topic 2 (biology of development) Flashcards
how any pairs of chromosomes do we have?
23
what is an autosome?
a non sex chromosome
how many pairs of autosomes do we have?
22
whats the difference between the structural DNA sequence and the regulatory DNA sequence?
- structural DNA sequences direct the assembly of particular proteins
- regulatory DNA sequences influences the expression of genes, acting as an on/off switch for particular genes
what is the difference between mitosis and meosis?
MITOSIS
- typical cell division
- 2 new cells are exact replicas of parent cell
MEOSIS
- type of cell division for sexual recombination
- original cell splits into 4 different cells
what are three ways that genetic variation is ensured in offspring
- Segregation- you only get one chromosome of each pair of chromosome transmitted
- independent assortment- the pairing of homogolous chromosomes is random
- Crossing over means that also the order of genes remains the same, which gene variant is inherited by the parent may vary
- this results in an infinite number of gene variation
what are different variants of genes called?
alleles
what are 4 prenatal environmental inputs on development?
hormones
substances consumed by mother
mothers illnesses
late gestation
what are 5 postnatal environmental inputs on development?
alcohol/druges
environmental toxins
infectious diseases
parental love
nutrition
what is a gene regulatory cascade?
a cascade of events after environmental triggers influence the expression of genes which then in turn influence the expression of other genes
what is canalisation?
the fact that “developmental reactions, as they occur in organisms submitted to natural selection…are adjusted so as to bring about one definite end-result regardless of minor variations in conditions during the course of the reaction
what are the two main types of epigenetic mechanisms?
- DNA methylation - when methyl groups are added to certain DNA bases
- Histone modification- when different molecules attach to the histones of DNA proteins, these alter the activity of the DNA wrapped around them
What is passive gene-environment correlation?
Passive gene–environment correlation refers to the association between the genotype a child inherits from their parents and the environment in which the child is raised.
Parents create a home environment that is influenced by their own heritable characteristics.
Whats evocative gene environment correlation?
- inherited tendencies evoke certain responses from others
- for example a child with a predisposition to behavioural problems may evoke harsher parenting which may exacerbate behavioural problems
what is active gene environment correlation?
- genetic make up encourages ‘niche’ choices
- e.g child who is genetically good at football decides to join a football club
what are 3 types of gene-environment correlation?
passive, evocative, active
what is the abbreviation for the heritability estimate?
h^2
(h squared)
what is the heritability formula?
heritability (h^2) = 2 x (MZ correlation - DZ correlation)
do twin studies measure the differences in means or the variance?
- twin studies are a measure of variance
- so if 90% of height is heritable, that does not mean that 90% of the height value is inherited, instead it means that 90% of the variation between individuals heights is accounted for by genes
what is 1 advantage and 1 disadvantage of twin studies?
ADV: allows us to estimate the relative contribution of genes vs environment in explaining individual variation in a trait
DISADV: the standard twin designs cannot tell us about the importants of gene environment interactions or gene environment correlations
what is pleiotropy?
- the finding that one gene can influence multiple traits
what does polygenic mean?
- when a trait is influenced by multiple genes
are most traits genetically homogenous or genetically heterogeneous?
- most traits are genetically heterogeneous
- this means that for different people, different sets of genes may be involved in a condition or a trait
what have studies into autism shown about the heritability of autism?
- twin studuies have shown that autism is highly heritable
- molecular genetic studies indicate that there is not one gene for autism
- different genes may be involved in autism for different people
- within each individual a combination of different genes may have contributed to the development of autism
- autism is genetically heterogenous and polygenic
do epigenetic modifications alter the sequence of base pairs?
- no
- epigenetic modifications create phenotypic modification without altering the base pair sequence of genes
what are 3 types of epigenetic modification?
- HISTONE MODIFICATION
- A methyl group may bind to the tails of histones
- This can cause DNA to be unwrapped or be stopped from unwrapping from the histone
- (histone unwrapping must take place in order for transcription to take place) - GENE METHYLATION
- A methyl can bind to the base pairs of genes
- This can prevent transcription from taking place - MRNA MODIFICATION
- mRNA modification can mean that mRNA translation can be enabled or blocked
how many sperm cells are there initially and how many end up reaching the egg?
- initially there are millions of sperm cells
- only 50-100 end up reaching the egg
- 1 sperm cell ends up penetrating the egg (the is a chemical process that stops the other sperm from penetrating)
what happens in the germinal stage?
implantation
after how many weeks is the embryo fully implanted?
