Lecture 8: Biology and Behaviour Flashcards
DNA
deoxyribonucleic acid. It is the molecule that carries the biochemical instructions involved in the formation and functioning of an organism
Gene
sections of chromosomes and portions of DNA. Basic unit of heredity in all living things.
Chromosome
thread-like molecules made up of DNA, containing many genes
Genome
the complete set of genes in any organism (human genome project –mapping the entire human genome)
What is DNA made out of
DNA is made of two linked strands that wind around each other in a double helix formation. It has two carbohydrate or sugar backbones – base pairs of protein in the middle
Human genome project
Human genome project – international project with goal of mapping the entire sequence of human genes
Genotype
the genetic material an individual inherits
Phenotype
the observable expression of the genotype, including body characteristics and behaviour
Environment
includes every aspect of the individual, and his or her surroundings, other than genes
Parent genotype to child genotype
Genetic material is passed on as chromosomes- long, threadlike molecules made up of DNA:
Carry all of the biochemical instructions involved in the formation and functioning of an organism
Genes are sections of chromosomes that are the basic units of heredity for all living things
Karyotype: an individual’s complete set of chromosomes ->
Karyotype of how each of the chromosomes (23 pairs) come together
Mechanisms contributing to genetic diversity
Mutation: A change in a section of DNA. Caused by random or environmental factors (e.g., teratogens)
Random assortment: The shuffling of the 23 pairs of chromosomes in the sperm and egg; chance determines which member of the pair goes into the new sperm and egg
Crossing over: The process by which sections of DNA switch from one chromosome to another during meiosis, further increasing genetic variability
Child genotype- phenotype
Although every cell in your body contains copies of all the genes you received from your parents, only some of those genes are expressed.
Regulator genes Largely control the continuous switching on and off of genes that underlie development across the lifespan
A given gene influences development and behaviour only when it is turned on
Important for healthy development
Gene expression - Alleles
About a third of human genes have two or more different forms, known as alleles.
The dominant allele is the form of the gene that is expressed if present.
The recessive allele is not expressed if a dominant allele (that is of the same role) is present.
A person who inherits two of the same alleles for a trait is described as homozygous.- two recessive or two dominant.
A person who inherits two different alleles for a trait is described as heterozygous.(one of each)
Mendelian inheritance patterns
Biological parents
B- dominant gene for brown hair
b-recessive gene for blond hair
Heterozygous
Children can have brown or blond hair
The “male” disadvantage
The Y chromosome has only about a third as many genes on it as the X chromosome
Many alleles on the X chromosome do not have a corresponding allele on the Y chromosome that could suppress the action.
Therefore, individuals with only one x-chromosome (as suppose to having two) are more likely to suffer a variety of inherited disorders caused by recessive alleles on the X chromosome (e.g., colour blindness)
Genetic origins of human diseases and disorders
Over 5,000 human diseases and disorders are presently known to have genetic origins
Recessive gene: PKU, sickle-cell anaemia, cystic fibrosis
Single dominant gene: Huntington’s disease
Sex-linked inheritance: Fragile-X syndrome, haemophilia
Errors in meiosis (resulting in a zygote with fewer or more than the normal complement of chromosomes) – e.g., Down syndrome
Down syndrome
Down syndrome (Trisomy 21)
21 st chromosome- 3 chromosomes instead of 2, causing down syndrome.
Polygenic inheritance
The mendelian dominant-recessive pattern of inheritance pertains to relatively few human traits (e.g., hair colour, blood type etc.)
Many other traits are governed by more than one gene (e.g., height, intelligence…- not determined by one gene)
Polygenic inheritance applies to most traits and behaviours of interest to behavioural scientists
The effects of environment on phenotype
A given genotype can develop differently in different environments - env meaning anything that is not the genetic info itself- everything around us
“Environment” relates to anything that is not the genetic information itself
This idea is expressed by the concept of the “norm of reaction
Norm of reaction (Dobzhansky, 1955)
Refers to all the phenotypes that could theoretically result from a given genotype, in relation to all the environments in which it could survive and develop
The case or PKU
Children with phenylketonuria (PKU)— a disorder that is related to a defective gene on chromosome 12—are unable to metabolise phenylalanine
Present in some foods such as sweeteners
With early diagnosis and a properly restricted diet, however, cognitive impairment resulting from PKU can be avoided
Genotype can result in different phenotypes depending on the environment
Behaviour genetics research design
How variation in behaviour and development results from the combination of genetic and environmental factors
The family study is the mainstay of modern behaviour-genetics research.
Correlations between the measure of the trait in individuals with different relationships are examined to see if they are higher for individuals who:
Are genetically more similar
Share the same environment
Types of family studies
Twin-Study Designs: Correlations for pairs of monozygotic twins (identical and share the same zygote) on a trait of interest are compared to those of dizygotic twins (non-identical twins)
Adoption Studies: Researchers examine whether adopted children are more like their biological or their adopted relatives (documentary Three Identical Strangers might be of interest)
Minnesota study of twins reared apart
Located and studied twin siblings who have not met since they were infants
Begun 1979, longitudinal study (followed up individuals in different parts of their lives)
The team of investigators were struck by the similarities they found in traits like IQ, reaction to stress, and traditionalism
Also personality, hobbies, professions…
These similarities may be influenced by selective placement and similarities in fostering environments as well as by genetic factors
Shared Environmental effects
Most obvious source of shared environment is growing up together in the same family
Behavioural geneticists, however, have found surprisingly little effect of shared environment on some aspects of development
Non-shared environment
Non-shared environment effects include experiences unique to the individual
Siblings may have quite different experiences within the same family and their experiences outside the family may diverge sharply
The primary effect of non-shared environmental factors is to increase the differences among family members
