Genetics - Cell Division, Karyotype

Front 1

What are the 4 basic cell cycle stages?

Back 1

G1, S, G2, M

Front 2

What happens during G2?

Back 2

DNA is already replicated. Chromosome compaction continues. Microtubule components necessary for spindle apparatus are synthesized and assembled; centrioles are visible, <b> DNA repair </b>

Front 3

What happens during S?

Back 3

DNA replication. At completion, each chromosome consists of two chromatids attached at centromere.

Front 4

Karyokinesis

Back 4

Movement and division of chromosomal material to two daughter cells

Front 5

Cytokinesis: what happens?

Back 5

Division of cytoplasmic material to daughter cells

Indpt of karyokinesis, but in most cells occurs after karyokinesis.

Bundle of actin filements form a contractile ring that pinches cells apart.

Front 6

Phases of mitosis

Back 6

Prophase, Metaphase, Anaphase, Telophase

Front 7

What happens during prophase?

Back 7

1)Nuclear Envelope breaks down
2) Chromosomes observed and consist of two sister chromatids attached at centromere
3) Additional spindle fibers extend between poles of cell

Front 8

What happens during metaphase?

Back 8

1) Chromosomes line up at metaphase plate (midway between cellular poles, attached to spindle)

2) Chromosomes are oriented so that sister kinetochores (attachments for microtubules) face opposite poles

Front 9

What happens during anaphase?

Back 9

1) Sister kinetochores separate and sister chromatids move toward opposite poles due to the shortening of mitotic spindles

2) Cell elongates in direction of poles.

Front 10

What happens during telophase?

Back 10

1) Kinetochore microtubules disappear

2) New nuclear envelope reforming around each set of daughter chromosomes (karyokinesis complete)

3) Chromosomes begin to elongate/decondense

Front 11

Where does chromosomal condensing begin and end?

Back 11

Begins as it enters prophase, ends as it returns to interphase

Front 12

Meiosis: defn

Back 12

Requires single DNA synthesis followed by two divisions/chromosomal segregation rounds.

Front 13

At the end of meiosis I, how many chromosomes and chromatids?

Back 13

Starts with 46 replicated chromosomes (4n), with 92 chromatids

Ends with 23 replicated chromosomes (2n) and 46 chromatids

Front 14

At the end of meiosis II, how many chromosomes and chromatids?

Back 14

Starts with 23 replicated chromosomes (2n) and 46 chromatids

Ends with 23 chromosomes/23 chromatids (they are the same at this point)

Front 15

Prophase I

Back 15

90% of meiotic process, 5 stages

Recombination takes place here

There are sex differences

Front 16

Metaphase I

Back 16

Homologous chromosome pairs align along equator following breakdown of nuclear membrane

Centromeres differentiate into kinetochores and orient themselves towards pole

Homologous centromeres separate (reduction division)

Each chromosome made of two chromatids

Front 17

Anaphase I

Back 17

Period of active chromosome movement, areas where chromatids had undergone genetic recombination (crossovers, or chiasmata) are no longer visible

Front 18

Telophase I

Back 18

Homologous centromeres reach poles.

Nuclear envelope may/may not reform, chromosome morphology only partially decondenses

Front 19

Interphase and Prophase II

Back 19

Transient stages consisting of absence of DNA synthesis and breakdown of nuclear membrane if present, and assemblage of microtubular apparatus

Front 20

Metaphase II

Back 20

Beginning to look more like mitotic division

Chromosomes align on metaphase plate

Sister kinetochores face opposite poles of cell

Front 21

Anaphase II

Back 21

Sister chromatids move to opposite poles

Front 22

Telophase II

Back 22

nuclear envelope reforms and chromosomes decondense, another cytokinesis.

Diploid number of chromosomes has been reduced to half (n=23)

Daughter cells contain haploid number chromosomes

Will be either 4 male or 1 female functional gamete.

Front 23

After meiosis, how similar are daughter cells?

Back 23

Dramatically different due to recombination and ploidy reduction.

Front 24

Meiotic recombination: what happens and purpose?

Back 24

During prophase I of meiosis, leads to formation of new combinations of alleles on same chromosome, areas that are close to each other on the same chromosome are less likely to be shuffled

Front 25

Oogenesis

Back 25

female

largely confined to prenatal development (all eggs exist before female is born and are arrested in <b> prophase I </b>)

Cytokinesis is uneven

Completion of Meiosis II occurs at fertilization

Front 26

For females, what stage of meiosis are eggs arrested at?

