HSC Biology Module 5: Heredity

Return to HSC Resources

HSC Biology – Heredity – Study Guide



Methods of Asecual Reproduction

  • Binary fission: 1 cell splits into 2 cells.

  • Multiple fission: 1 cell splits into many cells.

  • Budding: parent develops small bud which grows and breaks off as a new smaller organism.

There is unequal division of cytoplasm resulting in the buds being much smaller than the parent.

The bud may remain in contact with the parent cell to form a colony.

The buds may connect with each other to produce a chain of buds.

  • Fragmentation: body parts fragment and grow to become identical to parent.

  • Spores: parent plant produces lots of spores which grow into new identical plants.
  • Vegetative reproduction: cut part of parent plant and grow in soil.

  • Parthenogenesis: development of female gamete (egg) without sperm which develops into an embryo.

Explain the mechanisms of reproduction that ensure the continuity of a species, by analysing sexual and asexual methods of reproduction in a variety of organisms, including but not limited to:

Animals: advantages of external and internal fertilisation

Asexual reproduction Sexual reproduction
1 parent 2 parents
Mitosis Meiosis
Offspring are genetically identical to parent Offspring
Variation only arises from random mutations of DNA. Variation arises from gamete production (meiosis), genetic recombination and fertilisation.
Advantages Disadvantages Advantages Disadvantages
Efficient/simple. No genetic variation (if there is an environmental change there are no unique individuals that have variations that can tolerate the new selective pressure = extinction). Genetic variation = elimination of unfavourable traits and inheritance of favourable traits. This means populations are able to survive and adapt to changing environment. Energy and time to mate = slower reproductive rate.
If environment is stable → offspring well suited. Rapid reproduction = high competition for resources and overcrowding. In plants, seeds may land in unfavourable areas and fail to germinate.
Time and energy is minimal. Finding and competing for a mate.
No need to find mates.
Rapidly reproduce large numbers and outcompete unfavourable plants in an area.

External fertilisation: sperm fertilises egg outside female body.

Internal fertilisation: sperm inserted into female body.

Aquatic → terrestrial = external fertilisation → internal fertilisation.







Millions of gametes leading to more variation.

No guarantee fertilisation will occur.

Increased chance gametes meet.

Fewer offspring.

No specialised structures required.

High energy expenditure (lots of gametes).

Greater chance of zygote survival (predator/disease protection).

Organisms require specialised structures (penis etc.).

Parental care not essential.

Must take place in aquatic environment.

Greater selection of mates.

Energy needed for mating and giving birth.

Female continues to reproduce without waiting for first young to develop.

Exposed to predation, infection.

Can take place on dry land.

Parental care is lengthy.

Animals either use:

i) Sexual reproduction.

ii) Asexual reproduction:

Regeneration e.g. sea stars → detached part of parent grows into individual.

Fission e.g. planaria → growth of a structure on the parent organism which detaches to become a new individual.

Budding e.g. Hydra.

Fragmentation e.g. California blackworms.

Parthenogenesis e.g. water fleas.

Fungi: budding, spores

Budding (e.g. yeasts).

Spores (e.g. mushrooms) can either be

Asexual: produces mitospores by mitosis (haploid reproductive cells).

Sexual: produces meiospores (haploid spores) by meiosis → male and female cells combine.

Bacteria: binary fission

Protists: binary fission, budding

Binary (or multiple) fission.


NOTE some reproduce both sexually and asexually e.g. ciliates. They sexually reproduce when variation is needed in a changing environment.

Binary fission



No nucleus (since bacteria are prokaryotic).

Replication of membrane-bound nucleus.


Asexual: vegetative reproduction or artificial propagation.


Rhizome e.g. ginger: underground horizontal stem which produces shoots and roots to produce a new plant.

Runner e.g. strawberry plants: above ground horizontal stem.

Tuber e.g. potatoes: thick underground stem that produces buds which grow into new plants.

Bulb and corm e.g. daffodil: sideways growing buds which grow into new plants.

Sucker e.g. blackberries: shoots that grow from roots.

