Principle of Variation in Evolution

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Questions and Answers

What are the two types of nitrogenous bases mentioned?

Purines and pyrimidines (correct)

Thymine and cytosine

Adenine and guanine

Adenine and thymine

Identical twins have different genomes.

False

What role does alternative splicing play in biological processes?

Creates different proteins

Proteins create the skeletal system, muscles, the endocrine system, the immune system, the digestive system, and the __________ system.

nervous Signup and view all the answers

Match the nitrogenous bases with their correct pairing:

Adenine = Thymine Cytosine = Guanine Signup and view all the answers

What is the function of spliceosomes in the cell?

Create mRNA by removing introns Signup and view all the answers

Ribosomes are the sites of protein translation in a cell.

True Signup and view all the answers

What are codons?

Codons are triplets of nucleotides that specify amino acids in the genetic code. Signup and view all the answers

In histone acetylation, acetyl groups are attached to __________ in histone tails.

lysins Signup and view all the answers

Which type of mutation involves the addition or loss of an extra copy of a repeat motif?

Simple sequence repeat expansions Signup and view all the answers

Nonsense mutations lead to functional proteins.

False Signup and view all the answers

Locus is a particular site in the ____.

genome Signup and view all the answers

Match the following genetic characteristics with their descriptions:

Polymorphism = a locus for which there is more than one allele in the population SNPs = variation in a single nucleotide at a specific locus Polygenic traits = variation in phenotype related to alleles across multiple genes Signup and view all the answers

What is the effect of chronic stress on histone methylation?

suppression of gene activity Signup and view all the answers

What are the two levels of variation mentioned in Darwin's theory?

Phenotype and Genes Signup and view all the answers

What are ribosomes and their function?

Ribosomes are chemical factories where substances needed in cell functioning are synthesized. Signup and view all the answers

Genes always have identical sequences in all members of the same species.

False Signup and view all the answers

Amino acids are the molecular building blocks of ________.

proteins Signup and view all the answers

Match the following terms with their definitions:

Mitosis = Normal cell division process that produces genetically identical daughter cells Meiosis = Special cell division process that produces haploid gametes Genomics = Techniques to describe the entire genetic material (genome) of organisms DNA = Complex molecule containing genetic information and organized into chromosomes Signup and view all the answers

What are environments doing to genes that alter their impact?

Variations in maternal care lead to individual differences in gene expression Signup and view all the answers

DNA methylation can have implications for the transmission of traits from one generation to the next.

True Signup and view all the answers

What is the role of histones in relation to DNA?

Histones are proteins that DNA winds around, and modifications to histones can affect gene expression. Signup and view all the answers

DNA methylation involves tagging specific points in the DNA molecule with a __________ group that silences the genes.

methyl Signup and view all the answers

Study Notes

Variation and Evolution

Variation is crucial for understanding Darwin's theory, occurring both between and within species.
There are two levels of variation: phenotype (observable characteristics) and genotype (set of genetic variants).

Cellular Structure

Cells consist of different types, including eukaryotes (animals and plants with nuclei and mitochondria) and prokaryotes (bacteria).
Cells are made of various chemical compounds, including proteins that give cells shape and structure, connect tissues, function as hormones and antibodies, and control chemical reactions.

Proteins and Amino Acids

Proteins are made up of amino acids, with 20 types in total.
The sequence of amino acids determines the properties of the protein.
Phenotype is determined by the properties of proteins in cells, which are determined by the sequence of amino acids.

Genetics

Genes encode the amino acid recipes for particular proteins.
Genes come in alternate forms called alleles.
Individuals have two copies of each gene, one from each parent.
Genes have two functions: influencing physical characteristics and replicating themselves to produce new cells or individuals.

Central Dogma

Changes in DNA sequence can lead to changes in proteins, but not vice versa.
Alterations in the genotype lead to alterations in the phenotype, but not vice versa.
The flow of information is one-way, and characteristics acquired in a lifetime are not genetically transmittable.

Somatic and Germ Lines

Somatic cells make up the body, while germ lines produce new individuals (gametes).
Mitosis is the normal cell division process that produces daughter cells genetically identical to the parent cell.
Meiosis is the special cell division process that produces haploid gametes from diploid cells.

Molecular Genetics

Genes are made of DNA, which contains the instructions for making proteins.
DNA is a long, double-stranded molecule with a sugar-phosphate backbone and nitrogenous bases.
The sequence of nitrogenous bases determines the genetic code.

Genetic Code

The genetic code maps codons (triplets of bases) to amino acids.
The code is almost identical across all living beings.
Codons are read in sequence to assemble proteins.

Genome

The genome is the complete set of genetic material in an organism.
Most DNA is not genes, but rather non-coding regions.
Non-coding DNA includes transposable elements, pseudogenes, and regulatory sequences.

Evolution of Genome Size

Genome size tends to rise with phenotypic complexity.
Polyploidy and regulatory sequences may contribute to increased genome size.

Mitochondrial DNA

Mitochondria have their own small genomes.
Mitochondrial DNA is haploid and asexually transmitted from the mother.

Evidence for DNA as the Genetic Material

Prior to the 1950s, it was known that DNA is a polymer of nucleotides.
Base composition of DNA varies between species.
Chargaff's rules describe the base composition of DNA.

Human Genome

The human genome consists of 3 billion base pairs and about 25,000 protein-coding genes.
One-third of these genes are expressed only in the brain.

