topic 6 merge

Sexual reproduction

Type of reproduction

Involves the production of gametes by meiosis

A gamete from each parent fuses to form a zygote

Genetic info from each gamete is mixed so the zygote is unique

What are gametes

Sex cells (sperm cells and egg cells in animals and pollen and egg cells in flowering plants )

Haploid (half the numbers of chromosomes)

What’s meiosis

• Form of cell division involved in the formation of gametes in reproductive organs

• Chromosomes numbers is halved

• Involves two divisions

What must occur prior to meiosis ?

Interphase - copies of genetic info are made during this pro

What happens during the first stage of meiosis ?

Chromosomes pairs lineup along the cell equator

the pair of chromosomes are separated and move to opposite pole of the cell

chromosome number is halved

What happens during the 2nd stage of meiosis

The chromatid's are separated and moved to opposite poles of the cells

4 unique haploid gametes are produced

• Why is meiosis important for sexual reproduction? (2 marks )

Increase genetic variation

Ensure the zygote formed at fertilisation is diploid

Describe fertilisation and its resulting outcome

Gametes join together to restore the normal number of chromosomes and the new cell then divides by mitosis

As the embryos develops , cells differentiate

What is the advantage of sexual reproduction

It creates genetic variation in offspring , increasing the probability of a species adapting to and surviving environmental changes

Natural selection can be sped up by humans

Disadvantages of sexual reproduction

Two parents are required. Difficult in endangered species

More time and energy is required so fewer offspring produced

What is asexual reproduction

• Type of reproduction

• involves mitosis only

• produces genetically identical offspring known as daughter cells

describe 3 advantages of asexual reproduction

• only one parent required

• lots of offsprings can be produced in a short period of time, reducing competition from other species

• requires less time and energy , as no partner is required

What's the disadvantage of asexual reproduction?

No genetic variation reducing the probability of a species being able to adapt to any environmental change

Describe the circumstances in which malaria parasites reproduce sexually and asexually

Sexual reproduction in the mosquito and asexual reproduction in the human host

Describe the circumstances in which fungi reproduce sexually and asexually

Asexual reproduction by spores, sexual reproduction to give variation

Describe the circumstances in which plants reproduce sexually and asexually

Sexual reproduction to produce seeds, asexual reproduction by runners(strawberry plants) or bulb division(daffodils)

What is DNA?

A double stranded polymer of nucleotides wound to former double helix

The genetic material of the cell found in its nucleus

Define genome

The entire genetic material of an organism

Why is understanding the human genome important?

The whole genome has been studied and is important for the development of medicine in the future

• Searching for genes linked to different types of disease

• understanding and treating inherited disorders

• and tracing human migration patterns from the past

What is a chromosome?

A long coiled molecule of DNA that carries genetic information in the form of genes

How many chromosomes do human body cells have?

46 chromosomes in 23 pairs

How many chromosomes do human gametes have?

23 chromosomes

Define gene

A small section of DNA that codes for a specific sequence of amino acids which undergo polymerisation to form protein

What are the monomer of DNA?

Nucleotides

What are DNA nucleotides made up of?

• Sugar pentagon

• phosphate group circle

• one of the four bases ACGT rectangle

Describe how nucleotides interact for a molecule of DNA

• Sugar and phosphate molecules joint to form a sugar phosphate backbone in each DNA strand.

• Base connected to each sugar.

• Complementary base pairs (A pairs with T, C pairs with G) joined by weak hydrogen bonds.

Explain how a gene codes for protein

• A sequence of three bases in a gene forms a triplet.

• Each triplet codes for an amino acid.

• The order of amino acids determine the structure and function of protein form.

Why is the folding of amino acids important in protein such as enzymes?

The folding of amino acids determines the shape of the active site which must be highly specific to the shape of its substrate

What is protein synthesis?

The formation of a protein for a gene

What are the two stages of protein synthesis?

Transcription and translation

What does transcription involve?

The formation of mRNA from a DNA template

Describe transcription

• DNA double helix unwinds

• RNA polymerase binds to a specific base sequence of non-coding DNA in front of a gene and moves along the DNA strand

• RNA polymerase joints free RNA nucleotides to complementary basis on the coding DNA strand

• mRNA formation complete .mRNA detach and leaves the nucleus

What does translation involve?

A ribosome joins amino acids in a specific order dictated by mRNA to form a protein

Outline translation

• mRNA attaches to a ribosome

• Ribosome reads the mRNA bases in triplets each triplet codes for one amino acid which is brought to the ribosome by tRNA molecule

• A polypeptide chain is formed from the sequence of amino acid which joined together

What is a mutation?