Budding e.g. prickly pear.

Fragmentation e.g. Salix babylonica.


Grafting and cutting: preserves plants with favourable traits and prevents extinction of endangered plant species.


4 different groups of plants: gymnosperms, angiosperms, mosses and ferns.

Plants alternate between generations of haploid and diploid stages

Either the haploid (gametophyte) or diploid (sporophyte) stage dominates in a plant.







Vascular tissue (xylem/phloem) is present

No flowers

No vascular tissue

Root like structures underground called rhizoids



Flowers present



No flowers

Cone producing plants


Diploid sporophyte

Haploid gametophyte

Diploid sporophyte

Diploid sporophyte


Sexually with spores


Fertilisation of sperm + egg → zygote → produces sporophyte (diploid) which contains sporangium → sporangium produces spores by meiosis → spores grow into gametophytes (haploid) → gametophytes contain sperm and egg.

Fertilisation of sperm + egg → zygote → produces sporophyte (diploid) → produces spores by meiosis (haploid)→ mitosis of spores → spores will become either an egg or sperm.

Fertilisation of sperm + egg → zygote → seed → plant → anther produces pollen → pollen carried by animal to stigma → transferred down the style → fertilise the ovules in the ovary → ovule develops into a diploid seed → ovary develops into a fruit.

Fertilisation of sperm and egg → zygote → produces sporophyte → develops seeds → seeds disperse → grows into plant (sporophyte) → produces either seed cone (female) or pollen cone (male) → male cone contains microspores which divide by meiosis to produce pollen → female cone contains megaspores which divide by mitosis to produce eggs → sperm (pollen) travels by wind to fertilise egg.

Structure of angiosperms

  • Male structures (stamen)

Anther: male organ where pollen grains form.

Filament: stalk of the male sex organ.

  • Female structures (carpel)

Stigma: sticky top surface where pollen adheres.

Style: joins the stigma to the ovary.

Ovary: female organ where ovules are formed.

Analyse the features of fertilisation, implantation and hormonal control of pregnancy and birth in mammals

FERTILISATION: fusing of 2 haploid gametes to produce a diploid cell.

  • Gonads (testis and ovaries): reproductive organisms.
  • Germ cells: cells that produce gametes.
  • Gametes (sperm and egg): sex cells which are haploid that combine for fertilisation.
  • In a male: germ cells → diploid spermatocytes → 4 haploid sperm cells (by meiosis).
  • In a female: born with set number of eggs.





Uterus = nourishment of embryo.

Pouch = protection and nourishment of organism.

Female lays eggs which hatch (oviparous).

Babies are fed with milk after birth.

Fertilisation can occur while another organism is in pouch.

Young fed milk by mother.

Implantation: blastocyst attaches to uterus lining.

Hormonal Control of Pregnancy and Birth:

  • Hypothalamus = stimulates other glands to release hormones.
  • Pituitary gland

Follicle stimulating hormone stimulates release of oestrogen.

Luteinising hormone controls when eggs are released.

Prolactin controls milk secretion.

Oxytocin causes release of milk + causes uterine contractions.

  • Ovary gland

Oestrogen regulates menstrual cycle + promotes milk production.

Progesterone prepares uterus for pregnancy + controls uterine contractions.

Evaluate the impact of scientific knowledge on the manipulation of plant and animal reproduction in agriculture

Scientific knowledge = selective breeding/cloning = favourable traits are passed to offspring = higher quality food.

Selective Breeding

Wheat (plant example)

William Farrer (1870s) hybridized Indian wheat (drought tolerant and disease resistant) AND Canadian Fife (matured late and had best milling/baking qualities) to produce Bob’s variety = improved grain quality and yield.

Cattle (animal example)

Artificial insemination of cattle with higher muscle mass = higher quality and quantity of beef.




Food quality improved.

Animal rights/ethics.

Food quantity increased.

Unknown consequences of genetically modified organisms.

Genetically modified organisms compete with natural populations.

Less genetic diversity (biodiversity).

