Genetics, Natural Selection and Genetic Modification

What is meiosis?

The production of gametes

How many chromosomes do gametes have?

23 only

Main features of meiosis?

* Cells divide forming four gametes
* The gametes are genetically different from each other

What are the reproductive organs?

Testes and ovaries

How many cell divisions are there in meiosis and how many cells are produced?

2 cell divisions and 4 cells are produced

What does haploid mean?

Half set of chromosomes

What does diploid mean?

A full set of chromosomes

Stages of meiosis?

• The cell making the gametes has a full set of chromosomes. These chromosomes copy themselves and stay attached to each other

• The cell splits in two, with each new cell being haploid

• Each cell divides into two again. Each of the four daughter cells have a half set of chromosomes (23 chromosomes)

What does meiosis produce and why?

• 4 genetically unique daughter cells

• During meiosis, tiny changes are made to the chromosomes and they both only need half of the chromosomes because the other half comes from the other parent

When gametes fuse at fertilisation, what is the cell created called?

A zygote

What is asexual reproduction?

Reproduction where a partner is not needed, a perfect clone of the parent is made.

What is sexual reproduction?

Reproduction where a partner is needed. Fertilisation of a female sex cell by a male sex cell. This produces variation in the offspring

Advantage of sexual reproduction?

The genetically different offspring can change to adapt to their conditions and are more likely to survive in case of a disease or something else because of their adaptability.

Disadvantages of sexual reproduction?

It takes more time and energy to do

Advantages of asexual reproduction?

• Organisms do not have to find a mate making it faster and taking less energy

• It exploits ideal conditions as a genetically identic offspring will have the same adaptations as the parent to the environment

Disadvantages of asexual reproduction?

If the environment changes or a disease comes they are less likely to survive because of the lack of variation in their population.

What does DNA stand for?

Deoxyribonucleic acid

What is the function of DNA?

It contains the instructions needed for an organism to develop, survive and reproduce

What is the shape of DNA?

Double helix

What is the part of a DNA molecule that holds the two strands together

Complementary base pairs

What are the base pairs and what do they match up to?

Adenine-Thymine

Cytosine-Guanine

What is the bond between the base pairs?

Hydrogen bonding

How many hydrogen bonds between the base pairs?

Adenine and Thymine- 2

Cytosine and Guanine- 3

What are each of the bases connected to?

Each base is connected to a sugar and each sugar is connected to a phosphate.

What is a codon?

A series of three nucleotide bases that codes for a specific amino acid

What is an anticodon

Codons that are complimentary to the codon on the mRNA strand

What is the first stage of protein synthesis and where does it take place?

Transcription

* This involves DNA bases being used to make a strand of RNA (ribonucleic acid)
* This takes place in the nucleus

What happens during transcription?

• A section of DNA is unwound and the two strands separate

• An enzyme called RNA polymerase binds to the non-coding region of DNA

• RNA polymerase moves along the template stand and makes a strand of mRNA (messenger RNA) which has complimentary base pairs to the template strand

• In mRNA, thymine is replaced with uracil

• The RNA polymerase then detaches from the DNA and the mRNA leaves the nucleus through the nuclear pores and goes to a ribosome

• The two strands of DNA join back together

What replaces thymine in transcription (RNA)?

Uracil

What is the second stage of protein synthesis and where does it take place?

Translation

• The bases are read 3 at a time (a codon) coding for a specific amino acid to produce a protein

• This takes place in the cytoplasm at a ribosome

What happens during translation?

• The mRNA molecule attaches to a ribosome

• Amino acids are brought to the ribosome on carrier molecules called tRNA

• The ribosomes now read the triplets of bases called a codon on the mRNA and matches them with an anticodon and uses this to join together the correct amino acids in the correct order

• Once the polypeptide chain (a string of amino acids) is complete, it folds into a unique shape which creates a certain protein

What are mutations?

* Any change in the DNA sequence of a cell
* Mutations are the reason why genes exist in different forms called alleles

What can happen due to a mutation?

Genetic disorders or cancer

What is Gregor Mendel famous for?

Discovering the fundamental laws of inheritance

What does a punnet square look like?

What is a gene?

A small section of DNA that gives instructions for producing a particular characteristic

What is an allele?

An alternative form of the same gene

How many copies of each allele do you have?

One from your mother and one from your father

What can alleles be?

dominant or recssive

How do we show dominant alleles and how do they work?

• We show it with a capital letter (D for example)

• You only need one copy of the allele to express a particular characteristic

How do we show recessive alleles an how do they work?

