Biology Topic 6

Sexual Reproduction

The fusion of male and female gametes (sperm and egg in humans, pollen and egg in plants)

To create genetically different offspring.

Asexual reproduction

Involves only one parent and no fusion of gametes.

Asexual Reproduction - Creates genetically _______________ offspring(meiosis).

Creates genetically *identical* offspring(mitosis).

Advantages of Sexual Reproduction

1) Produces variation in the offspring.

2) Variation gives a *survival advantage* by natural selection.

Advantages of Asexual Reproduction

1) No mate is required so its time efficient, populations can increase faster.

2) Many identical offspring produced when conditions are favourable

3) Faster than sexual reproduction.

How do malarial parasites reproduce both sexually and asexually?

*Malarial parasites* reproduce *asexually* in the *human host*, but *sexually* in the *mosquito*.

How do fungi reproduce both sexually and asexually?

Many *fungi* reproduce *asexually* by *spores* but *reproduce sexually* to give *variation*.

How do plants reproduce both sexually and asexually?

Many *plants* produce *seeds sexually*, but reproduce *asexually* by *runners* such as strawberry plants.

Meiosis

Type of cell division that halves the number of chromosomes in the parent cell to produce 4 gametes.

1) The cell duplicates its chromosomes, ('x-shaped').

2) 'X-shaped' chromosomes lined up in pairs along the centre of the cell(from both parents)

3) Chromosomes pulled apart, to opposite ends on the cell and the cell divides forming 2 new cells

4) Chromosomes line up, in centre of cells again, and each arm is pulled to opposite ends.

5) 4 new gametes created, each with different set of chromosomes and half the amount of genetic material.

Fertilisation

Fertilisation restores the full number of chromosomes

Mitosis vs. Meiosis

• Mitosis: Produces 2 daughter cells, 1 cell division, creates diploid cells (46 chromosomes), cells are genetically identical to each other and the parent. Used for growth, repair, and asexual reproduction.

• Meiosis: Produces 4 gametes, 2 cell divisions, creates haploid cells (23 chromosomes), cells are genetically different from each other and the parent. Used for sexual reproduction.

Structure of DNA

• DNA is a polymer made from four different nucleotides. Each nucleotide consists of a common sugar and phosphate group with one of four different bases attached to the sugar (A, T, G, C).

• A sequence of three bases (codon) codes for a particular amino acid. The order of bases controls the order in which amino acids are assembled to produce a particular protein.

Human Genome

The genome is the complete genetic information of an organism.

Studying human genome helps identify disease-related genes, understand genetic disorders and study human migration.

Nucleotides

1) DNA is made up of nucleotides, each containing a sugar, phosphate group, and one of four bases: A, T, G, or C.

2) Groups of 3 bases (codons) code for amino acids, determining the proteins made.

3) A pairs with T, and G pairs with C.

Protein Synthesis

mRNA is created from DNA in the nucleus and travels to ribosomes in the cytoplasm.

• Ribosomes use mRNA to assemble amino acids into proteins based on the DNA sequence.

• When the protein chain is complete, it folds up to form a unique shape, enabling it to function as enzymes, hormones, or structural proteins like collagen.This process is essential for cellular function and growth.

Mutations

• Mutations are changes in DNA that can affect protein structure and function.

• Types of mutations: insertions, deletions, and substitutions.

• Most mutations do not alter the protein or only alter it slightly. However, some mutations can lead to diseases or dysfunctional proteins.

Genetic inheritance

…

Gametes

Sex cells (egg and sperm in animals)

Genes

Sections of DNA that code for specific proteins.

Alleles

Different versions of the same gene, inherited from each parent. Dominant alleles: Always expressed (uppercase letter). Recessive alleles: Only expressed if two copies are present (lowercase letter).

Homozygous an Heterozygous

Two identical alleles (e.g., BB or bb).

Two different alleles (e.g., Bb).

Genotype

The alleles an organism has for a specific trait.

Phenotype

The observable characteristics determined by the genotype.

How many pairs of chromosomes do humans have?

23 pairs of chromosomes

1) What do the first 22 pairs of chromosomes control? 2) What does the 23 pair of chromosome control?

1) They control traits 2) They control sex

Female and Male chromosomes?

Females have two X chromosomes (XX). Males have one X and one Y chromosome (XY).

What chromosomes do egg cells carry? What chromosomes do sperm cells carry?

Eggs - X Sperms - X or Y

Homozygous

 Two of the same alleles (e.g., BB or bb)

Heterozygous

Two different alleles (e.g., Bb).

Dominant allele

 Always expressed even if only one copy is present.

Recessive allele

Only expressed if two copies are present.

Cystic Fibrosis

Cause: Recessive allele (f). Effects: Leads to thick, sticky mucus in the lungs and digestive system.

Polydactyly

Cause: Dominant allele (D). Effects: Results in extra fingers or toes.

How do mutations contribute to variation?

• A mutation is a random change in DNA which therefore affects a gene and/or chromosome.                                                                        

• If a mutation causes a new phenotype that makes an organism better suited to a particular environment, it can lead to rapid change in the characteristics of the individuals in that species.

Embryo Screening

Purpose: To detect genetic disorders in embryos.

Methods: IVF embryos can be tested, and those with genetic disorders may be discarded.

Embryo Screening(advantages)

Helps prevent suffering by avoiding the birth of children with serious disorders. Reduces long-term healthcare costs.