Back 26

Prophase I

Front 27

Spermatogenesis

Back 27

Male

Ongoing throughout adult life

Cytokinesis is even --> 4 daughter cells

Front 28

Karyotype

Back 28

The use of nomenclature to describe

Front 29

What are some tissues that would be suitable for chromosomal studies in humans?

Back 29

Peripheral blood <b> lymphocytes </b> bc need nucleus

bone marrow

Chorionic villus biopsy

Amniotic fluid cells

Fetal blood cells via percutaneous blood sampling

Skin or organ biopsy

Front 30

Mitogen

Back 30

Chemical substance encouraging cell to enter division

Front 31

How to obtain chromosomes from healthy dividing cells?

Back 31

1) Add mitogen
2) Hypotonic swelling - turn cell into water balloons to make visual easier
3) Fixation
4) Analysis

Front 32

karyogram

Back 32

Chromosomes from a cell placed in standard sequence. Usually length (1 is the longest chromosome, etc)

Front 33

Karyotypically normal male

Back 33

46,XY

Front 34

Karyotypically normal female

Back 34

46,XX

Front 35

Primary morphological characteristics for individual chromosome

Back 35

Centromere: kinetochores attach, mitotic spindle pulls apart

Short arm (p)

Long arm (q)

Front 36

Letters for Short and Long arm

Back 36

P and Q

respectively

Front 37

Metacentric

Back 37

Chromosome where centromere is in middle

Front 38

Acrocentric

Back 38

Chromosome where centromere is toward an end

Front 39

Submetacentric

Back 39

Chromosome where centromere is closer to one side than another (displaced from center)

Front 40

G-Banding as a way of analyzing chromosomes

Back 40

Stain chromosomes during metaphase and view with fluorescence microscopy. Each has unique and reproducible series of alternating bright and dull bands

Steps.
1) Pretreat: Either with heat or some sort of protease (e.g., trypsin)

2) Stain with something that has high affinity for DNA

Front 41

Ideogram

Back 41

Diagrammatic representation of the karyotype based on the G-band pattern

Arranged and numbered according to International System for Human Cytogenetic Nomenclature

Front 42

International System for Human Cytogenetic Nomenclature

Back 42

Standardized way of naming chromosomes

Front 43

G-banding

Back 43

Most widely used procedure for routine examination

Any special studies will be based on what the cytogeneticist observes in these initial G-banded karyotypes

Involves pretreatment (with heat or protease) and staining

Front 44

High Resolution (HR) banding

Back 44

Alters the chromosome condensation cycle to get very long and extended chromosomes with many bands, allowing for a very detailed analysis

Front 45

Fluorescence In Situ Hybridization (FISH)

Back 45

Process by which the chromosomal location of a specific piece of DNA are identified

Involves denaturing the DNA, then attaching probes (pieces of DNA with added fluorescence), and allowing it to anneal back together. Examine with fluorescence microscope.

Front 46

Why would you use FISH?

Back 46

-Prenatal testing to provide a rapid screen for numerical abnormalities, with results available much faster than conventional chromosomal analysis (24 hrs vs. 1 week)

Front 47

DNA microarrays/Comparative genomic hybridization

Back 47

method for the analysis of copy number changes (gains/losses) in the DNA content of a given subject's DNA and often in tumor cells.

CGH will detect only unbalanced chromosomal changes. Structural chromosome aberrations such as balanced reciprocal translocations or inversions cannot be detected, as they do not change the copy number.

A bridge between high resolution but specific FISH and low resolution but broad karyotype analysis.

Front 48

Weakness of DNA microarrays/Comparative genomic hybridization

Back 48

Does not identify balanced rearrangements/ploidy changes; normal copy variants not always of clinical relevance (need family studies)

Front 49

Reasons for referring a patient or tissue sample for karyotype analysis

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1) Prenatal diagnosis in high risk pregnancies
2) Pregnancy failure
3) Postnatal diagnosis, ex., newborns with congenital malformations, adolescents with delayed growth and/or sexual development etc

Front 50

Three ways prenatal karyotyping can be done

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1) Chorionic villus sampling: 1st trimester,taking small sample of chorion via aspiration biopsy (7-14 days for results)

2) Amniocentesis: small sample of amniotic fluid obtained which contains viable fetal cells. 2nd trimester.

3) Percutaneous umbilical cord blood sampling: higher risk, called cordocentesis. Grow fetal blood cells in vitro for 2nd - 3rd trimester.