Cell Replication

Model the processes involved in cell replication, including but not limited to:

Mitosis and meiosis


Interphase: chromosomes replicate.

Prophase: chromosomes become visible and nuclear membrane removes.

Metaphase: chromosomes align in centre.

Anaphase:spindle fibres pull sister chromatids to opposite poles.

Telophase: nuclear membrane reforms around the 2 sets of chromosomes.

Cytokinesis: cytoplasm divides to form 2 identical daughter cells.


Meiosis I

Interphase I: DNA replicates.

Prophase I: Crossing over of DNA occurs (trade sections of DNA).

Metaphase I: Homologous chromosomes line up at equator.

Anaphase I: Homologous chromosomes are pulled to opposite ends of cell (random assortment).

Telophase I and Cytokinesis: Nuclear membrane forms and cells separate.

Meiosis II

Prophase II: Spindle fibres form to pull apart chromosomes.

Metaphase II: Chromosomes line up at equator.

Anaphase II: Chromosomes are pulled apart into chromatids to opposite ends of cell.

Telophase II and Cytokinesis: Nuclear membrane forms and cells separate.

DNA replication using the Watson and Crick DNA model, including nucleotide composition, pairing and bonding

The above Watson and Crick model is,

  • Composed of nucleotides.
  • Double stranded.
  • Twisted into helix shape (spiral).
  • Composed of a sugar-phosphate backbone.
  • Composed of bases attached to backbone: adenine, guanine, cytosine and thymine.

Bonding and pairing of nucleotides:

  • Nucleotides are joined by phosphodiester bonds.
  • Complementary nitrogenous bases are joined by hydrogen bonds.
  • Adenine always pairs with thymine: held by 2 weak hydrogen bonds.
  • Guanine always pairs with cytosine: held by 3 weak hydrogen bonds.

Steps in DNA replication

1. Double helix untwisted by enzymes (helicase and topoisomerase).

2. DNA unzips → 2 single strands.

3. Enzyme DNA polymerase attaches to single strand and attaches free nucleotides (AT, GC). This occurs in antiparallel direction. Another DNA polymerase ‘edits’ any incorrect additions.

4. New DNA molecule twisted back into double helix (semi-conservative since new strands contain 1 original strand).

Assess the effect of the cell replication processes on the continuity of species

Cell replication either

i) Replicates parent cells to maintain optimal functioning of an organism.

ii) Introduces genetic variation via mutation → evolution of a species.

Maintains genetic continuity AND evolutionary continuity.

DNA and Polypeptide Synthesis

Construct appropriate representations to model and compare the forms in which DNA exists in eukaryotes and prokaryotes



DNA is held in a membrane-bound nucleus. DNA is not held in a membrane-bound nucleus.
Multiple chromosomes per cell that are different shapes and sizes. 1 circular chromosome per cell.
Contains no plasmids. Some cells contain plasmids (small rings of DNA).
More DNA and genes. Less DNA and genes.
DNA is tightly packaged: coiled around histones (proteins) to form nucleosomes. DNA is not packaged since there isn’t a lot of DNA.

Double helix DNA.

Same nitrogenous bases (A, T, C and G).

mRNA is present.

Model the process of polypeptide synthesis, including:

Transcription and translation

Stage 1: TRANSCRIPTION (occurs in nucleus)

1. Initiation: Double stranded DNA unwinds a section.

2. Elongation: RNA polymerase moves along strand attaching loose RNA nucleotides to DNA (A-U and C-G).

3. Termination: Makes strand of mRNA which leaves nucleus into cytoplasm.

Stage 2: TRANSLATION (occurs in cytoplasm)

1. Initiation: Ribosomes bind to mRNA and produce corresponding tRNA anticodon (has complementary nitrogenous bases to those in mRNA). The anticodon has a specific amino acid.

2. Ribosome continues to move along mRNA to produce more tRNA molecules.

3. tRNA releases amino acids to attach to ribosome. tRNA leaves to find another amino acid in cytoplasm.

4. Elongation: As ribosome move along mRNA, more amino acids are attached and linked by peptide bonds.

5. Termination: Stop codon = polypeptide chain released into cytoplasm and either:

Folds to form protein OR

Bonds with other polypeptides and then folds to form protein.

