bio exam 2 heredity

law of independent assortment

the allel a gamete receives for one gene does not impact the allele received for another gene

P, F1 generations

P\= parental generation
F1\= first filial generation
F2\= second filial gen, etc..

Chromosome theory of inheritance

1. chromosomes contains DNA and genes
2. Chromosomes are replicated and passed to offspring
3. Nucleus of diploid cell contains 2 sets of chromosomes in homologous pairs
-each set carries full complement of genes
4. Chromosomes split, one to a nucleus, and not all at the same time necessarily
5. Gametes\= haploids that combine to form a diploid

Locus

Location of a gene on a chromosome

pedigree analysis

O\= female
square\= male

filled in\= affected
not filled in\= unaffected
half filled\= carrier

X-linked inheritance

A pattern of inheritance in which a recessive gene is carried on the X chromosome, so that males are more likely to be affected

Morgan's work with X-linked inheritance

showed that eye color is X-linked in Drosophila

Primary reason for recessive inheritance

Loss of function mutation (cannot express functional protein)
-50% of the functional protein is enough for dominant alleles

pleiotropic genes

affects several differnet aspects of bodily structure and function

incomplete dominance

Situation in which one allele is not completely dominant over another allele
Heterozygote has phenotype that is between either homozygote
Happens when 50% of functional protein is not enough

Codominance

A condition in which both alleles for a gene are fully expressed

What determines phenotype

A combination of genes and environment

norm of reaction

phenotype range that individuals exhibit in different environmental conditions

Epistasis

Gene interaction that occurs when alleles of one gene mask effects of alleles of another gene

By what factors are height and weight of an individual determined

they are polygenic properties (determined by multiple genes), along with other quantitative traits besides height and weight
-affected by environment as well
-follows bell curve distribution

Random sampling error

deviation between observed and expected values

what is the probability of two independent events occuring

the product (multiplication) of their probabilities

linked genes

Genes located on the same chromosome that tend to be inherited together in genetic crosses.
-inherited as a unit unless separated by crossing over

genetic mapping

The process of determining the location and chemical sequence of specific genes on specific chromosomes.
-tells order and distances between genes on a chromosome
-based on observed crossover frequency from test crosses

gene pool

Combined genetic information of all the members of a particular population

Polymorphism

presence of 2+ phenotypes in a population

monomorphic gene

makes up 99%+ of a gene's alleles

allele frequency

\# of specific alleles/ total pop of alleles for the gene

sources of new genetic material

random gene mutations, gene duplications, horizontal gene transfer

Methods of population evolution (alters allele + genotype frequencies)

natural selection, migration, genetic drift, nonrandom mating

Hardy-Weinberg equilibrium

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

Conditions necessary for allele and genotype frequencies to remain in Equilibrium

no new mutations arise, no natural selection occurs, pop size is very large, no migration occurs, and mating is random

natural selection

individuals w/ traits that favor survival and reproductive success tend to be more prevalent in a population

fitness

how well an organism can survive and reproduce in its environment

directional selection

one extreme phenotype is favored

stabilizing selection

individuals w/ intermediate phenotype have greater fitness

Diversifying selection

proces by which 2+ phenotypes are favored
-ex: a population that occupies a heterogenous environment

Balancing selection

occurs when natural selection maintains stable frequencies of two or more phenotypic forms in a population
-heterozygote advantage

Sexual selection

indiv w/ certain traits are more likely to engage in successful reproduction (chad fish)

Intrasexual selection

members of one sex choose partners based on desirable traits

Genetic drift + effects

changes in allele frequencies over time due to random chance
-occurs more quickly in small pops.
-leads to elimination or fixation (going from 2 to 1 allele) of the alleles

bottleneck effect

environmental effect reduces a pop. size and allele freq. change by genetic drift

Founder effect

when a small pop. changes location and genetic drift alters genetic composition of the pop.

neutral variation

accumulation of genes that do not promote reproductive success

What is the cause of most variation in DNA sequences?

Genetic drift is thought to be a larger contributor to DNA variation than natural selection

Gene flow

occurs when individuals migrate between populations with different allele frequencies
-enhances genetic diversity

What effects does inbreeding have on a pop?

Leads to increased proportion of homozygotes, and
homozygotes have lower fitness.
Effect called "inbreeding depression"

Taxonomy

The science of classifying organisms (extant and extinct)

systematics

study of biological diversity and classification of evolutionary relationships among species
-both extinct and extant species

taxa

level on a hierarchy

Organization of taxa

Domain -\> Supergroup (euk.) -\> Kingdom -\> Phylum -\> Class -\> Order -\> Family -\> Genus -\> Species

phylogenetic trees

viewed as hypotheses

phylogeny

Evolutionary history of a species

monophyletic group

group that consists of a single ancestor and all its descendants, excludes any organisms that are not descended from that common ancestor

3 domains of life

Bacteria, Archaea, Eukarya

What is proper biological nomenclature

genus + species

Paraphyletic group

contains most recent common ancestor but not all descendants. not a clade (branch)

Homology

similarities among various species that occur because the species are derived from a common ancestor.

