Genetics Final Review

Nucleotides

Nucleotides

building blocks of DNA

Base pairs in DNA

A-T

G-C

Allele

an alternative form of a specific gene

traits

characteristics of an organism

Ex: pea plant color, height, color of seed, etc.

homologs

one of the chromosomes in a pair of homologous chromosomes

haploid

refers to an organism of cells that contain 1 set of chromosomes

• humans this is our gametic cells (23)

diploid

refers to an organism or cell that contains 2 sets of chromosomes

• human somatic cells (46)

plant genome from seed to seedless

• diploids have seeds

• triploids are seedless

sister chromatids

unit of two identical chromatids and a centromere

homologous chromosomes

pair of chromosomes, one of which is from your mother, and the other is from your father

homozygous

same allele for a trait

heterozygous

two different alleles for a trait

dominant

AA or Aa

recessive

aa

genetic variation

the differences in inherited traits within a population

mendelian ratios

single trait ratios

Aa x Aa

• 25% AA, 50% Aa, 25% aa

• Genotypic ratio: 1:2:1

• Phenotypic ratio 3:1

Two trait ratios

AaBb x AaBb

• phenotypic 9:3:3:1

Mendel's law of independent assortment

two different genes randomly assort their alleles during the process that gives rise to gametes

dosage compensation

refers to the phenomena in which level of expression of many genes on the sex chromosome is similar in both sexes even though males and females have different sex chromosomes

Barr bodies

A structure in the interphase nuclei of somatic cell of female mammals that is a highly condensed X-chromosomes

• XX (has one barr body)

• XY (has no barr body)

• XXY (has one barr body)

• XXX (has two barr bodies)

Z-W system

Bird sex determination

• ZZ = male (homogametic)

• ZW = female (heterogametic)

Feedback inhibition

• used to regulate/control enzymatic reactions, typically containing many steps

• can be positive or negative

incomplete penetrance

• this pattern occurs when the dominant phenotype is not expressed even though an individual carries a dominant allele

EX: individual who carries the polydactyly allele (dominant allele) but has normal # of fingers

incomplete dominance

this pattern occurs when the heterozygote has a phenotype that is the intermediate between the corresponding homozygotes

• Red = AA, White = aa, Pink = Aa

Codominance

inheritance pattern occurs when the heterozygote expresses both alleles simultaneously without forming an intermediate phenotype

EX: AB blood type

Overdominance

when the heterozygote has a greater level of reproductive success than either homozygote

EX: sickle cell anemia

Nondisjunciton

failure of chromosomes to separate correctly during anaphase

trisomy

contains an extra chromosome 2n+1

Ex: trisomy 21

essential genes

genes that encodes for a protein that is considered necessary for survival

nonessential genes

not required for survival although likely beneficial

lethal alleles

an allele that has the potential to cause death

endosymbiosis

describes a symbiotic relationship in which the symbiotic usually lives in the host

EX: mitochondria and chloroplasts

Gene imprinting

refers to a pattern of inheritance that involves a change in a single gene or chromosome during gamete formation

• typically done by methylation

maternal effect

an inheritance pattern of certain nuclear genes in which the genotype of the mother directly determines the phenotype of her offspring

Snail coiling (maternal effect)

based off mother genotype

recombinant chromosomes

refers to the combination of alleles or traits that are different than parents

• is a result of crossing over

genetic linkage

is the phenomenon in which genes that are close together on the same chromosome tend to be transmitted as a unit

Autosomal linkage group

• All homologous chromosomes paired up that are autosomal (22 chromosomes in all humans)

What is the Hardy-Weinberg equation?

p² + 2pq + q² = 1

• p² = AA

• 2pq = Aa

• q² = aa

Natural selection

the process by which differential fitness acts on the gene pool. When a mutation creates a new allele that is beneficial, the allele may become prevalent within the future generations, because the individuals with the allele will have greater reproductive success and survival

genetic drift

mechanism of evolution occurs when allele frequencies change over generations due to random chance

translocation

when one segment of a chromosome becomes atached to a different part of the same chromosome

• can be an issue if important gene that are euchromatin get transolocated to section of heterochromatin (this would turn off the important genes)

terminal deletion

loss of a segment from the end of the linear chromosome

interstitial deletion

loss of an internal segment from a linear chromosome

paracentric inversion

centromere lies outside of the inverted region

pericentric inversion

centromere lies within the inverted region of the chromosome

concordance values

MEMORIZE THESE VALUES

For siblings: 0.5

Identical Twins: 1.0

Parent of Offspring: 0.5

Aunt/Uncle to Offspring: 0.25

Grandparent to Offspring: 0.25

used for narrow sense heritability

h² = observed/expected

transduction

a virus infects a bacterium and then transfers genetic material to bacteria

conjugation

involves a direct physical interaction between two bacterial cells one bacterium to another

transformation

is a process in which genetic material is released into the environment when a bacterial cell dies. This dead bacterial genetic material can then be taken up into the cell

Hfr

has fertility factor plasmid completely integrated into the host genome and can NOT form sex plus