2 weeks
when does a fertilised egg become an embryo?
when it is fully implanted
how many hours after fertilisation is the first division of the embryo?
2 hours
what is the cells bundle called 4 days after fertilisation and how many cells is it?
- morula
- 16 cells
what happens to the cells 5days after fertilisation?
outer and inner cells differentiate
it is now called a blastocyst
outer cells become the placenta and inner cells become the foetus
what happens to the blastocyst 16 days after fertilisation?
- blastocyst inner cell mass differentiates into ectoderm, mesoderm and endoderm
- this is called gastrulation
what 3 types of cell may an embryonic cell differentiate into?
ectoderm
mesoderm
endoderm
what 2 categories can ectoderm cells differentiate into?
skin
nerve tissue
what 3 categories can the mesoderm differentiate into?
muscle
organs
skeleton
what are three features of the embryonice stage (week 3-8)
- large changes in body structure
- large changes in size
- cells are differentiating
what are 2 features of the foetal stage (week 9-birth)
- characterised by heartbeat and facial features
-
at how many weeks can some foetuses survive with neonatal intensive care
22 weeks
at how many weeks do fully developed lungs appear?
28
what are homeobox genes?
- a homeobox is a DNA sequence found within genes that are involved within the regulation of patterns of anatomical development
- homeobox genes encode homeodomain proteins
- these proteins regulate genetic switches that affect the general structure and organisation of body parts
- these homeobox genes are highly specific resulting in species specific body parts
what is a teratogen?
- harmful environmental factors that can disturb prenatal development
- e.g medication taken by mother, pollution etc
- they largely exert effect during critical periods of development
what is the relationship between smoking and birth weight?
- there is a linear relationship between smoking and birth weight
- smoking is associated with a lower birth weight
- babies born to women who smoke weigh on average 200g less than babies born to non-smokers
outline foetal alcohol syndrome
foetal alcohol syndrome is caused by excessive alcohol use during pregnancy
it involves:
distinctive facial features
intellectual disability
behavioural and emotional problems
how does alcohol exposure and genetics in pregnancy interact?
the mothers genes may impact how harmful the alcohol is to the pregnancy
if the mother metabolises alcohol quickly the effects may be less harmful than if she didnt
outline thalidomide and pregnancy
- thalidomide was a drug used to treat morning sickness in the 1960’s
- it turned out to cause stunted growth of limbs
- it is thought that it interfered with the activity of the genes that regulate normal limb growth and/or with timing signals of the homeobox genes
- the specific effects of thalidomide depended on when in pregnancy the drug was used
what is microcephaly?
- being born with an abnormally small head
- it is often associated with severe brain damage
what teterogen virus is microcephaly associated with?
zika virus
roughly what percentage of children exposed to zika virus were born with microcephaly?
24%
what percentage of children exposed to zika virus had neurological abnormalities?
68%
what percentage of children exposed to zika virus had low and very low cognitive ability scores?
27% had low
9% had very low
what can vary the effect of a terotagen?
- genetics
- length and intensity of exposure
- timing of exposure
at how many weeks after conception does the neural tube start to form?
3 weeks
what happens 4 weeks after conception?
- the neural tube is almost completely closed
- the forebrain, midbrain and hindbrain are distinct
at how many weeks after conception are the cerebral vescicles present?
5 weeks after
what is the case by 10 weeks after conception?
major central nervous system structures are now visible
what is the brain like at 20weeks after conception?
the brain weighs about 100g
the cortical surface appears smooth
how much does the brain weigh at 38weeks- birth?
350 to 400 grams
what is the general order of development of cognitive structures/functions
- structures supporting vital functions such as heartbeat and breathing develop first
- Structures suporting basic motion and sensing stimuli develop next. These precede development of complex coordination
- Structures involved in complex reasoning and executive function develop last
what areas of the brain develop first and are vital for survival?
- the brainstem, which is involved in regulating heartrate, breathing and automatic processes
What area of the brain is last to develop?
the pre-frontal cortex, essential for executive functioning
what are the 3 main stages of prenatal neuronal development?
- Proliferation - new neurons being created (neurogenesis)
- Migration - new neurons are born in the centre of the developing brain and move outwards
- Synaptogenesis - the forming of synapses. This starts prenatally and continues postnatally
does myelination of sensory areas happen before or after birth?
before birth
does myelination of the cortical areas happen before or after birth?
after birth, continuing well into adulthood
what happens to the volume of grey matter as we age?
it decreases, due to programmed cell death and synaptic pruning
what happens to the volume of white matter as we age?
it increases, due to increased myelination
