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Cell and Molecular Bio > Cell and Molecular Bio- Meiosis and Mitosis (11) > Flashcards

Cell and Molecular Bio- Meiosis and Mitosis (11) Flashcards

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1
Q

Recap question: Explain cell theory:

A

Modern cell theory
All known living things are made up of cells
-The cells is the structural and functional unit of all living things
-All cells come from pre-existing cells by division

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2
Q

The cell cycle and cell division, All cells come from existing cells.

What are the 2 important processes?

A
  1. Growth
    - cell duplicates its contents (including DNA and organelles)
  2. Cell division
    - parent cell contents divide into two daughter cells
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3
Q

What is The cell cycle?

A

The process of cell growth and division

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4
Q

Why and how do cells divide?

A

The life cycle of an organism is linked to cell division

Unicellular organisms use cell division primarily for reproduction

Multicellular organisms, cell division is important in growth and repair of tissues

  1. Reproduction
  2. Growth
  3. Repair of tissues
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5
Q

What are the 4 events that must occur for cell division?

A
  1. Reproductive signal: to initiate cell division
  2. Replication: DNA to be duplicated
  3. Segregation: Distribution of the DNA into the 2 new cells
  4. Cytokinesis: Separation of the 2 new cells
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6
Q

Reproductive signal examples:

A
  1. Growth factors- external chemical signals that stimulate these cells to divide
  2. Platelet-derived growth factor that initiate blood clotting, stimulates skin cells to divide and heal wounds
    - some white blood cells produce interleukins that promote cell division in other white cells (important for defense against pathogens)
  3. Erythropoietin produced in the kidneys stimulates division of bone marrow cells and production of red blood cells
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7
Q

Why and How do prokaryotes undergo asexual reproduction?

A

Binary fission results in 2 new cells

Reproductive signals include external factors such as nutrient concentration and environmental conditions that initial cell division

  • For many bacteria, abundant food supplies speed up the division of the cycle
  • Most prokaryotes have 1 chromosome and usually circular
  • Replication begins at the ori site and moves towards the ter site (where replication ends)
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8
Q

Why and How do Eukaryotes divide?

A

Asexual and Sexual reproduction

Cell division is significant in growth and repair of tissues

Signals for cell division are related to the needs

Have many chromosomes, the processes of replication and the segregation are more intricate

DNA replication usually occurs between cell divisions

Sister Chromatids-newly replicated chromosomes are closely associated

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9
Q

How do Eukaryotic cells divide?

Explain Meiosis and Mitosis

A

Meiosis is nuclear division in cells involved in sexual reproduction
-resulting cells are not identical to the parent cells

Mitosis separates them into 2 new nuclei, identical to the parent cell

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10
Q

Role of cell division in a Asexual Life Cycle:

What is asexual reproduction?

A

Asexual reproduction is based on mitotic division of the nucleus

  • A unicellular organism may reproduce itself
  • Cells of multicellular organisms break off to form a new individual
  • The offspring are clones- genetically identical to the parent
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11
Q

Role of cell division in a Sexual Life Cycle:

What is sexual reproduction?

A

Sexual reproduction: the offspring are not identical to the parents

It requires gametes created by meiosis, two parents each contribute one gamete to an offspring

Gametes and offspring differ genetically from each other and from the parents

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12
Q

What role of cell division play in a Sexual Life Cycle?

A

Sexual reproduction generates diversity among individual organisms

It allows the random selection of half the diploid chromosome set-this forms a haploid gamete that fuses with another to make a diploid cell
-thus no 2 individuals have the same genetic make up

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13
Q

What are the differences between sexual reproduction and asexual reproduction?

A

Sexual- involves sex cells and fertilization

Asexual- Does not involve sex cells and fertilization
-Only 1 parent plant

Advantages/Disadvantages of Sexual

  • Offspring are not genetically identical to one another
  • There is variation in the offspring

Advantages/Disadvantages of Asexual

  • Offspring have no variation
  • Offspring are genetically identical to one another
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14
Q

Define the term Ploidy:

A

the number of sets of chromosomes in a cell

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15
Q

Define the term diploid and haploid:

A

Diploid (2n)-cells with 2 sets of chromosomes. Human cells have 23 pairs of chromosomes

Haploid(n)- cells with one set of chromosomes. Gametes have 1 set of chromosomes or total of 23 chromosomes

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16
Q

What are Somatic cells?

