What is sexual reproduction?
Sexual reproduction is the joining (fusion) of male and female gametes.
What are the names of the male gametes in animals?
The male gametes in animals are called sperm cells.
What are the names of the female gametes in animals?
The female gametes in animals are called egg cells.
What are the names of male gametes in flowering plants?
The male gametes in flowering plants are pollen.
What are the names of female gametes in flowering plants?
The female gametes in plants are egg cells.
What causes variation in sexual reproduction?
In sexual reproduction there is mixing of genetic information which leads to variety in the offspring.
Name the process that produces gametes.
Meiosis produces gametes.
How many parents are involved in asexual reproduction?
Asexual reproduction involves only one parent.
Is there fusion of gametes in asexual reproduction?
No, there is no fusion of gametes in asexual reproduction.
Is there mixing of genetic information in asexual reproduction?
There is no mixing of genetic information in asexual reproduction.
Are offspring produced by asexual reproduction genetically identical or genetically different?
Offspring produced by asexual reproduction are genetically identical (clones).
In asexual reproduction, is mitosis or meiosis involved?
Only mitosis is involved in asexual reproduction.
What does meiosis do to the number of chromosomes in gametes?
Meiosis halves the number of chromosomes in gametes.
What does fertilisation do to the number of chromosomes?
Fertilisation restores the full number of chromosomes.
How do cells in reproductive organs divide?
Cells in reproductive organs divide by meiosis.
What are the cells produced in reproductive organs called?
The cells produced in reproductive organs are called gametes.
Describe the process in which gametes are made.
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
What is it called when gametes join?
Gametes join at fertilisation
What happens to the number of chromosomes at fertilisation?
The normal number of chromosomes is restored.
Does a fertilised cell divide by mitosis or meiosis?
A fertilised cell divides by mitosis.
After fertilisation, what happens to the number of cells?
After fertilisation, the number of cells increases.
What is an embryo?
An embryo is an organism in the early stages of development.
What happens to cells as the embryo develops?
As the embryo develops cells differentiate.
What is the genetic material in the nucleus of a cell composed of?
The genetic material in the nucleus of a cell is composed of a chemical called DNA.
What is DNA?
DNA is a polymer made up of two strands forming a double helix.
What structures is DNA contained in?
DNA is contained in structures called chromosomes.
What is a gene?
A gene is a small section of DNA on a chromosome.
What does a gene code for?
Each gene codes for a particular sequence of amino acids, to make a specific protein.
What is the genome of an organism?
The genome of an organism is the entire genetic material of that organism.
Name three reasons why understanding the human genome is important.
- search for genes linked to different types of disease
- understanding and treatment of inherited disorders
- use in tracing human migration patterns from the past.
Explain the term gamete
Gametes are sex cells.
What is the name of the male gamete?
The male gametes are the sperm.
What is the name of female gametes?
The female gametes are the eggs.
Explain the term chromosome.
A chromosome is a long DNA molecule carrying genetic information.
Explain the term gene.
A gene is a short section of DNA.
Explain the term allele.
Alleles are different forms of the same gene sometimes referred to as variants.
Explain the term dominant allele.
The phenotype will be apparent in the offspring even if only one of the alleles is inherited.
Explain the term recessive.
A phenotype will only show up in the offspring if both of the alleles coding for that characteristic are inherited.
Explain the term homozygous.
Individual with two identical alleles for a characteristic. If the two alleles present are the same the organism is homozygous for that trait.
Explain the term heterozygous.
If the alleles present are different the organisms is heterozygous for that trait.
Explain the term genotype.
The genetic makeup of an individual for a particular characteristic, for example hair or eye colour. The alleles present, or genotype, operate at a molecular level to develop characteristics that can be expressed as a phenotype.
Name two characteristics controlled by a single gene.
Some characteristics are controlled by a single gene, such as: fur colour in mice; and red-green colour blindness in humans.
