Mitosis Core — Cambridge IGCSE Biology 0610 Revision Notes & Topical Questions

Section 1 of 21What mitosis is

Mitosis

Mitosis nuclear division giving rise to genetically identical cells.

Diploid cells

• Diploid cells most body cells have two copies of each chromosome.

Doubling beforehand

• Doubling beforehand chromosomes copy themselves before division so each new cell is still diploid.

Every body cell except the gametes comes from mitosis of the zygote.

Section 2 of 21Process of mitosis

1

Each chromosome in the nucleus copies itself exactly, forming X-shaped chromosomes.

2

The chromosomes line up along the centre of the cell.

3

Cell fibres pull the copies apart.

4

The cell divides into two, each with a copy of every chromosome.

• Chromosome number
  • maintained in each daughter cell.

Section 3 of 21Uses of mitosis

Growth

• Growth produces new cells, for example when a zygote divides to form an embryo.

Repair

• Repair replaces damaged or dead cells.

Replacement

• Replacement replaces cells such as skin cells and red blood cells.

Asexual reproduction

• Asexual reproduction produces offspring genetically identical to the parent.

Section 4 of 21Stem cells

Stem cells

• Stem cells unspecialised cells in many tissues that divide by mitosis.

Daughter cells

• Daughter cells can become specialised for specific functions.

Embryonic stem cells

• Embryonic stem cells the zygote divides by mitosis to form a ball of about 150 to 200 unspecialised cells.

Differentiation

• Differentiation these cells begin to specialise as the foetus develops, forming the tissues of the body.

Section 5 of 21More from the specification

1

Replication of nuclear genes

• Replication of nuclear genes precise chromosome replication during interphase ensures identical transmission of genetic genes into daughter cell nuclei.

2

Monohybrid inheritance

• Inheritance of one gene.

3

Exact Duplicate Nuclear Division

• Mitosis produces two genetically identical daughter nuclei with the same diploid chromosome number as the mother cell, essential for organismal growth, tissue repair,
  • and asexual propagation.

4

Preservation of Parental Allelic Identity

• Because DNA replication and mitotic segregation occur without crossing over, all daughter cells inherit identical copies of each allele, maintaining phenotypic fidelity across cellular generations.

5

Chromosome Condensation and Metaphase Alignment

• Chromatin condenses into distinct visible chromosomes that align symmetrically along the cellular equatorial plate, guided by microtubules attached to kinetochores.

6

Homozygous

• Having two identical alleles.

7

Sequence

• The order of bases in DNA or amino acids in a protein.

8

Phenotype

• The observable characteristic.

9

Heterozygous

• Having two different alleles.

10

Probability

• The chance that an offspring has a given genotype or phenotype.

11

Punnett square

• A grid predicting offspring genotypes.

12

Blood group

• A phenotype set by alleles I-A, I-B and I-O.

13

Protein synthesis

• Making proteins from amino acids using the DNA code.

14

Allele

• A version of a gene.

15

Inheritance

• Transmission of genetic information from generation to generation.

16

Recessive

• Expressed only when no dominant allele is present.

17

Dominant

• Expressed when present in the genotype.

18

Protein

• A long chain of amino acids containing carbon, hydrogen, oxygen and nitrogen.

19

Meiosis

• Reduction division giving four genetically different haploid cells.

20

Genotype

• The alleles an organism has.

Section 6 of 21Chromosomes and genes

Chromosome

• Chromosome a thread-like structure of DNA in the nucleus that carries genetic information.

Gene

• Gene a length of DNA that codes for a protein.

Diploid body cells

• Diploid body cells human cells have 46 chromosomes in 23 pairs, one of each pair from each parent.

Chromatids

• Chromatids before division DNA is copied so each chromosome is two identical chromatids joined at the centromere.

Section 7 of 21Definition and result

Mitosis

Mitosis nuclear division giving rise to genetically identical daughter cells with the same chromosome number as the parent.

Daughter cells

• Daughter cells two cells from one, each with 46 chromosomes in humans.

Genetic identity

• DNA was copied exactly, so daughter cells match the parent and each other.