A

Body cells that are not specialized for reproduction

All cells other than sexual gametes cells

Each somatic cell contains homologous pairs (diploid 2n) of chromosomes with corresponding genes

Undergo Mitosis

Daughter cells are genetically the same

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17
Q

Characteristics of Gamete cells

A

contain only 1 set of chromosomes (haploid) (23 chromosomes not pairs)

Used in Fertilization: 2 haploid gametes (female egg and male sperm) fuse to form a diploid zygote (2n)

Diplontic life cycle

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18
Q

Diplontic life cycle:

A

Human, mammals and some plants: gametes are the only haploid stage

Mature organism is diploid and produces gametes by meiosis

Gametes fuse to form diploid zygote

Zygote divides by mitosis to form mature organism

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19
Q

Haplontic Life cycle:

A

In protist, fungi and some algae-only zygote is diploid

After zygote forms it undergoes meiosis to form haploid spores, which germinate to form a new organism

Organism is haploid, produces gametes by mitosis- cells fuse to form zygote

(spend most of their time as haploids)

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20
Q

What are the phases of the Cell cycle?

A
  1. Interphase
    - non dividing stage
  2. Mitosis
    - nuclear division
  3. Cytokinesis
    - cytoplasm division
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21
Q

What occurs during the Interphase:

A
  1. DNA has replicated, but has not formed the condensed structure of chromosome. They remain as loosely coiled chromatin
  2. The nuclear membrane is still intact to protect the DNA molecules from undergoing mutation
  3. 3 stages
  4. G1-Gap 1/ Growth
  5. S- Synthesis of DNA
  6. G2-Gap 2/ Growth
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22
Q

What occurs during the Interphase-G1?

What is the purpose of this stage?

A

G1 phase- Stage before DNA replication

  • Decision to divide (move to S phase)(if there are any signals if not they don’t) or not to divide (move to G0 phase)
  • Doubling of organelles
  • Accumulation of materials for DNA synthesis
  • some cells, such as nerve, typically do not complete the cell cycle and are permanently arrested in G1.
  • they won’t ever continue to the S and G2 phases, they are instead said to be in a G0 stage

-Embryonic cells spend very little time in G1 and complete the cell cycle in a few hours (they undergo cell division for fetus formation)

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23
Q

What occurs during the Interphase-S phase?

What is its function?

A

S phase-DNA replication/synthesis

  • Semi-conservative replication
  • results in each chromosome being composed of two sister chromatids
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24
Q

What occurs during the Interphase-G2?

A

G2 phase- stage after DNA replication

  • synthesis of proteins needed for cell division
  • this is the preparation stage for meiosis
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25
Q

Chromatids and Chromosomes:

A

A chromatid is a very specific term for a newly-replicated chromosome that is still attached to it’s sibling chromosome

One chromosome replicates into 2 “sister chromatids”

Once replication and cell division is over, the chromatid reverts to being a plain old chromosome

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26
Q

Define the term Centrosome:

A

the microtubule organizing center of the cell. It replicates in S phase

centrosomes is composed of 2 centrioles surrounded by pericentriolar material

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27
Q

Function of centrosomes:

A

Key to the division of cells
-Before cell division, the centrosome duplicates and then, as division begins, the two centrosomes move to opposite ends of the cell.

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28
Q

What is Aster?

A

microtubules radiating from a centrosome

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29
Q

What are centrioles?

A

Cannot be seen when the cell is not dividing

The centrioles also help in the formation of the spindle fibers that separate the chromosomes during cell division…

-Plant cells do not have centrioles. The plant cells have the ability to reproduce even without the centrioles

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30
Q

What is the centromere and kinetochore?

A

The sister chromatids are held together at a region called centromere

The kinetochore is the protein complex assembled at centromere

specifies the attachments between the chromosomes and microtubules of the spindle and is thus essential for accurate chromosome segregation.

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31
Q

What are spindle fibres?

A

Long microtubules extend from the centrioles in all possible directions, forming what is called a spindle

Some of the spindle fibers attach to the chromosomes by connecting to kinetochores

32
Q

Summary:

Phases of the Cell cycle and their checkpoints

A

G1 checkpoint
Cell cycle main checkpoint. If DNA is damaged, apoptosis (death of cells) will occur.

Otherwise, the cell is committed to divide when growth signals are present and nutrients are available

G2 checkpoint
Mitosis checkpoint, Mitosis will occur if DNA has replicated properly
Apoptosis will occur if the DNA is damaged and cannot be repaired

M checkpoint
Spindle assembly checkpoint. Mitosis will not continue if chromosomes are not properly aligned

33
Q

Shorter summary of Checkpoint in Eukaryotic cells- progression can be arrested to prevent uncontrolled cell division

A

G1/S Boundary: G1

  • lack of growth factors
  • DNA damage

G2/M boundary: G2

  • DNA damage
  • Un replicated DNA

Metaphase/Anaphase boundary
-spindle checkpoint-kinetochore attachment

34
Q

What are the 2 ways cell death can occur?

