[B6] Inheritance, variation and evolution

What is sexual reproduction? (2)

A process which involves the fusion of male and female gametes

The mixing of the parents' genes means offspring are genetically different to their parents, causing variation

What cells are involved in sexual reproduction in animals and in plants? (2)

Sperm and egg cells in animals

Pollen and egg cells in flowering plants

What is asexual reproduction? (2)

A process which involves only one parent and no fusion of gametes so only mitosis is involved

There is no mixing of genetic information, so offspring are genetically identical, with no variation (clones)

What are some advantages of sexual reproduction? (2)

Produces variation in the offspring so, if the environment changes, it gives a survival advantage by natural selection

It means natural selection can be sped up by humans in selective breeding to increase food production

What are some advantages of asexual reproduction? (3)

Only one parent needed, making it more time and energy efficient as it doesn't need to find a mate

Faster than sexual reproduction

Many identical offspring can be produced when conditions are favourable

What is meiosis?

When cells divide twice to form gametes (which have half the number of chromosomes as body cells)

What happens during meiosis? (3)

The cell makes copies of its genetic information

The cell divides twice to form 4 gametes, each with a single set of chromosomes (23)

All the gametes are genetically different from each other

What happens during and after the fusion of gametes in fertilisation? (3)

Gametes join at fertilisation to restore the normal number of chromosomes

The new cell divides by mitosis and the number of cells increases

As the embryo develops, cells differentiate

What are gametes? (2)

An organism's reproductive cells, which have half the usual genetic information

Each cell carries only one copy of each chromosome

What are the female and male gametes called in animals? (2)

Female gametes are ova / egg cells

Male gametes are sperm

When do malarial parasites reproduce sexually?

When interacting with other mosquitos

When do malarial parasites reproduce asexually?

In the human host

When will fungi reproduce sexually?

To produce variation

When will fungi reproduce asexually?

To produce spores

What can plants produce through asexual production?

Runners such as strawberries and bulbs for daffodils

What is DNA? (2)

The chemical that a cell's genetic information is composed of

It is a polymer, made up of two strands forming a double helix

Where is DNA found?

It is found organised into chromosomes in the nucleus

What is a gene? (2)

A small section of DNA on a chromosome

Each one codes for a particular sequence of amino acids, to make a specific protein

What is a genome?

All of the genetic material of an organism

What can scientists do now that they understand the human genome? (3)

Search for genes linked to different types of disease

Understand and treat inherited disorders

Trace human migration patterns from the past

What is DNA made from?

A polymer made up of repeating nucleotide units

What are the four bases of DNA?

A (adenine) - T (thymine), C (cytosine) - G (guanine)

What does a sequence of three bases provide the code for?

How amino acids are assembled

What is protein synthesis? (2)

The process by which DNA codes to make proteins

In the cell, ribosomes assemble amino acids in the correct order to produce functional proteins

In strands of DNA, what is the complementary base pair to T molecules?

A

In strands of DNA, what is the complementary base pair to C molecules?

G

What are some of the functions of folder protein chains? (3)

Form enzymes

Produce hormones

Produce body structures such as collagen

What are the functions of non-coding DNA? (4)

Controls gene expression

Makes chromosomes stable

Contributes to variation (can mutate without affecting proteins)

It doesn’t produce protein

What is an allele? (2)

One of two or more versions of a gene

There are two alleles for each gene

What are dominant and recessive alleles? (2)

A dominant allele is always expressed, even if only one copy is present (DD or Dd)

A recessive allele is only expressed if two copies are present (dd)

Define heterozygous and homozygous.

Homozygous = a gene that has two identical alleles (e.g. DD or dd)

Heterozygous = a gene that has two different alleles (e.g. Dd)

What do genotype and phenotype mean? (2)

Genotype = the alleles present

Phenotype = the physical expression, or characteristics, of that trait (e.g. hair colour)

How does an organism's genotype relate to its phenotype?

