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Flashcards in Genetics 1 Deck (34)
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1
Q

Congenital Abnormalities.

A
  1. Apparent in 1/50 of newborn infants.

2. Accounts for 20-25% of all perinatal deaths and childhood (upto 10y/o)

2
Q

How much do genetic factors account for congenital abnormalities?

A

40%

3
Q

What are the classifications of congenital abnormalities?

A
  1. Malformation
  2. Disruption
  3. Deformation
  4. Dysplasia
  5. Sequence
  6. Syndrome
  7. Association

(MDDD single)
(SSA multiple)

4
Q

What is malformation?

A
  1. Primary structural defect

2. Usually single organ showing multifactorial inheritance

5
Q

What is disruption?

A
  1. Secondary structural defect of organ/tissue.
  2. Typically caused by ischaemia/infection/trauma
  3. Not genetic, but has predispositions
6
Q

What is deformation?

A
  1. Distortion of a structure due to abnormal mechanical force.
  2. Occurs usually in late pregnancy - usually has good prognosis
7
Q

What is syndrome?

A
  1. Consistent pattern of abnormalities with specific underlying cause.
8
Q

What is a sequence?

A
  1. Multiple abnormalities caused by a primary factor.

2. Initial factor could be genetic

9
Q

What is dysplasia?

A
  1. Abnormal organisation of cells in tissue
10
Q

What is association?

A
  1. Non-random abnormalities that are not explained by a syndrome.
  2. Unknown cause.
11
Q

What is metacentric?

A

If centromere in the middle exactly

12
Q

What is submetacentric?

A

If centromere is just off middle

13
Q

If the centromere is not on the middle, what is it called?

A

Acrocentric (small ends of chromatids called satellites\0

14
Q

When chromosomes are stained, they become banded. What are the short and long arms called?

A

Short arm = p

Long arm = q

15
Q

What are the types of chromosomal abnormalities?

A
  1. Numerical - aneuploidy - loss/gain of chromosome
  2. Structural - translocations/deletions/insertions/inversions/rings
  3. Mosaicism - different cell lines
16
Q

What are the autosomal aneuploidies?

A
  1. Monosomy - loss of one chromosome - almost always lethal
  2. Trisomy - gain of a chromosome - tolerable
  3. Tetrasomy - gain of 2 chromosomes - tolerable
17
Q

What is trisomy 21?

A

Down Syndrome

18
Q

What are the clinical features of Down’s syndrome?

A
  1. Newborn period - severe hypotonia/sleepy/excess nuchal skin
  2. Craniofacial - big tongue, small ears, epicanthic folds, Brushfield spots, gap between upper and lower eyelids.
  3. Limbs - single palmar crease, wide gap between 1st and 2nd toes
  4. Cardiac - atrial & ventricular septal defects
  5. Short stature
19
Q

What are 2 conditions that Down’s syndromes have increased risk of?

A

Leukaemia and Alzheimers.

20
Q

What causes Down’s syndrome?

A

Non-disjunction of homologous chromosomes in meiosis 1.

21
Q

What is the chromosomal abnormality spread of Down’s syndrome?

A

95% Trisomy (21)

4% Translocation (Robertsonian Translocation)

1% Mosaicism

22
Q

If mosaicism is the cause of Down’s syndrome, how does this happen? How severe does it affect children?

A
  1. Mitotic non-disjunction in the zygote

2. Children less severely affected

23
Q

Give an example of Monosomy X.

A

Turners Syndrome

24
Q

Give 2 signs that can be detected in the 2nd trimester for Turners syndrome.

A
  1. Generalised oedema

2. Swelling in the neck

25
Q

Give some clinical features of Turners syndrome.

A
  1. Short 4th metacarpals
  2. Webbed neck
  3. Aorta defect
  4. Normal intelligence
  5. Short stature in adults
  6. Ovarian failure
26
Q

How is Turners treated?

A

With oestrogen replacement (2ndary sex characteristics and prevents osteoporosis)

27
Q

How is Turners caused?

A

X/Y chromosome lost

Usually in paternal meiosis (80%)

Other causes include:
Ring chromosome
Single arm deletion
Mosaicism

28
Q

Give an example of polysomy X in males.

A

Klinefelters

29
Q

Describe Klinefelters.

A

1/1000 live Mal births

Clinical features:

  1. Clumsiness
  2. Verbal learning difficulty
  3. Tall
  4. 30% develop gynaecomastia.
  5. Risk of leg ulcers
  6. Osteoporosis
  7. Breast carcinoma in later life.
30
Q

What is dosage compensation?

A

Process by which species equalise gene expression between different sexes.

31
Q

How does dosage compensation work in humans?

A

In females, one X chromosome is inactivated.

32
Q

What is a Barr body?

A

Region of density in a cell denoting a switched off X chromosome.

33
Q

Explain how chromosome doesn’t equal gender.

A
  1. In embryonic stage of development, we are initially sexually indifferent.
  2. Whether we become males or females depends on SRY gene on Y chromosome.
  3. If SRY translocated from Y chromosome to X chromosome (during meiosis), there is an XX individual but male because one X chromosome has SRY.
  4. If SRY part of Y chromosome gets deleted, XY but female as no SRY.
34
Q

Give examples of genomic disorders.

A
  1. Di George syndrome

2. Cri du Chat syndrome