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Flashcards in Lecture 24 Deck (38)
1

What is a euploid ploidy?

A euploid ploidy means having an exact multiple of the haploid number of chromosomes. Normal gametes have the haploid number of chromosomes for humans: N = 23. A normal somatic cell is Diploid 2N = 46

2

What is polyploid ploidy?

Polyploid cells and organisms are those containing more than two paired sets of chromosomes.
3N = triploid: Meiosis division failure
4N = tetraploid: 1st mitotic division failure

3

What is aneuploid ploidy?

Any non-euploid number of chromosomes, resulting from nondisjunction of a single pair of homologous chromosomes during meiosis (ex: Trisomy, monosomy)

4

What is trisomy ploidy?

The presence of an extra copy of a single chromosome in a zygote

5

What is monosomy ploidy?

The absence of a single chromosome in a zygote

6

When does meiotic aneuploidy occur?

During an error in meiosis 1 or meiosis 2

7

What is the result of meiotic 1 aneuploidy?

1) Two Disomic gametes (each have 2 sets chromosomes instead of 1)
2) Two Nullosomic gametes (each have 0 sets chromosomes instead of 1)

8

What is the result of meiotic 2 aneuploidy?

1) Two normal gametes (each have 1 set of chromosomes)
2) One disomic gamete (2 sets of chromosomes instead of 1)
3) One nullosomic gamete (0 set of chromosomes instead of 1)

9

What is the most common trisomy among live born children?

1) Trisomy 21 - Down Syndrome
2) Frequency of about 1/600 to 1/1000 live births are down syndrome

10

What is the most common trisomy among live born children?

1) Trisomy 21 - Down Syndrome
2) Frequency of about 1/600 to 1/1000 live births are down syndrome

11

Autosomal monosomy results in ______

1) Underexpression of the genes on that chromosome
2) All prenatal lethals

12

Autosomal trisomy results in _______

1) Overexpression of the genes on that chromosome
2) Perinatal lethal except trisomy 21

13

Why do sex chromosomal trisomies have very mild if any phenotypic effects?

X-chromosome inactivation

14

What is Turner syndrome caused by?

A female is missing one of her two X chromosomes

15

What are indications that one should go for prenatal diagnosis of aneuploidy?

1) History of spontaneous abortion
2) Advanced maternal age (>35 years)
3) Family history of mental retardation/developmental delay
4) Fetal anomalies on ultrasound

16

What are indications for prenatal diagnosis of an aneuploidy?

1) History of spontaneous abortion
2) Advanced maternal age (>35 years)
3) Family history of mental retardation/developmental delay
4) Fetal anomalies on ultrasound

17

How is a Karyotype made and what can it be used for?

1) Amniocytes cultured for 7-10 days
2) Mitotic chromosomes are arrested at metaphase
3) Staining with Giemsa dye results in distinctive banding patterns (G-banding)
4) Aneuploidy (trisomy, monosomy), translocations, large duplications/deletions can be observed under the microscope

18

What is Fluorescence In Situ Hybridization (FISH)?

FISH is a cytogenetic technique that is used to detect and localize the presence or absence of specific DNA sequences on chromosomes

19

How does Fluorescence In Situ Hybridization (FISH) work?

1) FISH uses DNA probes tagged with fluorescent nucleotides that bind to only those parts of the chromosome with which they show a high degree of sequence complementarity
2) Fluorescence microscopy can be used to find out where the fluorescent probe is bound to the chromosomes

20

What is Fluorescence In Situ Hybridization (FISH) most commonly used for?

1) FISH is often used for finding specific features in DNA for use in genetic counseling, medicine, and species identification
a) Can be used to look for specific microdeletion or contiguous gene syndroms like Prader-Willi, Angelman or DiGeorge
b) Can be used to look carefully near the ends of chromosomes (subtelomeres) for a child with learning difficulties, mental retardation or autism
2) FISH can also be used to detect and localize specific RNA targets (mRNA, lncRNA and miRNA) in cells, circulating tumor cells, and tissue samples
a) Can be used to target oncogenes and tumor suppressor genes to identify amplified oncogenes or deleted tumor suppressor genes in tumors

21

What are advantages of Fluorescence In Situ Hybridization (FISH) over a Karyotype?

