Biology AQA-6.Inheritance, Variation and Evolution

meiosis leads to…

non-identical cells

mitosis leads to…

identical cells

Sexual reproduction involves the…

joining (fusion) of male and female gametes

In sexual reproduction there is mixing of…

genetic information which leads to variety in the offspring

The formation of gametes involves…

meiosis

Asexual reproduction involves only…

one parent and no fusion of gametes leading to genetically identical offspring (clones)

meiosis halves the number of…

chromosomes in gametes

fertilisation restores the…

full number of chromosomes.

When a cell divides to form gametes:

• copies of the genetic information are made

• the cell divides twice to form four gametes, each with a single set of chromosomes

• all gametes are genetically different from each other.

Gametes join at…

fertilisation

As the embryo develops cells…

differentiate

Advantages of sexual reproduction:

• produces variation in the offspring

• if the environment changes variation gives a survival advantage by natural selection

• natural selection can be speeded up by humans in selective breeding to increase food production.

Advantages of asexual reproduction:

• only one parent needed

• more time and energy efficient as do not need to find a mate

• faster than sexual reproduction

• many identical offspring can be produced when conditions are favourable.

Malarial parasites reproduce…

asexually in the human host, but sexually in the mosquito.

Many fungi reproduce…

asexually by spores but also reproduce sexually to give variation.

Many plants produce…

seeds sexually, but also reproduce asexually by runners such as strawberry plants, or bulb division such as daffodils.

The genetic material in the nucleus of a cell is composed of a chemical called…

DNA

DNA

polymer made up of two strands forming a double helix.

DNA is contained in structures called…

chromosomes

gene

small section of DNA on a chromosome.

Each gene codes for a…

particular sequence of amino acids, to make a specific protein.

genome of an organism

the entire genetic material of that organism

The whole human genome has now been studied and this will have…

great importance for medicine in the future.

DNA as 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

DNA contains four bases

A, C, G and T.

A sequence of ????? bases is the code for a particular amino acid

three

The order of bases controls the order in which…

amino acids are assembled to produce a particular protein.

The long strands of DNA consist of…

alternating sugar and phosphate sections.

What is a simple description of protein synthesis?

• DNA carries the genetic code for proteins

• A template is made from the DNA and moves to the ribosome

• Ribosomes use the code to join amino acids in the correct order

• This makes a specific protein

How can genetic variants influence phenotype?

• In coding DNA: a change can alter the activity or structure of a protein

• In non-coding DNA: a change can affect when, where, or how much of a gene is expressed

In the complementary strands a C is always linked to a…

G

In the complementary strands a T is always linked to a…

A

change in DNA structure may result in a change in the…

protein synthesised by a gene.

Carrier molecules bring…

specific amino acids to add to the growing protein chain in the correct order.

Mutations

are changes in DNA that occur continuously but most have no effect on the protein

Gamete

a sex cell

Chromosome

a thread-like structure of DNA carrying genetic information

Gene

a section of DNA that codes for a specific protein

Allele

a different version of the same gene (e.g. blue vs brown eye colour)

Dominant allele

always expressed, even if only one copy is present

Recessive allele

only expressed if both copies are recessive

Homozygous

two identical alleles (e.g. BB or bb)

Heterozygous

two different alleles (e.g. Bb)

Genotype

the genetic makeup (e.g. Bb)

Phenotype

physical appearance or characteristics (e.g. brown eyes)

Inherited disorders-Polydactyly

(having extra fingers or toes) is caused by a dominant allele.

Inherited disorders-Cystic fibrosis

(a disorder of cell membranes) is caused by a recessive allele.