Are most characteristics a result of a single gene, or multiple genes interacting?
Most characteristics are a result of multiple genes interacting, rather than a single gene.
What is a dominant allele?
A dominant allele is always expressed, even if only one copy is present.
What is a recessive allele?
A recessive allele is only expressed if two copies are present (therefore no dominant allele present).
Are most phenotype features the result of dingle or multiple genes?
Most phenotype features are the result of multiple genes rather than single gene inheritance.
Look at the genetic cross. What is the ratio of brown eyes to blue eyes in the offspring?
The ratio of brown eyes to blue eyes in the offspring is 3:1.
Complete the Punnett square diagram for the inheritance of eye colour.
What are inherited disorders caused by?
Inherited disorders are caused by the inheritance of certain alleles.
Is polydactyly (having extra fingers or toes) caused by a dominant or recessive allele?
Polydactyly (having extra fingers or toes) is caused by a dominant allele.
What is cystic fibrosis?
Cystic fibrosis is a disorder of cell membranes.
Is cystic fibrosis caused by a dominant or recessive allele?
Cystic fibrosis is caused by a recessive allele.
What are some of the issues concerning embryo screening?
Some of the issues concerning embryo screening include economic, social and ethical issues.
How many pairs of chromosomes do ordinary human body cells contain? -->
Ordinary human body cells contain 23 pairs of chromosomes.
In humans, how many pairs of chromosomes control characteristics and how many determine sex?
In humans, 22 pairs of chromosomes control characteristics only, and one pair carries the genes that determine sex.
What are the sex chromosomes in females?
In females the sex chromosomes are XX.
What are the sex chromosomes in males?
In males the chromosomes are different XY.
Carry out a genetic cross to show sex inheritance.
What influences the development of the phenotype of an organism?
The genome and its interaction with the environment influence the development of the phenotype of an organism.
What are differences in the characteristics of individuals in a population called?
Differences in the characteristics of individuals in a population is called variation.
What differences in the characteristics of individuals in a population (variation) be due to?
Differences in the characteristics of individuals in a population may be due to differences in:
• the genes they have inherited (genetic causes)
• the conditions in which they have developed (environmental causes)
• a combination of genes and the environment.
Is there usually much genetic variation within a population of a species?
There is usually extensive genetic variation within a population of a species.
What do genetic variants arise from?
All genetic variants arise from mutations.
Does a mutation always lead to a new phenotype?
Very rarely a mutation will lead to a new phenotype. Most have no effect on the phenotype; some influence phenotype; very few determine phenotype.
After a mutation, what can lead to a relatively rapid change in the species?
If the new phenotype is suited to an environmental change it can lead to a relatively rapid change in the species.
How often do mutations occur?
Mutations occur continuously.
Evolution is a change in the inherited characteristics of a population over time through a process of natural selection that give rise to phenotypes best suited to their environment which may result in the formation of a new species.
What is the theory of evolution by natural selection?
The theory of evolution by natural selection states that all species of living things have evolved from simple life forms that first developed more than three billion years ago.
How are new species formed?
If two populations of one species become so different in phenotype that they can no longer interbreed to produce fertile offspring they have formed two new species.
What is selective breeding?
Selective breeding (artificial selection) is the process by which humans breed plants and animals for particular genetic characteristics.
How long have humans been selectively breeding pants and animals?
Humans have been selectively breeding for thousands of years.
What were the first things to be selectively bred?
Food crops from wild plants and domesticated animals.
What does selective breeding involve?
Selective breeding involves 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.
Name some characteristics in selective breeding that are chosen for usefulness or appearance.
• Disease resistance in food crops.
• Animals which produce more meat or milk.
• Domestic dogs with a gentle nature.
• Large or unusual flowers.
What are some of the problems with selective breeding?
Selective breeding can lead to ‘inbreeding’ where some breeds are particularly prone to disease or inherited defects.
Describe the process of genetic engineering.