Chromosomes

Human chromosomes are similar to those of great apes.
Chromosomes have centromeres, which are regions without genes where the chromosome is attached to its new copy during cell reproduction.

Protein Function and Structure

Proteins create the skeletal system, muscles, endocrine system, immune system, and nervous system.
Protein shape can be altered through posttranslational changes, affecting function.

Microbiome and Epigenome

The microbiome refers to the genomes of microbes that live on and in the body.
The epigenome refers to chemical marks on DNA that may play a part in how the human genome functions and contributes to health, behavior, and disease.### Transcription and Translation
Transcription: the process of creating an RNA molecule from a DNA template
Translation: the process of creating a protein from an RNA molecule
Importance of transcription and translation:
- Carry genetic information from DNA to proteins
- Essential for gene expression and regulation

Transposable Elements

Ability to copy themselves into different parts of the DNA
Prone to mutations
Examples: Simple sequence repeats, microsatellites, and minisatellites

mRNA Synthesis and Translation

Spliceosomes remove introns to create mRNA (messenger RNA)
mRNA carries genetic message from DNA to protein-synthesizing machinery
Translation: the process of creating a protein from an RNA molecule
Change in language: monomers are amino acids rather than nucleotides

The Genetic Code

Codons: triplets of nucleotides that code for amino acids
64 possible codons (4^3)
The genetic instructions for a polypeptide chain are written in the DNA as a series of non-overlapping, three-nucleotide words
For each gene, only one of the two DNA strands is transcribed (template strand)

Regulation of Gene Expression

Gene expression is regulated at many stages, including transcription, translation, and post-translation
Regulation is essential for cell specialization and adaptation to environmental changes
Errors in gene expression can lead to diseases, including cancer

Epigenetic Inheritance

The inheritance of traits transmitted by mechanisms not directly involving the nucleotide sequence
Chromatin modifications, such as histone modifications and DNA methylation, can be passed on to future generations
Important for gene regulation and cellular differentiation

Post-Transcriptional Regulation

Mechanisms that operate after transcription, including RNA processing, mRNA degradation, and translation initiation
Allow for fine-tuning of gene expression in response to environmental changes

Genetic Variation

Types of mutations:
- Point mutations (single-base substitutions)
- Frameshift mutations (insertions or deletions)
- Simple sequence repeat expansions and contractions
- Transposable element insertions and segmental duplications
- Whole-genome duplication
Mutations can be silent, missense, or nonsense
Mutagens: physical and chemical agents that interact with DNA and cause mutations

Effects of Genetic Variation

Most genetic variation has no phenotypic effect
Reservoir of genetic variation from which phenotypic variation may result
Where mutations do have a phenotypic effect, they are usually deleterious
Occasional mutations can arise that improve biological performance### Genetic Mutations and Natural Selection
Rare advantageous mutations are spread by natural selection, which leads to a change in the genotype to phenotype.
A new non-synonymous mutation in a gene's coding sequence can result in a distinct allele, producing a different amino acid chain and protein.

Single-Gene Characteristics and Diseases

Single-gene characteristics are determined by which allele an individual has at a single genetic locus.
Examples of single-gene diseases include cystic fibrosis (chromosome 7) and Rhesus factor.

Gene Hunting

Linkage studies are used to localize genes underlying single-gene traits using a small number of genetic markers.
Association studies are powerful but require many genetic markers per chromosome, and can be used to identify genes involved in polygenic characteristics.

Polygenic Traits

Polygenic traits are variations in phenotype related to which allele is present across multiple genes.
Examples of polygenic traits include height, and they are hard to detect using linkage and association studies.

Genes for Physical Characteristics

Huntington's disease is a single-gene disease caused by a disease-causing allele of a gene on chromosome 4, leading to a protein that helps keep cells alive.
An association study on dogs found a strong association between a gene on chromosome 15 and size.

Genes for Behavior

A study on prairie voles found that a hormone arginine vasopressin causes a pair bond to form, and a gene that produces a receptor for this hormone is involved in this behavior.
A study on humans found that a gene involved in regulating serotonin (mood states) is associated with conduct disorder.

Epigenetics

Epigenetics is the study of mechanisms that change gene expression by modifying DNA without modifying its sequence.
Epigenetic mechanisms, such as DNA methylation and histone modification, can explain how early life experiences can influence behavior and physical health later in life.

Epigenetic Mechanisms

DNA methylation is the tagging of specific points in the DNA molecule with a methyl group, silencing genes.
Histone modification is the chemical modification of histone proteins that DNA winds around, changing how tightly or loosely the DNA is wound.
DNA methylation and histone modification interact with and depend on each other.

Importance of Nurturing

The way a rat mother nurtures her pups influences how they respond to stress in later life.
Less nurturing leads to increased methylation of the gene for BDNF (neural growth factor) and reduced glucocorticoid receptors.

Epigenetics and Development

Epigenetics can explain how early life experiences can influence behavior and physical health later in life.
Epigenetic mechanisms, such as DNA methylation and histone modification, are involved in development and can be influenced by nutrition.

Antisocial Behavior

Antisocial behavior is influenced by genetic and environmental factors.
Specific genes, such as MAOA, are associated with antisocial behavior.
Brain impairments, such as reduced volume of the amygdala, anterior cingulate, and orbitofrontal cortex, are associated with antisocial behavior.
Environmental influences, such as child abuse, can interact with genetic factors to predispose to antisocial behavior.

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Description

Explore the concept of variation in Darwin's theory, including variation between and within species, and its significance in understanding evolution at the phenotypic and genotypic levels.