4.6 Inheritance, Variation and Evolution

What process leads to the formation of non-identical cells?

Meiosis

What process leads to the formation of identical cells?

Mitosis

What are the male gametes in animals?

Sperm cells

What are the female gametes in animals?

Egg cells

What are the male gametes in plants?

Pollen cells

What are the female gametes in plants?

Eggs cells

Which reproduction process involves the mixing of genetic material?

Sexual reproduction

Which reproduction process involves no mixing of genetic material?

Asexual reproduction

What is formed when cells in reproductive organs divide by meiosis?

Gametes

What happens to the number of chromosomes in gametes during meiosis?

It halves

What happens to gametes during fertilisation?

They join to restore the normal number of chromosomes

After fertilisation how does the new cell divide?

By mitosis

List three 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

List four advantages of asexual reproduction

Only one parent needed, more time & energy efficient, faster than sexual reproduction, can produce many identical offspring when conditions are favourable

How do malarial parasites reproduce?

Asexually in the human host, sexually in the mosquito

How do many fungi reproduce?

The asexually by spores, sexually to give variation

How do plants reproduce?

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

What is a nucleotide?

A common sugar and phosphate group with one of four different bases attached to the sugar

What are the four bases in DNA?

A, C, G and T

What is the code for a particular amino acid?

A sequence of three bases

What is the DNA polymer made up of?

Repeating nucleotide units

What controls the order in which amino acids are assembled to produce a particular protein?

The order of bases

Where are proteins synthesised?

On ribosomes

What is the basic structure of DNA?

A polymer made up of two strands forming a double helix

What is a gene?

A small section of DNA on a chromosome that controls a characteristic of that organism, each gone codes for a particular sequence of amino acids to make a specific protein

What is a genome?

The entire genetic material of an organism

What is a chromosome?

A structure that contains the DNA of an organism

What is the importance of understanding the human genome?

-search for genes linked to different types of disease
-understanding and treatment of inherited disorders
- use in tracing human migration patterns from the past

In complementary strands what bases are linked to what?

-C is linked to a G
-T to an A

How would genetic variants influence the phenotype?

-In coding DNA by altering the activity of a protein
-In non-coding DNA by altering how genes are expressed

Describe what happens in protein synthesis?

1.Proteins are synthesised on ribosomes
1. The base sequence of a gene is copied onto mRNA
2.mRNA passes out of the nucleus and into cytoplasm
3.mRNA attaches to ribosomes
4.Carrier molecules brings amino acids specific to the template to add to the growing protein chain in the correct order

Why happens when the protein shape is complete?

It folds to form a unique shape, enabling the proteins to do their job as enzymes, hormones or forming structures in the body such as collagen

What to mutations do to a protein?

Most do not alter the protein, or only alter it slightly so that its appearance or function is not changed

What do a few mutations code for?

An altered protein with a different shape, an enzymes active site may no longer fit the substrate or a structural protein may lose its strength

Do all parts of DNA code for proteins?

No, non-coding parts of DNA can switch genes on and off, so variations in these areas of DNA may affect how genes are expressed

What is an allele?

The different form of a single gene

What is a phenotype?

The alleles present in an organism

What do we mean by a dominant allele?

A characteristic that is always expressed

What is a recessive allele?

A characteristic that is only expressed if two copies of the allele are present

What are homozygous alleles?

Where in an organism, two alleles are the same

What are heterozygous alleles?

Where in an organism, two alleles are different

What are some examples of when characteristics are controlled by a single gene?

Fur colour in mice, and red-green colour blindness in humans

What are most characteristics a result of?

Multiple genes interacting, rather than a single gene

What is polydactyly?

Having extra fingers or toes

Is polydactyly a dominant or recessive allele?

Dominant

What is cystic fibrosis?

A disorder of cell membranes

Is cystic fibrosis a dominant or recessive allele?

Recessive

How many pairs of chromosomes are there in the human body?

23

What sex is XX?

Female

What sex is XY?

Male

What is variation?

Differences in the characteristics of individuals in a population

What causes variation?

Differences in the genes inherited, the conditions in which they have developed or a combination of both

Describe the genetic variation within a population of a species

Usually extensive

How does variation occur?

Through mutations, most have no effect on the phenotype, some influence phenotype, very few determine phenotype

How often do mutations occur?

Continuously, 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

What is evolution?

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

What is the theory of evolution by natural selection?

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

When does one species form into two new species?

When the one species becomes so different in phenotype that they can no longer interbreed to produce fertile offspring

How might evolution through natural selection give rise to phenotypes best suited to their environment?