F⁺

Has a fertility plasmid not integrated into the host genome and can form a sex pilus

F'

Has fertility plasmid integrated into the host genome and rarely form a sex pilus

Prophage

bacteriophage that integrates genetic material with the host genetic material

virulent phage

bacteriophage that only has a lytic cycle as a means of reproduction

temperate phage

a bacteriophage that has both lytic and lysogenic cycles as a means of reproduction

lytic cycle

a viral reproductive cycle in which copies of a virus are made within a host cell, which then bursts open, releasing new viruses

lysogenic cycle

a viral reproductive stage where the virus's DNA is replicated using the host cell's DNA

• typically integrated and remains so until advantageous time like when the body is immunosuppressed

Episome

a segment of DNA such as a plasmid that can replicate independently of the chromosomal DNA and can also integrate into the chromosome

reverse transcriptase

• used to convert RNA to DNA

• used in viral integration like in HIV or in retrotransposition

HIV

• RNA virus

• RNA virus gets converted to DNA using reverse transcriptase then gets integrated into the host cell using integrase enzyme

• virus prone to many mutation which makes it very hard to treat due to it being an RNA virus

Transcription

• conversion of DNA to RNA

• Can occur simultaneously with Translation in prokaryotes (not eukaryotes)

Translation

• Conversion of RNA to protein

• can occur simultaneously with transcription in prokaryotes (not eukaryotes)

Conservative theory of DNA

• After one round of replictaion, half of the new DNA double helices would be composed of completely old, or original, DNA, and the other half would be completely new

semiconservative theory of DNA

• After one round of replication, every new DNA double helix would be a hybrid that consisted of one strand of old DNA bound to one strand of newly sythesized DNA

dispersive theory of DNA

the original DNA doubl helix breaks apart into fragments, and each fragment then serves as a template for a new DNA fragment

retrotransposone/retrotransposition

a transposable element that moves via transposition→transcribed into RNA then reverse transcriptase makes a second copy in DNA

Levels of chromosome compaction

1. Double helix (least)

2. Nucleosomes (beads on a string)

3. 30nm fibers

4. Loop domains

5. Metaphase chromosomes (most)

Helicase

unzips the DNA helix

DNA polymerase III

synthesizes the DNA in the leading and lagging strands

Toposiomerase II

(aka DNA gyrase) relaxes supercoiling ahead of the replicaiton fork

DNA ligase

glues together the okazaki fragments

single stranded binding proteins

Binds to single-stranded DNA to keep the two strands separated during replication

Directionality and orientation of DNA

• Always goes in the 5' to 3' direction when being synthesized

• is in the antisense confirmation

complementary DNA

5' ATCGATCG 3' is complementary to 3'TAGCTAGC 5'

Introns

non-coding sequences present in mRNA and do not lead to any protein production

exons

functional or coding sequences present in mRNA and lead to protein production (gene expression)

Alternative splicing

The phenomenon that a pre-mRNA can be spliced in more than one way

• allows you to make more than one gene product (protein) with just one gene

mRNA modifications

• 5' prime cap

• Poly A tail

tRNA

RNA molecule that carries the amino acids that correspond to codons in the mRNA. A tRNA molecule has an anticodon to pair with specific trinucleotide sequences

Charged tRNA

a tRNA with an amino acid attached to it

ribosomes

the large macromolecular complex that performs translation and composed of two subunits

Shine-Dalgarno sequence

Ribosomal-binding site that facilitates the binding of mRNA to the 30S subunit

Kozak sequence

like the Shine-Dalgarno sequence but for eukaryotes

Mutation

a heritable change in the genetic material

genetic testing

is for individuals looking to see if there is a genetic abnormality

genetic screening

population wide testing

amniocentesis

a type of genetic testing (individual) where amniotic fluid is sampled to look at fetal genetic abnormalities

Environmental mutagens

• mutagens outside the body

• include UV rays, gamma rays, and x-rays

CpG islands

clusters of C(ytosine) and G(uanine), associated with epigenetics via methylation of cytosines

• above promoter region

Constituitive

means to be expressed continuously at constant levels of expression

Repressor proteins

• proteins used in negative feedback loops

• repress/prevent the transcription of certain genes

tumor suppressor genes

• inhibit cell growth and division

• protect us from cancer

Oncogenes

• promote cell growth and division

• result in cancer

• specific age of onset

Beneficial mutuation

• mutations that are good for an organism

• typically leads to better reproductive success

conditional mutation

• mutations that depend on the environment like temperature

silent mutation

• mutation in which the codon for an amino acid gets changed, but due to the degenerate nature of codons still codes for the same amino acid

• do not alter the amino acid sequence (wobble)

euchromatin

less condensed regions of chromosomes, transcriptionally active

heterochromatin

tightly compacted regions of chromosomes, generally transcriptionally inactive

antisense RNA

an RNA strand that is complementary to mRNA (creates double stranded RNA which prevents translation

Mutagens

an agent that causes alternations in the structure of DNA