Inheritance And Evolution

Question 1

Sexual reproduction

Answer 1

1. Sexual reproduction involves the joining of male and female gametes, each containing genetic information from the mother or father.
   • Sperm and egg cells in animals
   • Pollen and egg cells in flowering plants
   Gametes are formed by meiosis, as they are non identical.
   A normal cell has 46 chromosomes. There are two sets of chromosomes (i.e. 23 pairs). In each pair, one chromosome is from the father and the second set is from the mother.
   Each gamete has 23 chromosomes and they fuse in fertilisation.
   The genetic information from each parent is mixed, producing variation in the offspring

Question 2

Asexual reproduction

Answer 2

2. Asexual reproduction involves one parent with no gametes joining.
   It happens using the process of mitosis, where two identical cells are formed from one cell.
   There is no mixing of genetic information.
   It leads to clones, which are genetically identical to each other and the parent.
   Examples of organisms that reproduce this way are bacteria, some plants and some animals.

Question 3

Meiosis

Answer 3

The cell makes copies of its chromosomes, so it has double the amount of genetic information.
The cell divides into two cells, each with half the amount of chromosomes (46).
• The cell divides again producing four cells, each with a quarter the amount of chromosomes (23).
• These cells are called gametes and they are all genetically different from each other because the chromosomes are shuffled during the process, resulting in random chromosomes ending up in each of the four cells.

Question 4

Mitosis

Answer 4

This cell divides by mitosis to produce many copies.
More and more cells are produced, and an embryo forms.
The cells begin to take on different roles after this stage (differentiation).

Question 5

Advantages of sexual production

Answer 5

Produces variation in offspring.
• Although some individuals may die, variation decreases the chance of the whole species becoming extinct
It allows us to use selective breeding.
• This type of reproduction mixes genetic information from two organisms
• Organisms with different desirable characteristics can be bred to produce offspring with even more desirable characteristics.
• This speeds up natural selection.
• An example is to increase food production by breeding two animals with lots of meat.

Question 6

Advantages of asexual reproduction

Answer 6

Only 1 parent is needed
Uses less energy and is faster due to not having to find a male

Question 7

How do some plants reproduce sexually and asexually

Answer 7

• Many reproduce sexually using pollen, which must reach the egg cells in the female parts of another flower. This is called pollination, and it forms seeds
• Strawberry plants reproduce asexually, as they produce runners. New identical plants grow off the runner.
• Daffodils reproduce asexually. They grow from bulbs. New bulbs can grow from the main one, producing a new identical plant.
• It is advantageous in plants as it means they can reproduce even if the flowers have been destroyed by frost or other animals.

Question 8

What’s a gene

Answer 8

A gene is a small section of DNA on a chromosome - Each gene codes for a particular sequence of amino acids, together a chain of amino acids can join to make a protein.

Question 9

What’s a genome

Answer 9

The genome is all the genes coding for all of the proteins within an organism.
The whole human genome has now been studied and this has improved our understanding of the genes linked to different types of disease, the treatment of inherited disorders

Question 10

What’s an allele,dominant allele,recessive allele,genotype and phenotype

Answer 10

Allele-The different forms of the gene
Dominant allele-Only one (out of the two alleles) is needed for it to be expressed
Recessive allele-Two copies are needed for it to be expressed
Genotype-The combination of alleles an individual has,
Phenotype-The physical characteristics that are observed in the individual,

Question 11

What are the 3 recessive disorders and how theyre caused

Answer 11

Polydactyly: having extra fingers or toes
• Caused by a dominant allele
Cystic fibrosis: this is a disorder of the cell membranes, resulting in thick mucus in the airways and pancreas
• Caused by a recessive allele
Both parents need to either be carriers (have one of the recessive alleles) or one must have CF themselves and the other is a carrier.
Embryonic screening allows scientists to observe whether the child will have a genetic condition or not.
• If the embryo is developed in the lab, cells can be taken from it and analysed
DNA from embryos in the womb can also be extracted

Question 12

Arguements for embryonic screening

Answer 12

Reduces the number of people suffering
Treating disorders are very expensive
Many regulations that stop it from getting out of hand

Question 13

Arguements against embryonic screening

Answer 13

Could encourage people to pick characteristics - creating designer babies (ethical).
It is expensive to carry out screening (economic).
May promote prejudice as it suggests that those with genetic disorders will not live a full life or are unwanted (social).

Question 14

Properties of x and Y chromosomes

Answer 14

Females have two X chromosomes, so therefore only pass on X chromosomes in their eggs.
• Males have one X chromosome and one Y chromosome so therefore can pass on X or Y chromosomes in their sperm.

