Fig. 13-2a

(a) Hydra

0.5 mm

Bud

Parent

DNA – lots of it in a small space

chromatin

ChromosomeKnow how to

label

Fig. 12-UN3

Fig. 12-14

SG1

M checkpoint

G2M

Controlsystem

G1 checkpoint

G2 checkpoint

Cyclins are proteins that control the cell cycle.They create chemical“checkpoints”through-out the process.

Fig. 12-UN1

Telophase andCytokinesis

Anaphase

Metaphase

Prometaphase

Prophase

MITOTIC (M) PHASE

Cytokinesis

Mitosis

SG1

G2

Fig. 12-9

Cleavage furrow100 µm

Contractile ring ofmicrofilaments

Daughter cells

(a) Cleavage of an animal cell (SEM) (b) Cell plate formation in a plant cell (TEM)

Vesiclesformingcell plate

Wall ofparent cell

Cell plate

Daughter cells

New cell wall

1 µm

What is the haploid number for each? Symbol for haploid? What kindof cells are haploid?

Fig. 13-3APPLICATION

TECHNIQUE

Pair of homologousreplicated chromosomes

5 µm

Centromere

Sisterchromatids

Metaphasechromosome

The processof creating a graphicdisplay of chromosomesfrom a cell to determineabnormal chromosomenumber. Homologuesare paired up andarranged in descendingorder according to length.

Fig. 13-4

KeyMaternal set ofchromosomes (n = 3) hapolid #Paternal set ofchromosomes (n = 3)

2n = 6Diploid number

Centromere

Two sister chromatidsof one replicatedchromosome

Two nonsisterchromatids ina homologous pair

Pair of homologouschromosomes(one from each set)

Fig. 13-5Key

Haploid (n)Diploid (2n)

Haploid gametes (n = 23)

Egg (n)

Sperm (n)

MEIOSIS FERTILIZATION

Ovary Testis

Diploidzygote(2n = 46)

Mitosis anddevelopment

Multicellular diploidadults (2n = 46)

The relationshipbetween mitosisand meiosis

Fig. 13-12-5Prophase Iof meiosis

Homologouspair

NonsisterChromatids

Centromere

Anaphase I

Anaphase II

Daughtercells

Recombinant chromosomes

TEM

Fig. 13-9a

MITOSIS MEIOSIS

MEIOSIS I

Prophase IChromosome

replication

Homologouschromosomepair

Chromosomereplication

2n = 6

Parent cell

Prophase

Replicated chromosome

Metaphase Metaphase I

Anaphase ITelophase I

Haploid n = 3

Daughter cells ofmeiosis I

MEIOSIS II

Daughter cells of meiosis IInnnn

2n2n

Daughter cellsof mitosis

AnaphaseTelophase

Fig. 13-9b

SUMMARY

MeiosisMitosisProperty

DNAreplication

Number ofdivisions

Occurs during interphase beforemitosis begins

One, including prophase, metaphase,anaphase, and telophase

Synapsis ofhomologouschromosomes

Does not occur

Number ofdaughter cellsand geneticcomposition

Two, each diploid (2n) and geneticallyidentical to the parent cell

Role in theanimal body

Enables multicellular adult to arise fromzygote; produces cells for growth, repair,and, in some species, asexual reproduction

Occurs during interphase before meiosis I begins

Two, each including prophase, metaphase, anaphase, andtelophase

Occurs during prophase I along with crossing overbetween nonsister chromatids; resulting chiasmatahold pairs together due to sister chromatid cohesion

Four, each haploid (n), containing half as many chromosomesas the parent cell; genetically different from the parentcell and from each other

Produces gametes; reduces number of chromosomes by halfand introduces genetic variability among the gametes

Fig. 13-UN3

DNA replication

Meiosis I –PMAT to separate homologouspairs. Have2 cells.

Meiosis II – before itstarts, NO DNA replication.PMAT separates sister chromatids. Four haploid cells produced. No pairsof chromosomes.

Fig. 13-UN4

NONDISJUCTION

• Failure of a particular chromosome to separate properly during meiosis.

• Can happen in meiosis I if a particular homologous pair fails to separate.

• Can happen in meiosis if sister chromatids of a particular chromosome fail to separate

• Remember the term nondisjunction applies to abnormal gametes. In humans, abnormal egg or sperm would be 24 or 22 chromosomes.