Variation

• Variation none is produced, apart from rare mutations.

Section 8 of 21Stages of mitosis

1

Interphase: the cell grows and the DNA is replicated.

2

Prophase: chromosomes become visible as pairs of chromatids and the nuclear membrane breaks down.

3

Metaphase: chromosomes line up along the equator of the cell.

4

Anaphase: spindle fibres pull the chromatids to opposite poles.

5

Telophase: new nuclear membranes form around the two sets of chromosomes.

6

Cytokinesis: the cytoplasm divides, giving two identical diploid cells.

Section 9 of 21The cell cycle

1Cell cycle

• Cell cycle interphase, then mitosis, then cytokinesis.

2Interphase

• Interphase not a resting phase, as the cell also makes extra organelles and proteins.

3Time spent

• Time spent most of a cell's life is in interphase.

4Non-dividing cells

• Non-dividing cells cells that rarely divide, like neurones, stay in a resting state.

5Checkpoints

• Checkpoints ensure DNA has been copied correctly before division proceeds.

6Cytokinesis

• Cytokinesis in plants a new cell plate forms, in animals the membrane pinches in.

Section 10 of 21Observing mitosis in root tips

1

Cut off the tip of a young onion or garlic root, where cells divide rapidly.

2

Place it in warm hydrochloric acid to separate the cells.

3

Put it on a slide and add a stain such as acetic orcein, which colours chromosomes.

4

Cover with a coverslip and press gently to spread one layer of cells.

5

View under a microscope and identify the stage of each cell by the position of the chromosomes.

Section 11 of 21Mitotic index

1Stage length

• Stage length the stage with the most cells is the longest.

2Mitotic index

• Mitotic index the number of cells in mitosis divided by the total number of cells.

3High values

• High values found in rapidly growing tissue and in cancers.

Section 12 of 21More from the specification

1

Monohybrid inheritance and Punnett squares

• Monohybrid inheritance and Punnett squares a Punnett square diagram calculates expected genotype ratios in offspring, determining probabilities for dominant and recessive phenotypes.

2

Recessive allele expression in offspring

• Recessive allele expression in offspring individual offspring exhibit recessive traits such as short stem height only when inheriting two identical non-dominant alleles.

3

Mitotic preservation of parental genes

• Mitotic preservation of parental genes mitosis replicates maternal and paternal alleles identically, ensuring daughter cells retain complete parental gene complements without segregation.

4

Mitosis and genetic consistency

• Mitosis produces two genetically identical diploid daughter cells, essential for growth, tissue repair, and asexual reproduction.

5

Monohybrid inheritance and Punnett squares

• A Punnett square models the segregation of maternal and paternal alleles, predicting genotypic and phenotypic ratios in offspring.

6

Dominant vs recessive alleles

• Dominant alleles are expressed in both homozygous and heterozygous individuals,
• whereas recessive traits only appear in homozygous recessive genotypes.

7

Blood group

• A phenotype set by alleles I-A, I-B and I-O.

8

Protein synthesis

• Making proteins from amino acids using the DNA code.

9

Monohybrid inheritance

• Inheritance of one gene.

10

Homozygous

• Having two identical alleles.

11

Sequence

• The order of bases in DNA or amino acids in a protein.

12

Gamete

• A haploid sex cell.

13

Phenotype

• The observable characteristic.

14

Specific

• Able to act on only one type of substrate.

15

Heterozygous

• Having two different alleles.

16

Probability

• The chance that an offspring has a given genotype or phenotype.

17

Punnett square

• A grid predicting offspring genotypes.

18

Allele

• A version of a gene.

19

Inheritance

• Transmission of genetic information from generation to generation.

20

Recessive

• Expressed only when no dominant allele is present.

21

Dominant

• Expressed when present in the genotype.

22

Meiosis

• Reduction division giving four genetically different haploid cells.

Section 13 of 21Why mitosis is needed

Growth

• Growth a zygote becomes a multicellular organism by repeated mitosis.

Repair

• Repair damaged or dead cells are replaced, for example skin after a cut.

