2.2.1 The Biological Basis of Individuality and The Monitoring of Fetal Development

OCR specifiaction based notes for AS Human Biology

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2.2.1 The Biological Basis of Individuality and The Monitoring of Fetal Development
(a) The Importance of Meiosis
Meiosis is needed to produce sex cells, or gametes. Sex cells must only contain one set of chromosomes;
making then haploid cells.
Meiosis is two stage division. Stage 1 produces 2 haploid cells, stage 2 produces 4 haploid gametes
which are all genetically different to each other.
(b) Meiosis
Prophase 1 ­ chromosomes condense, homologous chromosomes pair up as bivalents, chiasmata may
form. The nuclear membrane begins to break up. Spindle fibres begin to form. Centrioles begin to move
towards the poles of the cell.
Metaphase 1 ­ centrioles reach the poles of the cell, bivalents line up along the equator of cell. Spindle
complete. Random alignment of homologous chromosomes either side of the equator.
Anaphase 1 ­ whole chromosomes from each bivalent are pulled apart & move to opposite poles of the
cell.
Telophase 1 ­ chromosomes de-condense, nuclear envelopes reform around the two groups of
chromosomes. Nucleolus re-forms.
Prophase 2­ chromosomes condense, nuclear envelope begins to break down.
Metaphase 2­ spindle complete. Centrioles have migrated to opposite poles of the cell. Nuclear
envelope completely broken down. Chromosomes line up on the equator of the cell.
Anaphase 2­ chromosomes divide at the centromeres and the chromatids are split from each other and
move to opposite poles of the cells.
Telophase 2­ chromosomes de-condense, nuclear envelopes reform around the two groups of
chromosomes. Nucleolus re-forms, cell divides.
(c) Chiasma Formation
(c) explain the importance of chiasma formation,crossing over, independent assortment of
chromosomes (metaphase 1) and chromatids (metaphase 2) resulting in genetic variation between
gametes and subsequently genetic variation between individuals;
(d) Antenatal Care
When a woman becomes pregnant it is important for both her and her partner to stop smoking and for
her to stop drinking alcohol. It is also important to check for rubella immunity- and if not, get a vaccine.
Rubella can cause deafness and brain damage in the baby. After conception the woman goes for a scan
where a urine sample will be taken to test for protein or glucose- signs of gestational diabetes and
kidney damage. Another important thing to look out for is high blood pressure and swollen legs as this
can be a sign of pre-eclampsia.
(e) Diet During Pregnancy
DRV means Dietary Reference Value. These describe the required energy and nutrient intakes of the
British population. Proteins have many important functions in cell membranes and to make antibodies etc
Iron is an essential component of the haem group of haemoglobin molecules.
Vitamin A is transformed into retinol in the body. In epithelial cells, retinol is used to make retinoic acid, a
chemical that aids cell development and growth. Vitamin C is a highly effective antioxidant, and
necessary in the biosynthesis of many important molecules like collagen and dopamine.
Folic acid is important to help prevent disorders such as spina bifida.

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Measuring Fetal Growth
An ultrasound scan is used to check the baby's size and to make sure that they are developing correctly.
The crown rump length is the length of baby's back from the top to the head to the bottom. The
biparietal diameter is the width of the head at the widest part.
(g) Smoking and Alcohol
Carbon monoxide in cigarette smoke stops O2 combining to hemoglobin in the blood supply of both
mum and baby.…read more

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