structural numerical auto six chromosome

Question 1

• The ………… is the external appearance of an individual as
determined by his genotype.

Answer 1

phenotype

Question 2

Chromosomal Abnormalities

Answer 2

Numerical:
- Polyploidy: Multiple of the haploid (> Diploid).
- Aneuploidy: Abnormal number. * or -
Structural: as Translocation, Deletion & Others

Question 3

• …….. is the study of chromosomes and their role inheredity

Answer 3

Cytogenetics

Question 4

• For chromosomes-karyotyping, mitosis is arrested in the dividing cells in …………by the use of ………….

Answer 4

metaphase

mitotic spindle inhibitors.

Question 5

How can arranged the chromosomes in karyotyping

Answer 5

“Chromosomes are arranged in groups named A through G. depends on chromosome length.
- A -> the longest
G-> the shortest
• Groups within these letters depend on the p/qatio.

Question 6

Numerical Aberration’*

Answer 6

Autosomal:
- Trisomies: 1 chromosome extra, as trisomies 21-13-18.
- Monosomies: 1 chromosome missing.
Sex chromosomal:
extra x Chromosome
- Klinetelter syndrome (47, XXY male)
- Turner syndrome (45, XO female) X missing

Question 7

Structural Abnormalities:

Answer 7

1. Deletion: loss of a portion of a chromosome.
2. Duplication: extra piece of a chromosome. ••”
3. Inversion: fragmentation of a chromosome followed by reconstitution with a section inverted.
4. Ring chromosome.
5. Isochromosomes: division of a chromosome at centromere transversely instead of longitudinally.
   6-Translocation: the transfer of a chromosome or a segment of it to a non-homologous chromosome.

Question 8

’ An exchange of material between 2 different chromosomes is called a

Answer 8

reciprocal translocation.

Question 9

Metacentric chromosomes:

Answer 9

The centromere is present in the middle of the chromosome and p & q arms are almost equal
• The shape of metacentric chromosome is & x shape or V shape (as’ 1, 3rd, 16th, 19th & 20th are metacentric chromosomes in humans).

Question 10

• Acrocentric chromosome:

Answer 10

The centromere is not central & is instead located near the end of the chromosome.
• Humans usually have five pairs of acrocentric autosomes (chromosomes 13, 14, 15, 21, 22) and the chromosome.
• The acrocentric chromosome appears to be J-shaped.

Question 11

They are most often formed by breakage of
two acrocentri chromosomes (numbers 13,
14, 15, 21, 22) at or close to their centromeres, with subsequent fusion of their
Long arms to form one chromosome,
The short arms of each chromosome are
Lost

Answer 11

Robertsonian
Translocations:

Question 12

When to suspect chromosomal
abnormalities?

Answer 12

Abnormal features
* coarse facies
* Mongoloid eye
* Low set ears
* Micrognathia/cleft lip & palate
* Simian crease * Clinodactyly )→
Mental retardation Do chromosomal analysis
Ambiguous genitalia Do chromosomal analysis
)Delayed puberty:
Klinefelter syndrome and Turner syndrome

Question 13

Genetic types (Cytogenetics) of Down
Syndrome:

Answer 13

(1) Non-disjunction
# The most common form of DS which is due to nondisjunction during the synthesis of the gametes
meiosis
@ The total number of chromosomes in cells is 47
©* Incidence is higher with increasing maternal age
is age-dependent
Heredity is not a factor in trisomy 21nondisjunction

(2) Robertsonian Translocation: 4% of cases (Less Common from of DS).
@ The extra 21 chromosome is translocated to another chromosome e.g. (14/21) so total No. of chromosomes is 46but the genetic material is
that of 47 chromosomes .
Incidence is usually in young mothers The mother is called translocation carrier.
@There is a Hereditar component

(3) Mosaicism: 1 % of cases
After fertilization of the ovum and during the cell divisions of the zygote during early embryogenesis, an error occurs. Non disjunction of some cells during mitotic division results in 21 trisomy in some cells and 21 monosomy in others (21 monosomy not
allowed to divide and die).
• All trisomy 21 descendant cells will be trisomies 21 (47 chromosomes).
• Like trisomy 21, mosaic Down syndrome is
Not inherited

Question 14

Abnormal amounts of the trinucleotide repeat
sequences causing

Answer 14

fragile
syndrome, (CGG >200
copies in the FM.R-1 gene on X-chromosome ).

Question 15

Fragile X Syndrome
Clinical findings

Answer 15

Clinical findings in males in fragile X syndrome
• Moderate-severe learning difficulty (IQ 20-80, mean 50) yee pedis
• Macrocephaly
• Macro-orchidism - postpubertal
• Characteristic facies - long face, large everted ears,
prominent mandible and broad forehead, most evident in
affected adults.
• Other features - mitral valve prolapse, joint laxity,
scoliosis, autism, hyperactivity
•Fragile X syndrome is the second most common
genetic cause of severe learning difficulties after
Down’s syndrome.

Question 16

Turner Sundrome
Features:

Answer 16

• Lymphedema of hands and feet in newborn
• Short stature
• Webbing of neck
• Wide carrying angle
• Gonadal dysgenesis (1 ry amenorrhea)
• Renal anomalies and cardiac anomalies