Cladistics

classification based on common ancestry
species grouped by shared derived characters

cladistic approach

compares homologous characters' features which may exist in two or more character states. (ex. Front limb (character) can be a flipper, wing, or arm (character states)). Favors simplest approach (parsimony)

Shared derived character

a character shared by 2+ species or taxa derived from most recent common ancestor, unique to a clade
ex: eyes are primitive, arms w/ fingers are derived

Shared primitive character

a character shared by 2+ different taxa inherited from an old common ancestor
ex: eyes are primitive, arms w/ fingers are derived

Ingroup

group whose evolutionary relationships are of interest

outgroup

lacks one or more shared derived derived characters

Molecular Clock

assuming there is constant rate of accumulation of mutations, genetic data works as a "clock" to measure timing of evolution

horizontal gene transfer

when an organism incorporates genetic material from another organism without being its offspring
-due to HGT the 'tree of life' is more like the 'web of life'

Garrod hypothesis

some genetic diseases are caused by defect in gene encoding an enzyme
-based on studies of inborn errors of metabolism

One-gene/One-enzyme hypothesis

a single gene controls synthesis of a single enzyme
-Proposed by Beadle+Tatum

how are genes expressed at a molecular level

transcription + translation
genes are transcribed into mRNA, then mRNA is translated into a polypeptide on a ribosome

Central Dogma of Gene Expression

Transcription of DNA → mRNA→ polypeptide

Prokaryotic Transcription: initiation

recognition step, sigma-factor binds to RNA-polymerase, open complex is formed 10-15bp long

Transcription: elongation

polymerase builds DNA onto template strand

Splicing

removing introns and linking exons, done by spliceosome

The transcription process in a eukaryotic gene directly produces..?

Pre-mRNA that is capped and given a Poly A tail and spliced

What is the function and structure of the poly A tail?

The poly A tail increases mRNA stability in eukaryotes. -tail is necessary in eukaryotes bc unlike prokaryotes the mRNA must come out of the nucleus and into the cytoplasm in order to interact with ribosomes
It is a string of Adenine nucleotides added to the 3' end of mRNA

Transcription: termination

RNA polymerase and RNA transcript dissociate from DNA at the terminator

Promoter

site in a gene that specifies where transcription begins

Terminator

site in a gene that specifies where transcription ends

in which directions are genes in a chromosome transcribed

in different directions using either DNA stand as a template

RNA synthesis direction

5' to 3'

DNA synthesis direction

5' to 3',
reading: 3' to 5'

What features of meiosis allow for independent assortment of chromosomes?

random alignment of homologous chromosome pairs on the metaphase plate

The genetic code

specifies the relationship between the sequence of bases in the mRNA and the sequence of amino acids

do all codons code for a different amino acid?

no, more than one codon can code for the same amino acid. The third base of the codon is the degenerate/variable base

What is the structure of the mRNA cap

methylated guanine base attached to the 5' end of mRNA

introns

DNA sequences that are transcribed but not translated into proteins (essentially useless so they are removed from eukaryotic pre-mRNAw/ spliceosome)

what determines the amino acid sequence of polypeptides

recognition between mRNA and tRNA (mRNA codon and tRNA anticodon)

Directionality of polypeptides

first AA at N-terminus (amino end, has nitrogen on the end bc of the presence of an amino group NH2)
last AA at C-terminus (carboxyl end)

Nirenberg + Leder

determined many codons of the genetic code
used RNA triplets to promote binding of tRNAs to ribosomes

Peptide bond

Connects amino acids, the chemical bond that forms between the carboxyl group of one amino acid and the amino group of another amino acid

Codon

-a group of three bases, genetic code is read in codons -64 in total to be enough for the 20 amino acids with some overlap.
-Triplets and alternative splicing to get to 20.

Anticodon

three base sequence of tRNA that is complementary to and binds to the codon

mRNA

contains info for amino acid sequence according to genetic code

tRNA function

-transfer RNA, helps decode mRNA into polypeptide
-has two functional sites:
(1) where the anticodon binds to a codon
(2) where the amino acid is attached.

rRNA

forms a complex with ribosomes and helps mRNA interact with the complex

tRNA structure

Has common features and structure in all three domains, three stem loops and a fourth stem with a 3' single stranded region

Ribosome

-made up of many proteins and rRNA molecules
-has large and small subunits
-Provides a location for mRNA and tRNA to interact. -Ribosomes catalyze the formation of peptide bonds to make polypeptides

Translation factors

proteins needed for the three stages of translation, use GTP as an energy source

Transcription factors

proteins that influence ability of mRNA polymerase to transcribe genes

Eukaryotic stages of Translation

-Initiation: initiation factors + mRNA bind to the ribosome, tRNA recognizes start codon and binds to it
-Elongation: covalent bonding of amino acids together to create the polypeptide
-Termination: stop codon is recognized by release factor protein

Describe the initiation and elongation steps of prokaryotic translation

1. small ribosomal subunit binds to mRNA
2. initiator tRNA binds start codon on mRNA
3. large ribosomal subunit binds
4. tRNA entry and peptidyl transfer reaction
5. translocation of ribosome and release of tRNA

Describe a reason ribosomal genes are useful for comparing evolutionary relationships among organisms

All organisms possess these genes and they can be compared with each other.
-bc all organisms contain ribosomes

Archaea Domain

Single-celled prokaryotes, no cell nucleus

Bacteria domain

prokaryotic microorganisms

Eukarya Domain

domain consisting of all organisms that have a nucleus; includes protists, plants, fungi, and animals