• Written using lowercase letters (d for example)

• You need two copies of the recessive allele to express certain characteristics

What is a genotype?

The combination of alleles a person has inherited from their parents

What is a phenotype?

The characteristic expressed due to the combination of alleles (basically what you see)

What does homozygous mean?

Both alleles for one gene are the same

What does heterozygous mean?

The alleles for one gene are different

What does dominant mean?

The allele that will always be expressed if present

What does recessive mean?

The allele that can only be expressed if there are two of them present in a gene.

What two chromosomes define our sex?

X and Y

What are the two chromosomes that define sex called?

Sex chromosomes

Females have two X chromosomes and males receive one X and one Y chromosome. What does this mean?

That boys received a Y chromosome from their father and girls received an X chromosome from their mother and father but not the Y chromosome from their father

What is variation?

Differences between members of a species

What is inherited variation?

Parents passing on their characteristics

What is environmental variation?

Characteristics affected by an organism’s surroundings

What is continuous variation?

* Can have any value within a range- caused by genetic and environment
* Could be a unit of measurement for example centimetres

What is discontinuous variation?

* Can only have certain values- caused by genetics only
* A set name for something for example eye colour- blue, green, brown, black

What is evolution?

The process by which different kinds of organisms are believed to have developed from earlier forms during the history of Earth

What is binomial classification?

The system used to name species

* An organism has 2 latin words referring to the genus and species
* Example: Homo(genus) and Sapiens(The species)
* Organisms that share the first name are closely related

Evidence of evolution?

Fossils and stone tools found showing how humans gained more intelligence and were able to make more complex tools

What is the organism that many other organisms originate from called?

The common ancestor

What is survival of the fittest?

 The organisms best adjusted to their environment are the most successful in surviving and reproducing.

What happens because of survival of the fittest?

The ones who have better chances of surviving will reproduce giving birth to offspring with their characteristics, The characteristic will increase in the population over time.

What is the pentadactyl limb?

The five fingered limb

What does the pentadactyl limb suggest?

Suggests a common ancestor for many vertebrates and they have a similar bone structure to each other. The bones may have fused/ changed but the basic similarities are still there.

What is classification and what is it based on?

The organisation of living things according to their similarities: physical traits, behaviour, diet, DNA

What is the binomial system and what is the order?

The section where animals come from they range in specificity:

(Least specific to most specific): Kingdom, phylum, class, order, family, genus, species

What are the 5 kingdoms for classification?

Plants, animals, fungi, prokaryotes(bacteria) and protists

Characteristics of plants?

* Multicellular, cells arranged as tissues and organs, chloroplasts for photosynthesis, cells have nuclei, cellulose cell walls
* Examples: roses, algae, ferns, trees

Characteristics of animals?

* Multicellular with cells arranged as organs and tissues, cells have nuclei, no cell walls
* Examples: Humans, dogs, birds, reptiles, fish

Characteristics of fungi?

* Multicellular (apart from yeast), live in or on dead matter on which they feed, cells have nuclei, cell walls contain chitin
* Examples: Moulds, mushrooms

Characteristics of protists?

* Mostly unicellular, cells have nuclei, some have cell walls made of different substances
* Examples: amoeba, paramecium

Characteristics of prokaryotes?

* Unicellular, cells do not have nuclei, flexible cell walls
* Examples: Bacteria

What is selective breeding?

Choosing parents with particular characteristics to breed together and produce offspring with more desirable characteristics

What are breeds?

New animal species

What are varieties?

New plant species

What is inbreeding and what can it lead to?

When animals and plants are bred within a small gene pool, which can lead to some breeds being prone to inherited diseases or defects

What is genetic engineering?

Modifying the genome of an organism by introducing a gene from another organism to result in a desired characteristic.

How does genetic engineering work on a basic level?

• Enzymes are used to ‘cut out’ or isolate the required gene,

• This gene is inserted into a vector, which is usually a bacterial plasmid 

• The vector inserts the gene into required cells in the nucleus

• The genes are transferred to animal, plant or microorganism cells, during early development. This allows them to develop with the desired characteristics.

Advantages of genetic engineering?

* Genetic modification is a faster and more efficient than selective breeding.
* Improve crop yields or crop quality
* Introduce herbicide resistance, which results in less herbicides being used, as weeds are quickly and selectively killed.
* Insect and pest resistance can be developed and inserted into the plants. The plant produces toxins
* Sterile insects could be created such as a mosquito. They would breed, which would lead to infertile offspring. This may help with spread of diseases, such as malaria, dengue fever and the Zika virus.

