Biology Exam Review: Genetics, Evolution, and Systems

DNA

Deoxyribonucleic acid, a molecule that contains all the instructions for making all the proteins in a cell

Gene

A section of DNA that holds the instructions to produce a protein

Genome

The set of all genes and genetic material in an organism

Chromosomes

Condensed chromatin found during cell division, contains long strands of DNA that codes for many genes

Sister Chromatids

Constitutes a chromosome, divided into 2 parts and joined at a centromere

Homologous Chromosomes

Chromosomes that are found in pairs, one from mom and one from dad. They are structurally identical, and code for the same things, but are genetically different

Asexual Reproduction

When a single parent reproduces and produces offspring that are genetically identical to that of parents or clones.

Fragmentation

Asexual reproduction in animals by cutting off body parts, and regrowing them

Budding

Asexual reproduction in animals by growing a tiny offspring from its body

Crossing Over (Recombination)

Homologous chromosomes exchange pieces, giving rise to increased genetic variation (Occurs in Meiosis, Prophase I)

Independent/Random Assortment

Chromosomes line up randomly to increase genetic variation (Occurs Meiosis, Metaphase I)

Diploid

Cell with two sets of DNA (2n), produced by fertilization and mitosis

Haploid

Cell with one set of DNA (n), produced my meiosis

Allele

Different forms of a gene that occupy the same loci (position) on chromosomes

Dominant

A trait expressed preferentially over another trait

Recessive

A trait that is masked by a dominant trait

Genotype

The genetic constitution of an organism with respect to a trait

Phenotype

The physical trait of an organism for a particular trait, determined by the genotype

Homozygous (purebred)

A genotype that consists of two dominant/recessive alleles

Heterozygous (hybrid)

A genotype that consists of one dominant and one recessive allele

Function of Mitosis

Reproduction: For certain organisms, Growth: Make new cells for growth, Repair: Make new cells to repair damaged tissues or replace worn cells

Stages of Mitosis

1) Interphase (growth stage): a. G1: Cell grows and performs its function, b. S: Growth and replication of DNA, c. G2: Growth and final preparations for cell division, 2) Prophase: Centrioles move to opposite sides of the cell and spindle fibres appear, Chromatin condenses into visible chromosomes early, Nuclear membrane and nucleolus disappear, 3) Metaphase: Spindle fibres (proteins called microtubules) attach to the centromeres and move chromosomes toward the middle of the cell (equator), 4) Anaphase: Spindle fibres shorten and centromeres split, Sister chromatids move to opposite poles of the cell, towards the centrioles, 5) Telophase: Spindle fibres disappear, Nuclear membrane and nucleolus reappear, Chromosomes uncoil and become chromatin again, Cytokinesis occurs, 6) Cytokinesis: Cytoplasm and organelles divide

Result of Mitosis

Two identical daughter cells, genetic continuity, Cells are diploid

Purpose of Meiosis

Sexual reproduction, genetic variation

Stages of Meiosis

1. Interphase: Same as mitosis, 2. Prophase I: Synapsis - Homologous chromosomes pair up, Crossing over (recombination) - Homologous chromosomes exchange pieces, giving rise to genetic variation, i. Chiasma - Site of crossing over, 3. Metaphase I: Homologous chromosomes line up in pairs along the equator, Independent/Random Assortment - Chromosomes line up randomly to increase genetic variation, 4. Anaphase I: Homologous chromosomes are pulled apart from each other, Sister chromatids remain attached at the centromere

Telophase I

Complete cell division to produce two haploid daughter cells

Prophase II - Telophase II

Same process in Mitosis

Result of Meiosis

Four genetically different daughter cells that are haploid

Benefits of Sexual Reproduction

Variation increases the likelihood of surviving a change in the environment or a disease

Disadvantages of Sexual Reproduction

Finding a mate takes time and energy; One individual alone cannot increase the population

Haploid cells

Produced by meiosis; Chromosomes in humans: 23 (found in gametes)

Diploid cells

Produced by fertilization and mitosis; Chromosomes in humans: 46 (every cell except for gametes)

Gregor Johann Mendel

Father of genetics; Discovered the basic principles of heredity through pea plant experiments.

Mendel's Laws of Inheritance

1. The Law of Segregation: Only one of two gene copies present in a parent is randomly distributed to each gamete. 2. The Law of Independent Assortment: The alleles of different genes get sorted into gametes independently of one another.

Incomplete Dominance

Neither allele is dominant; Neither trait gets fully expressed; Heterozygous will express a phenotype in between the homozygous ones.

Co-Dominance

Both alleles are dominant; Heterozygous will express both traits.

Multiple Alleles

There are traits that have more than two alleles; Multiple alleles often exhibit incomplete dominance or co-dominance.

Polygenes

Some traits tend to show many intermediate forms in the population; They are controlled by more than one gene (in different chromosomes); Genes are often influenced by the environment.

Sex-linked Traits

Traits found on the sex-chromosomes; More commonly expressed in males.

