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Year 12 - Biology > C9 - Meiosis > Flashcards

C9 - Meiosis Flashcards

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1
Q

What is meiosis?

A

Cell division into four unique sighted cells which half the chromosomes of the parent cell.

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2
Q

What’s a somatic cell?

A

Any cell in the body other than gametes/sex cells.

They contain 46 chromosomes with 23 pairs of homologous chromosomes.

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3
Q

What’s a gamete?

A

A sex cell

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4
Q

What’s a haploid?

A

A half set of chromosomes

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5
Q

What’s a diploid?

A

A full set of chromosomes

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6
Q

How does the process of meiosis differ from mitosis?

A

It involves maternal and paternal chromosomes (homologous chromosomes) and there are two stages / two of each stage.

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7
Q

What is independent assortment of meiosis?

A

When the spindle fibres sort the chromosomes into homologous pairs determined by how they’re divided in order for crossing over to occur.

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8
Q

What are the stages of meiosis?

A

Prophase I
Metaphase I
Anaphase I
Telophase I

Prophase II
Metaphase II
Anaphase II
Telophase II

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9
Q

What occurs during meiosis?

A
  • Prophase I: Homologous chromosomes pair up and interweave to form a ‘bivalent’ structure. DNA sections are swapped as they cross over. The spindle forms, nucleolus disappears and nuclear envelope disintegrates.
  • Metaphase I: The bivalents line up across the cell equator and spindle fibres attach to the chromosomes centromeres.
  • Anaphase I: The homologous chromosomes are separated. Spindle fibres pull one member of a pair to one pole and the other chromosome to the opposite pole.
  • Telophase I: 2 haploid sets of chromosomes are present at opposite sides of the cell. In animal cells, 2 nuclear envelopes form around the 2 chromosomes and the cell divides by cytokinesis.
  • Prophase II: The nuclear envelope and nucleolus disappear, chromosomes condense and spindle fibres form.
  • Metaphase II: Chromosomes line up on the cell equator and spindle fibres attach to the centromeres.
  • Anaphase II: Centromeres divide and sister chromatids are separated and pulled to opposite poles
  • Telophase II: The nuclear envelope reforms around the four haploid sets of daughter chromosomes
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10
Q

What is crossing over?

A

When DNA is exchanged between homologous chromosomes.

When paired up, chromatids twist around adjacent chromosomes.
These interweaving parts are called chiasmata.

Genetic material can be exchanged at chiasmata in a process called crossing over.
This exchange creates new combinations of alleles.

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11
Q

How is the number of possible chromosome combinations calculated?

A

By calculating 2 to the power n.

E.g. Humans have a haploid number of 23 so it is 2^23 which is 8,388,608

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12
Q

How does pregnancy occur?

A

Meiosis produces haploid gametes.

A haploid nucleus from an egg cell and sperm cell will fuse during fertilisation.

This produces a diploid zygote.

Zygote will then divide to form an embryo then divide further to produce a foetus.

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13
Q

What pre-conceptual care advice is given before pregnancy?

A

Have both parents give up smoking

The mother is advised to limit her alcohol consumption

Women should check that they are immune to rubella before becoming pregnant.

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14
Q

Why is pre-conceptual care advice given before pregnancy?

A

No smoking - chemicals in cigarettes can impede the development of the fetus which increases the risk of premature birth, poor lung development or risk of still birth and death.

Alcohol consumption limited - A high consumption increases the risk of a baby having language and speech difficulties or fetal alcohol syndrome.

Immunisation against rubella - rubella can cause defects such as deafness or intellectual impairment therefore women are screened for rubella. Women should check that they’re immune before becoming pregnant.

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15
Q

What’s pre-conceptual care?

A

Advice given before pregnancy.

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16
Q

What’s antenatal care?

A

Care given during pregnancy

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17
Q

What sort of antenatal care is provided?

A

Dietary advice

Information on specific infections

Glucose testing

Blood pressure testing

Blood group identification

Genetic defects

Feral growth monitoring

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18
Q

Why is dietary advice given during antenatal care?

A

A balanced diet is necessary to ensure the baby receives the correct proportions of nutrients.

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19
Q

Why are specific infections monitored during antenatal care?

A

Specific infections are monitored and must be avoided e.g. Toxoplasmosis is a parasitic infection from raw meat, dangerous to young children.

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20
Q

What must glucose and blood pressure be monitored during antenatal care?

A

Glucose levels in urine can identify gestational diabetes.

Blood pressure must be monitored to see if the mother develops a deadly condition known as pre-eclampsia.

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21
Q

Why must blood groups be monitored in antenatal care?

A

To identify the mother’s rhesus status in case a transfusion is necessary for the delivery as well as the testing of infections e.g. HIV.

22
Q

Why are genetic defects and feral growth monitored during antenatal care?

A

It must be monitored to identify fetal development. This can be monitored by ultrasound.

23
Q

Why is protein necessary for the diet of a pregnant woman?

A

For the growth of the baby, uterus and placenta.

Amino acids from these proteins are used to synthesise cell structures, haemoglobin, enzymes and antibodies.

24
Q

Why is calcium necessary for the diet of a pregnant woman?

A

For strong teeth and bones as well as the functioning of the nervous system in the foetus.
However intake doesn’t need to increase dramatically

25
Q

Why is iron necessary for the diet of a pregnant woman?

A

For the synthesis of haemoglobin

26
Q

Why is vitamin A necessary for the diet of a pregnant woman?

A

It’s necessary for the pigment in rod cells of the eye (rhodopsin).
Other functions include roles in gene transcription and the immune system.

27
Q

Why is vitamin C necessary for the diet of a pregnant woman?

