Bio Ch 7

3 types of gene products

1. Protein

2. rRNA

3. tRNA

Mice Experiment that lead to determining DNA carried the genetic code

• There were 2 strains of Streptococcus pneumoniae used in this experiment, a deadly smooth coat (S) strain and a nondeadly rough coat strain (R)

• When mice were injected with live “S” they died

• When mice were injected with live “R” they survived

• When mice were injected with heat-killed “S” they survived

• When heat-killed “S” was mixed with live “R” and then mice were injected with the mixture, they died

This meant that some component in the dead “S” could be transferred to the “R” to make it deadly

• Scientists removed each type of molecule from the dead “S” in that last aforementioned step one at a time

• When anything except DNA was removed, the “R” strain still acquired the “S” traits and was deadly and live bacteria exhibiting “S” traits could be recovered from the sample

• When the DNA from the heat-killed “S” was removed, the mice survived

This lead to the discovery that the DNA in the “S” strain encoded the ability for the strain to be deadly and was the molecule that could be passed between organisms and generations

Virus Experiment that lead to determining DNA carried the genetic code

Hershey and Chase incubated 2 viral cultures, one with P32 and one with S35

• P32 is in DNA phosphates

• S35 is in proteins in Met and Cys

1. Allowed these viruses to infect separate bacteria

2. Grew the bacteria that were infected through a lysogenic cycle

3. Introduced unlabeled viruses to the newly grown already infected bacteria to perform a lytic cycle

4. New viruses that came out of the P32 samples had P32 DNA but viruses that came out of the S35 samples didn’t have S35 protein

Thus DNA carries genetic info not protein

Synapsis

The alignment of homologous chromosomes on top of each other during synapsis

Name of two homologous chromosomes in prophase 1

They become a bivalent or tetrad when they undergo synapsis

Crossing over / recombination

A tetrad is cut allowing the homologous chromosomes to mix and match pieces and exchange alleles

Synaptonemal Complex (SC) and how it works

Mediates synapsis to ensure tetrads are formed correctly

SYCP2 and SYCP3 each attach to the edge of a homologous chromosome and are connected by SYCP1 and other proteins which connects the two chromosomes like a zipper between SYCP2 and SYCP3

Meiosis Phases

1. Prophase I:

Homologous chromosomes undergo synapsis and form a tetrad which then crosses over using the synaptonemal complex

2. Metaphase I:

Tetrads line up on the metaphase plate

3. Anaphase I:

and homologous chromosomes separate now with exchanged alleles with sister chromatids staying together

4. Telophase I:

Cells separate now each with only one chromosome —- they are haploid. They still have sister chromatids on each chromosome

5. Prophase II:

Chromosomes re-condense

6. Metaphase II:

Singular chromosomes line up along metaphase plate

7. Anaphase II:

Sister chromatids are pulled apart

8. Telophase II: Cells divide leaving each of the four daughters with one sister chromatid (chromosome) of each type

Nondisjunction

Failure of either homologous chromosomes in Metaphase I or sister chromatids in Metaphase II to separate

This results in gametes with either 2 copies of a chromosome or no copies of a chromosome

If this nondisjunction gametes fuse to form a zygote the zygote will have a trisomy or monosomy

Trisomies and monosomies usually result in death

Trisomy 21

Down syndrome

• Intellectual disability

• Abnormal growth

Nondisjunction of sex chromosomes

usually nonlethal — can survive as long as you have one X

• Usually results in sterility and intellectual disability

• If you have a Y you will have male characteristics — SRY gene

• No Y = no male characteristics

Turner Syndrome

Only one X sex chromosome and no Y

Results in:

• Female appearance

• Sterility

• Underdeveloped ovaries

Law of segregation

two alleles of an individual are separated and only one is passed onto offspring

Law of independent assortment

Which gamete an allele of one gene goes into has no impact on the gamete that receives an allele from another gene

Mendel’s Two Laws

1. Law of segregation

2. Law of independent assortment

Pure breeding strain

Homozygous — always produce same phenotype

F₁ generation

the progeny of a testcross

Testcross

breeding a dominant phenotype with a homozygous recessive genotype to figure out if the dominant is homozygous or heterozygous.

If any of the F₁ generation (offspring) are phenotypically indicative of the recessive, the dominant parent has to be heterozygous

Incomplete dominance

Incomplete dominance — seen in human height

Given:

R = Red flower

and

r = white flower

RR = Red

Rr = Pink (a blend of red and white)

rr = White

Codominance

Codominance — seen in blood typing

Given:

R = Red flower

and

r = white flower

RR = Red

Rr = Red and White together (maybe red with white spots)

rr = white

Pleiotropic Inheritance

one genotype affects many phenotypes

Polygenic trait

a trait influenced by a combination of many genes

Penetrance

The odds that an individual with a given genotype will express the phenotype for that genotype

Epistasis

Expression of alleles for one gene is dependent on another

Ex. the gene for curly hair cannot be phenotypically displayed if the gene for baldness is activated

