Epigenetics and Imprinting

Question 1

Epigenetics

Answer 1

A change in the expression of a gene that changes the phenotype without permanently changing the gene itself, but changes the chromatin structure. heritable change.

Question 2

When is epigenetic repression very important?

Answer 2

In cell differentiation during embryonic development because it restricts access to certain genes

Question 3

What does DNA methylation involve?

Answer 3

The addition of a methyl to the 5’ position of a cytosine by DNA methyl transferase

Question 4

What are the steps involved in methylation inheritance and transcriptional repression?

Answer 4

1) Dnmt3 methylates unmethylated DNA
2) MeCP2 recruits either HDAC1 or Dnmt1
3) HDAC1 deacteylates histones
4) DNmt1 methylates hemimethylated DNA (1 strand is methylated, 1 isn’t)

Question 5

Deacteylation

Answer 5

Removing of the negatively charges methyl group, which makes chromosomes more active

Question 6

what is a really common form of methylation>

Answer 6

DNA methylation of globin genes in embryonic human blood stem cells which activates/inactivates different forms of the globin genes

Question 7

ICF

Answer 7

Mutation in the Dnmt3b gene which is required for the initial methylation of unmethylated DNA. Symptoms include facial dysmorphisms, mental retardation, infection, immune deficiency. Rare autosomal recessive. Centromere instability of chromosomes 1,9, and 16.

Question 8

Rhett Syndrome

Answer 8

X linked skewed inaction that is only found in girls. Loss of speech and acquired hand skills. Seizures, hand wringing, irregular breathing, and motor control problems. Caused by a mutation in the MeCP2.

Question 9

Genetic Imprinting

Answer 9

Gamete of origin dependent modification of phenotype. origin of allele determines if that allele will be expressed. Can appear with recessive or dominant inheritance patterns. Occurs during gametogenesis.

Question 10

Beckwith-Widemann Syndrome (BWS)

Answer 10

Enlarged tonight, higher birth weight, umbilical hernia, easy creates or pits, increased risk of cancer. Causes: maternal chromosomal rearrangements of 11p15, paternal disomy, and abnormal methylation at 11p15. Higher incidence in IVF babies

Question 11

What genes have been shown to have abnormal methylation and lead to cancer?

Answer 11

Insulin like growth factor (IGF2) and IGF2 receptor

Question 12

Incontienetia Pigmenti

Answer 12

Caused by a mutation of the X-linked IKBKG gene, which is lethal in males and has skewed X-inactivation in females

Question 13

Which population has a higher rate of hemochromatosis?

Answer 13

Celtics

Question 14

Which population has a higher rate of sickle cell?

Answer 14

African

Question 15

Which ethnic group has a higher rate of cystic fibrosis?

Answer 15

Northern Europe

Question 16

Which group has a higher rate of Tay-Sachs disease?

Answer 16

Ashkenzi Jews

Question 17

Which populations have a higher relate of a-and-b thalassemia

Answer 17

People who live in areas with endemic malaria

Question 18

Triploidy

Answer 18

Contains three copies of each chromosome (69 total)

Question 19

Tetraploidy

Answer 19

Contain four copies of each chromosome. Lethal. 92 total chromosomes

Question 20

Monosomy

Answer 20

Loss of a chromosome. Not compatible with life except for in the sex chromosomes

Question 21

Trisomy 21

Answer 21

Most common. Down Syndrome. Most common caused is nondisjunction in meiosis I. Congenital heart defects, intellectual all disability, one crease in hand, short, early onset of Alzheimer’s.

Question 22

Trisomy 18

Answer 22

Edward syndrome. Caused by nondisjunction during oogenesis. Features include clenched fist with overlapping fingers, rocker bottom feet, congenital heart defects, and intellectual disability. early death around 2 years old.

Question 23

Trisomy 13

Answer 23

Patau syndrome. Least compatible to life. Nondisjunction during oogenesis. Polydactyl, cleft life and palate, small eyes, microcephaly, intellectual disability, and cardiac anomalies.

Question 24

Turner Syndrome

Answer 24

45, X. Nondisjunction during meiosis. X chromosome Monosomy. Short, webbed neck, no puberty, no secondary sex characteristics, streak ovaries. Female phenotype.

Question 25

What does mosaicism indicate?

Answer 25

Mitotic nondisjunction

Question 26

Klinefelter Syndrome

Answer 26

XXY. Nondisjunction during meiosis. Symptoms include testicular atrophy, gynecomastia (enlargement of male breasts), female distribution of hair, and infertility.

Question 27

When is nondisjunction the most common?

Answer 27

In meiosis I in female

Question 28

Balanced Chromosoma; Abnormality

Answer 28

No gain or loss of genetic material

Question 29

Unbalanced Chromosomal Abnormality

Answer 29

Gain or loss of genetic material

Question 30

Reciprocal translocation

Answer 30

Exchange of genetic material between non-homologous chromosomes

Question 31

Alternate segreation

Answer 31

Typical Mendelian segreation where you get a normal gamete and a translocation carrier. Good segreation.

Question 32

Adjacent Segregation

Answer 32

Bad segregation which would lead to spontaneous abortion

Question 33

Philadelphia Chromosome

Answer 33

Translocation 9;22 which results in the activation of ABL protooncogenes which leads to chronic myeloid leukemia

Question 34

Robertsonion Translocation

Answer 34

translocation between chromosomes 13, 14, 15, 21, or 22 leading one chromosome to disappear resulting in a derived chromosome from the translocation between acrocentric chromosomes. The short arm is lost

Question 35

What does robertsonian translocation usually lead to?

Answer 35

Trisomy

Question 36

Large micro deletion (>4 Mb) syndromes

Answer 36

Wolf-Hirschhorn (4 p) and cri du chat (5 p)

Question 37

Cri-du-chat

Answer 37

Chromosome 5p loses some genetic material. Features include high-pitched, cat like cry, severe intellectual disability, speed problems, and microcephaly

Question 38

What tests are best for Cri-du-chat

Answer 38

Fish or CGH

Question 39

What micro deletion disorder is most common in humans?

Answer 39

DiGeorge

Question 40

Wolf-Hirschhorn Syndrome

Answer 40

Deletion of 4p. Facial anomalies with widely spaced eyes, prominent nose, and abnormal iris. Cardiac issues, intellectual and developmental delay.

Question 41

WAGR Syndrome

Answer 41

Small micro deletions in 11p13. Wilms tumor, aniridia, genitourinary malformations, and growth and development issues

Question 42

Pericentric Inversion

Answer 42

Involve the centromere

Question 43

Paracentric Inversion

Answer 43

Does not involve the centromere

Question 44

Can you see inversions using karyotype analysis?

Answer 44

Yes, because they change the banding pattern

Question 45

Isochromosomes

Answer 45

Loss of one arm of a chromosome and duplication of the other arm. Results in chromosomal and gene dosage imbalance.

Question 46

Ring Chromosomes

Answer 46

Forms when a chromosome loses genetic material at the terminal portion and the end fuse to form a ring like structure. Seen typically in radiations workers.