GENETICS EVERYTHING AFTER MIDTERM 3

lethal alleles

genetic variants that cause the death of the organism carrying them.

selection coefficient

denoted by the letter s, is a measure used in population genetics to quantify the relative fitness of a genotype compared to other genotypes

mutation rate (μ)

measures how frequently genetic changes occur over time

heterozygote advantage

an evolutionary phenomenon where an individual who is heterozygous has a higher survival and reproductive rate than those who are homozygous

recessive lethality

a genetic mutation that causes death only when an organism inherits two copies of the mutated gene recessively

dominant lethality

a genetic mutation that causes the death of an organism when present in just a single copy (heterozygous) or in both copies (homozygous) of a dominant allele

genetic drift

a mechanism of evolution where the frequencies of gene variants (alleles) in a population change randomly over time due to chance

allele fixation

occurs when an allele becomes the only variant present in a population

→ allele reaches a frequency of 1.0

→ allele is homozygous

forward genetics

approach in biology used to discover the genes responsible for a specific physical trait or disease

prototroph

an organism—typically a microorganism like a bacterium or yeast—that can synthesize all the essential nutrients and biochemical compounds required for its growth

auxotroph

an organism (like a bacterium or yeast) that has a mutation causing it to lose the ability to synthesize an essential nutrient required for its survival

mutagenic

an agent that increases/decreases the frequency of mutations above natural background levels

mutant screen

a powerful experimental technique in biology used to identify genes involved in specific biological processes

permissive condition

specific environmental circumstances—like a certain temperature or nutrient level—that allow an organism with a conditional mutation to develop and function normally

the phenotype of a ts mutant resembles that of the wild-type strain

restrictive condition

specific environmental circumstances—like a certain temperature or nutrient level—that the activity of the essential gene is substantially reduced or abolished, resulting in a slow-growth or lethal phenotype

colonies

groups of genetically identical cells (clones) derived from a single ancestor

loss of function mutation

a genetic alteration that reduces or completely abolishes the normal activity of a gene's product

usually recessive

gain of function mutation

genetic change that causes a gene's product (usually a protein) to acquire a new, abnormal function or exhibit significantly increased activity

usually dominant

+

the dominant or wild type

-

the mutant

complementation groups

a collection of distinct mutations that fail to complement one another, which indicates they are located within the same gene

saturation screen

an experimental technique designed to find every gene involved in a specific biological process. By introducing mutations at high rates, researchers exhaustively search the genome until no new genes are discovered, often generating multiple distinct mutant alleles

selection

WT dies and mutant survives ( swap)

linkage

the second test after a screen to confirm that the genes are in the same group

→ linkage refers to genes located close together on the same chromosome that tend to be inherited together. Complementation is a testing method used to determine if two similar mutations occur on the same gene or on different genes.

what is rate of mutation in completely lethal alleles?

q²

if rate of survival changes, mutation rate changes … (μ) ( for recessive)

if prob of survival = 0, μ = q²

if prob of survival = 1/2, μ = 1/2(q²)

if prob of survival is specific, μ = s(q²)

an allele frequency that is constantly changing means what…

its NOT in Hardy weinberg equilibrium

what is mutation rate in dominant lethal alleles (μ)

equal to the rate of the disease in the population

how does a smaller/ changing population affect HW equilibrium

each new generation has a new HW equilibrium that is similar to original population

why do we use yeast in forward genetics

single cell, eukaryote, divides by mitosis, can become diploid in meiosis

yeast gametes

a and alpha ( α)

What is the difference between using a genetic selection vs a genetic screen?

In a screen one must score the phenotype of every candidate, but in a selection only the desired mutants survive

If one recessive mutation is assigned to two different complementation groups, this probably reflects

a double hit (mutations in two genes)

Eric Wieschaus and Christiane Nüsslein-Volhard did a forward genetic mutant hunt for mutations that

caused embryo death

typically, why does each line have to be bred for a few generations before checking for any phenotypes in mutant screens?

 a gamete with a novel recessive mutation produces just one heterozygous carrier

mutant screen vs mutant selection

In a selection, the environment is manipulated so that only the desired mutants survive. All other cells die.

In a screen, the entire population is grown, and every individual or colony must be evaluated or tested to find the desired variant.