A
  1. Necrosis (accidental death of cells)
    Necrosis is not always related to an underlying condition. It may be caused by:
Injury (physical damage to tissues)
Extremely high or low temperature
Radiation
Chemicals
-cells start to swell 
-may lead to inflammation
  1. Apoptosis-programmed cell death
    not due to accidental death of cells
    natural for cells to die and generate new cells such as in the skin

-cells don’t swell like necrosis but shrink -no inflammatory response

35
Q

Cell death cycle is controlled by signals such as….

A
  1. Lack of a mitotic signal (growth factor)
  2. Recognition of damaged DNA
  3. External signals cause membrane proteins to change shape and activate enzymes called caspases- hydrolyze proteins of membranes
36
Q

How does unregulated cell division lead to cancer?

A

Cancer cells differ from original cells in several ways:

  • cancer cells lose control over cell division
  • cell evade programmed cell death
  • they can migrate to other parts of the body (metastasis)
37
Q

G1 checkpoint:

A
  • determines whether all conditions are favorable for cell division to proceed to progress to the S phase (DNA synthesis)
  • also called restriction point, point at which the cell irreversibly commits to the cell division process
  • External influences such as growth factors, play a large role in carrying the cell past the G1 checkpoint
  • check for DNA damage, check integrity of DNA
  • If cell cycle stops at this point if DNA is damaged and sent to to cell G0 to be repaired

-If DNA cannot be repaired it may undergo apoptosis (programmed cell death)

38
Q

G2 checkpoint:

A

The cell cycle halts here until the cell verifies that DNA has replicated properly
-prevents the initiation of the M stage unless the chromosomes are duplicated

-If DNA is damaged, arresting the cell cycle allows time for the damage to be repaired so that is not passed on to daughter cells

39
Q

Mitotic checkpoint:

A

aka Spindle assembly checkpoint

  • Occurs between metaphase and anaphase to make sure that chromosomes are properly attached to the spindle so can be distributed accurately to the daughter cells
  • Mitosis will not continue unless chromosomes are not properly aligned
40
Q

Mitosis and Cytokinesis:

A

Following interphase is M phase:
M phase has 2 stages:
Mitosis stage and cytokinesis
Mitosis is a type of nuclear division. Also referred to as duplication division since each new nucleus contains identical chromosomes as the former cell

Cytokinesis-division of the cytoplasm

41
Q

What are the Characteristics and Function of Mitosis?

A
  • cell division
  • forms identical chromosomes from parent cell

Asexual reproduction

  • Replace and repair body cells
  • Increase in cell number during growth
42
Q

What happens during mitosis?

A

During mitosis, a cell duplicates all of its contents, including its chromosomes, and splits to form two identical daughter cells

Critical process- carefully controlled number of genes
When mitosis is not regulated correctly, health problems such as cancer can result

43
Q

What are the 6 stages and 4 phases of Mitosis?

A
  1. Interphase
  2. Prophase
  3. Metaphase
  4. Anaphase
  5. Telophase
  6. Cytokinesis
44
Q

What occurs in the Early Prophase?

A

The DNA molecules progressively shorten and condense by coiling, to form chromosomes

The centrioles has migrate to opposite poles of the cell

The nuclear membrane and nucleolus begin to breakdown

45
Q

What occurs in the Late prophase stage?

A

Mitotic spindle (made from microtubule protein) if formed

It attaches to kinetochores located at the centromere of the chromosome

46
Q

What occurs during the metaphase

A

(lines up at the center, takes one spindle fibre)

Chromosomes are moved to the central or metaphase plate of the cell by the spindle microtubules

Sister chromatids line up in the middle of the cell

Each chromatid takes one spindle fibre which comes from the opposite poles

47
Q

What occurs in the Anaphase stage?

A

(splits and pulled to the ends)

The microtubules attached to the kinetochores of each chromosome shorten and the centromere splits, and separated sister chromatids are pulled to the opposite end of the cells

Each chromatid becomes an individual chromosome (identical to the original parent chromosome)

The unattached microtubules elongates stretching the cells

48
Q

What occurs in the telophase?

A

Begins when chromosomes arrive at the poles

Chromosomes become indistinct chromatin again
chromosomes uncoil

The spindle disappears

The nuclear envelope reappears

Characterized by the presence of 2 daughter nuclei

49
Q

What occurs during cytokinesis?