Disadvantages of genetic engineering?

* Transfer of the selected gene into other species. What benefits one plant may harm another.
* Some people believe it is not ethical to interfere with nature in this way. Also, GM crop seeds are often more expensive and so people in developing countries cannot afford them.
* GM crops could be harmful, for example toxins from the crops have been detected in some people’s blood.
* GM crops could cause allergic reactions in people.
* Pollen produced by the plants could be toxic and harm insects that transfer it between plants.

Stages of tissue culture (turn over for image)

What are fertilisers and what do they do?

Concentrated sources of plant nutrients. They provide mineral ions needed for healthy growth in plants

Why do farmers use fertilisers?

They massively increase crop yield which means more money.

Advantages of fertilisers?

• They are quick in providing plant nutrients and restoring soil fertility.

• They are portable and easy to transport.

• Plants easily absorb fertilizers.

• Fertilizers improve and increase the productivity/crop yield of many crops such as wheat, maize, and rice.

Disadvantages of fertilsers?

• They get washed away by water easily and cause pollution.

• They are expensive.

• They provide only short term benefits.

• They change the nature of soil, making it either too acidic or too alkaline, reducing soil biodiversity

One natural alternative to fertilisers?

Animal dung

What is a family pedigree?

A diagram showing the inheritance of a genetic condition within a family. It is used to predict the chance that someone will inherit a faulty allele

How is the sex/gender of humans controlled?

• By one pair of sex chromosomes

• The genotype XX produces a female

• The genotype XY produces a male

What are the four blood groups and what are their alleles?

Phenotype (blood group)	Genotype (alleles)
A	IAIA or IAIO
B	IBIB or IBIO
AB	IAIB
O	IOIO

What does this table show us about the dominant and recessive alleles in blood?

See image

• I stands for the blood group gene and the letter above the I shows the allele of that gene

• I^O is recessive to I^A and I^B because it is not expressed in the heterozygote

• I^A and I^B and codominant. This occurs when the heterozygous individual shows the effect of both alleles that they carry in the gene

What is haemophilia?

A sex-linked genetic disorder where blood doesn’t clot properly

What are the alleles for haemophilia?

• X^H and X^h

• X^H is the chromosome that produces normal blood clotting

• X^h is the chromosome that produces poor blood clotting

• Because boys have a Y chromosome, they can only inherit haemophilia if their mother is a haemophiliac or a carrier for the disease

What are some causes of variation?

• The different alleles and organism inherits

• Caused by the environment such as riding a bike or scars

• Combination of both such as weight and skin colour which are affected by both genetics and the environment

• Lifestyle

How do mutations work?

• A mutation is created if the sequence of bases in a gene is changed

• A mutation in the gene’s coding DNA can affect the phenotype of an organism

• If the amino acid sequence is altered, the activity of the protein produced may also be altered

How dangerous can a mutation be?

• Some mutations can be harmless or have little effect, but others can significantly affect the phenotype

• A mutation may also cause a large change in a protein produced

How can a mutation in the non-coding region of DNA affect proteins produced?

• A mutation may increase or decrease the ability of RNA polymerase to bind to DNA

• This could increase or decrease the amount of protein produced

What is the human genome project?

• A collaboration between scientists to decode the human genome (the order of bases or all human chromosomes)

• The results are being used to develop new medicines and treatments for disease

What are the advantages for the human genome project?

• Alerting people that they are at risk of a certain disease so they can make lifestyle changes to reduce the risk of the disease developing

• Distinguishing between different forms of diseases such as leukaemia or Alzheimer’s disease, as some drugs are beneficial for some but not others

• Allowing doctors to tailor treatments for some diseases to the individual, where different alleles effects how someone will respond to treatment

What are the disadvantages of the human genome project?

• People at risk of certain diseases may have to pay more to obtain life insurance

• It may not be helpful to tell someone they are at risk of a condition that has no cure

How does Darwin’s theory of evolution work?

• Adults produce more young than the environment can’t support leading to a ‘struggle for existence’ for the young

• Some individuals inherit characteristics that help them survive in the environment while others will be less adapted to the environment

• Individuals who have not adapted as well will either die out and will not produce young or they will produce less young than the adapted individuals

• Individuals with advantageous characteristics will pass on their genes to the next generation and will be more likely to survive

• More individuals in the next generation will have same gene

What two groups can prokaryotes be split into and why?

• Eubacteria and archaea

• This is because the genes or organisms in archaea work more like eukaryotes while eubacteria work a little differently