Fundamental Genetics: Mendel's Pea Plants and Gene Expression

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Questions and Answers

What is the key implication of Mendel's discovery that the offspring from the second cross have a 25% chance of having white seeds?

The inheritance of traits is determined by the environment

The inheritance of traits is strictly determined by the genetic factors (correct)

The traits of the offspring are influenced by the traits of both parents

The traits of the offspring are influenced by the traits of only one parent

What is the term for the process of cell division that produces gametes with half the usual number of chromosomes?

Recombination

Mitosis

Replication

Meiosis (correct)

What is the role of activators in gene expression?

To increase gene expression (correct)

To transcribe DNA

To regulate gene expression

To decrease gene expression

What is the term for the study of heritable changes in gene function that occur without a change in the DNA sequence?

Epigenetics Signup and view all the answers

What is the term for the process of creating a new DNA molecule from an existing DNA molecule?

Replication Signup and view all the answers

What is the term for the sequence of three nucleotide bases that instructs the ribosome to add a specific amino acid to a protein?

Codon Signup and view all the answers

What is the main contribution of the Human Genome Project?

The compilation of a map of the sequence of all 3 billion nucleotide bases that compose human chromosomes Signup and view all the answers

What is the term for the process by which chromosomes exchange genetic material?

Recombination Signup and view all the answers

What is the term for the type of RNA that carries the genetic code out of the nucleus of the cell?

Messenger RNA Signup and view all the answers

What is the term for the process of converting the genetic code from DNA into a sequence of amino acids?

Translation Signup and view all the answers

What percentage of human DNA contains protein-encoding genes?

1% Signup and view all the answers

What is the term for the study of the development of an individual through their lifespan?

Ontogeny Signup and view all the answers

What is the process by which a methyl group attaches to a DNA molecule, usually at Cytosine sites, in mammals?

DNA methylation Signup and view all the answers

What is the term for the catalogue of all the modifications to DNA within a particular cell type, other than changes to the nucleotide base sequence?

Epigenome Signup and view all the answers

What is the term for the modifications of RNA that occur after transcription, but do not involve changes to the RNA base sequence?

Epitranscriptome Signup and view all the answers

What is the process by which histones change their shape, affecting the shape of an adjacent DNA?

Histone remodeling Signup and view all the answers

What is the percentage of RNA molecules that are of the large protein-encoding variety?

1.2% Signup and view all the answers

What is the term for the transmission of experiences via epigenetic mechanisms across generations?

Transgenerational epigenetics Signup and view all the answers

What is the term for the study of the mechanisms that influence the expression of genes without changing the genes themselves?

Epigenetics Signup and view all the answers

What is the term for the development of a species through the ages?

Phylogeny Signup and view all the answers

What is the primary concern regarding psychosurgery?

The lack of detailed assessment of its effects on large sample sizes Signup and view all the answers

What is the term used to describe the general intellectual climate of our culture?

Zeitgeist Signup and view all the answers

What is the primary flaw in thinking about the biology of behavior in terms of traditional physiological-psychological and nature-nurture dichotomies?

It oversimplifies complex issues Signup and view all the answers

What is the term used to describe a simple way of thinking, such as good-bad or right-wrong?

Dichotomy Signup and view all the answers

Why were patients often judged as improved after undergoing psychosurgery?

They were more manageable Signup and view all the answers

What was the primary issue with Moniz and others' evaluation of psychosurgery?

They failed to carefully evaluate the consequences of the surgery Signup and view all the answers

What is the primary problem with impressions that the operation was therapeutically effective?

They were based on the physicians' opinions rather than the patients' outcomes Signup and view all the answers

What is the primary goal of describing the origins of the physiological-psychological and nature-nurture ways of thinking?

To illustrate the flaws in traditional dichotomies Signup and view all the answers

Study Notes

Mendelian Genetics

Gregor Mendel, an Augustinian monk, studied dichotomous traits in true-breeding lines of pea plants.
Dichotomous traits are characteristics that occur in one form or another, never in combination.
True-breeding lines are interbred members that always produce offspring with the same trait generation after generation.
Mendel's key findings: when true-bred brown and white peas are crossed, all offspring from the first cross have brown seeds, whereas 25% of offspring from the second cross have white seeds.
Dominant trait: appears in 100% of first-generation offspring.
Recessive trait: appears in 25% of second-generation offspring.
Phenotype: an organism's observable traits.
Genotype: genetic traits passed on to offspring.

Mendel's Theory

2 kinds of inherited factors for each dichotomous trait.
Each inherited factor is called a gene.
Each organism possesses 2 genes for each of its dichotomous traits.
2 genes that control the same trait are called alleles.
Homozygous: organisms that possess 2 identical alleles.
Heterozygous: organisms that possess different alleles.
One of the 2 kinds of genes for each dichotomous trait dominates the other in heterozygous organisms.

Chromosomes

Chromosomes: threadlike structures in the nucleus of each cell.
Chromosomes occur in matched pairs in all multicellular organisms.
Humans have 23 pairs of chromosomes, with an allele on each chromosome.
Meiosis: the process of cell division that produces gametes (egg and sperm cells).
Genetic recombination: crossover of chromosomes to exchange genetic material.
Mitosis: all other cell division in the body.

Structure and Replication

Each chromosome is a double-stranded molecule of deoxyribonucleic acid (DNA).
Each strand is a sequence of nucleotide bases attached to a chain of phosphate and deoxyribose.
4 nucleic bases: adenine, thymine, guanine, cytosine.
Nucleotides on strand 1 always pair with specific nucleotides on strand 2.
Replication: a critical process of the DNA molecule.
Sometimes chromosome replication errors can have clinical consequences, such as mutations.