Fig. 15-13-3

Meiosis I

Nondisjunction

(a) Nondisjunction of homologous chromosomes in meiosis I

(b) Nondisjunction of sister chromatids in meiosis II

Meiosis II

Nondisjunction

Gametes

Number of chromosomes

n + 1 n + 1 n + 1n – 1 n – 1 n – 1 n n

• Aneuploidy results from the fertilization of a gamete in which nondisjunction occurred• Offspring with this condition have an abnormal number of a particular chromosome

• REMEMBER – aneuploidy means abnormal numberof a particular chromosome in a ZYGOTE (FERTILIZATION HAS HAPPENED). We are not discussing

the gamete any more.

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Two types of aneuploidy:•Monosomy: A monosomic zygote has only one copy of a particular chromosome. In humans an example would be Turner’s syndrome: Female child only has only 1 sex chromosome (X) in each diploid cell instead of XX, she has a total of 45 chromosomes in diploid cells instead of 46.

•Trisomy: A trisomic zygote has three copies of a particular chromosome. In humans an example would be Down’s Syndrome: Child has 3 copies of chromosome 21 in all diploid cells for a total of 47.

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Another Trisomic disorder Patau Syndrome (Trisomy 13)

• cleft palate• fetuses with this condition rarely to go to term• so it occurs in only 1 in 6000 live births • It is rare for babies to survive for very long if liveborn because of

the multitude of anomalies • atrial septal defect • inguinal hernia• polydactyly of hands and feet• Sometimes cyclopia or absence of eyes

Patau Syndrome (Trisomy 13)

Edward Syndrome (Trisomy 18)• Sometimes due to translocation• Survival rate of Edwards Syndrome is very low • Approximately 95% die in utero. • Of liveborn infants, only 50% live to 2 months, and only 5–10% will survive

their first year of life. • The median life span is five to fifteen days• One percent of children born with this syndrome live to age ten, typically in

cases of the less severe Edwards syndrome.• heart defects at birth • intestines protruding outside the body• Feeding and breathing difficulties• Microcephaly• Clenched fists

• Polyploidy is a condition in which an organism has more than two complete sets of chromosomes– Triploidy (3n) is three sets of chromosomes– Tetraploidy (4n) is four sets of chromosomes

• Polyploidy is common in plants, but not animals• Polyploids are more normal in appearance than

aneuploids

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Down Syndrome (Trisomy 21)

• Down syndrome is an aneuploid condition that results from three copies of chromosome 21

• It affects about one out of every 700 children born in the United States

• The frequency of Down syndrome increases with the age of the mother, a correlation that has not been explained

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Fig. 15-16a

Fig. 15-16b

2 processes for collecting fetalcells for karyotyping.

Aneuploidy of Sex Chromosomes

• Nondisjunction of sex chromosomes produces a variety of aneuploid conditions

• Klinefelter syndrome is the result of an extra chromosome in a male, producing XXY individuals

• Monosomy X, called Turner syndrome, produces X0 females, who are sterile; it is the only known viable monosomy in humans

• Poly X – 3 copies of XXX• Jacob Syndrome - XYY

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•Almost all (95%) have •Short stature •Loss of ovarian function

•Caused by the absence of a set of genes from the short arm of one X chromosome •1 out of every 2,000-2,500 female live births •Single X chromosome

•75-80% single X is contributed by mother •X-O = Female (Turner Syndrome) •X-X-Y=Male (Klinefelter Syndrome)

•Appearance •Short stature

•Absent adolescent growth spurt •Average adult height is 4 feet 8 inches •Loss of SHOX gene necessary for growth of long bones

•Short fingers (4th metacarpal) •Newborns – puffy, bulbous hands and feet

Alterations of Chromosome Structure

• Breakage of a chromosome can lead to four types of changes in chromosome structure:– Deletion removes a chromosomal segment– Duplication repeats a segment– Inversion reverses a segment within a chromosome– Translocation moves a segment from one

chromosome to another

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Fig. 15-15

DeletionA B C D E F G H A B C E F G H(a)

(b)

(c)

(d)

Duplication

Inversion

Reciprocaltranslocation

A B C D E F G H

A B C D E F G H

A B C D E F G H

A B C B C D E F G H

A D C B E F G H

M N O C D E F G H

M N O P Q R A B P Q R

Disorders Caused by Structurally Altered Chromosomes

• The syndrome cri du chat (“cry of the cat”), results from a specific deletion in chromosome 5

• A child born with this syndrome is mentally retarded and has a catlike cry; individuals usually die in infancy or early childhood

• Certain cancers, including chronic myelogenous leukemia (CML), are caused by translocations of chromosomes

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