The alleles present in an organism, or genotype, operate at a molecular level to determine its characteristics that are expressed as a phenotype

Give two examples of characteristics that are controlled by a single gene (MOST characteristics are a result of multiple genes interacting) (2)

Fur colour in mice

red-green colour blindness in humans

Give two examples of disorders caused by the inheritance of certain alleles (2)

Polydactyly (having extra fingers or toes)

Cystic fibrosis (a disorder of cell membranes causing excess mucus build up)

Is polydactyly caused by a recessive or dominant allele?

Dominant

Is cystic fibrosis caused by a recessive or dominant allele?

Recessive

What could be some advantages of embryo screening? (3)

Alleviate suffering

Reduce treatment costs for disorders

There are laws which prevent boundaries being crossed (e.g. people choosing desired characteristics, like sex or eye colour)

What could be some disadvantages of embryo screening? (3)

It could imply that people with genetic problems are "undesirable" - leading to prejudice

Screening is expensive

There is a risk that people will start to seek screening in order to select desirable traits (sex, eye colour) for their babies

How many pairs of chromosomes do ordinary human body cells contain?

23 pairs

How many chromosomes do human gametes have?

23

What are the sex chromosomes in males and females?

Females: XX
Males: XY

What is a species?

A group of similar organisms that can interbreed to produce fertile offspring

What is variation?

Differences in the characteristics of individuals in a population

What can cause variation within a population? (3)

The genes organisms inherit (genetic causes)

The conditions in which they develop (environmental causes)

A combination of genes and the environment

Why is there usually extensive genetic variation within a population of a species?

All variants of genes arise from continuously occurring mutations

What are mutations?

Random alterations in DNA which occur continuously

When do mutations lead to changes in a species? (3)

Most mutations have no effect on the phenotype of an organism

Very rarely, a mutation will lead to a new phenotype

If the new phenotype is suited to an environmental change, it can lead to a relatively rapid change in the species

How can cloning be used to preserve rare plant species?

Tissue cultures (a small group of cells) can be used to grow new plants

How can many identical plants be made from one parent plant?

By taking and planting cuttings

How do embryo transplants work? (2)

By splitting a cell from a developing animal embryo before they become specialised

Then transplanting the identical embryos into host mothers

Why was Darwin's work on the origin of species not originally published? (2)

There was insufficient evidence at the time

It challenged the idea that God created all plants and animals

What does survival of the fittest mean? (2)

Organisms with characteristics most suited to the environment are more likely to survive to breed successfully

They will pass this trait onto their offspring

What is speciation?

The formation of new and distinct species in the course of evolution

What did Mendel observe in his study of plants?

The inheritance of each characteristic is determined by 'units' that are passed on to offspring

What is evolution? (2)

the inherited characteristics of populations over successive generations

This occurs through natural selection

What does the theory of evolution state?

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

Who proposed the theory of evolution by natural selection?

Charles Darwin

What are the key points in Darwin's theory of evolution by natural selection? (4)

Organisms within a particular species show a wide range of variation for a given characteristic

Individuals with characteristics (phenotypes) most suited to the environment are more likely to survive to breed successfully

The characteristics that have enabled these individuals to survive are then passed on to the next generation

Over time, beneficial characteristics become more common in the population

Why was Darwin's hypothesis on evolution eventually accepted over others? (3)

Other scientist's hypotheses were rejected because experiments didn't support them

Darwin's hypothesis was supported because it's been shown that characteristics are passed on to offspring in genes

There is further evidence for Darwin's hypothesis in the fossil record and in antibiotic resistance

What is selective breeding?

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

How is selective breeding done? (3)

Parents with the desired characteristic are chosen and bred together

From their offspring, those with the desired characteristic are bred together

This continues over many generations, until all the offspring show the desired characteristic

What has selective breeding been used to produce? (4)

Disease resistance in food crops

Animals which produce more meat or milk

Domestic dogs with a gentle nature

Large or unusual flowers

What is the main drawback of selective breeding? (2)

Leads to inbreeding, where organisms are particularly prone to inherited defects and disease

A disease that can kill one can likely kill them all

What is genetic engineering?