A

Division of the cytoplasm and organelles

An indentation called a cleavage furrow passes around the circumference of the cell

Actin filaments form a contractile ring; as the ring becomes smaller, the cleavage furrow pinches the cell in half

Cytokinesis happens at the same time as telophase in many cells, so they are often presented together

Each daughter cell contains the same number and same quality of chromosome

50
Q

What happens during Mitosis for plant cells?

A

Plant cells have cell walls, so cytokinesis cannot proceed with a cleavage furrow.

During telophase a cell plate forms across the cell in the location of the old metaphase plate

Vesicles from the Golgi apparatus migrate to the plane of cell division (metaphase plate). These fuse to form a new plasma membrane

Contents of vesicles form the cell plate- the beginning of the new cell wall

51
Q

What happens during Meiosis?

A

Consists of 2 nuclear divisions but DNA is replicated only once. The function of meiosis is to:

reduce the chromosome number from diploid to haploid and produce 4 gamete cells

Ensure that each haploid has a complete set of chromosomes

Generate genetic diversity in the gamete cells

52
Q

What is the importance of meiosis?

A

It is required to produce egg and sperm cells for sexual reproduction

During reproduction, when the sperm and egg unite to form a single cell, the number of chromosomes is restored in the offspring

Generate genetic diversity in the gamete cells

53
Q

Meiosis I and II:

A

The process is split into meiosis I and meiosis II

Meiosis I is a type of cell division unique to germ cells, while meiosis II is similar to mitosis

54
Q

Define the term Homologous chromosomes:

A

or homologs, are a set of one maternal and one paternal chromosome that pair up with each other inside a cell during meiosis

Have the same genes in the same loci where it enables a pair of chromosomes to align correctly with each other before separating during meiosis

55
Q

What are the two main purposes of Meiosis I?

A
  • reduction division
  • genetic recombination
  1. It is the reduction division, so it reduces the number of chromosomes in half, making the daughter cells haploid (when the parent cell was diploid)
  2. Most genetic recombination occurs here
56
Q

What is Synapsis?

A

The pairing of homologous chromosomes

Crossing over (homologues exchange pieces of chromosomes)

57
Q

Alignment of chromosomes differs between Meiosis 1 and Mitosis

What is the difference between Meiosis 1 and Mitosis alignment?

A

Meiosis 1
-Sister chromatids do not split but fuse together to the opposite ends of Anaphase 1

How it goes about:
Chiasmata hold homologues together. The kinetochores of sister chromatids fuse and function as one

Microtubules can attach to only one side of the centromere

Microtubules pull the homologous chromosomes apart but sister chromatids are held together

Mitosis
Homologues do not pair
Kinetochores of sister chromatids remain separate; microtubules attach to both kinetochores on opposite sides of the centromere

Microtubules pull sister chromatids apart

58
Q

What occurs in the Pre-meiotic interphase?

A

Prior to meiosis, all chromosomes are duplicated (process similar to duplication prior to mitosis)

-2 centrosomes are produced by the duplication of a single centrosome during pre- meiotic interphase

59
Q

What occurs during Prophase 1 in Meiosis 1?

A

During prophase 1, the complex of DNA and protein known as chromatin condenses to form chromosomes

The pairs of replicated chromosomes (chromatids), remain joined at a central point called the centromere

A large structure called the meiotic spindle also forms microtubules (long proteins)

Short:

  • chromatin condenses to form chromosomes
  • chromatids remain joined at the centromere
  • meiotic spindle forms microtubules

keep in mind:
During anaphase, they do not split apart like in mitosis because there are no spindle fibers attached to each of the sister chromatids (just one sent binded to the kinetochore)

60
Q

What occurs in Prophase 1 after the meiotic spindle forms microtubules?

A

At this point, each homologous chromosome pair is visible as a bivalent (tetrad), tight grouping of 2 chromosomes, each consisting of 2 sister chromatids

crossing over occurs as chromosomes condense

Nuclear envelope breaks down

Centrosomes travels to opposite poles of the cell to form the spindle

61
Q

S phase of premeiotic interphase:

A

chromosome appear as sister chromatids

Meiosis begins following one round of DNA replication in cells within the male or female sex organs

62
Q

Bivalent (Tetrad):

A

paired maternal and paternal homologous chromosomes with 2 chromatids each

63
Q

Explain the continuation of prophase 1 after genetic crossing occurs:

A

nucleolus disappears during prophase 1

in the cytoplasm, the meiotic spindle, consisting of microtubules and other proteins, forms between the 2 pairs of centrioles as they migrate to opposite poles of the cell

nuclear envelope disappears at the end of prophase 1, allowing the spindle to enter the nucleus

64
Q

What occurs during Metaphase 1 in Meiosis 1?

