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Flashcards in Epigenetics and Imprinting Deck (46):
1

Epigenetics

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.

2

When is epigenetic repression very important?

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

3

What does DNA methylation involve?

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

4

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

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)

5

Deacteylation

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

6

what is a really common form of methylation>

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

7

ICF

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.

8

Rhett Syndrome

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.

9

Genetic Imprinting

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.

10

Beckwith-Widemann Syndrome (BWS)

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

11

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

Insulin like growth factor (IGF2) and IGF2 receptor

12

Incontienetia Pigmenti

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

13

Which population has a higher rate of hemochromatosis?

Celtics

14

Which population has a higher rate of sickle cell?

African

15

Which ethnic group has a higher rate of cystic fibrosis?

Northern Europe

16

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

Ashkenzi Jews

17

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

People who live in areas with endemic malaria

18

Triploidy

Contains three copies of each chromosome (69 total)

19

Tetraploidy

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

20

Monosomy

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

21

Trisomy 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.

22

Trisomy 18

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.

23

Trisomy 13

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

24

Turner Syndrome

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

25

What does mosaicism indicate?

Mitotic nondisjunction

26

Klinefelter Syndrome

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

27

When is nondisjunction the most common?

In meiosis I in female

28

Balanced Chromosoma; Abnormality

No gain or loss of genetic material

29

Unbalanced Chromosomal Abnormality

Gain or loss of genetic material

30

Reciprocal translocation

Exchange of genetic material between non-homologous chromosomes

31

Alternate segreation

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

32

Adjacent Segregation

Bad segregation which would lead to spontaneous abortion

33

Philadelphia Chromosome

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

34

Robertsonion Translocation

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

35

What does robertsonian translocation usually lead to?

Trisomy

36

Large micro deletion (>4 Mb) syndromes

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

37

Cri-du-chat

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

38

What tests are best for Cri-du-chat

Fish or CGH

39

What micro deletion disorder is most common in humans?

DiGeorge

40

Wolf-Hirschhorn Syndrome

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

41

WAGR Syndrome

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

42

Pericentric Inversion

Involve the centromere

43

Paracentric Inversion

Does not involve the centromere

44

Can you see inversions using karyotype analysis?

Yes, because they change the banding pattern

45

Isochromosomes

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

46

Ring Chromosomes

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.