A

One function is within collagen formation.

Collagen is a structural protein and significant component of many tissues e.g. Skin, tendons, bones and blood vessels.

28
Q

Why is folic acid necessary for the diet of a pregnant woman?

A

(A.k.a vitamin B9)
It is essential for DNA synthesis, cell division and red blood cell production.

Shortage of folic acid in the diet of pregnant women can hinder brain development within the baby and increase risk of spine abnormalities e.g. Spina bifada.

29
Q

How’s an ultrasound carried out?

A

A small, handheld transducer is moved back and forth over the abdomen.

The transducer emits sound waves into the mother’s body.

The waves are reflected back by the foetus and placenta, producing an image that can be viewed on a monitor screen.

30
Q

What information can ultrasound images provide during pregnancy?

A

How many babies the mother carries.

The structure of organs

Blood flow through the umbilical chord, indicating if the baby receives insufficient oxygen or nutrients

The position of the placenta - too close to the cervix can cause excessive bleeding

Measurements of the foetus

31
Q

How does alcohol affect foetal development?

A

It increases the risk of the baby developing speech and language difficulties.

32
Q

How does the carbon monoxide from cigarettes affect foetal development?

A

It binds to haemoglobin more readily than oxygen.

This reduces the supply of oxygen from the mother to the foetus.

33
Q

How does nicotine from cigarettes affect foetal growth?

A

It narrows the diameter of blood vessels, reducing the supply of oxygen across the placenta to the foetus.
It also stimulates the release of adrenaline, causing the baby’s heart to beat faster.

34
Q

What does pre-natal mean?

A

Pre-natal implies something before pregnancy / before becoming pregnant.

35
Q

What does diagnosis mean?

A

A diagnosis is the identification of an illness or condition. It is “the identification of the nature of an illness or other problem by examination of the symptoms”.

36
Q

What are the 2 types of DNA / cell sampling methods used on foetuses?

A

Amniocentesis and CVS (chorionic villus sampling)

37
Q

What is CVS?

How is it carried out?

A

Chorionic villus sampling which is a method for testing foetal DNA.
Foetal cells can be obtained from the developing placenta by CVS.
It requires ultrasound to locate the position of the foetus and placenta.
A needle is then inserted to remove the sample. It is used to detect birth defects, genetic diseases, and other problems during pregnancy.

38
Q

Where are the cells taken from for CVS?

A

Cells for CVS are obtained from chorionic villi which is taken from the placenta where it is attached to the uterus wall.

39
Q

What are the risks associated with CVS?

A

Compared to amniocentesis, CVS has a higher risk of miscarriage (approx. 1%) as well as the risk of resulting in foetal deformities. It could also cause infection or Rh sensitization where some of the baby’s blood cells enter the mother’s bloodstream.

40
Q

What is an amniocentesis?

How is it carried out?

A

Amniocentesis is a type of prenatal test, again involving an ultrasound scanner and needle by taking a sample of cells from the amniotic fluid that surrounds the foetus in the womb/uterus. This can help to identify genetic or chromosomal conditions e.g. Down’s syndrome.

41
Q

Where are the cells taken from for an amniocentesis?

A

From the amniotic fluid that surrounds the foetus in the womb.

42
Q

What are the risks associated with an amniocentesis?

A

There is a risk of miscarriage although the risk is smaller than with CVS. There’s also the risk of infection, rhesus disease or club foot (ankle & foot deformity).

43
Q

What is karyotyping?

A

Testing to identify the size, shape and number of chromosomes in a sample of eukaryotic/body cells. This helps to identify and diagnose genetic disorders.
Foetal cells are cultured in a lab and stimulated to divide by mitosis.

A chemical called colchicine is added which stops mitosis at metaphase. The chromosomes can then be photographed to produce a karyogram.
A stain is added to improve their visibility. The chromosomes can be sorted into pairs.
Doctors are then able to determine sex and assess whether foetus has any chromosomes.

44
Q

What types of chromosomal mutations can be diagnosed using karyotyping?

A

Down’s syndrome, Turner’s syndrome and Klinefelter’s syndrome can be identified.

45
Q

Describe the karyotype for the Down’s syndrome

A

A karyogram would show three copies of chromosome 21 instead of 2. It is characterised by distinctive facial features and some degree of learning disability and delayed development.

46
Q

Describe the karyotype for Turner’s syndrome

A

Babies with this syndrome only have one X chromosome and no Y chromosome, written as XO. Symptoms include short stature and lack of mensuration.

47
Q

Describe the karyotype for Klinefelter’s syndrome

A

It is indicated by 2 X chromosomes and one Y chromosome. Symptoms include tall stature and a feminised physique.

48
Q

A scan is carried out at around 12 weeks of pregnancy in order to establish the ‘gestational age’ of the fetus.

How is gestational age estimated from images obtained during a 12 week ultrasound scan?

A

The crown - rump length and biparietal diameter is measured. 

Data is then extrapolated from growth charts.

49
Q

An energy intake during pregnancy that is in excess of the energy requirement can increase the risk of conditions such as gestational diabetes.
Suggest how excess energy intake can be monitored in a pregnant woman during routine antenatal visits:

A

Calculate BMI or identify its weight.

50
Q

How is gestational diabetes monitored during pregnancy in routine antenatal visits?

A

Test a urine sample for glucose.

51
Q

Describe the technique used to produce images of chromosomes:

A

Karyotyping

Cells are taken from a bodily fluid e.g. via amniocentesis.
The cells are stimulated to divide by mitosis - mitosis is stopped in metaphase.

The chromosomes are then stained and arranged to produce a photograph.

Year 12 - Biology (15 decks)

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