Organism Survival cont.

Growth, maintenance & reproduction III

4 haploid cells

Zygote

Adult

Gametes and Fertilization

Interphase, Mitosis and Cytokinesis

Basic sexual life cycle revised

Meiosis and Cytokinesis

2n

n

?

Recall that meiosis and cytokinesis result in4 genetically variable, haploid cells being produced from 1 diploid germ (reproductive) cell

Differentiated haploid cell = Gamete (recall: differentiation is a change in structure for a particular function)

Not all haploid (n) cells will mature (differentiate) to form gametes

Variation in gamete maturation:• between genders of a species (male & female)

Sperm – flagella for motility, +++ mitochondria for energyEgg – increased volume for biochemical support (e.g.

nutrients)

What is the fate of a haploid cell?

Spermatogenesis

GrowthMeiosis I,

Cytoplasmic DivisionMeiosis II,

Cytoplasmic Division

differentiation

spermatids (haploid)

secondary spermatocytes

(haploid)primary

spermatocyte (diploid)

spermato-gonium (diploid )

sperm (mature, haploid male gametes)

GrowthMeiosis I,

Cytoplasmic DivisionMeiosis II,

Cytoplasmic Division

ovum (haploid)

primary oocyte (diploid)

oogonium (diploid)

secondary oocyte

(haploid)

first polar body

(haploid)

Oogenesis

differentiation

three polar bodies

(haploid)

What is the fate of a haploid cell?Recall that meiosis and cytokinesis result in4 genetically variable, haploid cells being

produced from 1 diploid germ (reproductive) cell

Differentiated haploid cell = Gamete (recall: differentiation is a change in structure for a particular function)

Not all haploid (n) cells will mature (differentiate) toform gametes

Variation in gamete maturation:• between genders of a species (male & female)• between species

What is the fate of a haploid cell?

Recall that meiosis and cytokinesis result in4 genetically variable, haploid cells being

produced from 1 diploid germ (reproductive) cell

Differentiated haploid cell = Gamete (recall: differentiation is a change in structure for a particular function)

Not all haploid (n) cells will mature (differentiate) toform gametes

Variation in maturation:• between genders of a species (male & female)• between species• between plants and animals

Animal Sexual Life Cycle

adult

gametes

zygote

meiosisfertilization

mitosis

Diploid

Haploidmeiosisfertilization

Egg (ovum) and sperm adult

gametes

zygote

mitosis

Diploid

Haploidmeiosisfertilization

BIOL 102

Plant Sexual Life CycleOvules and pollen

What is the fate of a gamete?

Male and female gametes unite

The 2 haploid nuclei fuse, producing a diploid nucleus (recall homologous chromosome

pairs) in the zygote (new cell) = Fertilization

Fertilization:>> restores chromosome number

(n 23 + n 23 = 2n 46)

>> introduces further genetic variation as gametes combine randomly

Meiosis, the differentiation of gametes and fertilization, define sexual reproduction

Sexual Reproduction

Offspring are genetically variable as they inherit new combinations of alleles (versions of the same gene)

(which drives the process of evolution)

>> Crossing Over (Recombination) of non-sister chromatids in Prophase I

>> Random Alignment (Independent Assortment) of chromosomes in Metaphase I (Anaphase I)

>> Random combination of gametes at fertilization

Dominates the life cycles of multicellular Eukaryotes

Sexual life cycle completed

gametes

zygote

female adult

2n

n

2n

2n

2n

2n

Meiosis and

cytokinesis

male germ cell

female germ cell

Mito

sis

and

cyto

kine

sis

n

nnnnn

nnnn

Fertilization

nn D

ifferentiatio

n

new cycle

Gro

wth

an

d m

ain

ten

anc

e

Asexual ReproductionReproduction in the absence of meiosis, gamete

formation and fertilization

>> offspring are identical (genetic clones) to each other and to the single parent

By what process do you think the cells of the offspring are produced?

Apart from growth and maintenance, Mitosis also functions in asexual reproduction

Dominates the unicellular eukaryotes (protistans – Why?) Common in plants and fungi, and rare in animals

FunctionsAsexual reproduction (clones)Growth, repair • Occurs in somatic cells• Produces genetically identical cells

Process• One nuclear division• Chromosome number maintained

• 2 diploid daughter cells

• Prophase – homologous pairs do not interact

• Metaphase – chromosomes align

• Anaphase – separates sister chromatids

Mitosis Vs. MeiosisFunction Sexual reproduction

• Occurs in germ cells• Produces genetically variable cells

Process• 2 nuclear divisions• Chromosome number halved

(reduction division)• 4 haploid daughter cells

• Prophase I – crossing over occurs

• Metaphase I – homologous pairs align for random assortment

• Anaphase I – separates homologous pairs

• Anaphase II – separates sister chromatids

Starr and Taggart: The Unity and Diversity of Life

Chapter 9 (Cell Division and Mitosis)

Chapter 10 (Meiosis)

www.ukzn.ac.za/biology/BIOL101SmallerSideofLife256.aspx