Biology Chapter 23

4 Reasons Why Natural Selection cannot produce the perfect organsim

1. It can only act on existing variations 2. It is limited by historical constraints 3. Adaptations are often compromises 4. Weather/ chance events influence natural selection

Effects of Genetic Drift

1. can cause allele frequencies to change at random 2. is significant in small populations 3. can lead to a loss of genetic variation in a population 4. can cause harmful alleles to become fixed

3 Mechanisms Contributing to Shuffling of Alleles

1. crossing over 2. independent assortment of chromosomes 3. fertilization

Potential Sources of Variation are...

1. duplication of genes due to errors in meiosis 2. slippage during DNA replication 3. activities of transposable elements

4 types of genetic variation:

1. formation of new alleles 2. altering gene number or position 3. rapid reproduction 4. sexual reproduction

What are 3 mechanisms that alter allele frequencies and cause evolutionary changes?

1. natural selection 2. genetic drift 3. gene flow

5 Conditions for Hardy-Weinberg Equilibrium

1. no mutations 2. random mating 3. no natural selection 4. large population sizes 5. no gene flow

Crossing over, resulting in an increase in genetic variation, occurs between _____.

nonsister chromatids of homologous chromosomes

Natural Selection acts directly on____ and indirectly on____?

phenotype, genotype

Mutation rates are high in __________.

prokaryotes and viruses

Allele frequencies in a gene pool may shift randomly and by chance. What is this random shift called?

genetic drift

Modern travel along with migration reduces the probability of _____ having an effect on the evolution of humans.

genetic drift

Microevolution

a change in allele frequencies in a population over generations.

Population

a group of individuals of the same species that live in the same area and interbreed

Neutral Variation

differences in DNA sequences that are not a selective advantage or disadvantage.

Sexual Dimorphism

differences in secondary characteristics between males and females.

The Bottleneck Effect

A sever drop in the population size. Some alleles may be over represented by survivors and other may be underrepresented.

Which of these individuals is a homozygous genotype?

AA

Genetic Drift

chance events, in small populations, that cause allele frequencies to fluctuate unpredictably from one generation to the next.

All the genes in a population are that population's _____.

gene pool

Homologous pairs of chromosomes are lined up independently of other such pairs during _____.

metaphase 1

The ease with which humans travel across the globe is likely to increase _____.

gene flow

Relative Fitness

the contribution an individual makes to the gene pool of the next generation compared to the contributions of others.

Frequency-Dependent Selection

the fitness of a phenotype depends on how common it is in the population

Genetic drift is a process based on _____.

the role of chance

Gene Flow

the transfer of alleles into/ out of a population due to the movement of fertile individuals. Reduces genetic differences between populations

A mutation occurs when _____.

there is a change in the DNA sequence of a gene

How are new alleles formed?

They are formed from mutations and are passed on to offspring only through multicellular organism's gamete cells.

Gene Pool

all copies of every type of allele at every locus in all members of a population

Disruptive Selection

conditions favor individuals at both extremes of a phenotypic range.

Directional Selection

conditions favor one extreme of a phenotypic range, thereby shifting the populations frequency curve. Common when a populations environment changes.

Sexual Selection

form of natural selection where individuals with certain characteristics are more likely to obtain mates.

The Founder Effect

when a few individuals become isolated from a larger population, this smaller group produces their own, new population.

Hardy-Weinberg Equilibrium

when allele and genotype frequencies remain constant from generation to generation, the population is not evolving

You read about soapberry bugs and select the correct statement describing relative fitness in these individuals.

A soapberry bug with high relative fitness has a relatively high number of offspring that survive to reproductive age.

Every few years a giant axe chops off the head of every person who is over 6 feet tall. How will this affect the human population?

Alleles that promote "tallness" will decrease in frequency.

What are 3 modes of selection?

1. Directional 2. Disruptive 3. Stabilizing

Stabalizing Selection

acts against both extreme phenotypes. Reduces variation and favors individuals who provide higher reproductive success

Genetic Variation

differences among individuals in the composition of their genes. Can be quantified as the average percentage of loci that are heterozygous

What are 2 types of genetic drift?

1. founder effect 2. bottleneck effect

Adaptive Evolution

evolution that results in a better match between organisms and their environments.

In human gamete production there is an average of _____ crossover events per chromosome pair.

2-3

What type of chromosomal changes are harmful?

Changes that delete, disrupt, or rearrange many loci are harmful. Also, duplication of large chromosomal segments

What does Natural Selection result in?

It results in alleles being passed to the next generation in proportions that differ from those in the present generation.

Which statement correctly describes the role of chance in evolution?

The ultimate source of new alleles is mutation, random changes in the nucleotide sequences of an organism's DNA.

Without ____ , evolution cannot occur

genetic variation

Heterozygote Advantage

if the heterozygote locus has a greater fitness that both homozygotes, it is an advantage

When is it a fixed gene pool?

if there is only one allele that exists for a particular locus in a population

Balancing Selection

includes heterozygote advantage and frequency dependent selection

Intersexual Selection

individuals of one sex are choosy in selecting their mates

Intrasexual Selection

individuals of one sex compete directly for mates of the opposite sex. Occurs among males

Generation-to-generation change in the allele frequencies in a population is _____.

microevolution