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
Growth Meiosis I,Cytoplasmic Division
Meiosis II,Cytoplasmic
Division
differentiation
spermatids (haploid)
secondary spermatocytes
(haploid)primary
spermatocyte (diploid)
spermato-gonium (diploid )
sperm (mature, haploid male gametes)
Growth Meiosis I,Cytoplasmic Division
Meiosis 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 Cycleadult
gametes
zygote
meiosisfertilization
mitosis
DiploidHaploid
meiosisfertilization
Egg (ovum) and sperm adult
gametes
zygote
mitosis
DiploidHaploid
meiosisfertilization
BIOL 102Plant Sexual Life Cycle
Ovules 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 ReproductionOffspring 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
gameteszygote
female adult
2n
n
2n
2n
2n
2nMeiosis and
cytokinesis
male germ cell
female germ cell
Mitosis
and
cyto
kines
is
n
nnnnnnnnn
Fertilization
nn Differentiation
new cycle
Gro
wth
and
mai
nten
ance
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