Biology Variation and Selection Unit

DNA

Long list of instructions on how to put an organism together and make it work.

Genome

All of an organisms’s DNA

What does each gene in a DNA molecule contain?

Chemical instructions that codes for a particular proten, replicating to make genetically identical copies to pass on to offspring.

Where is DNA located?

In the nucleus as chromosomes

Alleles

Different versions of the same genes that determine inherited characteristics.

Describe the structure of DNA

Double helix shaped, double stranded chain of nucleotides

DNA complementary base pairing

A-T, C-G

Nucleotide components

Phosphate group (circle), Pentose sugar (pentagon), nitrogenous base (rectangle)

RNA structural difference from DNA

Single-stranded nucleotide chain, having ribose sugar instead of deoxyribose. It has U instead of T.

mRNA

Copy of DNA during transcription

tRNA

Carrier amino acids to ribosomes to make protein during translation.

Gene

Section of DNA that codes for a particular protein

Codon

A sequence of three nucleotides in a gene each amino acid is coded for

Describe the process of DNA Replication (5 steps)

1. DNA double helix separates.

2. Each strand is a template for the new DNA strand.

3. DNA polymerase puts new nucleotides together forming a new strand.

4. Two identical copies of DNA are made.

5. Each strand contains a parent strand and a new complementary strand.

Transcription process (4 steps)

1. RNA polymerase binds to a region of non-coding DNA in front of a gene.

2. Double stranded DNA seperates, exposing the nitrogen bases, and the RNA polymerase moves along one of the strands of DNA.

3. mRNA is formed from the template strand using the complementary base pairing rules

4. mRNA leaves the nucleus into the cytoplasm (to the ribosome)

Transcription

Converts DNA to mRNA in the nucleus

What are proteins made by?

Ribosomes

RNA polymerase

Enzyme involved in joining together the base sequence to make mRNA.

Translation

Converts mRNA into protein

Translation process (4 steps)

1. A codon is read to make one amino acid.

2. tRNA has an anti-codon which is complementary to the codon on mRNA.

3. tRNA carries one amino acid to the ribosome, this process repeats for the whole gene.

4. Ribosomes join together these amino acids to form a protein.

Mutation

A change in the nitrogenous base sequence of DNA in a cell.

When does mutation occur?

During DNA replication

Duplication (mutation)

Extra copy/copies of a nucleotide

Deletion (mutation)

Missing nucleotide(s)

Substitution

Different nucleotide(s) replace an original

Inversion

Part of the nucleotide sequence is reversed

Mutagen

An agent such as radiation or chemical substance that causes genetic mutation

Template strand/ Non-coding region

Involved in protein synthesis but do not code for any amino acids

Diploid number of human cells

46

Haploid number of human cells

23

Homologous pair/chromosomes

Pairs of the same chromosome in diploid cells

Mitosis

When a cell reproduces itself by splitting to form two cells with identical sets of chromosomes.

Mitosis process (5 steps)

1. DNA is all spread out in long strings. (interphase)

2. DNA forms X-shaped chromosomes in order to duplicate its DNA. (prophase)

3. The chromosomes line up at the centre of the cell and cell fibres pull them apart, the two arms of each chrosomes going to opposite ends of the cell. (Metaphase and Anaphase)

4. Membranes form around each of the new sets of chrosomes, becoming the nuclei of the two new cells. (Telophase)

5. The cell membrane splits and produces two genetically identical daugher cells (cytokinesis)

Why is mitosis important?

Replace lost layers of skin cells, replace lining of intenstines, create new blood cells, understanding cancer cells

Meiosis

Produces 4 haploid cells whose chromosomes are not identical.

What process forms gametes?

Meiosis

Meiosis process (6 steps)

1. Chromosomes condense and pair up in homologous pairs.

2. Chromosomes line up in pair in the centre of the cell.

3. Chromosomes are pulled apart into seperate chromatids.

4. The nucleus splits, producing two daugher cells.

5. Chromatids in each nucleus line up again in the centre of the cell.

6. Chromatids are pulled apart to seperate ends again, and cell division occurs to produce four genetically diverse haploid cells.

How does meiosis introduce genetic variation?

When the cell divides, each new cell has some of chromosomes are from the organisms’s father and some are from the mother. This mixing up of chromosomes creates genetic variation.

Zygote

A fertilized egg cell when the male gamete fuses with the female gamete.

Genotype

The alleles an organism has for a certain feature

Phenotype

The characteristics the alleles produce.

Dominant allele

The allele that will result in the phenotype of an organism

Recessive allele

The allele that will not become the phenotype, it will only be carried by the organism

Heterozygous

When an individual has two different alleles for a particular gene

Homozygous

When an individual has the same two alleles for a particular gene

When are pedigree diagrams used?

When showing more than two generations of how a gene is passed on

Monohybrid inhertiance

The inhertiance of a single charactertistic

Polygenic inhertiance

Many characteristics are controlled by multiple genes working together to create a range of phenotypes, known as continous variation.

Complete dominance

One dominant allele completely hides the phenotype on the recessive allele

Codominance

Both alleles contribute to the phenotype

Factors affecting environmental variation for plants

sunlight, moisture levels, temperature, mineral content

Theory of evolution

Life began as simple organisms from which more complex organisms evolved.

Natural selection

Species show variation in their characteristics. Changing environment favors a particular characteristic, and therefore the frequency/population of well-adapted individuals increase.

Selective advantage

When changing environment favors a particular characteristic

Survival of the fittest

Population of species with a selective advantage grows whereas other die out.

Describe the process of bacteria becoming antibiotic resistant (4 steps)

1. Random mutations occur in bacteria

2. Some strains may give them resistance to an antibiotic

3. Resistant strain have selective advantage over other strains, so they increase in population while others die out.

4. Resistant bacteria can pass on genes to future generations or other species.

Selective Breeding / Artificial Selection

Breeding only those individuals with desirable features, by human choice/pressures.

Artificial insemination

Farmers can buy semen to inseminate female animals and produce offspring with desirable characteristics.

Reasons for selective breeding in animals

More product, more offspring, increased resistance to disease, perform certain tasks

Micropropogation process (5 steps)

1. Stem tips are removed from plant.

2. Surface of explants are sterilize to kill microorganisms that may cause disease.

3. Explants are placed in agar.

4. Growing explants are transferred to a different growth medium that encourages root growth.

5. Once roots have grown, they are transferred to soil in greenhouses.

How might surface of explants be sterlized?

Using chemicals (alcohol) or UV radiation

Why are explants placed in agar during micropropagation?

It is a growth medium that contains nutrients and hormones to encourage growth

What does it mean if a cell is diploid?

They have two copies of each chromosome

Process that ensures the mRNA is a complementary copy of the gene

Complementary base pairing