Replacement

• Replacement red blood cells and gut lining cells are constantly renewed.

Asexual reproduction

• Asexual reproduction mitosis produces offspring identical to the parent.

Section 14 of 21Asexual reproduction

Asexual reproduction

Asexual reproduction production of genetically identical offspring from one parent by mitosis.

Examples

• Examples bacteria divide, Hydra and yeast bud, and plants form runners and bulbs.

Advantage	Disadvantage
Only one parent needed	No genetic variation
Fast, with many offspring	Disease can wipe out the whole population
Good traits are preserved	Cannot adapt to change

Section 15 of 21Natural clones

Organism	Method
Strawberry plant	Runners grow new plants
Potato	Tubers sprout new plants
Yeast	Budding
Bacteria	Binary fission

Section 16 of 21Stem cells

Stem cells

• Stem cells unspecialised cells that divide by mitosis and can differentiate into many cell types.

Embryonic stem cells

• Embryonic stem cells can become any cell type.

Adult stem cells

• Adult stem cells for example in bone marrow, are more limited.

Medical uses

• Medical uses replacing damaged tissue and treating blood disorders.

Ethical concern

• Ethical concern using embryos to obtain stem cells.

Section 17 of 21Control of division and cancer

Normal control

• Normal control new cells are made only when needed.

Tumour

• Tumour a mutation in control genes can make cells divide uncontrollably, forming a lump.

Cancer

• Cancer occurs when cells from a malignant tumour spread to other parts of the body.

Risk factors

• Risk factors ultraviolet light, tobacco smoke and some viruses.

Treatment

• Treatment surgery, radiation and chemotherapy; early detection improves survival.

Chemotherapy

• Chemotherapy targets dividing cells, so it also affects hair follicles and skin.

Section 18 of 21Cloning and tissue culture

1Tissue culture

• Tissue culture small pieces of plant tissue grow on sterile nutrient agar with plant hormones, giving many identical plantlets quickly.

2Uses

• Uses propagating rare plants and plants with desirable traits, such as disease-resistant crops.

3Dolly the sheep

• Dolly the sheep the first mammal cloned from an adult cell, by placing the nucleus of a body cell into an egg cell whose nucleus had been removed.

4Benefits

• Benefits uniform crops and preservation of endangered species.

5Risks

• Risks loss of genetic diversity and vulnerability to a single disease.

6Differences between clones

• Differences between clones are due to the environment, since the genotype is the same.

Section 19 of 21More from the specification

1

Chromosomes and Mitotic Replication

• Prior to mitosis, each chromosome replicates its DNA to form two identical sister chromatids;
  • during division, chromosomes line up and separate to ensure each daughter cell receives an exact copy of parental genes.

2

Monohybrid Inheritance and Alleles

• Alternative forms of a single gene are known as alleles;
  • an individual carrying two identical alleles is homozygous,
• whereas an individual with two different alleles is heterozygous.

3

Punnett Square Genetic Crosses

• A Punnett square is a grid used to determine genotypes and phenotypes of offspring resulting from the combination of maternal and paternal gametes during sexual inheritance.

4

Dominant vs Recessive Phenotypic Expression

• A dominant allele masks the phenotypic effect of a recessive allele; a recessive trait is only expressed phenotypically when an individual is homozygous recessive.
  • (such as cystic fibrosis or short height mutations)

5

Chromosomes and Mitotic Replication

• Prior to mitosis, each chromosome replicates its DNA to form two identical sister chromatids;
  • during division, chromosomes line up and separate to ensure each daughter cell receives an exact copy of parental genes.

6

Monohybrid Inheritance and Alleles

• Alternative forms of a single gene are known as alleles;
  • an individual carrying two identical alleles is homozygous,
• whereas an individual with two different alleles is heterozygous.

7

Punnett Square Genetic Crosses

• A Punnett square is a grid used to determine genotypes and phenotypes of offspring resulting from the combination of maternal and paternal gametes during sexual inheritance.

