1.2: Genetics and Heredity Flashcards
What is DNA?
Genetic ‘instruction manual’
Double-helix structure of base pairs (nucleotides)
Contained in chromosomes in the cell nucleus, also in mitochondria
How many chromosomes and base pairs do humans have?
46 chromosomes
Approx. 3 billion base pairs
Coding DNA
Information on chains of amino acids that dictates protein structure
Coding DNA makes up 1-2% of the genome
Non-coding DNA
Has regulatory functions
What are proteins for? (5)
Muscle Amylase (digestive enzyme) Immunoglobulin (antibodies) Insulin (hormone) Red blood cells
Gene
DNA that codes for certain traits (e.g. TCHH gene codes for trichohyalin in hair)
Allele
Variant of the gene
Genotype
Type of relevant genes for a trait (could involve multiple genes and alleles)
Phenotype
Trait that is expressed
How are chromosomes inherited in sexual reproduction?
23 pairs of chromosomes (46 total)
Inherit one chromosome from each pair from each parent
Composition of chromosomes
22 pairs + 1 sexual pair
Sex chromosomes: XX female, XY male
Inheritance of sex chromosomes
Y chromosome inheritance is always from father to son
Mitochondria inheritance always from mother to her children
Types of traits (5)
Adaptive (increases fitness) Neutral (no effect) Maladaptive (decreases fitness) Discrete (attached/detached earlobes) Continuous (height)
Which process is a problem for maintaining variation with sexual reproduction?
Blended inheritance reduces the variability and competition needed for natural selection
Mendelian inheritance
Transmission of hereditary traits in peas (yellow and green, round and wrinkled)
Inheritance works by dominant and recessive traits
This inheritance can be mapped in a punnett square
Reason inbreeding is detrimental
Hidden variation (recessive genes) is more likely to be expressed
More likely to have the same recessive genes if related
Many recessive genes are detrimental – harder for it to be ‘selected’ out
Increased risk of expressing detrimental phenotypic traits with inbreeding
Two reasons why Darwin dismissed Mendel?
Mendel had no knowledge of genes
Mendel looked at discrete traits, therefore his findings did not explain polygenic continuous traits
Who are the three fathers of the modern synthesis/population genetics? What information did they combine?
Fisher
Haldane
Wright
Combined information on evolution and genetics
Population genetics
Study of gene frequencies in a population; distribution and change
What are the 5 processes that affect gene frequency in a population?
Mutation Natural selection Non-random mating Genetic drift Gene flow
How does mutation affect gene frequency in a population?
Errors in DNA coding during replication
Introduces new alleles into the population
Starting point for changes in gene frequencies in populations
Example of the problem of large effect mutation
Hox genes are conserved genes that determine body plans, a small error in hox genes can cause large errors in body plans
For example, a mutant deficiency in Drosophilla hox genes can cause the small balancing organ to grow into a second wing, which punctuates equilibrium
Why are small effect mutations better than large effect mutations?
Series of small mutations are better than large jumps and are commonly selected for because they are more likely to bring positive outcomes
How does natural selection affect gene frequency in a population?
Change in frequency of alleles based on selection for adaptive phenotypes and selection against maladaptive phenotypes (relative to the population)
Three different types of natural selection
Directional
Stabilising
Disruptive
What is directional selection? Provide example.
Changing the average phenotype of a population in one direction
E.g. spread of lactase persistence in Europe; direction selection for lactase production into adulthood
What is stabilising selection? Provide example.
Selection against extremes
E.g. human birth weight; higher infant mortality for very low and very high weight babies;
Very low weight babies cannot meet the energetic requirements of the brain
Very high weight babies cannot fit through the vaginal opening in childbirth (obstetric dilemma)
What is disruptive selection? Provide example.
Selection against the mean
E.g. If chinook salmon males are medium sized they would be bad at both sneaking and fighting to win females, therefore they are ether small are good at sneaking, or they are large and good at fighting off competitors
How does non-random mating/sexual selection affect gene frequency in a population?
More frequent mating with those who display certain phenotypes, then associated genotype will increase
How does genetic drift affect gene frequency in a population?
Random changes in population gene frequency
Most likely to happen in small populations and spread by chance
What are the two main processes that increase likelihood of genetic drift?
Bottleneck
Founder effect
What is the bottleneck effect? Provide example.
Drastic reduction in population, survivors pass on their genes, remaining genotypes are split unevenly
In 1775 a typhoon killed 90% of the population of Pingelap, a Micronesian island. One of the survivors carried a recessive gene for a rare type of colour-blindness. Because of low rates of interbreeding on the island, just under 10% of the population is completely colour-blind.
What is the founder effect? Provide example.
Migrating somewhere else and starting a new population
E.g. African diversity and the migration from Africa
How does gene flow affect gene frequency in a population? Provide example.
Gene flow between populations can introduce new alleles from one population to the other, which increases variation
E.g. Neanderthals contributed 1-4% of their genes to modern, non-African populations
Out of the 5 process that affect gene frequency in a population, which are random and which are non-random?
Random: mutation, genetic drift, gene flow
Non-random: natural selection, non-random mating
Epigenetics
The environment and behaviour determines which genes are expressed, which in turn determines behaviour
Three types of behaviour that influences gene expression (epigenetics). Give examples.
Stress: poor sleep leads to higher stress levels, leading to higher insulin levels, which increases body weight
Diet: in mammals, disrupted or reduced growth hormone and insulin-like growth factors alters longevity.
Caloric Restrictions also suppresses growth hormone and insulin-like growth factors, which is also associated with extended longevity in animal models.
Love: methylation of genes associated with oxytocin and vasopressin hormones create love and trust that cause voles to mate for life instantly
Why would epigenetic mechanisms evolve? Provide example.
Mother prepares the baby using cues of the environment
Maternal gastrointestinal bypass causes 5696 genes to be expressed differently in babies concieved after the bypass (genes associated with heart health and metabolism, insulin levels and weight)
Two examples of the paternal-maternal conflict in epigenetics
Genes of paternal origin, expressed in infants, have been selected to favour more intense suckling than genes of maternal origin
Genes of maternal origin may favour slower childhood growth but earlier sexual maturation