Ordinary human body cells contain…

23 pairs of chromosomes.

the genome and its interaction with the environment influence the development of the…

phenotype of an organism.

evolution

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

theory of evolution by natural selection states…

all species of living things have evolved from simple life forms that first developed more than three billion years ago.

speciation

If two populations of a species become so different in phenotype that they can no longer interbreed to produce fertile offspring, they are considered two new species

Selective breeding (artificial selection)

the process by which humans breed plants and animals for particular genetic characteristics.

selective breeding advantages

Increases useful traits, e.g.:

• Disease resistance in crops

• More milk/meat from animals

• Gentle temperament in dogs

• Large or decorative flowers

selective breeding disadvantages

Can lead to inbreeding, which increases risk of:

• Genetic disorders

• Inherited defects

• Reduced variation in the gene pool

genetic engineering

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

Plant crops have been genetically engineered to be…

resistant to diseases or to produce bigger better fruits.

Bacterial cells have been genetically engineered to…

produce useful substances such as human insulin to treat diabetes.

the main steps in the process of genetic engineering.

• enzymes are used to isolate the required gene; this gene is inserted into a vector, usually a bacterial plasmid or a virus

• the vector is used to insert the gene into the required cells

• genes are transferred to the cells of animals, plants or microorganisms at an early stage in their development so that they develop with desired characteristics.

Tissue culture

using small groups of cells from part of a plant to grow identical new plants. This is important for preserving rare plant species or commercially in nurseries.

Cuttings

an older, but simple, method used by gardeners to produce many identical new plants from a parent plant.

Embryo transplants

splitting apart cells from a developing animal embryo before they become specialised, then transplanting the identical embryos into host mothers.

Adult cell cloning

• The nucleus is removed from an unfertilised egg cell.

• The nucleus from an adult body cell, such as a skin cell, is inserted into the egg cell.

• An electric shock stimulates the egg cell to divide to form an embryo.

• These embryo cells contain the same genetic information as the adult skin cell.

• When the embryo has developed into a ball of cells, it is inserted into the womb of an adult female to continue its development.

Lamarck

believed changes during an organism’s life could be inherited (e.g. a giraffe stretching its neck). This has since been disproved.

Darwin’s theory of evolution

• Organisms in a species show variation

• Those with the best-adapted traits survive and reproduce

• These traits are passed on to the next generation

• Over time, this leads to evolution

Why was Darwin’s theory of evolution controversial?

challenged religious ideas, lack of evidence, little knowledge of inheritance mechanisms

What was Wallace’s role in the theory of evolution?

worked worldwide gathering evidence for evolutionary theory. He is best known for his work on warning colouration in animals and his theory of speciation.

In the mid-19^th Century Gregor Mendel carried out…

breeding experiments on plants. One of his observations was that the inheritance of each characteristic is determined by ‘units’ that are passed on to descendants unchanged.

Evidence for evolution

fossils and how resistance to antibiotics evolves in bacteria

Fossils may be formed:

• from parts of organisms that have not decayed because one or more of the conditions needed for decay are absent

• when parts of the organism are replaced by minerals as they decay

• as preserved traces of organisms, such as footprints, burrows and rootlet traces.

Fossils

‘remains’ of organisms from millions of years ago, which are found in rocks.

scientists cannot be certain about how life began on Earth because…

Many early forms of life were soft-bodied, which means that they have left few traces behind

Extinctions

no remaining individuals of a species still alive.

Why can bacteria evolve rapidly?

reproduce quickly, allowing them to undergo frequent mutations

How do mutations in bacterial pathogens lead to new strains?

• Mutations in the DNA of bacteria can result in new strains of bacteria.

• Some of these strains may have resistance to antibiotics, meaning they are not killed by treatment.

The resistant strains of bacteria will spread because…

people are not immune to it and there is no effective treatment.

What is MRSA?

a strain of bacteria that is resistant to many antibiotics

How can doctors help reduce the development of antibiotic-resistant strains like MRSA?

not prescribe antibiotics inappropriately to reduces the chance of developing resistance.

Linnaeus classes

kingdom, phylum, class, order, family, genus and species

Archaea

primitive bacteria usually living in extreme environments

Bacteria

true bacteria

Eukaryota

includes protists, fungi, plants and animals