Genetics and Evolution Flashcards

What are genes or loci?

Sequences of DNA that encode all, or part of, instructions for particular trait

Where are genes found?

On chromosomes in the nucleus

What is a complete chromosome set?

Contains the minimum number of chromosomes containing unique assortment of organism's genes

What are haploid (monoploid) cells?

Cells that contain only one complete set of chromosomes

What are diploid individuals?

Individuals that have two complete chromosome sets

What are gametes in terms of ploidy?

Egg and sperm cells are haploid gametes

What happens when egg and sperm fuse?

Fusion of egg and sperm creates single diploid cell

What do homologous chromosome pairs contain?

Same assortment and arrangement of genes, though genes may take on different forms

What does the ploidy level of a cell designate?

How many complete sets of chromosomes are present in that cell's nucleus

How is a complete set designated?

By "n" - the number of chromosomes of complete sets

What are alleles?

Different forms of a particular gene

Do all alleles result in unique observable traits?

No, not all alleles result in unique observable traits, but some can

What are two ways both alleles in diploid organisms can contribute to traits?

1) BOTH alleles contribute to observed trait, or 2) ONE allele is dominant and only trait encoded by dominant allele is observed

What is a dominant allele represented by?

A (capital letter)

What is a recessive allele represented by?

a (lowercase letter)

What are the possible genotype combinations for dominant/recessive alleles?

AA (homozygous), Aa (heterozygous), aa (homozygous)

What is genotype?

Combination of alleles for a gene (i.e. AA, Aa, aa)

What is phenotype?

Resulting observed trait (dominant phenotype for AA and Aa, recessive phenotype for aa)

Do dominant and recessive terms indicate how widespread alleles are in a population?

No, dominant and recessive do NOT indicate how widespread alleles are in a population

Do dominant/recessive terms indicate if an allele is beneficial or harmful?

No, neither term provides direct information about how beneficial or deleterious a given allele is for an organism

How can evolution be viewed?

As change in genetic structure of a population from one generation to the next

What does evolution specifically refer to?

Changes in allele frequencies for a particular gene across generations

What is the formula for total individuals in a population?

NTotal = NAA + NAa + Naa

What is the total number of alleles in a diploid population?

2 x Ntotal

What is p in allele frequency calculations?

Frequency of dominant allele

What is q in allele frequency calculations?

Frequency of recessive allele

What is the formula for calculating p (dominant allele frequency)?

p = (2NAA + NAa)/2Ntotal

What is the formula for calculating q (recessive allele frequency)?

q = (2Naa + NAa)/2Ntotal

What is the relationship between p and q?

p + q = 1

What can variation in heritable traits lead to?

Differential survival and reproduction

What are the two most important parameters to look for in differential survival and reproduction?

Survival and reproduction

What was Darwin's and Wallace's hypothesis about natural environment?

Natural environment can influence frequency of biological traits and characteristics that prevail in population across generations

How do populations adapt according to Darwin and Wallace?

Populations adapt over successive generations to their natural environments

What happens to traits that maximize survival and reproduction?

Traits that maximize survival and reproduction in an environment increase in frequency throughout populations over successive generations

What is natural selection?

One of several mechanisms that causes proportion of individuals in a population who are better adapted to given environment to increase over successive generations

What does "better adapted" mean?

Greater chance of surviving and having offspring

What is Darwinian fitness?

Refers to adaptation in terms of survival and reproduction

Is natural selection a random process?

Natural selection itself is NOT a random process, unlike the appearance of new genetic variants in a population

What process is random in evolution?

The process generating diversity is random (mutations), NOT natural selection

What is required for natural selection to occur?

There MUST exist some variation of heritable traits in a population's genetic structure

What are mutations?

Changes in DNA sequence of an organism

What do mutations serve as?

Ultimate source of genetic and allelic variation

When do mutations often occur?

Often occur RANDOMLY during DNA replication

What are the possible effects of mutations on survival?

Depending on physical environment, mutations may be neutral, harmful, or beneficial for survival

Do genetic mutations occur purposefully?

No, genetic mutations do not occur purposefully to solve a particular survival problem

What does natural selection rely on?

Pre-existing variation caused by random mutations

What is artificial selection?

Selection done intentionally to achieve desired outcomes

What is allele frequency?

Gives proportion of a particular allele in the gene pool

What is genotype frequency?

Gives frequency of particular allele combination (genotype) in a population

What is a gene pool?

Sum of all alleles for a given gene (or all genes) in a population

What does the gene pool contain?

The genetic variation that all mechanisms of evolution can act on

What is a genetic locus?

Physical location on a chromosome where a given gene is located

How is genetic locus used?

Used synonymously with gene

What are the three key concepts reviewed about evolutionary theory?

1) Studies populations not individuals, 2) Natural populations show genetic variation among members for certain genes, 3) Different mechanisms can cause populations to evolve with regards to specific traits across successive generations

What indicates that a population has evolved?

Change in allele frequencies for given gene from one generation to the next

What are the four mechanisms of evolution besides natural selection?

Gene flow, genetic drift, nonrandom mating, and sexual selection

What is gene flow?

Migration of individuals (and their genes) between populations that changes allele frequencies in original and/or target population

What is genetic drift?

Changes in allele frequencies from one generation to the next that occur entirely by chance

Which populations are more affected by genetic drift?

It affects virtually all populations, but is much more noticeable in smaller populations

What are population bottlenecks?

Large reductions in population size caused by environmental events with an accompanying reduction in genetic variation

What can cause population bottlenecks?

Natural events or disasters, as well as intervention

What is nonrandom mating?

When organisms' phenotype influences its success in attracting mates, so mating does not occur at random

What does nonrandom mating result in?

Sexual selection

What does sexual selection explain?

Retention of traits that seem detrimental for survival

What are the five conditions for Hardy-Weinberg equilibrium?

1) No mutations occur that introduce new alleles, 2) No selection occurs that favors certain genotypes, 3) No gene flow (migration), 4) Population size is very large so genetic drift is insignificant, 5) Random mating occurs

What happens under Hardy-Weinberg equilibrium?

Allele frequencies for a given gene remain constant over successive generations, and genotype frequencies can be predicted solely from allele frequencies

What does the Hardy-Weinberg principle use?

Simple rules of probability to predict genotype frequencies from allele frequencies

What are the genotype frequencies under HW conditions for two alleles A and a?

AA = p², Aa = 2pq, aa = q²

How quickly can a population reach HW equilibrium?

After just one generation of random mating, assuming ALL other HW conditions are met

Do natural populations ever meet HW conditions perfectly?

Natural populations almost never meet the conditions of HW equilibrium perfectly, but they can approximate them

When is the HW model useful?

To estimate approximate genotype frequencies when mutation rates are very low, and as a 'null model' to determine what genotype frequencies would be in absence of evolution

What are quantitative traits?

Traits that show continuous variation (e.g. height or weight) rather than just 2 or 3 different phenotypes

How are quantitative traits encoded?

By more than one gene

What is stabilizing selection?

Favors average phenotypes

What is directional selection?

Favors phenotypes that vary in one direction from the mean

What is disruptive selection?

Favors phenotypes that vary in both directions from the mean

What is the purpose of natural selection acting on quantitative traits?

To maximize fitness by affecting genetic variation in populations in different ways