Kaplan Biology Ch. 12: Genetics and Evolution

Genotype vs. Phenotype

Genotype = actual alleles

Phenotype = observable trait as a result

All but one type of chromosome exist as homologous pairs, what is that one type?

Male sex chromosomes, rather than having an X with a homologous X chromosome, they just get a Y

How are genes mapped?

By their locus, human genes all exist in the same places on particular chromosomes

Because a chromosome implies a homologous pair, humans all have two whats for each gene?

alleles

How to know when an allele is dominant

You only need one copy for it to be fully expressed

Capital Letter

How to know when an allele is recessive

Two copies are needed for it to be fully expressed

Lowercase letter

What does it mean to be homozygous?

Two identical alleles

What does it mean to be heterozygous?

Two nonidentical alleles

What does it mean to be hemizygous?

You only have one allele (happens in males because they don't always have complete homologues)

What does complete dominance mean?

Only one dominant and one recessive allele exist for a given gene, nothing else. (purple flower + white flower = purple flower)

What does codominance mean?

Two dominant alleles exist for one gene, and if someone has both, both will be fully expressed (Blood type A and Blood type B = Blood type AB)

What does incomplete dominance mean?

A dominant and recessive allele exist for one gene, but if someone has both, the expression will sit somewhere in between both (red flower + white flower = pink flower)

What does penetrance measure?

The proportion of individuals with a particular genotype who express the expected phenotype. Kind of a ranking for how dominant or recessive something is. The greater the proportion, the greater the dominance. The lower the proportion, the more recessive something is.

What does expressivity mean in the context of genetics?

It means that people with identical genotypes can still have different phenotypes.

What does it mean if expressivity is constant?

Then people with identical genotypes will have identical phenotypes

What does it mean if expressivity is variable?

Then people with identical genotypes will have different phenotypes

Mendel's first law of Segregation

1) Genes have alleles (variable forms)

2) Organisms have two alleles for each gene, one from each parent

3) Gametes have one allele for each gene due to anaphase I of meiosis where homologous chromosomes are separated, leaving each new cell with only one homologue

4) Alleles can be either dominant or recessive

Mendel's second law of Independent Assortment

1) The inheritance of one allele for one gene does not affect the inheritance of another allele for a different gene

2) Recombination occurs during prophase I of meiosis (where tetrads swap alleles to create novel chromosomes)

What does virulent mean?

disease-causing

What does consanguinity mean?

same blood lineage (genetically related)

What is the transforming principle?

Bacteria can take in exogenous (external) DNA and incorporate it into its current DNA to evolve and increase genetic diversity

What was the Griffith experiment?

The transformation principle in a bacterial infection of mice, where a nonvirulent strain was exposed to dead virulent strains, and the nonvirulent strains took up the dead virulent DNA to become virulent

What was the Hershey and Chase experiment?

Infection of bacteria with radio labeled bacteriophages (viruses). One virus had radio labeled sulfur (in proteins only) and the other virus had radio labeled phosphorous (in DNA only). After centrifuging to separated the infected bacteria from the external environment, it was found that only DNA entered the cell to replicate genetic material, so it was proven that DNA is genetic material

What is a bacteriophage?

A virus that infects bacterium by sending its genetic material inside the bacteria to hijack the bacteria's replication machinery

What is a gene pool?

All of the possible alleles for a given gene within a given species

What are three ways to alter the gene pool?

Mutations

Leakage

Genetic Drift

What are mutagens?

substances that cause mutations

What's an example of a mutagen?

transposons

What are transposons?

Elements that can hop in and out of the DNA sequence to relocate, usually without detriment. If they happen to jump in or out during coding though, they can disrupt the process and cause an error in replication

Frameshift mutations may be subcategorized into what and what?

Insertion and deletion mutations

A large scale deletion mutation can mean what?

That a portion of genetic information on a chromosome is simply removed, and those genes will now be missing. It may also cause a frameshift if it is not in multiples of 3

A large scale insertion mutation means what?

That a portion of genetic information from one chromosome is moved from that chromosome and inserted into another. This can cause a frameshift if not in multiples of 3

What is a duplication mutation?

A gene or portion of a sequence gets repeated one or more times when it shouldn't

What is an inversion mutation?

