Genetics exam 2

Tetrad

4 sister chromosomes present during crossing over

Double strand break

Physical breakage and rejoining of DNA

Chiasmata

Physical chromosome conformations that give rise to crossing over

Cis allele orientation

Two dominant alleles are on the same chromosome

Trans allele orientation

Two dominant alleles are on different chromosomes

Linked genes

Genes on the same chromosome

Recombinants

New combinations of alleles that were not present in either parent

Genetic map units

AKA centimorgans, distance between genes for which 1% of meiosis is recombinant

Three point cross

Cross with 3 genes

SNPs

Single nucleotide polymorphisms

Minisatellite markers

Variants are 15-100bp long

Microsatellite markers

Variants are 2 - 3 bp long

Physical map

Sequence-based map of actual genomic DNA

Genetic/recombination map

Chromosome map based on recombination frequencies. Represent the spatial arrangement of genes on chromosomes

DNA heteroduplexes

Double strand breaks are repaired through …

Gene products

Proteins, funtional RNAs

Complete dominance

1:2:1 & 3:1

Haploinsufficiency

One allele is not enough to achieve the phenotype. Need 2 good alleles

Dominant negative

1:2:1 & 3:1 but mutant is dominant, one allele is enough to disrupt phenotype

Incomplete dominance

1:2:1 & 1:2:1, traits blended

Codominance

1:2:1 & 1:2:1, both traits visible. Human blood groups

Recessive lethal

Homozygous recessive condition causes lethality, they are not observed. 2:1 ratio

Allele penetrance

% of individuals that express the phenotype. Affected by environment, other genes, and the subtlety of the mutation

Allele expressivity

The degree to which a geneotype is expressed in a phenotype. Affected by environment, other genes, and subtlety of the mutation

Synthetic pathway

Gene-interaction networks responsible for making bilding blocks

Complementation test

Test to determine if two mutations that effect the same phenotype are in different genes or the same gene

Epistasis

1 gene suppresses phenotype of 2nd gene

Recessive epistasis

9:3:4

Dominant epistasis

12:3:1

Suppressors

Mutant allele that suppresses the phenotype of another mutation

Revertants

Genetic mutation that restores the function of another mutant gene

Synthetic lethals

A double mutant that is lethal, but the single mutations are not. 9:3:3 ratio

Prokaryote

A microscopic single-celled organism that has neither a distinct nucleus with a membrane nor other specialized organelles.

Bacteriophage

Virus-like, parasitize prokaryotes

Prototropic

Wild-type state, can live minimal medium

Auxotropic

Results from mutations, requires building blocks to grow

Plasmid

Circular DNA molecules

R plasmid

Drug-resistant plasmids

Vertical transmission

Inheritance of DNA from parent cells. Reproduction, meiosis

Horizontal transmission

Inheritance of DNA from a member of the same generation

Conjugation

Horizontal gene transfer through direct cell contact

Pilus

Cell structures used for DNA exchange in conjugation

F plasmid

Plasmid that can undergo conjugation

Origin

Start point of replication, first to be transferred in conjugation

Fertility factor (F+)

Allows plasmids to be DNA donors

HFR

High frequency of recombination

1:1:1:1

Expected phenotype ratio from dihybrid female and tester male

Crossing over happens during….

Prophase 1

Trihybrid cross no linkage

1:1:1:1:1:1:1:1

Molecular markers

Sequence variants used to map phenotypes to chromosomal regions. Used to find the genes for traits. Usually not in coding genes

Duplicative recessive epistasis

9:7