1) Rapid diagnosis relative to routine karyotype: FISH can be performed on interphase cells, so it does not require growth and metaphase arrest in cell culture
2) Can identify small, submicroscopic changes on chromosomes invisible to karyotyping as well as aneuploidies and large duplications/deletions (Prader-Willi, Angelman or DiGeorge)

22

What are advantages of Fluorescence In Situ Hybridization (FISH) over a Karyotype?

1) Rapid diagnosis relative to routine karyotype: FISH can be performed on interphase cells, so it does not require growth and metaphase arrest in cell culture
2) Can identify small, submicroscopic changes on chromosomes invisible to karyotyping as well as aneuploidies and large duplications/deletions

23

When is it helpful to use FISH on metaphase chromosomes rather than interphase chromosomes?

When looking for a particular deletion on a particular chromosome that may be small (DiGeorge)

24

Why is FISH important in breast cancer diagnosis?

1) FISH can determine how many copies of Her 2-neu genes (oncogenes) are overexpressed in an individual
2) 1/3 of women with breast cancer overexpress Her 2-neu genes
3) Herceptin can be prescribed to particularly target Her 2-neu and reduce overexpression

25

What are SINES and LINES?

1) SINEs are short internuclear elements and LINEs are long internuclear elements
2) Both are repeat sequences that make up parts of introns

26

What are two types of intra-chromosomal rearrangements?

1) Deletions
2) Inversions

27

What are three types of inter-chromosomal rearrangements?

1) Deletions
2) Duplications
3) Translocations

28

How can one describe the two chromosomes produced from unequal crossing over in meiosis (interchromosomal recombination)?

1) Deletion of genes (the loss of genes are transferred to the other chromosome)
2) Duplication of genes (the gain of genes are from the other chromosome)

29

How can one describe the result of an intrachromosomal recombination of a chromosome?

1) Deletion with a lost deleted fragment
2) Paracentric inversion (if it occurs on an arm) or Pericentric inversion (if it occurs with the centromere)

30

What is an inversion?

1) Form by intra-chromosomal recombination between repetitive sequences (lines and sines)
2) Usually no abnormal phenotype in balanced carriers (unless breakpoints interrupts important genes)

31

What is an inversion?

1) Form by intra-chromosomal recombination between repetitive sequences (lines and sines)
2) Usually no abnormal phenotype in balanced carriers (unless breakpoints interrupts important genes)

32

What are two types of inversions?

1) Paracentric - within one arm
2) Pericentric - includes centromere

33

What is the result of meiotic recombination within a paracentric inversion?

1) 2 inviable gametes (0 or 2 centromeres with deletion/duplication)
2) 2 viable gametes (one normal and one inversion carrier)
(1/4 normal, 1/4 inversion carriers/ 1/4 acentric, & 1/4 dicentric)

34

What is the result of meiotic recombination within a pericentric inversion?

1) 2 gametes carrying complementary duplication/deletions (possibly viable)
2) 2 viable gametes, 1 normal and one inversion carrier
(1/4 normal, 1/4 inversion carrier, 1/4 each of two dup/del gametes)

35

What are two types of inter-chromosomal translocations (between non-homologous chromosomes)?

1) Reciprocal translocation
2) Robertsonian translocation

36

What is a Robertsonian translocation?

1) Rare form of chromosomal rearrangement that in humans occurs (non-lethally) in the five acrocentric chromosome pairs, namely 13, 14, 15, 21, and 22
2) During a Robertsonian translocation, the participating chromosomes break at their centromeres and the long arms fuse to form a single chromosome with a single centromere
3) The short arms also join to form a reciprocal product, which typically contains nonessential genes and is usually lost within a few cell divisions

37

What are the results from a Robertsonian translocation once meiosis has finished and gametes are formed?

1) 1/3 Meiosis - normal and balanced translocation carrier gametes - normal phenotype kids
2) 2/3 meiosis - unbalanced defective or inviable gametes - spontaneous abortion or birth defects

38

What is recommended for women who have multiple unexplained miscarriages?

Recommended to have karyotype or FISH analysis to identify balanced translocation/inversion carriers