Guided Studies W7/8 Flashcards

1
Q

Identify the main histological features of spermatogonia, spermatocytes, spermatids and sperm in a section of a seminiferous tubule.

A

Spermatogonia:
-spherical nuclei close to the BM

Primary spermatocytes:

  • numerous in any section of seminiferous tublules.
  • easy to identify, since they have the largest nuclei with thick, prominent chromosomes.

Spermatids:
-close to the lumen

Sperm:
-highly condensed, tear-drop shaped nuclei

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2
Q

Recognise spermatogonia, spermatocytes and spermatids in a section of a seminiferous tubule.

A

Refer to http://medpub2.st-andrews.ac.uk/slidebox/repromale/pages/Seminepi2VHP.html.

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3
Q

What is the molecular basis of Duchene Muscular Dystrophy? What is the inheritance pattern?

A

Disruption of DMD gene on X-chromosome. Dystrophin forms part of an important structural unit in the membrane of muscle cells, which links the muscle fibre to the
extracellular matrix.

X-linked

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4
Q

If a mother carries the DMD gene but is not affected, what are the chances that a child would be affected.

A

She has one defective copy (one good X and one X with mutation). As a result, if male, 50% of inheriting defecting X so 50% change of affected. If female, 0% chance (because even if inherit mutation, will have second X that is not affected).

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5
Q

What genetic test can be performed to test for DMD on an embryo ?

A

CVS to obtain cells from embryo. Cytogenetic analysis to determine sex of embryo.
Then if male do molecular analysis to see if have inherited deletion.

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6
Q

What is the molecular basis of Tay-Sachs disease? What is the inheritance pattern ?

A

Mutation in the HEXA gene, alpha subunit of lysosomal storage enzyme beta-Nacetylhexosaminidase A. Cells are unable to break down gangliosides, a type of lipid, so they accumulate in cells, with detrimental effect, especially in neuronal cells.

Autosomal recessive

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7
Q

What factors may influence the risk of a carrier of Tay Sachs to have affected children.

A

Whether his partner is from the same ethnic group. In general population about one in 300 are heterozygote carriers. Tay Sachs is more prevalent in the
Ashkenazi Jewish population, about 1/30 are carriers.

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8
Q

What is the molecular basis of the most common form of Charcot-Marie Tooth Disease? What is the inheritance pattern in this disease?

A

Most common form of the disease (CMT1) is due to mutations in the gene encoding peripheral myelin protein 22 (PMP22) on chromosome 17. This protein is normally a
major component of myelin sheath. In many cases the gene is duplicated and too much protein is produced, impairing the structure and function of the sheath. Can
result in degeneration of the nerves and symptoms such as weakness of the distal muscles and reduced ability to feel hot/cold/pain.

Autosomal dominant

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9
Q

Interpret this karyotype: 46,XX,der(14)t(14;17)(p11.2;p11.2)

A

Normal number of chromosomes BUT one of her chromosomes is a hybrid of chromosome 14 and 17. It is largely chromosome 14 but also carries some
information which would normally be found on chromosome 17.

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10
Q

The following karyotype
46, XY, t(14;17)(p11.2;p11.2)
is abnormal, but the person is phenotypically normal. How would you explain this?

A

Balanced translocation of short arms of chromosomes 14 and 17. No obvious additional/missing genetic information overall.

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11
Q

Anna is 12 hours old. She was born at 37 weeks following complications of intrauterine growth retardation. An ultrasound scan in the third trimester was otherwise normal. Birth weight was 1.45kg (this is below the third centile). Multiple anomalies were noted soon after birth, including microcephaly, club feet, high, narrow palate, low-set posteriorly rotated ears, fifth finger clinodactyly and hypotonia. Both parents are phenotypically normal. Full karyotype analysis is requested.

The result from the cytogenetics lab show a karyotype:
46,XX,der(14)t(14;17)(p11.2;p11.2)

The parents decide to have chromosomal analysis. The father is found to have the
following karyotype:
46, XY, t(14;17)(p11.2;p11.2)

How does the fathers karyotype increase understanding of Anna’s karyotype?

A

Anna received the derivative chromosome from her father (ie copy of 14 with the
additional part of chromosome 17), as well as a normal chromosome 17 from the
father (and normal chromosomes 14 and 17 from the mother). Thus Anna is trisomic
for part of chromosome 17, and monosomic for part of chromosome 14. This gain and
loss of genetic information is likely to be clinically significant.

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12
Q

Anna is 12 hours old. She was born at 37 weeks following complications of intrauterine growth retardation. An ultrasound scan in the third trimester was otherwise normal. Birth weight was 1.45kg (this is below the third centile). Multiple anomalies were noted soon after birth, including microcephaly, club feet, high, narrow palate, low-set posteriorly rotated ears, fifth finger clinodactyly and hypotonia. Both parents are phenotypically normal. Full karyotype analysis is requested.

The result from the cytogenetics lab show a karyotype:
46,XX,der(14)t(14;17)(p11.2;p11.2)

Anna’s mother had two miscarriages before Anna was born. Do these findings have relevance for those miscarriages as well?

A

May be coincidence but the father is at risk of creating sperm with unbalanced karyotypes (eg with derivative 14 and normal 17 as occurred in Anna or it could be
the derived chromosome 17 and a normal 14). In some cases the chromosome imbalances may cause miscarriage.

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