Evolution

The gradual change in inherited traits present in a population over time

Adaptation

A feature that is common in a population since it provided some improved functions which leads to improved survival or reproductive success

Structural Adaptation

A body part or colour

Behavioural Adaptation

An action

Physiological Adaptation

A feature of the way the body works

Fitness

An organism's ability to survive and reproduce - and ultimately leave its genes in the next generation

Natural Selection

The process of traits that increase an organism's fitness being passed down to a greater number of offsprings and can change the characteristics of a population over time

Homologous Traits

Structures that share a common origin but serve different functions in modern species

Vestigial Traits

Rudimentary and non-functional structures that are homologous to structures in closely related species

Example of Vestigial Traits

Pelvic bone found in whales

Stabilizing Selection

Favours individuals with the most common/average traits in the population

Directional Selection

Favours individuals with an extreme form of a trait in the population

Disruptive Selection

Favours individuals with two or more extreme variations of a trait

Sexual Selection

Favours the selection of any trait that influences the mating success of an individual

Intersexual Selection

Females chose mates based on physical or behavioural traits

Intrasexual Selection

Males defend their territory from other males to attract or forcibly detain females

Sexual Dimorphism

Difference of male and female physical appearance and behaviours

Runaway Selection

A gene in females for choosing a favourable trait is favoured which can lead to an overexaggerated trait in males

Kin Selection

A behaviour or trait of one individual that enhances the success of closely related individuals, thus increasing the first individual's fitness indirectly

Examples of Kin Selection

Bee colonies, Ant colonies, etc.

Gene Flow

Individuals move into/out of a population, bringing their alleles.

Genetic Drift

The change in the composition of a gene pool because of a chance or random event (more pronounced in small populations) - reduces genetic variation and non-random sample of genes from original populations.

The Founder Effect

A new colony is started by a few members of the original population.

Population Bottleneck

A population size is significantly reduced by a chance or catastrophic event for at least one generation.

Species

A group of organisms that are capable of interbreeding and producing viable, fertile offspring.

Pre-zygotic Isolating Mechanisms

Prevents different species from mating and fertilization.

Geographic Isolation

Species are separated by a geographical distance or physical barrier.

Ecological Isolation

Species occupy different habitats.

Temporal Isolation

Species breed during different times/seasons/years cannot mix gametes.

Behavioural Isolation

Unique behavioural patterns and rituals.

Mechanical Isolation

Structural body differences or reproductive organ differences.

Gametic Isolation

Sperms from one species may not be able to fertilize the eggs of another species.

Post-zygotic Isolating Mechanisms

When mating and fertilization occur, prevents offsprings to be viable and fertile.

Reduced Hybrid Viability

Zygotes or embryos die before birth or do not live long after birth.

Reduced Hybrid Fertility

Offspring is viable and vigorous, but they may be sterile (not fertile).

Derived Trait

A shared, derived characteristic of organisms inherited from a common ancestor.

Fossil records

A progression of evolution (change over time).

Fossils

Preserved remains or imprints of an ancient living thing.

Homologous structures

Structures that share a common origin but serve different functions in modern species.

Analogous structures

Structures that are superficially similar for functions but evolved separately from different ancestors, showing how different species can have similar adaptations.

Vestigial structures

Rudimentary and non-functional structures that are homologous in closely related species.

Comparative embryology

Similar structures appearing during development.

Comparing protein sequences

Differences in protein sequences can be mapped out and compared.

DNA hybridization

The DNA code can be directly compared to find degrees of differences and similarities by separating two different strands of DNA and connecting them to see if they are easy (not closely related) or difficult (closely related) to separate.

Bio-geographical evidence

Species with common ancestry being across different continents because of the breakup of Pangea.

Artificial selection

The breeding of domesticated animals prove that selection can cause substantial changes in a population over time.

Charles Darwin

Proposed the theory of evolution through natural selection.

Darwin's Finches

Mainland only had one species of finches, but he found 14 on the Galapagos Island.

Darwin's Theory of Evolution

All life is related and has descended from a common ancestor - descent with modifications.

Natural Selection

Variation - Different versions of a specific trait.

Differential Reproduction

Not all individuals get to reproduce to their full potential since the environment cannot support unlimited population growth; those with the best adaptation will reproduce more.

Example of Differential Reproduction

Giraffes with the longest neck will reproduce more since having a long neck is best for survival.

Heredity

The trait gets passed down to offspring.

Example of Heredity

The alleles for long neck get passed down to offspring.

Trait rarity

The more advantageous trait is inherited by a greater number of offspring and becomes more common in the population, causing a change in the frequency of alleles.

Example of Trait rarity

More giraffes have long necks in the population.

Trait exaggeration

Over time, most individuals will express the most adaptive trait, and it can become exaggerated in the population.

Example of Trait exaggeration

Over time, the majority of the giraffe population have long necks, and for some, the length of necks are even longer.

Mutation

Random changes in DNA add new alleles to a population; it is the ultimate source of genetic variation but beneficial mutations rarely occur.

Gene Flow

People carry alleles into or out of a population.

Non-random Mating

Selective mate choice (sexual selection) or assertive mating can result in some alleles becoming more common.