A segment of DNA is flipped so that it will be read in reverse order

Translocation mutation?

Pieces of two chromosomes are removed and swapped for each other

There are two types of translocation mutations, what are they?

Balanced (reciprocal)

Unbalanced (nonreciprocal)

Describe balanced or reciprocal translocation

It means that the same amount of information is transferred from each chromosome, resulting in no loss of information

Describe an unbalanced or nonreciprocal translocation

It means that differing amount of genes leave each chromosome, meaning some information simply goes missing. This can result in some duplicated information and some missing information in gametes.

What is the difference between translocation in gametes during meiosis and translocation in somatic cells during mitosis?

During meiosis, the affected gamete may become a zygote and affect every subsequent cell that that zygote ever makes.

During mitosis of a somatic cell, the affected cell will reproduce cells only of that type, so the effect is limited

Mutations can be helpful and provide selective advantages, or they can be what?

deleterious (bad)

What are inborn errors of metabolism?

deleterious mutations that affect the body's ability to metabolize certain things, leading to a build up of toxins that can be deadly

What is genetic leakage?

The flow of genetic information between similar but nonidentical species

Leakage often occurs as a result of what?

Hybrids reproducing with an animal of one of its parent species! Recombination will cause some of the other species's DNA to work its way over to what will be an offspring of the parent species, not a hybrid

What are hybrids?

offspring of two related species (horse + donkey = mule)

What is genetic drift?

changes in the gene pool that happen by random chance

What's an example of genetic drift?

the founder effect

What's the founder effect?

a portion of the population gets cut off so that their population for breeding gets bottlenecked, vastly reducing the gene pool

What's a common problem within the founder effect?

Inbreeding

What does inbreeding cause?

More homozygous people, so less genetic diversity.

Because there is less genetic diversity, there is less fitness in the population. This is called

inbreeding depression

By contrast, what is outbreeding or outcrossing?

Increased fitness and diversity of a population due to bringing in new unrelated individuals to the breeding group and thus expanding the gene pool

What's another way of phrasing natural selection?

Survival of the fittest

Describe natural selection

chance variations in organisms may lead to traits which are more "favorable" when it comes to surviving and producing viable offspring. These favorable characteristics, since they help with survival and offspring, tend to be passed down more and more, increasing the "fitness" of the population of the species with those favorable characteristics over other members of the species. This causes evolution.

Natural selection is a BLANK of evolution, it is NOT blank itself

mechanism

evolution

What is the modern synthesis model, termed neo-Darwinism?

Basically agrees with Darwin's natural selection, but explains that the contribution of one organism's favorable traits changes the GENE POOL as a whole and thus the POPULATION itself evolves, rather than one single lineage/family within a species. An individual cannot evolve, but a population can.

This means that INCLUSIVE FITNESS also plays a role. Evolution due to natural selection does not only change the gene pool to cause natural selection, but certain favorable traits being selected may be selected because the organisms with those traits help the rest of the population survive whether or not they have the traits themselves.

What does differential reproduction mean?

basically means natural selection. Those organisms with more favorable traits will reproduce more, and those organisms with less favorable traits will reproduce less

What is punctuated equilibrium?

changes in species (evolution) occurs in short bursts rather than slowly over long periods of time

What are the three modes of natural selection?

Stabilizing, Directional, Disruptive

What is stabilizing selection?

Narrowing of a normal curve by selecting against extremes on either end

What is directional selection?

shifting of a normal curve toward one preferential extreme

What is disruptive selection?

splitting of a normal curve to select for extremes on either end

What is adaptive radiation?

rapid rise of different species from one common ancestor (they're radiating) so that the little changes allow them to not compete directly with each other.

How does adaptive radiation prevent organisms from competing directly with each other?

Instead they occupy environmental niches that the others are not involved in

What are some niche examples?

way of life, habitat location, utilization of resources

What is speciation?

The formation of a species through evolution

How does speciation happen?

Take one species and separate them geologically for a long time. The different environmental pressures would cause different adaptive selections to the point where the two organisms from the same species would be so different that they could no longer produce viable offspring. They are now different species.

This inability to produce viable offspring together is called what?

isolation

What are the two ways that reproductive isolation may occur?

