9 Meiosis, growth and development

Question 1

what is the purpose of meiosis?

Answer 1

to produce genetically varied haploid gametes

Question 2

why does genetic variation occur?

Answer 2

crossing over of chromatids at chiasmata

independent assortment of chromosomes during anaphase I and II

random fertilisation

Question 3

how is the haploid number calculated?

Answer 3

haploid number = 2^n

in humans = 2^23 = 8,388,608

Question 4

what is the definition of a stem cell?

Answer 4

an undifferentiated cell that is capable of differentiating into a range of cell types

Question 5

what is the definition of differentiation?

Answer 5

the development of unspecialised cells to form specialised cells

Question 6

what is a totipotent stem cell?

Answer 6

a stem cell that has the ability to form a whole organism and extra-embryonic membranes

Question 7

what is a pluripotent stem cell?

Answer 7

a stem cell that is found in embryos at the 50-100 cell stage

Question 8

what is a multipotent stem cell?

Answer 8

a stem cells that has the ability to differentiate into a limited range of different cell types

Question 9

give two uses of multipotent/pluripotent stem cells

Answer 9

bone marrow transplants (as haemocytoblasts)

leukaemia and bone cancer treatment

Question 10

what are the ethical issues surrounding the use of embryonic stem cells?

Answer 10

embryos denied human right of consent

destroying a human life

against religious beliefs

risk of human cloning

Question 11

what is the pre-conceptual advice given to couples?

Answer 11

give up smoking/alcohol

mother should be immunised against rubella (3 months before conception)

Question 12

what is the antenatal care/advice given to pregnant women?

Answer 12

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

Question 13

outline the features and explanations of the recommended dietary changes for pregnant women

Answer 13

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

Question 14

outline the effects of alcohol on foetal development

Answer 14

< 2 units/week –> increased risk of language/speech problesm

> 6 units/day –> ethanol damage to NS –> psychological and behavioural problems

Question 15

outline the effects of smoking on foetal development

Answer 15

poorly developed lungs

increased chance of premature birth

nicotine narrows blood vessels and increases foetal heart rate

Question 16

what are the three measurements taken of foetuses and babies?

Answer 16

crown-rump length

biparietal diameter

femur length

Question 17

aside from measurements, what else is observed during ultrasound scans?

Answer 17

number of foetuses

location, size and structure of internal organs (18w+)

blood flow through umbilical cord

position of placenta

Question 18

how is an ultrasound scan performed?

Answer 18

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

Question 19

what are the advantages of an ultrasound scan?

Answer 19

non-invasive and safe

cost-effective

real-time images

Question 20

explain the use of percentiles

Answer 20

used to estimate gestational age of foetus(es)

predict birth date

Question 21

how is the growth rate calculated?

Answer 21

(change in [x] / number of weeks passed) x 100 = [z] [units]/week

Question 22

what is CVS?

Answer 22

{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

Question 23

when is CVS offered?

Answer 23

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

Question 24

what are the risks associated with CVS?

Answer 24

small risk of miscarriage (1-2%)

risk of infection

risk of limb defects

Question 25

what is amniocentesis?

Answer 25

the removal and testing of ~ 20 cm^3 amniotic fluid to test for genetic abnormalities

Question 26

when is amniocentesis offered?

Answer 26

mother over 35

mother has medical history that could lead to abnormality

family history of inherited genetic conditions

Question 27

what does amniocentesis test for?

Answer 27

Down’s

Edward’s

Patau’s

Question 28

what are the risks associated with amniocentesis?

Answer 28

invasive ∴ small risk of miscarriage (1%)

risk of infection/injury from needle

sensitising complications if Rh+ baby and Rh- mother

Question 29

what is karyotyping?

Answer 29

the photographing of paired, sized chromosomes to identify chromosomal abnormalities from malfunctions or disease

Question 30

how are the chromosomes in karyotyping obtained?

Answer 30

amniocentesis/CVS

blood

bone marrow

Question 31

outline the procedure of karyotyping

Answer 31

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

Question 32

what do normal karyotypes look like?

Answer 32

24 chromosomes in 22 pairs + 1 sex pair

in normal size, shape and structure