Life Cycles(Mitosis and Meiosis)

Mitosis

• Cell replication

• The segregation of identical chromosomes into 2 new cells, each containing exact copies of the DNA in the original cell.

• Function?

– Growth

– Repair

– Asexual Reproduction

• Haploid cells have only one copy of each chromosome (N) or cells without paris of homologous chromosomes.

• Diploid cells have two copies of each somatic chromosome (non-sex chromosomes), usually one from the mother and one from the father (2N).

Meiosis

• Separates homologous chromosomes

• Formation of gametes (sex cells)• 4 cells with ½ the number of chromosomes as the parent cell.

– e.g. sperm and egg cells• Function?

– Sexual Reproduction

Life cycles – general rules

• In biology, a life cycle includes the major sexual stages of a species, especially in regard to its ploidy.

• There are three types of cycles:

– zygotic meiosis (fungi, some green algae, protozoa)

– gametic meiosis (animals, some brown algae)

– sporic meiosis (plants, many algae)

• All sexual cycles feature the alternating haploid and diploid phases.

• The haploid organism becomes diploid through fertilizations of gametes, resulting in a zygote. To return to the haploid stage, meiosis occurs.

Stages of Life

• Haploid or Diploid

• Produce cells either by meiosis or mitosis

• Cells produced by mitosis are always identical

• Cells produced by meiosis – dividing cells must be diploid and produced cells are haploid

Gametic Cycle: Diploid life cycle• No multicellular stage is

haploid

• Unicellular stage is haploid and produced by meiosis

• Organism - Animals

Put these in the correct position: 1. mitosis and growth2. multicellular diploid adults3. gametes4. fusion of gametes5. zygote6. ploidy (n or 2n)

diploid cycle diploid cycle

Zygotic Cycle: Haploid life cycle

• Unicellular diploid stage

• Multicellular haploid stage

haploid cyclehaploid cycle

Sporic Cycle: Diploid/Haploid life cycle• Spore – gametes of higher vascular

plants

• Multicellular diploid stage

• Multicellular haploid stage

• Mitosis occurs in both diploid and haploid phase

• A sporophyte is the diploid structure or phase of life of a sexually reproducing plant

• A gametophyte is the haploid structure or phase of life of a sexually reproducing plant

• Alternation of generations: This life cycle is characterized by there being two separate free-living plants, the gametophyte (haploid plant) and the sporophyte (diploid plant) in each generation.

Alternation of generations - ferns

Alternation of generations - Flowering plants

Diploid = 2 N

Meiosis Haploid = 1 N

Mitosis

Diploid = 2 NFertilization

Life Cycle Summary

Diploid Life cycle

Haploid Life cycle

Alternation of Generations

Mitosis?

Meiosis?

Fertilization

Mitosis after meiosis?

Mitosis after fertilization?

Multicellular diploid stage?

Multicellular haploid stage?

What you should be able to do:• Identify the main functions of meiosis and mitosis.

• Use the terms haploid and diploid correctly in regard to meiosis and life cycle diagrams.

• Identify the products of mitosis and meiosis: In terms of number of cells, and the relative amount of the DNA in each of the cells produced as well as the relationship between the offspring cells.

• Identify the appropriate life cycle diagram for an animal, plant or fungus.

• Explain how each of the life cycles results from alternating haploid and diploid forms.

• Identify the "ploidy" level (haploid vs diploid) of each stage in a life cycle diagram, given the locations of mitosis and meiosis in the life cycle, and vice-versa.

• Identify the stages in the butterfly and mouse life cycles; order them in the proper sequence.