Genetic engineering is a process which involves modifying the genome of an organism by introducing a gene from another organism to give a desired characteristic.
What have plant crops been genetically engineered to be?
Plant crops have been genetically engineered to be resistant to diseases or to produce bigger better fruits.
What have bacterial cells been genetically engineered to do?
Bacterial cells have been genetically engineered to produce useful substances such as human insulin to treat diabetes.
What happens in genetic engineering?
In genetic engineering, genes from the chromosomes of humans and other organisms can be ‘cut out’ and transferred to cells of other organisms.
What are crops that have had their genes modified called?
Crops that have had their genes modified are called genetically modified (GM) crops.
What do genetically modified crops include?
GM crops include ones that are resistant to insect attack or to herbicides. GM crops generally show increased yields.
What are the concerns about genetically modified crops?
Concerns about GM crops include the effect on populations of wild flowers and insects.
What concerns do some people have about GM crops?
Some people feel the effects of eating GM crops on human health have not been fully explored.
What is modern medical research exploring to overcome some inherited disorders?
Modern medical research is exploring the possibility of genetic modification to overcome some inherited disorders.
Describe the main steps in the process of genetic engineering.
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.
Describe some of the evidence for evolution.
The evidence for evolution includes fossils and antibiotic resistance in bacteria.
Why is the theory of evolution by natural selection now widely accepted?
Evidence for Darwin’s theory is now available as it has been shown that characteristics are passed on to offspring in genes. There is further evidence in the fossil record and the knowledge of how resistance to antibiotics evolves in bacteria.
How may fossils be formed?
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.
Why can’t scientists be certain about how life began on Earth?
Many early forms of life were soft-bodied, which means that they have 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 we learn from fossils?
We can learn from fossils how much or how little different organisms have changed as life developed on Earth.
Extinctions occur when there are no remaining individuals of a species still alive.
Describe factors which may contribute to the extinction of a species.
Factors which may contribute to the extinction of a species include:
- changes to the environment, such as a change in climate
- new diseases
- new predators
- new competitors
Why can bacteria evolve rapidly?
Bacteria can evolve rapidly because they reproduce at a fast rate.
Why are mutations of bacterial pathogens a problem?
Mutations of bacterial pathogens produce new strains. Some strains might be resistant to antibiotics, and so are not killed. They 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.
Why is MRSA difficult to treat?
MRSA is difficult to treat because it is resistant to antibiotics.
How can the rate of development of antibiotic resistant strains be reduced?
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
• agricultural use of antibiotics should be restricted.
What are the problems with the development of new antibiotics?
The development of new antibiotics is costly and slow. It is unlikely to keep up with the emergence of new resistant strains.
What were living things traditionally classified into groups by?
Traditionally living things have been classified into groups depending on their structure and characteristics in a system developed by Carl Linnaeus.
What did Linnaeus classify living things into?
Linnaeus classified living things into kingdom, phylum, class, order, family, genus and species.
How are organisms named?
Organisms are named by the binomial system of genus and species.
What caused new models of classification to be proposed?
As evidence of internal structures became more developed due to improvements in microscopes, and the understanding of biochemical processes progressed, new models of classification were proposed.
Who developed the ‘three-domain system’ of classification?
Carl Woese developed the ‘three-domain system’ of classification.
Why did Carl Woese develop the ‘three-domain system’ of classification?
Due to evidence available from chemical analysis there is now a ‘three-domain system’ developed by Carl Woese.
In the ‘three-domain system’ of classification, what three groups are organisms divided into?
In ‘three-domain system’ of classification organisms are divided into:
• Archaea (primitive bacteria usually living in extreme environments)
• Bacteria (true bacteria)
• Eukaryota (which includes protists, fungi, plants and animals).
What do evolutionary trees show?
Evolutionary trees are a method used by scientists to show how they believe organisms are related.
How are evolutionary trees made?
They use current classification data for living organisms and fossil data for extinct organisms.