B5 - Genes, Inheritance and selection

Question 1

What is variation and the two causes for it?

Answer 1

Variation are the differences within a species and the causes are:

• genetic variation - the genetic material you inherit from your parents
• environmental variation - the environment in which you live

Question 2

What is continuous and discontinuous variation?

Answer 2

Continuous variation:

• can take any values within a range
• caused by genetic and environmental
• multiple genes control
• examples include height and skin colour

Discontinuous variation:

• can only result in specific values
• caused by genetic
• one or few genes control
• examples include blood type and gender

Question 3

What is asexual reproduction and what are the advantages and disadvantages?

Answer 3

Asexual reproduction produces genetically identical offspring through the process of mitosis and only requires one parent.

Advantages:

• only requires one parent so there is no need to find a mate so offspring are produced faster
• if the parent is well adapted to an area the organism will share identical characteristics

Disadvantages:
- negative changes to the environment may destroy the whole species as they are genetically identical

Question 4

What is sexual reproduction and what are the advantages and disadvantages?

Answer 4

Sexual reproduction requires two parents and therefore the offspring produced are genetically different. Organisms produce sex cells called gametes through the process of meiosis.

Advantages:
- variation in offspring can lead to positive adaptations in a species to cope with environmental pressure

Disadvantages:
- requires two parents so reproduction is slower and results in fewer offspring

Question 5

What is a zygote?

Answer 5

a fertilised egg cell

Question 6

Describe the process of meiosis:

Answer 6

Stage 1:

• The chromosomes are copied
• These chromosomes then line up along the middle of the cell in pairs (mother and father)
• One member of each pair is pulled to opposite ends of the cell(DNA may be exchanged)
• Two nuclei then form
• Then the cell splits in two and two separate cells are formed

Stage 2:

• The chromosomes line up along the middle of the cell again
• Each chromosome is pulled in half so one copy of each chromosome goes to opposite ends of the cell
• Each cell then divides in two and this results in 4 genetically variant haploid cells

Question 7

What are alleles?

Dominant and recessive?

Answer 7

Alleles - different forms of a gene

If there is a dominant allele it is always present in the phenotype
For a recessive allele you need a copy from both parents

Question 8

What is the genome, genotype?

Answer 8

Genome - the entire genetic information of an organism
Genotype - the combination of alleles present in an organism

Homozygous dominant - BB
Homozygous recessive - bb
Heterozygous - Bb

Question 9

What is a mutation?

Answer 9

A mutation occurs when the sequence of DNA bases is altered. Most of them are harmful(cancer), some are neutral(rolling toungue) and some are beneficial(antibiotic resistance for bacteria).

Question 10

What happens if a mutation occurs within a gene?

Answer 10

If a mutation occurs within a gene, DNA bases may be added, changed or deleted, this changes the sequence of DNA bases, therefore during transcription the order of bases in mRNA produced may be different. Therefore the amino acids may be assembled in a different order and an incorrect protein may be produced or it may fold incorrectly.

For example if the protein is an enzyme the active site may change shape and it will not be able to bind to its substrate causing problems

Question 11

What happens if a mutation occurs before a gene?

Answer 11

There are sequence of bases before a gene that trigger the process of transcription, which are located in the non-coding section of DNA. If a mutation occurs here the gene may not be transcribed into mRNA and a protein will not be made for these gene codes

Question 12

Who was George Mendel and what did he find?

Answer 12

1866 - George Mendel carried out experiments on peas and observed that characteristics such as height and colour are passed on from parent to offspring. He found that:

• Characteristics in plants were determined by hereditary units
• Hereditary units are passed down from parents to offspring
• Hereditary units are dominant or recessive

Question 13

What is evolution?

Answer 13

Evolution is the gradual change in a species over time

Question 14

What is natural selection?

Answer 14

• A mutation causes a variation in an organism
• The organisms with the characteristics best adapted to the environment survive and reproduce and the less well adapted organisms die(survival of the fittest)
• The genes from the successful organisms are passed down to their offspring
• Over time this continues for many generations and may lead to a new species being developed

Question 15

Evolution in peppered moths:

Answer 15

Before the 19th century most peppered moths were pale and could blend in with trees. A mutation occurred in some moths which meant they were dark coloured however they could not camouflage as well so they were more likely to be eaten and the pale moths were more likely to reproduce resulting in them being more common.

However after the industrial revolution many trees were covered in soot turning the bark black. This means that the black moths were more adapted to the environment and more likely to reproduce which resulted in dark moths becoming more common in urban areas.

Question 16

Evolution in antibiotic resistance bacteria:

Answer 16

• A mutation occurs in a bacterium
• This mutation conveys resistance to an antibiotic for the bacterium
• When antibiotics are added to a medium, the bacterium with the resistance will survive.
• Those bacteria without resistance will die.
• Surviving bacteria reproduce rapidly by mitosis and the gene for antibiotic resistance is passed on to the offspring bacteria.
• If reproduction is allowed to continue for long enough, this specific species of bacteria may become resistant to this specific antibiotic.

Question 17

What are fossils and how are they formed?

Answer 17

Fossils are formed when animal or plant remains/traces are preserved in rocks:

• The plant or animal dies and falls into soft mud or silt that is found at the bottom of a lake or sea
• The body becomes covered in the silt or mud
• Over time, this turns into rock, which encases the dead body
• Over millions of years, the hard parts of the body (leaves in a plant and bones and shells in animals) are replaced by minerals
• If the earth moves, causing the land to rise, the fossils become exposed at the surface

Question 18

How do fossils provide evidence for the theory of evolution?

Answer 18

• Finding similarities in anatomy between a modern day organism and one from million of years ago which supports that closely related organisms have evolved from the same ancestor
• Fossils of organisms such as bacteria are found in the oldest rocks whereas the fossils of organisms like vertebrates are found in more recent works which supports the theory that simple life forms gradually evolved into more complex ones as bacteria are simpler organisms than vertebrates
• Plant fossils appear before animal fossils which supports animals require plants to survive

Question 19

What 3 ways besides evolution provide evidence for the theory of evolution?

Answer 19

• Extinction- Some species are extinct (estimated that about 99% of the species that have ever lived are now extinct)which supports that those species that are unable to adapt to changes in their environment will die out as evolution shows organisms need to be able to adapt
• Rapid changes in species- Antibiotic resistance in one bacterium becomes common across the bacterial population - Evolution is seen in action as the advantageous characteristic is rapidly passed from generation to generation
• Molecular comparison - Comparison of the order of nucleic acids in DNA or the order of amino acids in proteins - Closely related species have the most similar DNA and proteins whereas those with fewer similarities are more distantly related

Question 20

What is classification and why is it used?

Answer 20

Classification is the process of sorting living organisms that share similar features into groups.
Scientists classify organisms to:
- identify species 
- predict characteristics 
- find or show evolutionary links

Question 21

What are the seven taxonomic levels?

Answer 21

Kingdom, Phylum, Class, Order, Family, Genus and Species

Question 22

What is the difference between artificial and natural classification?

Answer 22

Artificial classification systems use observable characteristics to group organisms together. This is highly inaccurate.

Natural classification uses DNA sequencing to link evolutionary relationships between organisms.