolation.
True or false?

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True dat homie

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Bird wings have five bony supports which resemble distorted human fingers.
Example of what structure?

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Homologous Structures

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Physical features shared by two different species as a result of a common ancestor.

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Homologous Structures

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Structures that serve the same function in two different species but not due to a common ancestry.

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Analogous Structures

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The flagellum of human sperm and bacteria flagella are an example of what kind of structure?

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Analogous Structures

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When two different species possess many analogous structures due to similar selective pressures.

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Convergent Evolution

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Bats and birds appear to be very similar, even though bats are mammals.
This is an example of what kind of evolution?

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Convergent Evolution

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When divergent selection causes cladogenesis, this is termed

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Divergent Evolution

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Two species go through similar evolutionary changes due to similar selective processes

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Parallel Evolution

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In the Ice age, all organisms would be selected for their ability to tolerate the cold. Example of what kind of evolution?

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Parallel Evolution

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When two different alleles dor a single trait result in a blended phenotype

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Incomplete Dominance

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When the expression of one gene depends on the expression of another

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Epistasis

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Genes that affect many aspects of the overall phenotype

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Pleiotropic

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Traits that are affected by many different genes

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Polygenic

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The likelihood that a particular genotype will result in a given phenotype, and can be affected by several factors including age, environment, and lifestyle.

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Penetrance

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Homologous structures are the result of

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Divergent evolution that creates a new species

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Analogous structures are the result of

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Convergent evolution in which different species must meet similar environmental challenges.