-Mutations causes variation
-Gives organism with variation a specific advantage compared to organisms without the advantage
-This advantage allows them to survive
-Allowing them to reproduce, passing these genes to their offspring

What is selective breeding?

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

How long have humans been doing selective breeding?

For thousands of years since they first bred food crops from wild plants and domesticated animals

What does selective breeding involve?

Choosing parents with the desired characteristic from a mixed population. They are bred together. From the offspring those with the desired characteristic are bred together. This continues over many generations until all the offspring show the desired characteristic.

What is a danger of selective breeding?

'Inbreeding' where some breeds are particularly prone to disease or inherited defects

List four desired characteristics from selective breeding

Disease resistance in food crops, animals that produce more meat or milk, domestic dogs with a gentle nature, large or unusual flowers

What is genetic engineering?

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

How have plant crops been genetically engineered?

To be resistant to diseases or to produce bigger better fruits

How have bacterial cells been genetically engineered?

To produce useful substances such as human insulin to treat diabetes

What are genetically modified crops?

Crops that have had their genes modified by genetic engineering

What are the main steps in 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

What are typical characteristics of genetically modified crops?

Resistance to insect attack, resistance to herbicides, increased yields

What are the concerns about genetically modified crops?

May decrease the wild population of wild flowers and insects, some people feel the effects of eating GM crops on human health have not been fully explored

Why is modern medicine exploring the possibility of genetic modification?

To overcome some inherited disorders

What is tissue culture?

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

Why is fissure culture important?

For preserving rare species or commercially in nurseries

What is taking cuttings?

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

What are embryo transplants?

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

What are the steps of 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

What are the benefits of cloning in agriculture and medicine?

Prevents extinction, embryos can be used to grow new organs and tissues which would be genetically identical to the parent preventing tissue rejection

What are the risks of cloning in agriculture and medicine?

Low success rate, ecological concerns, ethical issues

What happens during evolution?

-Individual organisms within a particular species show a wide range of variation for a characteristic
-Individuals with characteristics 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

When did Darwin publish his ideas in 'On the origin of species'?

1859

Give three reasons why natural selection was only gradually accepted

The theory challenged the idea that God made all the animals and plants, there was insufficient evidence, the mechanism of inheritance and variation was not known until 50 years after the theory was published

What was Alfred Russel Wallace known for?

For his work on warning coloration in animals and his theory of speciation

What did Jean-Baptiste Lamarck propose?

Proposed the idea of the inheritance of acquired characteristics (not true)

What is speciation?

Formation of new species

Describe the steps which give rise to new species?

-2 populations of the same species have become geographically isolated
-prevents interbreeding among all of the species
-different mutations take place on isolated groups, causing new phenotypes
-over time this forms a new species

What did Gregor Mendel do?

Carried out breeding experiments on plants, his observations as that the inheritance of each characteristic is determined by 'units' that are passed onto descendants unchanged

Why were Mendel's results ignored when they first came out? Vs modern society?

No one really understood his results because it was too advanced for his time
Modern: staining and microscopes can be used, this was invented to find the link between units and chromosome behaviour (in the late 19th century)

What is the evidence for evolution?

Fossils and antibiotic resistance in bacteria

What are fossils?

The 'remains' of organisms from millions of years ago, which are found in rocks

How are fossils formed?

From parts of organism that have not decayed, where parts of an organism are replaced by minerals as they decay or as preserved traces of organisms, such as footprints, burrows and rootlet traces

Why is the fossil record incomplete?

Many forms of life were soft-bodies meaning that they left few traces behind, what traces there were have been mainly destroyed by geological activity

What can we learn from fossils?

How much or how little 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 contribute to the extinction of a species?

Environment changes, new predators, a new disease, they cannot compete with another species for food, a catastrophic event (like a volcanic eruption)

Why can bacteria evolve quickly?

Because they reproduce at a fast rate

What happens to antibiotic resistant bacteria?

Mutations of bacterial pathogens produce new strains and they may be resistant to antibiotics and so are not killed. They survive and reproduce so the population of resistant strain rises, the resistant strain will then spread bc ppl are not immune to it and there is no effective treatment

What is MRSA?

A relatively common 'superbug' that is really hard to get rid of

What could be done to reduce the rate of development of antibiotic resistant strains?

-doctors should not prescribe antibiotics inappropriately, such as treating non-serious or viral infections
-patients should complete their course of antibiotics so all bacteria are killed and none survive to mutate and form resistant strains
-the agricultural use of antibiotics should be restricted

What is the issue with the development of new antibiotics?

It is costly and slow, it is unlikely to keep up with the emergence of new resistant strains