Prezygotically or postzygotically

What does the prezygotic mechanism of isolation imply?

the zygote is prevented from forming

What are some of the prezygotic mechanisms at play?

There are 5.

temporal isolation (breed at different times), ecological isolation (breed in different locations), behavioral isolation (have different courtship behaviors or different pheromones), reproductive isolation (reproductive organs are incompatible), gametic isolation (the sperm and egg cannot combine)

What does the postzygotic mechanism of isolation imply?

the zygote forms, but the offspring is either nonviable or sterile

What are some of the postzygotic mechanisms at play?

There are 3.

Hybrid inviability (zygote doesn't develop to term), Hybrid sterility (hybrid cannot reproduce), Hybrid breakdown (hybrid can only reproduce one generation)

What are the three patterns of evolution?

Divergent, Parallel, Convergent

Similarity between species is not always caused by BLANK, but can rather be caused by BLANK

common ancestor

common environment

What is divergent evolution characterized by?

common ancestor with VERY different environments, so very different species (seals and cats)

What is parallel evolution characterized by?

uncommon ancestor, but similar species evolve in similar or same environment, so they remain similar (squirrels and chipmunks)

What is convergent evolution characterized by?

uncommon ancestor, but different species evolve in similar or same environment, becoming more similar over time (fish and dolphins)

The rate of evolution is equal to what?

The RATE of change in genotype over change in time

Rate of evolution is related to what?

environmental stress. If there is none, rate is likely to be slow. If there is a lot, rate is likely to be fast.

What is the molecular clock model?

Percent similarity in genome between two species directly correlates with the amount of time it has been since their species diverged. (So humans and mice diverged a loooong time ago, but humans and apes diverged not too long ago)

What is a species?

largest group of organisms capable of breeding with one another to produce offspring

What does it mean to do a monohybrid cross?

Examine only one gene in your punnet square (so red and white flowers get crossed and you get some red, some pink, and some white ones)

What does it mean to do a dihybrid cross?

Examine only two genes in your punnet square (so red and white flowers as well as smooth or rough seed coatings)

What is the parent, or P generation?

The generation that is crossed first

What is the filial, or F generation?

The offspring of the parent generation

What is the F2 generation?

The offspring of the F generation

In a case of COMPLETE dominance, crossing two heterozygotes results in what genotypic and what phenotypic ratios?

1:2:1 for genotypes (homozygous dominant: heterozygous: homozygous recessive)

3:1 for phenotypes (dominant: recessive)

A test cross may also be called a what?

A back cross!

What is a test cross?

Crossing an unknown genotype with a homozygous recessive, then looking at the ratios of phenotypes in offspring to determine the likely genotype of the parent

A heterozygous dihybrid cross with COMPLETE DOMINANCE of both traits will result in what phenotypic distribution ratio?

9:3:3:1 (dominant in both: dominant in first and recessive in second: recessive in first and dominant in second: recessive in both)

In a heterozygous dihybrid cross with complete dominance of both traits, what phenotypic ratio still exists among each trait separately?

3:1 dominant to recessive if they were put into individual monohybrid crosses

That ratio with a dihybrid cross holds true because of Mendel's second law (independent assortment). Genes are inherited separately, and the inheritance of one does not influence the inheritance of another. This does not hold true when we have BLANK traits

LINKED traits. This is only true for unlinked traits.

What's a popular example of a linked trait?

Sex-linked traits!

When you think about sex-linked traits, the trait is ESSENTIALLY ALWAYS linked on the what chromosome?

X chromosome

Also, sex-linked traits are ESSENTIALLY ALWAYS dominant or recessive?

Recessive

What does it mean if you are a female with one affect sex-linked trait?

You are a carrier for that disease. You do not have it, but you can pass it down.

How do you draw punnet squares for sex linked situations?

Put X and X on one side, but X and y on the other side, then label one or more of the Xs with a subscript to denote that it is affected with a recessive allele

If a male has a sex-linked trait, all of his daughters will be what by necessity?

carriers

If a male has a sex-linked trait and his partner is a carrier of that trait, his daughters will be what?

Either a carrier or affected

If a male has a sex-linked trait, his sons will be what?

FINE