• Mutation is a random change in the basic sequence of DNA which results mostly no change to the protein code for or genetic variance of the protein

• Mutations are continuously

Describe the effect of a gene mutation in coding DNA

• If a mutation changes the amino acid sequence protein structure and function may change(an enzyme may no longer fit it substrate binding site or a structural protein may lose its strength)

• If a mutation does not change amino acid sequence there is no effect on protein structural function

What is non-coding DNA?

DNA, which does not code for a protein but instead of controls gene expression

Describe the effect of a gene mutation in non-coding DNA

Gene expression may be altered affecting protein production and the resulting phenotype

What are alleles

Different versions of the same gene

What is a dominant allele

A version of a gene only one copy is needed for it to be expressed

What is a recessive allele

A version of a gene where two copies are needed for it to be expressed

What is meant when an organism is homozygous?

When an organism has two copies of the same allele (two recessive or two dominant)

What is meant when an organism is heterozygous?

When an organism has two different versions of the same gene(one dominant and one recessive)

What is the genotype?

The genes present for a trait

What is a phenotype?

Visible characteristic

How are dominant alleles represented in a punnet square?

Their represented using uppercase letters

What is the problem with single gene crosses?

Most characteristics are controlled by multiple alleles rather than just one

What is an inherited disorder?

A disorder caused by the inheritance of certain alleles

Give two examples of inherited disorders

Polly dactyl(having extra fingers or toes)-caused by dominant allele

Cystic fibrosis (a disorder of cell membranes) caused by recessive allele

How are embryos screened for inherited disorders?

During IVF once out is removed from an eight cell embryo and tested for disorder causing alleles. If the cell doesn't have any indicator alleles than the originating and is implanted into the uterus.

What are the ethical issues concerning embryo screening?

• It could lead to beliefs in society that being disabled or having a disorders less human or associated with inferiority.

• The destruction of embryos with inherited disorders are seen by some as murder as these would go on to become human beings.

• It could be viewed as part of the concept of designer babies as it may be for parents convenience or wishes rather than the child's well-being

What are the economic issues concerning embryo screening?

Cost of hospital treatment and medication will need to be considered if it is known that a child will have an inherited disorder and financial support explored if necessary

What are the social issues concerning embryo screening?

• Social care for children with inherited disorders may need to be considered if parents are unable to provide care.

• If an embryo is found to have an inherited disorder and is terminated, this can prevent a child in its parents from potential suffering in the future due to the disorder

What are sex chromosomes?

A power of chromosomes that determine sex:

• Males have an X and Y chromosome

• Females have 2 X chromosomes

Why does the inheritance of a Y chromosome mean that an embryo develops into a male?

Testes develop in an embryo is stimulated by a gene present on the Y chromosome

What is variation?

Differences in characteristics of individuals in a population

Two causes of variation within a species

• Genetics

• Environment

• A mix of genetics and environment

What is genetic Varey

• Variations in the genotype of organisms of the same species due to the presence of different alleles

• Create differences in phenotypes

What creates genetic variation in a species?

• ]Spontaneous mutations

• Sexual reproduction

What is a mutation?

Change to the base sequences in DNA which results in genetic variance ,they occur continuously

Explain how a gene mutation may affect an organism phenotype (three marks)

• Neutral mutation does not change the sequence of amino acids, protein structure and function same no effect on phenotype

• Mutation make towards a minor change in an organism phenotype e.g. change in eye colour

• Mutation may completely change the sequence of amino acids. This may result in a non-functional protein . severe changes to phenotype.

What is the consequence of a new phenotype caused by mutation being suited to an environmental change?

There will be a rapid change in the species

What is evolution?

• A gradual change in the inherited traits within a population overtime

• A cause due to natural selection which may be resulting in the formation of a new species

Outline the theory of natural selection

All species of living things have evolved from simple life forms that first developed more than 3 billion years ago

• Genetic variation exist due to spontaneous mutations

• Selection pressures, e.g. competition and disease exist

• Random mutation gives an organism a selective advantage

• Organism is better adapted to the environment and survives

• Organism reproduce is passing on its beneficial alleles

• Frequency of advantageous alleles increase

How do two populations become different species?

When their phenotypes become different to the extent that they can no longer into breed to produce fertile offspring

What is selective breeding?

The process by which humans artificially select organisms with desirable characteristics and breed them to produce offspring with similar phenotypes

Outline the main steps involved in selective breeding

• Identify a desired characteristic, e.g. disease resistance

• Select parent organisms that show the desired traits and breed them together

• Select offspring with the desired traits and breed them together

• Process repeated into all offsprings have the desired traits

Give examples of characteristics selected for in selective breeding

• Disease resistance in crops

• Higher milk or meat production in animals

• Gentle nature in domestic dogs

• Large flowers

What is the main advantage of selective breeding?