Video resource: https://www.youtube.com/watch?v=gG7uCskUOrA

Assessing the importance of mRNA and tRNA in transcription and translation

mRNA (messenger) = carries genetic code outside nucleus into cytoplasm which is read by ribosomes. IMPORTANT FOR TRANSCRIPTION.

tRNA (transfer) = carries amino acids to ribosomes to form polypeptide chain, there is a different type for every amino acid. At the bottom of tRNA is an anti-codon that and at the top there is an amino acid. IMPORTANT FOR TRANSLATION.

Analysing the function and importance of polypeptide synthesis

Correct polypeptide synthesis ensures correct proteins are made.

For analysing the function/importance of polypeptide synthesis look in 4.3

Assessing how genes and environment affect phenotypic expression

Genotype: homozygous or heterozygous e.g. 50% Bb, 50% bb.

Phenotype: physical appearance e.g. 50% black, 50% white.

Both an organism’s Genotype and Enviroment determine phenotype.

E.g. if 1 identical twin is undernourished as a child, they will not be as tall as the other child.

E.g. flower colour in different soils hydrangeas in acidic soil are blue and in neutral/alkaline are pink.


Investigate the structure and function of proteins in living things


Proteins: complex macromolecules made of one or more polypeptides chains.

Polypeptide chain: sequence of amino acids linked by peptide bonds.

Primary structure: sequence of amino acids to form a polypeptide chain.

Secondary structure: folding the polypeptide chain into a specific shape.

Tertiary structure: further folding the polypeptide chain.

Quaternary structure: protein contains 2 or more polypeptide chains.

Fibrous proteins Globular proteins


No/little tertiary structure

E.g. keratin in hair (structural protein)Compactly folded


Tertiary and quaternary structure

E.g. enzymes and hormones


Enzymes Catalysing biochemical reactions = efficient metabolism e.g. amylase.
Hormones Control body functions e.g. insulin regulates blood sugar.
Antibodies Immune response.
Contractile and motor proteins Movement of muscles e.g. myosin.
Structural proteins Make up an organism e.g. keratin is in hair.
Transport proteins Found in cell membrane and carry vital substances between or in/out of cell.
Receptor proteins Respond to stimuli to maintain homeostasis e.g. neurotransmitter.
Storage proteins Storage of ions and amino acids e.g. casein.


  • Temperature:

Low temperature: Low kinetic energy → substrate and enzyme molecules are not coming into contact frequently.

Medium temperature: More kinetic energy → substrate and enzyme come into contact and collide frequently.

High temperature: Too much kinetic energy puts strain on bonds in enzyme → break → change in active site → denature enzyme

  • pH:

Enzymes are held together by strong bonds.

Charge of H+ interact with bonds in enzyme → bonds break → enzyme active site changes shape.

  • Substrate concentration:

Increases until saturation point, rate thereafter is constant.

Increasing concentration: more collisions.

Saturation point: substrate + enzyme colliding maximum rate all available enzymes being used.

Genetic Variation

Conduct practical investigations to predict variations in the genotype of offspring by modelling meiosis, including the crossing over of homologous chromosomes, fertilisation and mutations

Genetic variability comes from:

1. Gamete Formation

  • Crossing over: homologous chromosomes exchange genes.

  • Independent assortment and random segregation.

2. Sexual Reproduction/Fertilisation

  • Since gametes contain different recombined genetic material the different combinations of gametes fusing together during fertilisation increases variation.

3. Mutation

  • Mutation = change nucleotide sequence in DNA → new alleles → protein production → variation. Comes from:

Error in DNA replication.


  • Mutations can be neutral advantageous, disadvantageous.

NOTE alleles are alternative forms of genes that determines phenotype.

Dominant allele: expressed (visible).

Recessive allele: hidden/masked.

Model the formation of new combinations of genotypes produced during meiosis, including but not limited to:

Interpreting examples of autosomal, sex-linkage, co-dominance, incomplete dominance and multiple alleles

Pattern of inheritance Key features
Autosomal dominant Gene on autosome.

