Genetic Abnormalities

Question 1

4 types of abnormalities

Answer 1

1. monogenic
2. polygenic
3. mitochrondral gene
4. chromosomal

Question 2

monogenic abnormalities (single gene)

Answer 2

• d/t defective or mutant allele at a single gene locus
• pattern of inheritance depends on whether phenotype dominant or recessive and whether gene located on an autosomal or sex Chr
• leads to formation of abn protein or dec protein production of a gene product

Question 3

formation of abn proteins/dec protein production of gene product results in:

Answer 3

• defective enzyme/dec amount of an enzyme
• defects in receptor proteins and their Fx
• alterations in non-enzyme proteins
• mutations resulting in unusual rxns to drugs

Question 4

3 types of monogenic abnormalities

Answer 4

1. autosomal dominant disorder
2. autosomal recessive disorder
3. X-linked disorders or “sex linked disorders”

Question 5

autosomal dominant disorder

Answer 5

• a single mutant allele from an affected parent is transmitted to an offspring regardless of sex
• affected parents has 50% chance of transmitting disorder to each offspring

Question 6

autosomal recessive disorder

Answer 6

• manifested only when both members of the gene pair are affected
• both parents could be unaffected but carriers of defective gene
• heterozygous carriers to not usually produce symptoms

Question 7

autosomal recessive disorder: if one parent fully affected than how many % of children are carriers?

Answer 7

100%

Question 8

autosomal recessive disorder: if both parents are carriers of the mutant gene how many are affected, carriers, and unaffected and non-carriers?

Answer 8

• 25% affected
• 50% carriers
• 25% unaffected and non-carriers

Question 9

X-linked disorders or “sex linked disorders”

Answer 9

• most sex Chr defects are on the X (fem) Chr
• males most often affected
• females = XX (if 1 Chr affected, there’s another normal X Chr to make up for it; carrier of mutation)
• males = XY (no other normal X Chr to make up for it –> mutation mnfts into disorder)

Question 10

X-linked disorders: an unaffected mother carries 1 normal and 1 mutant allele on the X Chr… what are the chances of transmitting defective gene to her sons?

Answer 10

• 50% chance

Question 11

X-linked disorders: an affected father procreates… does he transmit the defective gene to his daughters?

Answer 11

yes, he transmits the defective gene to all his daughters who become carriers of the mutant gene

Question 12

X-linked disorders: an affected father procreates… does he transmit the defective gene to his sons?

Answer 12

no, b/c Y Chr genes are unaffected –> male does not transmit defect to any of his sons (sons cannot be carriers)

Question 13

polygenic/complex abnormality

Answer 13

• caused by multiple genes (2 or more) and environ factors (ex. viral infect)
• expressed during fetal life and present @ birth; or may be expressed later in life (enviro factors)

Question 14

mitochrondrial gene disorders

Answer 14

dysfunctional mitochondria, the organelle that produces ATP

Question 15

mitochrondrial genes

Answer 15

• DNA not only in nucleus, but small amount also in mitochondria
• 37 mitochondrial genes
• involved in prod of ATP
• code for enzymes in electron transport chain in the mitochondria
• most mitochondrial defects mnft in neuromuscular defects

Question 16

chromosomal defects abnormality

Answer 16

• defect in # OR structure of Chrs
• can use karyotype test
• extra or missing Chr or abn positions of Chr pieces –> cause problems w person’s growth, development and body Fx

Question 17

numerical abnormality – aneuploidy (Chr)

Answer 17

problem r/t # of Chr (more or less than usual)

Question 18

numerical abnormality – monosomy (Chr)

Answer 18

1 Chr pair lacking a Chr (1 missing Chr)

- usually lethal, unless it occurs in sex Chr

Question 19

numerical abnormality – trisomy (Chr)

Answer 19

extra Chr in a pair

• named by Chr pair affected
• Ex. Down Syndrome = Trisomy 21

Question 20

Turner’s syndrome

Answer 20

• female has missing X Chr (monosomy)
• 1 in 2500 births
• instead of XX, gametes written as XO
• autosomal Chr vital to cellular Fx and sustaining life, but sex Chr are not necessary for survival
• — there fore, someone can live with Turner’s syndrome, but may have issues w reproduction

Question 21

Klinefelter’s syndrome

Answer 21

• male has extra X Chr (trisomy)

- XXY – pt has 47 Chr

Question 22

structural defects (Chr)

Answer 22

• under certain circumstances, a section of a Chr can break off

Question 23

structural defects – deletion (Chr)

Answer 23

lose a piece of a Chr (one in pair)

• detached segment does not reattach to the original Chr
• leads to loss of genetic material and shortening of the Chr

Question 24

structural defects – inversion (Chr)

Answer 24

piece of Chr inverts (top –> bottom)

• reverses its orientation and reattaches to the original Chr
• 2 breaks in a single Chr (pericentric = around the centromere; paracentric = away from the centromere)
• the entire Chr does not invert, but a portion of the Chr

Question 25

structural defects – translocation (Chr)

Answer 25

piece transferred over to other Chr

- segment breaks off and attaches to non-homologous Chr

Question 26

balanced translocation

Answer 26

2 nonhomologous Chrs exchange the same segment of DNA

Question 27

Robertsoninan Translocation

Answer 27

2 nonhomologous acrocentric (centromere close to one end) Chr break near their centromeres and then fuses to form one large metacentric (centromere in the middle) Chr

Question 28

isochromosomal translocation

Answer 28

faulty centromere division, leads to duplication of long arm and deletion of short arm, or the reverse (divide horizontally across centromere instead of vertically)