Bio 001 Midterm 2

Directional selection

Individuals with one extreme end of a phenotype do the best

What happens to the mean and variance in directional selection?

There is a shift in mean and no change in variance

Stabilizing selection

Phenotypes closes to average do best

What happens to the mean and variance in stabilizing selection?

There is no shift in mean and decrease in variance

Disruptive/diversifying selection

Both phenotypic extremes have high fitness

What happens to the mean and variance in disruptive/diversifying selection?

There is no shift in mean and increase in variance

Frequency dependent selection

The fitness of a phenotype depends on how common it is in the population

Negative frequency-dependent

Rare phenotypes do best

What happens to variation in negative frequency-dependent selection?

Maintain phenotypic variation

Positive frequency-dependent selection

More common phenotypes do best

What happens to variation in positive frequency-dependent selection?

Removes variation very quiclkly

Balancing selection

Umbrella term to describe any selection pattern that maintains variation and it isn’t a specific type of selection

Balancing selection: _______ variation in selection patterns

Spatial

Balancing selection: _______ variation in selection pressures

Temporal

What are drivers of natural selection?

Species interactions, mate choice, competition, environmental pressures

Many human disease alleles are recessive and rare. Why aren’t these alleles eliminated from the population by selection?

Because they are recessive and natural selection doesn’t always see rather and you need to copies to have the phenotype

What is the sickles cell anemia caused by?

It is caused by a single mutation in one of the hemoglobin genes

Why is the HbS allele more common in some parts of the world (especially western Africa) and so rare everywhere else?

Heterozygous individuals with 1 sickle allele have 90% less mortality from malaria

Huntington’s Disease

Progressive breakdown of nerve cells in the brain, usually beginning in middle-age

The Huntington’s allele is dominant. So why hasn’t it been removed from the population by natural selection

Because of the late onset of phenotypic effects

How is variation maintained in populations?

Disruptive selection, negative frequency dependent selection, spatial/temporal variation, heterozygote advantage, recessive allele, late onset effects

Constraints of natural selection

Natural selection can only tinker with existing organisms

What are some constraints of natural selection?

ecological interactions like predators prevent certain preys from enhancing their fitness

In the example of the constraints of natural selection about the birds. Why don’t bird just have lots of really big babies?

It’s a trade-off they can’t invest that many resources without a cost to themselves

Gene

Section of DNA that codes for a particular protein

Allele

Different version of a gene

Chromosome

Long strand of DNA that contains many genes

Genome

All the genetic material of an individual

How many chromosomes and pairs of chromosomes do we have?

We have 46 chromosomes or 23 pairs of chromosomes

DNA is a ______

Double helix

How many base pairs of DNA chromosomes do we have?

246 million base pairs

The Central Dogma

DNA transcribes to RNA, then it translates to protein

Wobble principle

Provides redundancy so that it makes mistakes less catastrophic

Synonymous

Mutations that occur that don’t change the amino acid

Non-synonymous

mutations that alter the identity of the amino acid

Regulatory region

It controls when, where, and to what extent a gene is expressed

Coding region

Part that makes the code for the proteins

Where can mutations occur?

In the regulatory and coding region

Genes have multiple ______.

Alleles

The combination of you alleles is your _______.

Genotype

Your genotype in combination with your environment determines your ______.

Phenotype

What are the 3 base pairs mutations?

Substitution, insertions, deletion

What type of base pair mutations do you think would have the largest phenotypic effect?

Insertion or deletion

What is trisomy?

Having three chromosomes instead of two and can result in down syndrome

Do you expect base pair or chromosomal mutations to have larger phenotypic effects?

Chromosomal mutations because they carry thousands and thousands of genes

How many alleles of any gene do humans have?

Two

At the population level how many alleles do humans have?

Many

True-breeding

When self-pollinated all offspring match parents

Inheritance factor

There are two copies of inheritance factors, one could be hidden other was visible

Diploid

Two copies of every chromosome (gene)

Games are ______.

Haploid

Gametes only contains _________.

Half of their genome

Homozygous

Both alleles are the same

Heterozygous

Alleles are different

Dominance

An allele is dominant if its phenotype is present in the heterzygote

Can you have the same phenotype but different genotypes?

Yes

Law of segregation

When an individual produces gametes, the gamete only receives one allele, two copies of a gene the separate so that each gamete receives only one copy

Gametes

sperm and eggs, more generally the results of meiosis

Simple/Complete Dominant

A single dominant allele produces the dominant phenotype. The homozygous dominant and heterozygous genotypes have the same phenotype

Incomplete Dominant

The heterozygote phenotype is intermediate between the two homozygous phenotypes

Codominant

the heterozygote phenotype is both of the homozygous phenotypes expressed simultaneousl

When is codominance rare?

At large scales

When is codominance common?

At the molecular scales

Law of Independent Assortment

Alleles of different genes assort independently of one another during gamete formation

Linkage

Two genes are linked together because they are on the same chromosome

Genes on the same chromosome ______________ but ___________.

Are linked and tend to be inherited together but they can be broken up by recombination

Pleiotropy

A single gene has many effects

Epistasis

when multiple genes interact with each other to influence a trait

What is an extension gene?

Recessive allele lacks any pigment in the fur

Polygenic inheritance

many genes contribute to a phenotype

What else affects phenotype?

Environmental influences