A

The centrioles are at opposite poles of the cell

Spindle fibers from one pole of the cell attach to one chromosome of each pair (seen as sister chromatids)

Homologous chromosomes pair up and align in the middle of the cell

Independent assortment: homologous chromosome pairs line up in random orientations at the middle of the cell:
-a maternal or paternal chromosome goes to either pole

65
Q

What occurs during Anaphase 1 during meiosis 1?

A

Anaphase 1 begins when the 2 homologous chromosomes separate and start moving toward opposite poles of the cell as a result of the action of the spindle

The sister chromatids remain attached at their centromeres and move together toward the poles

Key difference between mitosis and meiosis is that the sister chromatids remain joined after metaphase in meiosis 1 where in mitosis they separate

66
Q

What occurs during Telophase 1 in Meiosis 1?

A

The homologous chromosome pairs complete their migration to the 2 poles as a result of the action of the spindle

Now a haploid set of chromosomes is at each pole, with each chromosome still having two chromatids

67
Q

Telophase 1 in Meiosis 1:

What happens in telophase 1 when cells have to undergo rapid meiosis?

A

When cells have to undergo rapid meiosis they do not decondense chromosomes to become chromatins in telophase 1

other cells do exhibit chromosome de-condensation at this time; the chromosomes then re-condense in prophase II

68
Q

What occurs during Meiosis II-Prophase II?

A

Meiosis begins without any further replication of the chromosomes

Chromosomes condense (shorten and thicken)

The nuclear envelope breaks down

The centrioles duplicate, travel to the opposite poles of the cells

The spindle apparatus forms

69
Q

What occurs during Meiosis II-Metaphase II?

A

Chromosomes line up in the middle of the cell

Each chromatid attached to 1 spindle fibre that comes from the opposite spindle poles

70
Q

What occurs during Meiosis II-Anaphase II?

A

Sister chromatids break apart at the centromere and move to opposite poles

Each chromatid becomes an individual chromosome

71
Q

What occurs during Meiosis II-Telophase and Cytokinesis II?

A

Chromosomes have reached their respective ends/ poles and decondense

Nuclear envelope re-form

Cytokinesis takes place to divide the cells
(haploid daughter cells forming)

Four haploid daughter cells are genetically different from each other and from the parent cell

72
Q

Mitosis vs Meiosis table summary:

A

Mitosis
2 daughter cells
Identical

1 nuclear division

Ends with Diploid

Homologous
chromosomes do not pair up

In anaphase- sister chromatids separate

its function is growth and asexual reproduction

Occurs in the body cells

Meiosis
4 daughter cells are made

Non-identical and genetically different daughter cells

2 Nuclear divisions

Ends with Haploid

Homologous chromosomes pair up

In Anaphase 1: homologous chromosomes separate

Anaphase II: sister chromatids separate

Function is to make gametes (sex cells)

Occurs in the Gonads

73
Q

Meiosis and Gamete formation:

A

Spermatogenesis (gamete formation in males)

  • lots of sperm cells can be made
  • diploid sperm cell

Oogenesis (gamete formation in the female)

  • diploid egg cell
  • limited number of egg cells (must be big) to contain enough nutrients for it to undergo many cell divisions and provide nutrients to the fetus through the umbilical cord
74
Q

Abnormal chromosome inheritance:

A

Nondisjunction may occur during meiosis I (usually during the checkpoint before the M stage the cell ensure the spindle fibers are attached and pulled apart properly) sometimes this does not occur properly and result in extra chromosomes

-Homologous chromosomes during separation do not separate properly and the spindle fibres are not attached properly they do not separate but move towards the opposite ends together

  • Nondisjunction is the failure of homologous chromosomes or sister chromatids to separate properly during cell division. This results in an abnormal number of chromosomes of gametes
  • can happen in meiosis I or II leading to genetic disease
  • about 10% of fertilized human eggs result in an embryo with an abnormality in chromosome numbers

-50% of all spontaneous abortions are due to this abnormality
remaining 50 % will survive and develop despite the abnormalities usually in sex chromosomes

75
Q

Abnormal chromosome inheritance examples:

A 
Trisomy 
21 
Down syndrome
Mental impairment 
Abnormal pattern of palm creases, slanted eyes, flattened face, short stature 
Trisomy 
18
Edward syndrome 
Mental and Physical impairment 
Facial abnormalities 
Extreme mucle tone 
Early death 
Trisomy 
13
Mental and physical impairment 
Early death 
Wide variety of organ defects

Cell and Molecular Bio (13 decks)

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