Biology Exam 3

Gene

Gene

unit of heredity

ex. tongue rolling

Allele

variation of a gene

ex. can or can’t tongue roll

Homozygous

both alleles are the same

ex. AA or aa

Heterozygous

alleles are different

ex. Aa

Dominant

trait that masks the other trait

Recessive

trait that gets masked

Genotype

combination of alleles that an individual has

Phenotype

physical characteristics the person displays

Gregory Mendel

experimented on pea plants which showed genetic inheritance

Monohybrid cross (punnett square)

only looking at a single characteristic

Dihybrid cross (punnett square)

looking at 2 characteristics

illustrates independent assortment

Test cross

take an unknown genotype (dominant phenotype) and cross with recessive (phenotype) to find if it is dominant or recessive

Dominant pedigree

phenotype shows up in every generation

Recessive pedigree

have to have homozygous recessive to have phenotype

has carriers

can skip a generation

Carrier

heterozygous individual who carries recessive gene but does not have phenotype

Autosomal pedigree

any information not on sex chromosomes

X-linked pedigree

traits are linked to X chromosomes

Consanguineous

mating between blood relation (shown as a double line on pedigree)

Co-dominance (incomplete dominance)

neither characteristic expresses itself over another

ex. mating red and white flowers produces pink flowers

consequence: genotypical ratio = phenotypical ratio

Polygenic Inheritance

many gene inheritance or characteristics that are influenced by more than one gene

ex. height

X-linked characteristics

genes that are inherited by the x sex chromosome

females should all be carriers of the characteristics and males display phenotype if they inherit the infected x

Central dogma of biology

DNA replication → transcription → RNA → Translation → protein

Nucleotides

5 carbon sugar, phosphate, nitrogenous base

DNA

deoxyribose sugar, CGAT, and double stranded

RNA

ribose sugar, CGAU, and single stranded

Phosphodiester bond

links 2 nucleotides together

5’ end of 1 nucleotide to 3’ end of other

Backbone of DNA

sugars and phosphates connected with phosphodiester bond

Hydrogen bonds

hold together nucleotides in DNA and is strong in numbers

Chargaff rules

amount of cytosine always equals guanine and bonded with 3 hydrogen bonds

amount of thymine always equals adenine and bonded with 2 hydrogen bonds

Purines

adenine and guanine

2 rings

Pyrimidines

Cytosine, Thymine, and Uracil

1 ring

How DNA replicates

semi-conservative manner

Primase

lays down RNA primer and acts as an RNA polymerase

Leading strand

synthesizes new strand of DNA continuously

DNA ligase

joins together fragments on the new strand of DNA

DNA polymerase I

removes primer and synthesizes DNA in a 5’ to 3’ direction

DNA helicase

“unzips” the DNA by separating base pairs

DNA polymerase III

synthesizes DNA in a 5’ to 3’ direction on the main poymerase

Lagging strand

synthesizes new strand of DNA discontinuously

Okazaki fragments

fragments of synthesized DNA on the lagging strand

RNA primer

sequence of RNA bound to DNA to get DNA polymerase III to synthesize DNA

rRNA

part of the ribosome and helps make up its complex

mRNA

takes message of DNA codon from nucleus to ribosome

tRNA

transfers amino acids to the ribosome, contains the anticodon, and there are 64 versions of them

Properties of the genetic code

degenerate or redundant → multiple codons code for the same amino acid

Universal

• both minimizes affects of mutations

Missense mutation

changes one amino acid that the codon codes for

ex. AAA → CAA

Silent mutation

the codon changes but it does not change the amino acid it codes for

ex. GCG → GCA

Nonsense mutation

when the codon codes for the polypeptide to stop prematurely

ex. UUG → UAG

Frameshift mutation

addition or deletion of a nucleotide which changes the reading frame thus changing the whole peptide

Genetic variation

differences in alleles of genes found within individuals in a population

evolution results in a change in the genetic composition of a population

is the raw material for selection

is the rule in nature

Evolution

how an entity changes through time

• changes in allele frequencies

Charles Darwin

believed species developed differences as a result their descendants are different from ancestors and new species form

proposed natural selection as mechanism of evolution

ex. the giraffes with longer necks could reach more food so they had more offspring and that trait became dominate

Jean-Baptiste Lamarck

believed evolution was by inheritance of acquired characteristics

• everything ancestors do in life passes to offspring

• ex. giraffe stretches for branch so their offspring have longer necks

Polymorphic loci

more than 1 allele at frequencies greater than mutation alone

theres 1 gene with several alleles

Heterozygosity

probability that a randomly selected gene will be heterozygous in a randomly selected individual

Hardy-Weinberg equilibrium

null hypothesis used to measure allele frequencies in a population

Hardy-Weinberg’s ways that proportions of genotypes stay the same in a population

1. no mutation takes place

2. no genes are transferred to or from other sources

3. random mating is occurring

4. the population size is very large

5. no selection occurs

Mutation mechanism of evolution

rates generally low

other evolutionary processes usually more important in changing allele frequencies

ultimate source of genetic variation

makes evolution possible

ex. types of mutations

Gene flow mechanism of evolution

movement of alleles from 1 population to another

animal physically moves into new population

drifting of gametes or immature stages into an area

mating of individuals from adjacent populations

ex. migration, pollination in different areas, seed dispersal

Nonrandom mating mechanism of evolution

assortative mating

• phenotypical similar individuals mate

• increase proportion of homozygous individuals

• ex. white cat only mates with white cat and black only mates with black

disassortative mating

• phenotypically different individuals mate

• produces excess of heterozygous

• ex. white cat mates with black cat

Genetic drift mechanism of evolution

in small populations, allele frequency may change by chance alone

magnitude of genetic drift is negatively related to population size

entirely random

founder effect

bottleneck effect

Founder effect of genetic drift

smaller population breaks off from large population and only brings certain alleles with them

ex. only red birds travel to an island off mainland

Bottleneck effect in genetic drift

a large population shifts to a small population which causes alleles to be lost

ex. northern elephant seal

Artificial selection

what we do to influence an organism’s genetics

ex. breeding dogs or corn

Natural selection

happens in environment and the the strongest traits survive due to the organism’s conditions

ex. rhino horns being longer

3 conditions for natural selection to occur and result in evolution

1. variation must exist among individuals in a population

2. variation among individuals must result in differences in the number of offspring surviving in the next generation

3. variation must be genetically inherited

Fitness

individual with one phenotype leave more surviving offspring in the next generation than individuals with an alternate phenotype

the most fit phenotype is the one that produces the greatest number of offspring

Components to fitness

1. survival

2. sexual selection - some individuals more successful at attracting males

3. number of offspring per mating

4. traits favored for one component may be disadvantage for others

Autosomal recessive

usually skips a generation in a pedigree and has “carriers

X-linked recessive

expressed in males more often than females

Autosomal dominant

having any amount of the affected allele causes the phenotype

Interaction

mutations and genetic drift may counter selection

• mutations rarely counter selection

• drift may decrease an allele favored by selection

Heterozygote advantage

heterozygotes are favored over homozygotes

works to maintain both alleles in the population

ex. sickle cell anemia

Disruptive selection

acts to eliminate intermediate types

takes normal shaped curve and forms two peaks

ex. African black bellied seedcracker finch beaks

Directional selection

acts to eliminate one extreme

often occurs in nature when the environment changes

normal shaped curve shifts right or left

ex. drosophila (flies don’t go towards light)

Stabilizing selection

acts to eliminate both extremes

makes intermediate more common by eliminating extremes

makes the normal shaped curl skinnier

ex. infants birth weight