Gen Bio Unit III

Genetics 

the study of inherited variation in humans 

Difficulties in studying human genetics

few offspring

long generations

unethical

Ways to study human genetics

population studies of extended families

natural experiments 

DNA sequencing from many generations

Pedigree 

a family tree that shows inheritance over several generations 

Autosomal recessive

genetic condition that requires 2 copies of an altered gene (homozygous recessive)

Sickle cell disease

the most common inherited condition among people of African descent

Autosomal dominant

genetic condition that only requires one copy of an altered gene

Disomy

has two copies of each chromosome (1 homologous pair)

Aneuploidy

genetic disorder which causes a presence of an atypical number of chromosomes

Trisomy

has 3 copies of a chromosome 

2n + 1 

Monosomy

lacks 1 chromosome from a pair

2n -1

Changes in chromosome structure

due to errors during meiosis, radiation, and chemical mutations

4 main chromosomal structural changes 

1. deletion

2. duplication

3. inversion

4. translocation 

Deletion

removes a chromosome segment

Duplication

repeats a chromosome segment

Inversion 

reverses a segment within a chromosome 

Translocation

moves a segment from one chromosome to a different chromosome

Fetal testing

genetic tests done before birth

Newborn screening

genetic tests done at birth

Carolus linnaeus findings

created the hierarchical classification system and the binomial nomenclature

James huttons findings 

gradualism 

Gradualism

observable processes that change and accumulate over time 

Charles lyells findings

redefined ideas of gradualism into to theory of uniformitarianism 

Uniformitarianism  

geological processes are uniform over time 

Jean-Baptiste Lamaracks findings

proposed that evolution was a natural mechanism

2 natural mechanisms for evolution

1. use and disuse

2. inheritance of acquired traits

Use and disuse mechanism 

body parts that are used become larger and stronger

body parts that are not used deteriorate 

Inheritance of acquired traits mechanism

traits that are acquired via use will be passed to offspring 

Charles darwin’s findings 

proposed natural selection as a mechanism for evolution 

Darwins 4 observations

1. overproduction

2. unequal survival and reproduction

3. heritable variation

4. non-random survival and reproduction

Overproduction

more offspring are born compared to the amount than can survive

Unequal survival and reproduction 

some organisms survive longer and have more offspring → competition

Heritable variation

when individuals have variation their offspring will resemble their parents

Non-random survival and reproduction 

survival and reproduction are based on phenotype

better adapted individuals → more offspring 

Descent with modifications

populations change over time as beneficial traits increase in frequency and detrimental traits decrease in frequency

Fitness

genetic contribution to the next generation relative to other members of the population

Evolutionary fitness 

an organism's ability to survive and reproduce

Illustrations of evolution

1. artificial selection

2. direct observations

3. homology

4. fossil records

Artificial selection

humans pick which individuals reproduce based on desired traits

Homology

structures/features inherited from a common ancestor

Fossil record

remains or traces of previously existing organisms in sedimentary rock

Evolution

change in allele frequencies in populations over generations 

Phenotype variation

observable differences between individuals

Genetic variation

differences among individuals in a gene sequence

Population genetics 

the study of genetic variation within a population

Gene pool

all genes in a population at any time given

Allele frequency

proportion of a specific allele at a locus within a population

Fixed allele 

allele at a frequency of 1 in a population → the only allele at a locus 

Genetic equilibrium

no change in allele frequency from generation to generation

Hardy-Weinberg equilibrium

a population’s allele and genotype frequencies will remain constant if no evolutionary forces act upon it

HW equations 

model allele and genotype frequencies in a non-evolving population

Equation for allele frequencies

P + Q = 1

P variable

frequency of the dominant allele in a population

Q variable 

frequency of the recessive allele in a population 

Equation for genotype frequencies 

P^2 + 2PQ + Q^2 = 1 

P^2 variable

frequency of a homozygous dominant offspring

2PQ variable

frequency of a heterozygous offspring

Q^2 variable

frequency of a homozygous recessive offspring

5 conditions required for HW

1. no mutation

2. no migration

3. no natural selection

4. random-mating

5. large population size

Mutation

any heritable change in DNA

Random mating 

individuals in a population are equally likely to mate

Non-random mating 

individuals in a population mate based on traits

Interbreeding 

mating of closely related individuals

Genetic drift

random changes in allele frequency

Bottleneck effect 

a population drastically decreases in size

Founder effect

a small group colonizes a new environment

Gene flow 

movement of alleles between populations 

Speciation

the process by which 1 species splits into 2

Biological species concept (BSC)

a group of individuals that can interbreed and produce viable and fertile offspring

Morphology species concept 

a group of individuals with similar shapes/features

Ecological species concept

a group of individuals with the same ecological niche

Reproductive isolation 

prevent members of different species from producing viable/fertile offspring 

Hybrids

offspring of 2 different species

Prezygotic barriers

operate prior to zygote formation → prevent fertilization

5 prezygotic barriers

1. habitat isolation

2. temporal isolation

3. behavioral isolation

4. mechanical isolation

5. gametic isolation

Habitat isolation 

prevents species from interbreeding due to different habitats

Temporal isolation

prevents species from interbreeding due to the time of day / season / year

Behavioral isolation

prevents species from interbreeding due to different behaviors

Mechanical isolation

prevents species from interbreeding due to different sizes / shapes

Gametic isolation 

prevents species from interbreeding due to molecular differences

Postzygotic barriers

barriers that occur after zygote formation

3 postzygotic barriers

1. reduced hybrid viability

2. reduced hybrid fertility

3. hybrid breakdown

Reduced hybrid viability

hybrid offsprings have low survival rates

Reduced hybrid fertility

hybrid offsprings are viable but not fertile

Hybrid breakdown 

F1 hybrids are viable and fertile but F2 and subsequent are not 

Allopatric speciation

species are separated by a geographic barrier

Sympatric speciation

reproductive isolation due to sexual selection and habitat differentiation

Sexual selection

individuals in a population mate based on traits that promote reproductive success

Habitat differentation

individuals in a population evolve to use different habitats that are not being used by the rest of the population

Systematics

the study of diversity and evolutionary relationships 

Taxonomy

the science of naming and classifying organisms

Binomial nomenclature

two-part scientific naming system for organisms

Taxon

groups organisms together based on shared characteristics

Phylogeny

the evolutionary history of a group of organisms 

Phylogenetic species concept

defines species as a group of organisms that share a unique evolutionary history

Cladistics

a method of systematics based on evolutionary relationships (phylogenetics) 

Phylogenetics

the study of the evolutionary history and relationships of biological entities

Phylogenetic tree

represents the evolutionary history of a group of organisms

Root

a branch that represents the most recent common ancestor (MRCA)