Bio44 Unit 1 Big Ideas

What were some early beliefs about the origin and nature of life and species, and how did scientific observations from the 1600s to early 1800s begin to challenge these ideas?

Early beliefs included spontaneous generation and fixed species. Observations such as fossil evidence and microscopic life challenged these ideas, leading to a greater understanding of evolution and species variation.

What are the shared characteristics of living organisms, and why are viruses generally not considered living?

Living organisms share characteristics such as maintaining boundaries, nutrients for metabolism, growth, reproduction, and movement in response to stimuli. Viruses, however, lack cellular structure and cannot carry out metabolic processes independently, which is why they are generally not classified as living organisms.

How did early scientists like Linnaeus, Lamarck, Hutton, and Lyell contribute to changing ideas about species and the age of the Earth?

They developed classification systems, proposed theories of evolution, and introduced geological concepts, shifting the perception of species as fixed and the Earth as young.

Question: What central idea did Darwin and Wallace propose regarding the origin of existing species, and what mechanism did they identify for this process?

Darwin and Wallace proposed that existing species evolved from common ancestors through the process of natural selection, where advantageous traits become more common in a population over generations. They theorized this occurred through the accumulation of beneficial and heritable traits over time, a process known as evolution or descent with inherited modification. They identified natural selection as the primary mechanism for this evolution

What are some key lines of evidence that support the theory of evolution by descent with inherited modification?

• Homologous features

• Biogeography

• Fossils

• Selective breeding / artificial selection

Explain the process of natural selection as the main mechanism of evolution, including the concepts of heritable variation, competition, fitness, and adaptation.

Natural selection is the process by which individuals with advantageous heritable traits survive and reproduce more effectively in their environment. This leads to a gradual increase in the prevalence of these traits within a population, resulting in adaptation to changing environments over time.

How has modern genetics, specifically the understanding of DNA, enhanced our understanding of evolution compared to Darwin's time?

Modern genetics has revealed the molecular mechanisms of inheritance, showing how mutations in DNA contribute to genetic variation and evolution. This understanding provides a clearer picture of how natural selection acts on heritable traits and enhances our insights into evolutionary processes.

Why is variation important for natural selection, and how did Mendel's work change the understanding of inheritance compared to the "blended" idea?

Variation is crucial for natural selection because it provides the raw material for evolution, allowing some individuals to possess traits that enhance their fitness in a given environment. Mendel's work introduced the concept of discrete units of inheritance (genes), demonstrating that traits are passed down in a way that preserves variation, countering the earlier belief in blending inheritance.

What was Gregor Mendel's key finding about inheritance?

Gregor Mendel's key finding was that traits are inherited as discrete units, now known as genes, which operate independently and preserve variation across generations, rather than blending together.

Explain the concepts of diploidy, genes, alleles, and dominant/recessive relationships as described by Mendel.

Diploidy refers to the presence of two sets of chromosomes in an organism, one inherited from each parent. Genes are segments of DNA that determine traits, while alleles are different versions of a gene. Dominant alleles express their trait in both homozygous and heterozygous conditions, whereas recessive alleles only manifest when present in a homozygous state.

Define and differentiate between genotype and phenotype, and explain the terms homozygous and heterozygous.

Genotype refers to the genetic makeup of an organism, specifically the alleles present for a particular trait, while phenotype is the observable expression of that trait. Homozygous individuals have two identical alleles for a trait, whereas heterozygous individuals have two different alleles.

Describe different patterns of inheritance beyond simple Mendelian, such as incomplete dominance, codominance, epistasis, and polygenic inheritance. What is the difference between discrete and continuous characters?

Different patterns of inheritance include incomplete dominance, where heterozygous phenotypes are intermediate; codominance, where both alleles are expressed equally; epistasis, where one gene masks the effect of another; and polygenic inheritance, involving multiple genes influencing a single trait. Discrete characters are distinct categories (e.g., flower color), while continuous characters display a range of variations (e.g., height).

How did the understanding of Mendelian inheritance support and strengthen Darwin's theory of natural selection?

Mendelian inheritance provided a genetic basis for the variation observed in natural populations, demonstrating how traits are passed down through generations. This understanding helped explain how certain traits can become more or less common in a population due to natural selection, supporting Darwin's theory of evolution.

