Biological development Flashcards
DNA
deoxyribonucleic acid, Made up of genes.
mutation
A genetic variation of known or unknown cause. Creates a disruption in the coding which makes the gene faulty.
allele
Humans have 46 chromosomes and 23000 genes. Chromosomes are paired into 22 autosome pairs and final pair is the sex chromosome pair, which is XX for female and XY for male. 23 chromosome from father and 23 from mother. Thus a gene for each position from father and mother and the copies at a locus, are alleles.
human blood groups
Blood types may be A, B, AB,or O. Genotype possibilities are: A (AA or AO), B (BB or BO) AB (AB)and O (OO). A and B are both dominant over O, but together are codominant.
rH factor
Human blood groups also describes as positive or negative. this refers to the presence of an antibody on the rbc surface. Presence is determined by dominant rH gene. Homozygous recessive negative for rH is less than 25% of people. For an rH negative mother to bear an rH positive child, means that body will be sensitised to target and destroy if have a second rH positive child. Ideally, anti- rH serum (eg Rho-gam, an immunoglobulin) is given to mother 72 hours prior to birth of 1st and subsequent Rh positive offspring. otherwise offspring at great risk of haemolytic anaemia
dominant, recessive, co-dominant gene
When there are different alleles, if there is a dominant gene, this is expressed, whereas the recessive one is not. For recessive genes to be expressed, must be homozygous (have 2 alleles both of recessive type). (homozygous = 2 alleles same.heterozygous = 2 alleles different. If genes are co-dominant, can have 2 different alleles and both will be expressed.
genotype and phenotype
Phenotype =physical characteristic, eg Type A blood.
Genotype= genes causing expression of phenotype (eg AA or AO).
describe how red/green colour recognition is inherited.
Inherited via X chromosome. There is a faulty recessive gene. Females may carry 1 recessive gene but if have a normal dominant gene, will not have re-green colour blindness. But male will only have 1 allele, and if is recessive faulty type, will have red-green colour blindness.Therefore, far more men affected.
genetic predisposition
inherited susceptibility. Not a definite will get disease, but are more likely, especially if combined with at-risk environments eg sun exposure for melanoma
consanguinity
a relationship between related people (shared blood)
degrees of relationship
first degree relatives share half their dna. eg.parent and child or full brother/sister.
2nd degree relatives share a quarter of their dna. eg. half sibling, aunt/uncle and nephew/niece or garndparent and grandchild.
3rd degree share 1/8th of dna eg half uncle, 1st cousin.
More closely related parents are more likely to have offspring with serious birth defects. Normal risk is 2-3%.For first degree relatives, risk is 30%.
Australian law and degrees of relationship
Permits marriage between cousins. Permits between uncle and niece. Forbids between siblings or half siblings, or between grandparent and grandchild. Forbiddings apply even if adopted.
Foetal Alcohol Syndrome
range of effects seen in offspring born to mother’s wh drank during pregnancy. 5drinks per day have 30% chance of being severely effected.Most usual signs are smaller birth weight,smaller heads, smaller brains, smooth upper lip, narrow, widely spaced eyes, heart and limb defects, mental retardation,irritability an behavioural abnormalities. Do not catch up.
Thalidomide
teratogen. Anti-nausea med prescribed to pregnant women in the 1960’s. Birth defects when exposed during 4th-6th week of pregnancy. Defects included limb defects, heart and gi defects and facial defects.
amnion, chorion,allantois yolk sac
amnion=inner membrane forms around trophoblast.
chorion=outer membrane around trophoblast.
amniotic fluid forms between foetue and amnion.
Yolk sac forms within amnion and produces blood cells until role taken over by spleen, liver and bone marrow.
Chorion forms the allantois which forms the foetal part of the placenta. Placenta has maternal and foetal origins.
prenatal periods
- Germinal period.(period of the zygote).First 2 weeks. Zygote becomes blastocyst. Blastocyst has outer trophoblast layer which will implant and inner embryonic disc which will form embryo.Foetal membranes and placenta form
- embryonic period.Implantation to 8th week.Organs develop. responds to some stimuli. Ectoderm (will form skin, hair and nervous system), Mesoderm (will form bones, muscle, organs and circulatory system) and Endoderm (will form digestive system, urogenital system, lungs and glands) form by end of third week.limb buds form. yolk sac becomes defunct.
- Period of the foetus. week 9 to 9 months.
pregnancy trimesters
9 months of pregnancy divided into trimesters of 3 months each. Period of the foetus begins 2/3rds of the way through the first trimester.
by end of 1st trimester foetus approx 75mm long and weighs approx 25grams. spinal cord present.and kidneys can secrete.
By end of 2nd trimester,foetus approx 360mm long and weighs approx 900grams. Movements can be felt and eyes seem to move. surfactin in lungs beginning to be produced.All organs fully formed except cns. Survival possible with exceptional medical care.
In third trimester a layer of brown fat is laid down. sleep and wake cycles are clearly present.
Syphilis
teratogen having effect 18 weeks plus into pregnancy. Bacterial disease.May cause miscarriage, mental retardation, blindness, later death. signs may not be detected until after a few years.
teratogen
substance causing harm to foetus in utero. may have specific effects on specific tissues (tissue specific effect) and may have periods during pregnancy where foetus is far more susceptible (sensitive period).
May also have a dose-dependent response in severity
canalisation(embryology)
process of forming a tube.Beginning week 5, endoderm of GIT multiplies to point of occlusion, then is re-canalised so that by end of week 8, is a tube again. Abnormalities in process cause stenosis or diverticulae.
Canalisation (genetics)
process by which genetics are restricted to a range of outcomes. Those having strong canalisation are highly genetically determined with very little environmental influence (eg infant babbling), whereas IQ, personality and temperament are far less canalised and far more influenced by environment.
reaction range
genes set the limits on environment influence. ie can only with the best envionment, reach the geatest IQ which ones genes allow.
niche-picking
where individuals seek out an environment which suits their genetic make-up.eg an introverted child will seek out activities such as reading
heritability co-efficient (H)
a numerical estimate varying from 0 to 1, describing how inheritable a characteristic is. Determined by comparing
correlations (r) of characteristics of monozygotic (MZ) and dizygotic( DZ) twins.
H=2{ r(MZpairs) - r(DZpairs)}
