9 Meiosis, growth and development Flashcards
what is the purpose of meiosis?
to produce genetically varied haploid gametes
why does genetic variation occur?
crossing over of chromatids at chiasmata
independent assortment of chromosomes during anaphase I and II
random fertilisation
how is the haploid number calculated?
haploid number = 2^n
in humans = 2^23 = 8,388,608
what is the definition of a stem cell?
an undifferentiated cell that is capable of differentiating into a range of cell types
what is the definition of differentiation?
the development of unspecialised cells to form specialised cells
what is a totipotent stem cell?
a stem cell that has the ability to form a whole organism and extra-embryonic membranes
what is a pluripotent stem cell?
a stem cell that is found in embryos at the 50-100 cell stage
what is a multipotent stem cell?
a stem cells that has the ability to differentiate into a limited range of different cell types
give two uses of multipotent/pluripotent stem cells
bone marrow transplants (as haemocytoblasts)
leukaemia and bone cancer treatment
what are the ethical issues surrounding the use of embryonic stem cells?
embryos denied human right of consent
destroying a human life
against religious beliefs
risk of human cloning
what is the pre-conceptual advice given to couples?
give up smoking/alcohol
mother should be immunised against rubella (3 months before conception)
what is the antenatal care/advice given to pregnant women?
avoid specific food (e.g. raw meat/unpasteurised dairy)
urine tests
- for glucose (gestational diabetes)
- for proteins (kidney diseases/hypertension)
blood pressure monitoring
blood group and Rh status tests
genetic screening
outline the features and explanations of the recommended dietary changes for pregnant women
protein - growth of baby, uterus and placenta
calcium - growth of teeth, bones and nervous system
iron - haemoglobin synthesis
vitamin A - production of rhodopsin; gene transcription; immune system
vitamin C - collagen formation
folic acid - DNA synthesis; erythrocyte production
outline the effects of alcohol on foetal development
< 2 units/week –> increased risk of language/speech problesm
> 6 units/day –> ethanol damage to NS –> psychological and behavioural problems
outline the effects of smoking on foetal development
poorly developed lungs
increased chance of premature birth
nicotine narrows blood vessels and increases foetal heart rate
what are the three measurements taken of foetuses and babies?
crown-rump length
biparietal diameter
femur length
aside from measurements, what else is observed during ultrasound scans?
number of foetuses
location, size and structure of internal organs (18w+)
blood flow through umbilical cord
position of placenta
how is an ultrasound scan performed?
gel smeared on abdomen; transducer moves over skin
ultrasound waves emitted into woman’s body and reflected back from structures (i.e. foetus(es) and placenta)
reflections detected by computer and converted to real-time image
what are the advantages of an ultrasound scan?
non-invasive and safe
cost-effective
real-time images
explain the use of percentiles
used to estimate gestational age of foetus(es)
predict birth date
how is the growth rate calculated?
(change in [x] / number of weeks passed) x 100 = [z] [units]/week
what is CVS?
{chorionic villus sampling}
the removal and testing of small same of placental and chorionic villus cells to test for genetic abnormalities using a transcervical/transabdomial needle
when is CVS offered?
if there is a known risk of a certain genetic disease (e.g. cystic fibrosis)
if previous pregnancies have had complications
if an abnormality was detected during a routine ultrasound
what are the risks associated with CVS?
small risk of miscarriage (1-2%)
risk of infection
risk of limb defects
what is amniocentesis?
the removal and testing of ~ 20 cm^3 amniotic fluid to test for genetic abnormalities
when is amniocentesis offered?
mother over 35
mother has medical history that could lead to abnormality
family history of inherited genetic conditions
what does amniocentesis test for?
Down’s
Edward’s
Patau’s
what are the risks associated with amniocentesis?
invasive ∴ small risk of miscarriage (1%)
risk of infection/injury from needle
sensitising complications if Rh+ baby and Rh- mother
what is karyotyping?
the photographing of paired, sized chromosomes to identify chromosomal abnormalities from malfunctions or disease
how are the chromosomes in karyotyping obtained?
amniocentesis/CVS
blood
bone marrow
outline the procedure of karyotyping
cell grown in tissue culture and harvested
treated with phytohemagglutin –> division by mitosis
colchine added –> prevents spindle fibre formation ∴ mitosis halted at metaphase
cells placed in dilute salt solution –> chromosomes spread out
cells stained and viewed under the microscope
chromosomes identified by size
what do normal karyotypes look like?
24 chromosomes in 22 pairs + 1 sex pair
in normal size, shape and structure