Recessive lethal alleles

homozygous genotype that results in the death of the organism

Linkage

the failure of genes to display independent assortment relative to one another when close together on the same chromosome

Mitochondrial Inheritance

Inheritance of traits contained within mitochondrial DNA which is only passed down through the mother

Usually given the prefix “mt”

Ex. mt-Atp6 — encodes an ATP synthase subunit

hemizygous

when a diploid organism only has one copy of a gene

Ex. all mitochondrial genes

X Linked traits common example

Hemophilia

Much more common in males than females

X Chromosome Recombination

X-linked allele combinations may be different in offspring than they are in the female parent because the two female X chromosomes can recombine altering their genotypes during meiosis

Population

members of a species that mate and reproduce with one another

Hardy-Weinberg Law

states that the frequencies of alleles in the gene pool of a population will not change over time

Hardy-Weinberg Assumptions (5)

1. No mutation

2. No migration

3. No natural selection

4. Random mating

5. Large population

Hardy Weinberg Equations

p² + q² = 1

p² + 2pq + q² = 1

p = dominant allele freq

q = recessive allele freq

p² = homozygous dominant genotype freq

2pq = heterozygous genotype freq

q² = homozygous recessive genotype freq

Fitness

how successful an organism is at reproducing and passing its alleles on to future generations

HAS NOTHING TO DO WITH THE INDIVIDUAL’S ABILITY TO BE PHYSICALLY FIT OR COMPETE FOR FOOD — JUST REPRODUCTIVE SUCCESS

Directional Selection

Selecting for one extreme of a trait over the other

Ex. giraffes having longest necks possible

Divergent Selection

Selects for both extremes of a trait leaving the average phenotypes out

Ex. Small deer being selected for because they can hide and large deer being selected for because they can fight but mid-size deer being selected against because they can do neither

Stabilizing Selection

Selecting for the average phenotype and against the extremes

Ex. human birth weight being most successful at a medium weight because too small or large of babies have complications that can impact fitness

Artificial Selection

Humans using controlled mating to select for certain traits in some animals and crops

Sexual Selection

Selecting for traits that attract a mate regardless of how they impact the individual’s survivability

Ex. the bright feathers of a peacock are selected for as they attract more mates

Kin Selection

Describes an individual sacrificing themselves to save their kin

Species

a group of organisms capable of reproducing with each other sexually and producing successful, fertile offspring

Horses and donkeys can mate to make a mule but the mule is sterile. Therefore horses and donkeys aren’t the same species

Two types of reproductive isolation

1. Prezygotic — prevent the formation of the zygote

2. Postzygotic — prevent the development, survival to maturity, or reproduction of the offspring

Types of prezygotic reproductive isolation (5)

1. Ecological — the organisms live in different habitats with an uncrossable barrier

2. Temporal — the organisms mate at different times of day, seasons, or times of year

3. Behavioral — the organisms don’t use the same mating rituals

4. Mechanical — reproductive organs are incompatible

5. Gametic — gametes cannot fuse to form a zygote

Types of postzygotic reproductive isolation (3)

1. Hybrid Inviability — hybrid offspring do not develop normally and usually die in the embryonic stage

2. Hybrid Sterility — hybrid develops normally but is unable to reproduce

3. Hybrid Breakdown — the second generation of hybrids is biologically defective

Speciation

creation of a new species

Homologous Structures

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

Analogous Structures

Structures that serve the same function in two different species but cannot be drawn to a common ancestor

Convergent Evolution

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

Divergent Evolution

When two species become phenotypically different due to differing selective pressures

Parallel Evolution

When two species undergo similar simultaneous evolutionary changes

Ex. all animals evolving cold resistance through the ice age

Taxonomy

science of biological classification

binomial classification

Gives every organism a two word classification consisting of genus and species

Invented by Carolus Linnaeus

Ex. Homo sapiens

Descending order of taxonomic categories

Domain Kingdom Phylum Class Order Family Genus Species

Anterior

Front Facing

Posterior

Back Facing

Dorsal

On top or spinal side

Ventral

On bottom or opposite spinal side

Superior

Closer to the head

Inferior

Further from the head, closer to the feet

Cephalad

Towards the head

Caudad

Towards the tail

Two important characteristics of early earth atmosphere

1. It was anaerobic (No O₂)

2. It was a reducing environment with plentiful electron donors

Abiotic synthesis

the process by which polymers were made on the early earth using metals and clays at catalysts and lightning, radioactive decay, volcanic activity, or sunlight as energy

Proteinoids

polypeptides made through abiotic synthesis

Microspheres

droplets of proteinoids in water

liposomes

lipids covering a microsphere of proteinoids

Coacervate

Molecules that include polypeptides, nucleic acids, and polysaccharides formed using enzymes

Protobionts

Classification that includes Microspheres, Liposomes, and Coacervates

Resemble a cell in that they:

• Have a protected inner environment

• Can perform chemical reactions

• Split into two when they get too big

They lack heredity

Ribozymes

RNA enzymes that splice mRNA

RNA self-replication

one small RNA strand can line up with another and spontaneously polymerize by base pairing with a fairly low error rate