What are the Hardy-Weinberg equations, and what does it mean for a population to be in Hardy-Weinberg equilibrium?

The Hardy-Weinberg equations describe the genetic variation of a population at equilibrium, specifically the relationship between allele frequencies and genotype frequencies. A population is in Hardy-Weinberg equilibrium when allele frequencies remain constant over generations in the absence of evolutionary influences.

What two main components are required for evolutionary change (modification) to occur in a population?

Modification (change) requires two main components30:

1. The introduction of new genetic variation30.

2. Mechanisms that alter the prevalence (frequencies) of existing genetic variants

What are the primary sources of new genetic variation in a population?

The primary sources of new genetic variation in a population include33...:

• Mutations: Random changes in DNA, which can occur due to errors in replication/repair or exposure to chemicals/radiation22 Mutations are the sources of new alleles22.

• Genetic shuffling (new combinations of alleles): This occurs during meiosis and sexual reproduction33 Processes like recombination (crossing over) and random alignment of chromosome pairs create new combinations of existing alleles33

Horizontal gene transfer: A process where DNA is incorporated from another organism without being its offspring33 This is common in bacteria

What are some specific types of genetic changes that are thought to have potentially large effects on phenotypes and evolution?

• Gene duplication: The duplication of a gene, resulting in two copies on the same chromosome34 The extra copy can acquire new functions over evolutionary time36. Gene duplication can have large effects on phenotypes and is thought to be a major driver of evolution34

• Changes in regulatory genes: These genes regulate the expression of other genes, controlling developmental processes34 Small changes in regulatory genes can affect when and where structural genes are expressed and are thought to have particularly large phenotypic effects and be major drivers of evolution

What are the main mechanisms that cause changes in the frequencies of existing genetic variants (alleles) within a population?

The main mechanisms that alter the prevalence (frequencies) of existing genetic variants (alleles) within a population are14...:

• Natural selection8.

• Genetic drift31.

• Gene flow32.

• Non-random mating

 Explain natural selection as a mechanism for changing allele frequencies and leading to adaptations. Describe the different types of natural selection

• Directional selection: Occurs when individuals at one extreme of a phenotypic range have greater reproductive success13 This tends to decrease variation13.

• Stabilizing selection: Occurs when individuals with intermediate phenotypes are favored and have greater reproductive success14 It selects against individuals at both extremes33 and tends to decrease genetic variation33.

• Diversifying (AKA: disruptive) selection: Occurs when two or more different genotypes or phenotypes are favored, typically in heterogeneous environments14 This may potentially lead to speciation33.

• Balancing selection: Occurs when natural selection keeps alleles in balance, resulting in a balanced polymorphism14 This type does not change overall genetic variation33. It includes heterozygote advantage (where heterozygotes are favored over homozygotes, sometimes explaining the persistence of alleles deleterious in homozygotes, like sickle cell trait and malaria resistance)14... and negative frequency-dependent selection (where the fitness of a genotype decreases as its frequency increases, meaning common individuals have lower fitness, which can lead to cycles in genotype frequencies)14 As previously noted, natural selection itself is not random (though mutation is) and does not have a goal14. Not all traits are adaptations

What are homologous features, and how do they provide evidence for evolution?

Homologous features are anatomical structures that share a common ancestry, despite potentially differing in function. These similarities provide evidence for evolution by demonstrating how different species have diverged from a common ancestor while adapting to their environments.

What is biogeography? How does the distribution of organisms provide evidence for evolution?

Biogeography is the study of the distribution of species and ecosystems in geographic space and through geological time. The distribution of organisms provides evidence for evolution by illustrating how species adapt to their environments and how different species have evolved in response to geographic barriers and historical events.

What is a fossil? How does the fossil record provide evidence for evolution?

A fossil is the preserved remains or traces of organisms from the past, typically found in sedimentary rock. The fossil record provides evidence for evolution by showing the chronological order of life on Earth and revealing how species have changed over time, including transitional forms that illustrate the evolutionary process.

What is selective breeding / artificial selection? How does this practice provide evidence for evolution?

Selective breeding, or artificial selection, is the process by which humans breed plants and animals for specific traits. This practice provides evidence for evolution by demonstrating how selective pressures can lead to significant changes in the characteristics of species over relatively short periods.