Embryo Screening(disadvantages)

Ethical concerns about destroying potential life.

May imply that individuals with disorders are undesirable.

Screening procedures can be expensive.

Potential for misuse in selecting preferred traits(designer baby).

Variation

Differences in characteristics of individuals in a population are called variation.

What are the causes of variation?

1. Genetic causes (inherited genes).

2. Environmental causes (conditions during development).

3. Combination of genes and environment.

Evolution

Evolution is a change in the inherited characteristics of a population over time through natural selection, which may result in the formation of a new species.

Charles Darwin - Theory of Evolution by Natural Selection

- Proposed species evolve through natural selection.

- Variations lead to survival of advantageous traits.

- Supported by fossil evidence (e.g., finches).

Darwin - Iniitially not believed

- Lack of genetic understanding at the time.

- No evidence.

Alfred Russel Wallace - Co-discovered Natural Selection

- Developed the same theory as Darwin.

- Studied species distribution, leading to the idea of geographic isolation in evolution.

- Contributed to natural selection's validation.

Alfred Russel Wallace - Iniitally not believed

- Initially overshadowed by Darwin’s work.

- His work wasn't widely recognized until later.

Gregor Mendel - Father of Genetics

- Discovered the basic principles of inheritance (dominant/recessive alleles).

- Proposed laws of inheritance: Segregation & Independent Assortment.

- Laid foundation for genetics.

Gregor Mendel - Iniitally not believed

-  Did not know about chromosomes

- Mendel was not part of academic establishment - a monk

Jean-Baptiste Lamarck - Theory of Inheritance of Acquired Characteristics

- Proposed organisms change traits during their lifetime due to environmental factors, and these traits are passed on.

- Early attempt to explain evolution.

Jean-Baptiste Lamarck - Initially not believed

- Later disproved as acquired traits are not genetically inherited.

- Modern genetics showed his theory was incorrect.

Speciation

Speciation occurs when two populations of a species become so different that they can no longer interbreed to produce fertile offspring.

What is natural selection?

Individuals with characteristics most suited to the environment are more likely to survive and breed successfully, passing on their advantageous traits.

What is selective breeding?

Selective breeding (artificial selection) involves choosing parents with desired characteristics to breed together over many generations.

What are examples of selective breeding?

• Disease resistance in crops.

• Animals that produce more meat or milk.

• Domestic dogs with gentle temperaments.

• Large or unusual flowers.

What are the risks of selective breeding?

Reduced genetic variation increases vulnerability to pests and diseases.

Selecting traits can preserve harmful genes.

What is genetic engineering?

Genetic engineering involves modifying the genome of an organism by introducing a gene from another organism to give a desired characteristic.

What are examples of genetic engineering?

• GM crops resistant to diseases or producing bigger fruits.

• Bacteria engineered to produce human insulin.

What are concerns about genetic engineering?

• Effects on wild populations.

• Crops resistant to viruses can cause virus to mutate to even worser virus

What is tissue culture in cloning?

Using small groups of cells from a plant to grow identical new plants.

What are cuttings in cloning?

• Take a healthy plant cutting (stem, leaf, or root).

• Plant the cutting in soil or water in warm, moist conditions.

• Wait for roots to develop and the cutting grows into a new plant.

What are embryo transplants in cloning?

• Fertilize an egg cell to create an embryo.

• Split the embryo into smaller sections.

• Grow each section into separate embryos.

• Implant embryos into a surrogate’s womb to produce clones.

Adult cell cloning

• 1. Remove an egg cell from the ovary and remove its nucleus to create an empty egg cell.

  2. Insert the nucleus from a body cell into the empty egg cell.

  3. Apply a small electric shock to stimulate the egg to divide and form a ball of cells (an embryo).

  4. Implant the embryo into the womb of a female, leading to the birth of a cloned animal.

  
  

Natural selection

1. Individuals within a species show variation.

2. Those with characteristics most suited to the environment survive and reproduce.

3. Advantageous traits are passed to the next generation.

Extinction

 Species dying out because of:

• Environmental changes

• New predators

• New diseases

Fossils

 Remains of organisms from millions of years ago, found in rocks.
Formed by:

• Plant/animal covered in mud

• Soft parts decay

• Minerals enter bones

Why the fossil record is incomplete

• Conditions not right for fossilisation

• Fossils not yet found

What is evidence for evolution

Evidence includes fossils, antibiotic resistance in bacteria, and genetic studies.

Why do bacteria evolve rapidly?

Bacteria evolve rapidly due to fast reproduction rates.

How do antibiotic-resistant strains arise?

Mutations can produce antibiotic-resistant strains, which survive and spread.

How can we reduce antibiotic resistance?

1. Doctors should prescribe antibiotics appropriately.

2. Patients should complete antibiotic courses.

3. Restrict agricultural use of antibiotics.

Classification

Organising living organisms.
Original system by Carl Linnaeus:
Domain,  Kingdom, Phylum, Class, Order, Family, Genus, Species. (Don’t know peter crouch, oh for goodness sake)                            

Binomial name = Genus + Species

What is the modern classification system?

The three-domain system:

1. Archaea (primitive bacteria).

2. Bacteria (true bacteria).

3. Eukaryota (protists, fungi, plants, animals).

What are evolutionary trees?

Evolutionary trees show relationships between organisms based on current and fossil data.