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

What has genetic engineering been used to produce? (3)

Plant crops to be resistant to diseases

Produce more and better yield

Bacterial cells to produce useful substances, such as human insulin to treat diabetes

What are some benefits of genetic engineering? (4)

Increased yields

Resistant to insect attack or herbicides

Crops in developing countries can be modified to contain a nutrient that people there lack in their diets

Research is exploring the possibility of GE to overcome some inherited disorders

What are some concerns that some people have about genetic engineering? (2)

Some say GM crops will have a destructive effect on populations of wild flowers and therefore of insects

Some are concerned that the effects of eating GM crops on human health have not been fully explored

[𝐇𝐢𝐠𝐡𝐞𝐫] Describe the process of genetic engineering. (4)

Enzymes are used to isolate the desired 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 cells of the other organism (animal/plant/microorganism)

Genes are transferred to cells at an early stage in their development, so that they develop with the desired characteristics

What are fossils?

The remains of organisms from millions of years ago, embedded in rocks

How are fossils formed? (3)

From organisms that have not decayed because one or more of the conditions needed for decay are absent (e.g. in peat bogs or glaciers)

From parts of an organism that are replaced by minerals as they decay

From impression from organisms, such as footprints, burrows and rootlet traces

Why is the fossil record incomplete? (2+1)

Many early forms of life were soft-bodied, so left few traces behind

What traces there were have been mainly destroyed by geological activity

This is why scientists cannot be certain about how life began on Earth

What can be learned from fossils?

How much different organisms have changed as life developed on Earth

What is extinction?

when there are no remaining individuals of a species still alive

What factors may contribute to the extinction of a species? (5)

Environment changes too quickly for a species to adapt (e.g. a destruction of habitat)

New predator

New disease

Catastrophic event, like a natural disaster

Species is unable to compete with another for resources

Why can bacteria evolve rapidly?

Because they reproduce at a high rate

How can a strain of bacteria become resistant to an antibiotic? (4)

Mutations of bacterial pathogens produce new strains

Some strains may be resistant to antibiotics, and so are not killed

These ones survive and reproduce, so the population of the resistant strain rises

The resistant strain will then spread, because people are not immune to it, and there is no effective treatment

Give an example of an antibiotic-resistant bacterium.

MRSA

What can and should be done to reduce the rate of development of antibiotic resistant strains? (3)

Doctors should not prescribe antibiotics inappropriately (treating non-serious or viral infections)

Patients should complete their course of antibiotics, so that all bacteria are killed and none survive to mutate and form resistant strains

Agricultural use of antibiotics should be restricted

Why is antibiotic resistance such a big problem? (2)

The development of new antibiotics is expensive and slow

It is unlikely to keep up with the emergence of new resistant strains

How have living things traditionally been classified? (3)

Living things have been classified into groups depending on their structure and characteristics

This system was developed by Carl Linnaeus

Now, they are classified using the three-domain system

How did Linnaeus classify living things? (7)

Kingdom

Phylum

Class

Order

Family

Genus

Species

How are organisms named? (2)

By the binomial system: genus and species. e.g. Homo sapiens

Always capitalise genus, but never species

How have our classifications systems for living organisms has developed over time? (3)

Evidence of internal structures (e.g. cells) has became more developed

This is due to improvements in microscopes, and the understanding of biochemical processes

Now, new models of classification are proposed

What are the three domains in the 'three-domain system' of classification of living organisms? (3)

Archaea (primitive bacteria, usually extremophiles)

Bacteria (true bacteria)

Eukaryota (includes protists, fungi, plants and animals)

Who developed the 'three-domain system' of classification of living organisms?

Carl Woese