Genetics Exam 2

CH 4, 5, 6, 7

Universal donor type

Type O blood

Universal recipients

Type AB blod

Transferases

Enzyme, catalyzes the movement of a functional group from a donot molecule to an acceptor molecule

In blood: catalyzes the addition of specfic sugars to the terminal sugar on the RBC surface

• O allele produces no fucntional transferase

Red blood cell

Erythrocyte

White blood cell

Leukocyte

ABO gene

Codes for an antigen molecule on RBC that can induce an immune response

Contains the I^A, I^B, and i alleles

• i (O) is recessive

• I^A and I^B are codominant

Antigen

Foreign susbtance that can trigger the immune system

Antibody

Protein that can identify and neutralize foreign invaders

Co-dominant

When 2 alleles of the same gene are fully expressed in the phenotype

C gene

Codes for an enzytme active in the production of melanin.

Hypomorphic (leaky)

Partial loss of gene function

defined under Muller

Hypermorphic

Increases normal activity or amount of gene’s product compared to the wild-type allele, (gain of function)

Amorphic (null)

Complete loss of normal gene function

Wild-type (WT)

Standard, most common, non-mutated form of a gene as it naturally occurs in a wild population

Haplosufficient

An allele in a diploid organisms is enough to produce a normal phenotype

Haploinsufficient

One allele is inactivated, deleted, or mutated, and the single remianing functional copy is not enough to produce the normal amount of protein needed for healthy function.

Lethal alleles

Mutant alleles that are deadly, homozygosity is lethal, always recessive, low frequency, present as distortion in offspring ratios

Agouti gene

controls the distribution and type of melanin pigment produced in mammalian hair

Gene promoter

A specific region of DNA located just upstream (towards the 5' end) of a gene that acts as a "landing pad" and on/off switch to initiate the transcription of that gene into RNA

Sex-limited gene expression

The trait is only ever seen in one of the sexes

• Located in autosomes: any numbered chromosome that is not a sex chromosome

• Require male or female hormones foe expression

Sex-influenced gene expression

The trait can be seen in either sex, but is more common or more pronouced in one sex

• Result in different phenotypes in males and females of the same genotype

• Can be seen in either sex if homozygous

Penetrance

Degree to which the phenotype matches the underlying genotype

• Complete penetrance: genotype and phenotype always match

• Nonpenetrant: Genotype doesn’t produce the corresponding phenotype at all

• Incomplete penetrance: The phenotype matches the genotype in some indivduals but not all

Expressivity

The intensity of the phenotype, can vary among indivudals with the same genotype

Phenylketonuria

Metabolic disorder where the body cannot break down the amino acid phenylalanine. Commonnewborn screening

• Autosomal recessive; missing enzyme for phenylalanine breakdown

Pleiotropy

When a mutation in a single gene alters multiple distinct traits

Epistatis

The expression of one gene is masked, inhibited, or modified by the expression of one or more other genes

• most often occurs between genes in the same pathway

• In dihybrid cross the phenotype ratio of F2 will not be 9:3:3:1

Law of Segregation

The two alleles for a trait segregate when gametes are formed, and one allele randomly goes into each gamete

Law of Independent Assortment

During gamete formation, the segregation of alleles at one locus in indpendent of those at another

• Dihybrid cross — 9:3:3:1 phenotypic ration in F2 generation

Parental gametes

Contain the same allele combination as members of the P generation

Nonparental gametes

Inherit one maternal and one paternal allele

Syntenic genes

Located on the same chromosome

• Genetic linkage: Occurs when two syntenic genes cannot assort independently, leads to greater parenta; combinations of alleles

Recombinants

Gametes in which crossing over has separated the two parental alleles (AKA nonparental gametes)

• Recombination frequency is r (the distance between the two genes)

  • Number of recombinants/total number of offspring

Test Crosses

Purpose: For analyzing linkage of two (or three) genes

• Complete or incomplete

• What is r?

• How far apart are they?

Method: cross between a known heterzygote (F1) and a known double recessive individual

Intereference

The proportion (%) of expected double crossover (DCO) offspring that are “missing” from the total.

1 - (Observed DCO/ Expected DCO)

Origin of replication

Site where DNA helix unwinds to begin replication (created replication bubble)

• bacteria have a single origin of replication

• Eukaryotes have multiple

Replication forks

Ends of replication bubble where nucleotides are added to newly-synthesized strands

Replisome

Protein complex consisting of helicase, Topoisomerase, single-strand binding proteins, primase, DNA polymerase, sliding clamp, and ligase

Helicase

Breaks hydrogen bonds between bases to “unzip” the helix

• One helicase at each replication fork

• This creates the replication bubble

Topoisomerase

Relaxes supercoils. Makes one (Topo I) or two (Topo II) cuts in the DNA backbone to allow the DNA to rotate, releving torsional stress

• Then the backbone is sealed again

Single-strand binding proteins (SSBP)

• Bind to the newly separated DNA strands

• Prevent hydrogen bonds from re-formed between separated strands

Primase

Gets new strands started

• Type of RNA polymerase

• Builds an RNA primer to start new strands

DNA polymerase

Can’t begin replication by itself- only adds nucelotides to previous nucleotides

• DNA polymerase III adds nucleotides to the 3’ end of a growing DNA strand

Leading strand

Continous synthesis toward the replication fork

Lagging

Discontinuous synthesis away from replication fork

• Okazaki fragment