8

Dominant vs Recessive Phenotypic Expression

• A dominant allele masks the phenotypic effect of a recessive allele; a recessive trait is only expressed phenotypically when an individual is homozygous recessive.
  • (such as cystic fibrosis or short height mutations)

9

Chromosomes and Mitotic Replication

• Prior to mitosis, each chromosome replicates its DNA to form two identical sister chromatids;
  • during division, chromosomes line up and separate to ensure each daughter cell receives an exact copy of parental genes.

10

Monohybrid Inheritance and Alleles

• Alternative forms of a single gene are known as alleles;
  • an individual carrying two identical alleles is homozygous,
• whereas an individual with two different alleles is heterozygous.

11

Punnett Square Genetic Crosses

• A Punnett square is a grid used to determine genotypes and phenotypes of offspring resulting from the combination of maternal and paternal gametes during sexual inheritance.

12

Dominant vs Recessive Phenotypic Expression

• A dominant allele masks the phenotypic effect of a recessive allele; a recessive trait is only expressed phenotypically when an individual is homozygous recessive.
  • (such as cystic fibrosis or short height mutations)

13

Blood group

• A phenotype set by alleles I-A, I-B and I-O.

14

Protein synthesis

• Making proteins from amino acids using the DNA code.

15

Monohybrid inheritance

• Inheritance of one gene.

16

Homozygous

• Having two identical alleles.

17

Sequence

• The order of bases in DNA or amino acids in a protein.

18

Gamete

• A haploid sex cell.

19

Phenotype

• The observable characteristic.

20

Heterozygous

• Having two different alleles.

21

Probability

• The chance that an offspring has a given genotype or phenotype.

22

Punnett square

• A grid predicting offspring genotypes.

23

Daughter cell

• Cell produced by cell division.

24

Chromosome

• A thread-like structure of DNA carrying genes.

25

Allele

• A version of a gene.

26

Inheritance

• Transmission of genetic information from generation to generation.

27

Recessive

• Expressed only when no dominant allele is present.

28

Dominant

• Expressed when present in the genotype.

29

Protein

• A long chain of amino acids containing carbon, hydrogen, oxygen and nitrogen.

30

Meiosis

• Reduction division giving four genetically different haploid cells.

Section 20 of 21Key terms

Term	Meaning
Mitosis	Nuclear division giving genetically identical cells.
Replication	Exact copying of chromosomes before division.
Stem cell	An unspecialised cell that divides and can become specialised.
Differentiation	Specialisation of a cell for a function.
Diploid	Having two sets of chromosomes.

Term	Meaning
Mitosis	Nuclear division giving genetically identical cells.
Chromatid	One of the two identical copies of a replicated chromosome.
Interphase	The stage when the cell grows and DNA is replicated.
Cytokinesis	Division of the cytoplasm.
Mitotic index	Cells in mitosis divided by total cells.
Spindle fibre	A fibre that pulls chromatids to the poles.

Term	Meaning
Asexual reproduction	Reproduction giving genetically identical offspring from one parent.
Stem cell	An unspecialised cell that can divide and differentiate.
Tumour	A lump of cells formed by uncontrolled division.
Cancer	Disease in which cells divide uncontrollably and spread.
Tissue culture	Growing plant cells or tissue on sterile nutrient agar.
Clone	A genetically identical organism.

Section 21 of 21Exam technique

1

Saying mitosis halves the chromosome number — it keeps it the same.

2

Saying the daughter cells are different — they are genetically identical.

3

Saying mitosis makes gametes — meiosis does.

4

Saying chromosomes are copied after division — they are copied before.

1

Saying mitosis halves the chromosome number — daughter cells keep the same number.

2

Saying interphase is a resting phase — DNA is copied and organelles are made.

3

Putting the stages in the wrong order — prophase, metaphase, anaphase, telophase after interphase.

4

Saying DNA is copied after division — it is copied before.

1

Saying mitosis makes gametes — meiosis does.

2

Saying stem cells are already specialised — they are unspecialised.

3

Saying clones have different genes — they share the same genotype.

4

Saying cancer is caused by controlled mitosis — it is uncontrolled cell division.