• Create organisms with desirable features such as:

• Crops produce a higher yield of grain

• Plants produce larger fruit

• Cows produce a great supply of milk

• Domesticated animals

Other than in agriculture where else is selective breeding useful

• In medical research

• In sports such as horse racing

Outline the 4 disadvantages of selective breeding

• Reduction in the gene pool, which becomes especially harmful if sudden environmental changes occur

• In breeding results in genetic disorders

• Development of the other physical problems, e.g. respiratory problems in bulldogs

• Potential to unknowingly select harmful recessive alleles

What is genetic engineering

• The modification of the genome of an organism by the insertion of a desired gene from another organism - jeans from chromosomes of humans and other organisms can be cut out and transferred to cells of other organisms

• Enable the formation of an organism with beneficial characteristics

Given an example of uses for genetically modified plants

• Disease resistance

• Produce larger fruits

What is the use for genetically modified bacteria cells?

To produce human insulin to treat diabetes mellitus

Describe three benefits of genetic engineering

• Increased crop yards for growing population, e.g. herbicide resistant and disease resistance

• Useful in medicine, e.g. insulin producing bacteria, antithrombin and goat milk, possibility to overcome some inherited disorders

• GM crops produce scarce resources, e.g. GM golden rice produces beta carotene a source of vitamin A

Describe four risks of genetic engineering

• Long-term effects of consumption of GM crops is unknown

• Negative environmental impacts, e.g. reduction in biodiversity, impact on a food chain, contamination of non-GM crops forming super weeds

• Late onset health problems in GM animals

• GM seeds are expensive and low income development countries may be unable to afford them or maybe dependent on businesses that sell them

How is genetic engineering used to protect crops against insects?

• The gene for toxin production in BT can be isolated and inserted into DNA for crops

• BT crops not secret the toxin which kills any insect larvae that feed on it

Outline the theory of evolution by natural selection

Individuals of a species show a wide range variation for a characteristic

Those with the characteristic most suited to the environment will survive breed most successfully

The desirable characteristics that has enabled the individuals to survive are passed onto the offspring

Why was Darwin the theory of evolution not accepted initially?

Most people believe believed in creationism

Insufficient evidence to prove the theory

The mechanism of variation and inheritance was not known at the time

What was Jean Baptiste Lamarck’s theory of inheritance?

That changes during the lifetime of an organism can be inherited

What is speciation?

The formation of a new species when two population become so vary that they cannot interbreed to produce fat offspring

What is the definition of a species?

A group of organisms with similar characteristics which are able to enter breed to produce fertile offspring

Outline this process of speciation through geographic isolation

Two populations of the same species are separated geographically

Geographic isolation prevents into breeding and mixing of genes between the populations

Due to different selection pressure different mutations are occur producing different phenotypes in each population

Overtime the two populations may evolve so that they are not able to enter breed

Why is genetic variation important in speciation?

Genetic variation produces phenotypic variation, some of which are better suited to the environment and are selected for

How did Mendel study inheritance?

Through Carrie breeding experiments on plants and analysing the ratio of characteristics in offspring

Why was Mendel's work not recognised until after his death?

He could not explain the mechanism of inheritance as chromosomes were only discovered after his death

It was not communicated well to other scientists and not published and reputable scientific journals

State the two kinds of evidence used to show evolution

Fossils

antibiotic, resistance in bacteria

How are fossils formed?

Parts of an organism that have not decayed due to conditions needed for decay being absent

Parts of organisms that have been replaced by minerals as they decayed

Traces of organisms are preserved covered in sediment and becoming rock

Why are there few traces of early lifeforms left behind?

They are mostly softbodied

How do fossils act as evidence of evolution?

Scientist can identify the ages of the fossils and use them to show how organisms change over time

What do branches in evolutionary trees indicate?

Where speciation has occurred

What is extinction?

When there are no individuals of a species left alive

State factors that may lead extinction

New disease

Predation

Competition

Changes an environment

Catastrophic events

What enables bacteria to evolve quickly?

The fast rate of their reproduction

Outline the process of antibiotic resistance bacteria evolving

Mutations are occurring bacteria producing genetic variation

Certain strains of resistant to antibiotic antibiotics and I'm not killed when the antibiotics applied

Resistant strain survive and reproduce

Overtime the population of the resistant strains increase

Why are resistant strains of bacteria dangerous?

People have no immunity to them, and there is no effective treatment

State an example of resistant strain of bacteria

MRSA

What can be done to reduce the rate of development of antibiotic resistant bacteria?

Refrain from inappropriately prescribing antibiotics e.g. for viral disease diseases

Patient should complete the prescribed course of antibiotics

Restrict agricultural uses of antibiotics

Why is it difficult to keep up with emerging resistance strains?

Developing antibiotics have a high cost and take a long time to develop

What are the classes of organisms as determined by Carl Linnaeus?

Kingdom

Phylum

Class

Order

Family

Genus

Species