Sex Chromosomes and Sex-Linked Traits

Autosomal chromosomes: typical chromosomes that come in matched pairs.
Sex chromosomes: the pair of chromosomes that determines an individual's sex.
Females have XX chromosomes, males have XY chromosomes.
Sex-linked traits: traits influenced by genes on the sex chromosomes.
All controlled by genes on the X chromosome.
Dominant sex-linked traits on the X chromosome will be seen more commonly in females.
Recessive sex-linked traits on the Y chromosome more commonly in males.

Genetic Code and Gene Expression

Structural genes: contain information for the synthesis of proteins.
Proteins: long chains of amino acids.
Control the physiological activities of cells and are important components of cellular structure.
Stretches of DNA that lack structural genes include portions called promoters/enhancers.
Promoters/enhancers: determine whether particular structural genes are converted into proteins through a 2-phase process called gene expression.
Control of gene expression by promoters is an important process because it heavily influences how a cell will develop and function once it is mature.
Gene expression involves 2 phases: transcription (DNA base-sequence code to RNA base-sequence code) and translation (RNA base-sequence code to protein).

Transcription

Strand of DNA unravels and serves as a template for the transcription of a short strand of RNA.
Ribonucleic acid (RNA): contains the nucleotide base Uracil instead of Thymine and has a phosphate and ribose backbone instead of a deoxyribose backbone.
Messenger RNA: the strand of transcribed RNA.
Carries the genetic code out of the nucleus of the cell.

Translation

Messenger RNA attaches to any one of the many ribosomes present in the cell's cytoplasm.
Ribosome moves along the strand of messenger RNA, translating the genetic code as it proceeds.
Codon: 3 consecutive nucleotide bases along the messenger RNA strand.
Instructs the ribosome to add 1 of the 20 different kinds of amino acids to the protein it's constructing.
Each kind of amino acid is carried to the ribosome by molecules of transfer RNA.

Human Genome Project

Purpose: compile a map of the sequence of all 3 billion nucleotide bases that compose human chromosomes.
3 major contributions:
- Establishing genomes for many species, including extinct species, leading to insights into evolution.
- Humans have about 21,000 structural genes, similar to mice, but fewer than corn.
- New technology allows for the study of genomes.### Human Proteome and Gene Expression
Human proteome: a nearly complete map of the entire set of proteins encoded by our genes
Only about 1% of human DNA constitutes protein-encoding genes
Many genes have been linked to each disease, but interactions among genes are difficult to sort out
Even when many genes are linked to a disease, they often account for only a small portion of its heritability (e.g., 18 gene variants linked to adult-onset diabetes, but they account for only 6% of the heritability)

Modern Genetics: Growth of Epigenetics

Epigenetics (1942): focuses on mechanisms that influence the expression of genes without changing the genes themselves
4 factors that led to the rise of epigenetics:
- Human Genome Project generated new research techniques
- Discovery that protein coding genes constitute only about 1% of human DNA (remaining 99% is "junk DNA")
- Most RNA molecules are small (only 1.2% are of the large protein-encoding variety)
- Mechanisms of gene-experience interactions were unknown
5 important discoveries in epigenetics:
- Nongene DNA is not "junk DNA" as it controls structural gene expression
- Epigenetic mechanisms can modulate gene expression (e.g., DNA methylation, histone remodeling)
- Worldwide effort to catalogue the epigenome of each cell type
- Epigenetic effects can involve post-transcription alterations to RNA
- Epigenetic mechanisms can be induced by experiences (e.g., neural activity, hormonal state, environmental changes)

Epigenetics of Behavioral Development

Epigenetic mechanisms can influence gene expression in response to experiences
Transgenerational epigenetics: examines the transmission of experiences via epigenetic mechanisms across generations
Epigenetic mechanisms can control gene expression, influencing behavioral development

Classic Research on Behavioral Development

Selective breeding of maze-bright and maze-dull rats:
- Cooper & Zubek (1958) study: maze-bright and maze-dull rats reared in impoverished or enriched environments
- Results: maze-dull rats made more errors than maze-bright rats only when reared in impoverished environments
Tryon (1934) research: behavioral traits can be selectively bred
- Bred fittest maze-bright rats and dullest maze-dull rats for 21 generations
- Results: almost no overlap in maze learning performance between the two groups of rats

Phenylketonuria (PKU): A Single-Gene Metabolic Disorder

PKU: neurological disorder discovered in 1934, caused by a single gene mutation
Symptoms: intellectual disability, vomiting, seizures, hyperactivity, irritability, and brain damage
PKU develops only in homozygous individuals (aa) due to a recessive gene
PKU homozygotes lack phenylalanine hydroxylase, an enzyme required for the conversion of phenylalanine to tyrosine
Behavioral symptoms result from an interaction between genetic and environmental factors

Genetics of Human Psychological Differences

Importance of distinguishing between the development of individuals and the development of individual differences
Heritability estimates: commonly misinterpreted, they describe the proportion of variation in a trait that can be attributed to genetic factors
Twin studies: used to study the interaction of genes and experience (nature and nurture)
- Two ways to use twin studies:
  - Within-pair comparisons: comparing the similarity of twins reared together or apart
  - Between-pair comparisons: comparing the similarity of different twin pairs

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Description

This quiz covers the basics of genetics, including Mendel's work with pea plants, chromosome structure and function, gene expression, and modern advances in genetic processes, including epigenetics.