Chromosome Disorders

Question 1

Codominance.

Answer 1

both alleles contribute to phenotype of heterozygote

Question 2

Polymorphism.

Answer 2

existence of multiple alleles for a particular gene

Question 3

Meiosis vs. Mitosis

Answer 3

Meiosis: 1) homologous chromosomes split 2n to 1n 2) chromatids split Mitosis: chromatids split, 2n to 2n

Question 4

What are the types of numerical chromosomal abnormalities?

Answer 4

aneuploidy & polyploidy

Question 5

Aneuploidy

Answer 5

loss or gain of one or more chromosomes

Question 6

Polyploidy

Answer 6

presence of more than 2 complete sets of chromosomes

Question 7

Euploid.

Answer 7

exact multiple of the haploid number of chromosomes (i.e. 2n, 3n, 4n)

Question 8

Mosaicism.

Answer 8

presence of genetically distinct cell lines in the same individual. due to mitotic error after fertilization

Question 9

Partial monosomy.

Answer 9

only a portion of the chromosome has one copy

Question 10

Monosomy.

Answer 10

a chromosome has only one copy

Question 11

Trisomy.

Answer 11

a chromosome has three copies

Question 12

Describe the normal human karyotype.

Answer 12

46, XX or 46, XY 23 homologous chromosome pairs: 22 autosomal, 1 sex

Question 13

Down Syndrome (Trisomy 21)

Answer 13

47, XX, +21 or 47, XY, +21

• growth & mental retardation
• risk of trisomy 21 increases w/ maternal age (meiosis non-disjunction)
• can also be an inhereted condition where parent has unbalanced translocation in chromosomes 14 and 21 (Robertsonian translocation), and her gamete ends up with one chromosome 21 and one hybrid 14q21q —> when paired with normal gamete, zygote has one chromosome 14, two chromosome 21, and one hybrid 14q21q (i.e. three chromosome 21)

Question 14

Turner Syndrome (X monosomy)

Answer 14

45, X female, intrauterine oedema, short stature, infertility

Question 15

Klinefelter Syndrome

Answer 15

47, XXY male, tall stature, infertility

Question 16

Triple X (X trisomy)

Answer 16

47, XXX female, no physical abnormalities, mild learning difficulties

Question 17

XYY

Answer 17

47, XYY male, tall stature, normal fertility, mild learning and behavior difficulties

Question 18

What are the types of structural chromosomal abnormalities?

Answer 18

balanced & unbalanced chromosome rearrangements- arise through breakage and incorrect rejoining of chromosomes

Question 19

Translocation

Answer 19

exchange of chromosome segments between non-homologous chromosomes; reciprocal or Robertsonian (two acrocentric chromosomes fuse at centromere)

https://www.uic.edu/classes/bms/bms655/lesson9.html

Question 20

Insertion

Answer 20

segment of one chromosome inserted into a non-homologous chromosome

Question 21

Duplication

Answer 21

extra copy of part of a chromosome, leading to partial trisomy

Question 22

Inversion

Answer 22

breakage and rejoining of a chromosome segment in reverse order, pericentric if the centromere is included, paracentric if not

Question 23

Ring Chromosome

Answer 23

deletion of telomeres and fusion of broken ends to form a ring; unstable during mitosis and frequently lost

Question 24

Isochromosome

Answer 24

chromosome with one arm duplicated and the other arm lost; occurs when centromere divides abnormally and can involve either short (ISO p) or long (ISO q) arms

Question 25

Microdeletion

Answer 25

unequal crossing over between two homologous chromosomes occurs, leaving one chromosome with a duplication and the other with a deletion

Question 26

Williams Syndrome

Answer 26

• congential microdeletion of long arm of chromosome 7
• distinct elfin facial appearance, cardiovascular abnormalities mental retardation, distinctive cognitive profile

Question 27

Medical consequences of structural chromosomal abnormalities?

Answer 27

• balanced
  
  • none/ minimal effect
• unbalanced
  
  • gene disruption
  • partial trisomy and/or monosomy
  • mitotic and meiotic instability