Chromosomes, chromosome abnormalities and birth defects Flashcards Preview

MCD - Genetics > Chromosomes, chromosome abnormalities and birth defects > Flashcards

Flashcards in Chromosomes, chromosome abnormalities and birth defects Deck (30):
1

Definition of congenital abnormalities

Abnormalities present at birth that may be due to genetics or infection.

2

Definition and example of malformation

Primary structural defect - atrial septal defect, cleft lip

3

Definition and example of disruption

Secondary abnormal structure of organ or tissue - amniotic band wrapping around blood vessel cutting off blood supply to an organ

4

Definition and example of deformation

Abnormal mechanical force distorting a structure - club foot, hp dislocation

5

Definition and example of syndrome

Consistent pattern of abnormalities with a specific underlying cause - Down syndrome

6

Definition and example of sequence

Multiple abnormalities initiated by primary factor - Reduced amniotic fluid leads to Potter's sequence

7

Definition and example of dysplasia

Abnormal organisation of cells into tissue - thanatophoric dysplasia

8

Definition and example of association

Non-random occurrence of abnormalities not explained by syndrome. Cause usually unknown - VATER association

9

Definition of teratogen

An agent that interferes with normal embryonic or foetal development

10

Whole-chromosome factors of congenital defects

Numerical - loss or gain of chromosomes
Structural - Translocations, deletions, insertions, inversions
Mosaicism - Normal development of mutated chromosomes alongside normal chromosomes (stage at which mutation occurs affects degree of expression e.g. early mutation = obvious effects)

11

Effect of age on genetic risk

Increased age of either or both parents results in increased risk of a child with genetic abnormalities

12

Normal human karyotype

46 chromosomes in somatic cells
23 chromosomes in germ cells
Males have XY as sex-determining pair
Females have XX as sex-determining pair

13

Process of chromosome banding

Bands labelled according to chromosome number
Short (p) or long (c) arm
Numbered out from centromere.
Used to identify different chromosomes

14

Nomenclature of karyotyping

- Write total number of chromosomes
- Then a comma
- Then sex chromosomes
e.g. 46,XY or 46,XX

15

Definition of aneuploidy

An abnormality in the number of chromosomes, caused by the loss or gain of one or more chromosomes

16

The 3 types of aneuploidy, their definition and whether they can be tolerated or not

Monosomy - loss of one chromosome, nearly always fatal
Trisomy - gain of one chromosome, can be tolerated
Tetrasomy - gain of two chromosomes, can be tolerated

17

Definition of chromosome translocation

The transfer of genetic material from one chromosome to another when a chromosome break occurs during mitosis or meiosis

18

The two types of translocation

Balanced
Unbalanced

19

Features and consequences of balanced translocation

- Even exchange of genetic material between the two chromosomes
- No genetic data lost
- Chromosomes likely to remain the same length
- Little to no physiological effect seen

20

Features and consequences of unbalanced translocation

- Uneven exchange of genetic material
- Loss or gain of genetic data
- Chromosomes unlikely to remain the same length
- More likely to cause disease

21

Explain copy number variant/variation

- Phenomenon where sections of the genome are repeated
- Number of repeats in the genome varies between individuals
- Specifically large scale duplication or deletion events that cause variation

22

Aim of meiosis

To create 4 haploid cells each containing 23 chromosomes

23

Non-disjunction definition

The failure of the chromosomes to separate correctly in meiosis I or II

24

Consequences of non-disjunction

- Creates diploid and empty germ cells
- Hence when a diploid and a haploid germ cell combine, a trisomal zygote is created, diploid-diploid = tetrasomal, haploid-empty = monosomal.

25

The three chromosome aberrations that lead to Down syndrome

- Trisomy 21
- Robertsonian translocation
- Mosaicism

26

Clinical features of Down syndrome

Newborn period - sever hypotonia, sleepy, excess nuchal skin
Craniofacial - macroglossia, small ears, epicanthic folds, upward sloping palpebral fissures (gaps between upper and lower eyelids)
Limbs - single palmar crease (should be 3, they have 2) wide gap between first and second toes
Cardiac - atrial and ventricular septal defects
General - Short stature, duodenal atresia (abnormal closure/absence of lumen of duodenum)
Low IQ but advanced social skills

27

Dosage compensation definition

A genetic mechanism in which alleles of a gene automatically regulate the amount of useful product produced such that heterozygous individuals produce the same amount of product as homozygous dominant individuals.

28

Mechanisms of dosage compensation

- One of each X chromosome in female cells is inactivated. Selection of chromosome to be inactivated is random
- Increased (2x) expression of X chromosome genes in males
- Decreased (0.5x) expression of X chromosome genes in hermaphrodites

29

Mechanism of sex determination

The SRY gene causes development of testes. Can be translocated to X chromosome in SRY recombination.

30

Consequences of SRY recombination

SRY gene now on X chromosome
- XX males develop testes but are sterile as other genes on Y chromosome needed for spermatogenesis
- XY females have mutations in SRY gene that lead to sterile phenotypically female individuals