Affected individuals carry at least 1 dominant allele.Autosomal recessiveGene on autosome.

Affected individuals must carry 2 recessive alleles.X-linked dominant (sex-linkage)Does not skip generations.

Affected males transmit the trait to all daughter and no sons.

Unaffected mothers have unaffected sons.X-linked recessive (sex-linkage)Affected females (homozygous) pass trait to all sons.Co-dominancePair of alleles do not show dominance.

In a heterozygous individual both alleles are expressed as separate, unblended phenotypes.

E.g. AB blood.Incomplete dominancePair of alleles do not show dominance.

In a heterozygous individual both alleles are expressed as blended phenotypes.

E.g. white parent plant + red parent plant = pink flowers.Multiple alleles3 or more alternative forms of a gene (alleles).

Only 2 alleles are present in an individual.

E.g. blood type can be A, B or O. An individual can express AA, BB, OO, AB. AO or BO.

NOTE there are VERY FEW Y-linked traits, however they are possible.

Constructing and interpreting information and data from pedigrees and Punnett squares


Punnet Squares: shows the possibilities of the offspring genetic combinations from parents’ genotype.

In the above example there is a 3:1 ratio of expression of dominant : recessive traits.

Collect, record and present data to represent frequencies of characteristics in a population, in order to identify trends, patterns, relationships and limitations in data, for example:

Examining frequency data

  • Single DNA sequence from a useful genetic marker enables scientists to clearly see the difference between individuals in a population → determine genetic relatedness between individuals/species.
  • DNA sequence is only taken from 1 chromosome.

Analysing single nucleotide polymorphism

  • Looks at single bases simultaneously across many chromosomes → gives an overall idea of genetic variation.

Inheritance Patterns in a Population

Investigate the use of technologies to determine inheritance patterns in a population using, for example:

DNA sequencing and profiling

DNA sequencing: Gene from DNA isolated, copies of gene made, fluorescent dye distinguish between 4 bases. Computer graphs sequence.

  • DNA sequencing enables restriction fragment length polymorphism (RFLP) → inheritance pattern technique.

DNA profiling: used to distinguish individuals from each other e.g. identify criminal, identify bodies after disasters.

  • Uses genetic markers (DNA regions) to distinguish an individual.
  • E.g. STRs are genetic markers that have DNA with repeating sections of nucleotides. The number of repeating sections in each individual is unique → identify individuals.
  • Method:

1. DNA extracted.

2. DNA added to primer for each STR (genetic marker).

3. STR amplified.

4. Difference in size of STRs between 2 people is detected by

i) Standard gel electrophoresis

ii) Capillary electrophoresis

NOTE genetic markers are pieces of DNA that are analysed.

Investigate the use of data analysis from a large-scale collaborative project to identify trends, patterns and relationships, for example:

Example: The Human Genome Project

Objective: Sequence all 23 chromosome pairs → discover order of nucleotides in DNA and the number of genes in 1 human.

Outcome: Discovered number of base pairs and sequencing in human DNA → helped scientists locate genes on chromosome → determine gene function, early detection of disease and understanding susceptibility to disease.

The use of population genetics data in conservation management

Population genetics measures genetic variation by analysing the different genetic markers of individuals.

  • More genetic variation = organisms adapt to environmental change = conservation of species.
  • Inbreeding can make unfavourable recessive alleles more common → higher chance that offspring suffers from genetic diseases.

Population genetics studies used to determine the inheritance of a disease or disorder

  • Isolated populations → inbreeding occurs more frequently → unfavourable recessive genes are inherited → unfavourable genetic traits become more common.

Population genetics relating to human evolution

Population genetics enables discovery of evolutionary pathways/relationships. It was discovered that:

  • Humans share 98.8% DNA with chimpanzees and bonobos → closest living relatives.
  • The closest extinct relative to humans is Neanderthal.
  • Denisovans interbred with homo sapiens (evolution).
/**google code below*/ /**google code above*/