#4 cell division and early development

somatic cells

cells that make up the body

how many chromosome pairs do humans have

23

homologous

pair of chromosomes with recipes for the same protein (ex. hair color)

alleles

different versions of the same gene

chromosomes 1-22 are _____ chromosomes

autosomal

what chromosome is chromosome 23?

sex chromosome

haploid number (n)

number of different chromosomes a species will have

• humans: 23

diploid number (2n)

total number of chromosomes an individual will have

• humans: 46

stages of cell cycle

1. interphase (90% of the cycle)

2. mitotic phase

what happens in interphase

duplicates cell content for two cells

what happens in mitotic phase

1. mitosis: nuclear division (dividing DNA to 2 cells)

2. cytokinesis: cytoplasmic division (dividing organelles to 2 cells)

3 phases of interphase

1. G1

2. S

3. G2

G1 phase (interphase)

• intense growth and metabolism

• centrosomes replicate at the end

S phase (interphase)

• DNA is replicated, making copies of each chromosome (sister chromatids)

• attached together by a centromere

• kinetochore protein attaches to centromere

kinetochore

protein / DNA complex that is attached to the centromere of one chromosome

G2 phase (interphase)

• more growth and metabolism

• enzymes and proteins for cell division are made

• each chromosome with 2 sister chromatids attached to one another at the centromere

2 steps of mitotic phase

1. mitosis: division of nuclear contents

2. cytokinesis: division of cytoplasmic contents (occurs at same time as telophase)

mitosis functions and results in…

• growth and tissue repair

• 2 genetically identical, somatic daughter cells

prophase

setting up cell to divide nuclear contents

• chromatin condenses

• nuclear membrane and nucleoli disappear

• centrosomes move to opposite poles of cell

• spindle apparatus forms at centromere

kinetochore microtubules

kinetochore proteins attached to spindle microtubules

metaphase

46 chromosomes line up

anaphase

• kinetochores separate

• 46 sister chromatids migrate to each pole

• cytokinesis begins

telophase

reverse of prophase

• spindle apparatus disassembles

• cytokinesis completed

• mitosis ends

• now 2 identical daughter cells

meiosis

takes place in sex cells

• reduction division from a 2n diploid cell to an n haploid cell

how many chromosomes do diploid cells in humans have

2n=46

how many chromosomes do haploid cells in humans have

n = 23

why do gametes need to have the haploid number of chromosomes

fertilization functions to restore the diploid number

meiosis 1

separates homologous pairs

• cell becomes haploid

• pmat1 + cytokinesis

meiosis 2

separates sister chromatids from one another

• makes 4 haploid gametes

• pmat2 + cytokinesis

meiosis synapsis

homologous pairs match up side by side

tetrad

2 sister chromatids from one member of the homologous pair and 2 sister chromatids from the other

crossing over

sister chromatids exchange genetic material

cytokinesis 1

• overlaps with telophase 1

• forms 2 haploid daughter cells, two sister chromatids per chromosome

diploid zygote is formed when

haploid sperm and haploid oocyte (egg) come into contact

pre-embryonic development

• first two weeks after fertilization

• diploid zygote divides by mitosis to make many cells (cleavage divisions)

• produces a solid ball of 16-32 cells (morula)

blastomere

cell produced by cleavage divisions

what is produced as the morula divides further (~5 days after fertilization)

blastocyst

blastocoele

fluid filled cavity in the blastocyst

what is the blastocyst composed of

1. trophoblast cells surround blastocyst, provides nourishment to the developing embryo

2. embryoblast (will become the embryo)

implantation

attachment of the blastocyst to the endometrium of the uterus

• embryoblast develops into the embryonic disk

embryonic disk consists of

1. epiblast layer: will give rise to fetus

2. hypoblast layer: will give rise to yolk sac