Question 15

What does the phenotype of an organism depend on

Answer 15

Genotype: the genes it inherited
• Genes are passed on from the parent in sex cells.
• The combining of genes from the mother and father creates genetic variation.
• Only identical twins have the same genotype.
• There is lots of genetic variation in a population.
2. Environment: the place it lives in
• The conditions the organism grows and develops in also affects its appearance.

Question 16

What’s the theory of evolution

Answer 16

Theory of Evolution: All species have evolved from simple life forms that first developed more than three billion years ago.

Question 17

How does evolution occur

Answer 17

• Mutations occur which provide variation between organisms.
• If a mutation provides a survival advantage the organism is more likely to survive to breeding age.
• The mutation will then be passed onto offspring.
• Over many generations, the frequency of the mutation will increase within the population.

Question 18

What is selective breeding

Answer 18

Selective breeding is when humans choose which organisms to breed in order to produce offspring with a certain desirable characteristic

Question 19

What is the procces of selective breeding

Answer 19

Parents with desired characteristics are chosen.
• They are bred together.
• From the offspring those with desired characteristics are bred together.
• The process is repeated many times until all the offspring have the desired characteristic.

Question 20

What is inbreeding and what’s the problems of it

Answer 20

Breeding those with similar desirable characteristics means it is likely you are breeding closely related individuals.
• This results in the reduction of the gene pool, as the number of different alleles reduce (as they mostly have the same alleles).
• This means if the environment changes or there is a new disease, the species could become extinct as they all have the same genetic make-up

Question 21

What is genetic engineering

Answer 21

Genetic engineering: Modifying the genome of an organism by introducing a gene from another organism to give a desired characteristic.
• Plant cells have been engineered for disease resistance or to have larger fruits
• Bacterial cells have been engineered to produce substances useful to humans, such as human insulin to treat diabetes.

Question 22

Procces of genetic engineering

Answer 22

1. Genes from chromosomes are ‘cut out’ using restriction enzymes leaving
   ‘sticky ends’ (short sections of exposed, unpaired bases)
2. A virus or bacterial plasmid is cut using the same restriction enzyme to also create sticky ends. This also contains an antibiotic marker gene.
3. The loop and gene sticky ends are then joined together by DNA ligase
   enzymes
4. The combined loop is placed in a vector, such as a bacterial cell, and then allowed to multiply as it will now contain the modified gene. As the bacteria grows we can see which ones are resistant to antibiotics. The colonies that are will be the bacteria that are also producing the modified gene, as they were inserted together.
   In plants the vector is put into meristematic cells

Question 23

Genetic modification in crops and medicine.

Answer 23

Genetically modified crops
• They are engineered to be resistant to insects and to herbicides.
• This will result in increased yields as less crops will die.
Genetic modification in medicine
• It may be possible to use genetic engineering to cure inherited disorders.
• It is called gene therapy and involves transferring normal genes (not faulty) into patients so the correct proteins are produced.

Question 24

Pros of genetic modification

Answer 24

In agriculture it can be used to improve yields by:
• Improving growth rates
• Introducing modifications that allow the crops to grow in different conditions,
Crops can be grown with extra vitamins
Greater yield can help solve world hunger

Question 25

Cons of genetic modification

Answer 25

Gm crops may have an effect on wild flowers and therefore insects
•genres could spread to wild animals
People do not understand the effects of gm crops on human health
They could create resistances in other plants

Question 26

Evidence for evolution

Answer 26

Fossils: the remains of organisms from many years ago, which are found in rocks
2. Antibiotic resistance in bacteria: the selection pressure of antibiotics leads to advantageous mutations being selected for in bacteria populations so they are no longer killed when exposed to antibiotics.

Question 27

How are fossils formed

Answer 27

1. Parts of organisms that have not decayed because oxygen or moisture were not present, meaning that the microbes that cause decay cannot survive.
2. Parts of the organism such as teeth, shells and bones are replaced by minerals as they decay, forming a rock structure of the original part.
3. Preserved traces such as footprints, burrows and rootlet traces (the plants roots) remain due to the ground hardening around them and forming a cast.

Question 28

Why can fossils not tell us how life started on earth

Answer 28

Most early life forms are soft-bodied and therefore decay completely, so there are few fossils of them.
• Any traces left have been destroyed by geological activity.

Question 29

What factors contribute to exinction

Answer 29

Changes in environment which the species cannot adapt fast enough to.
2. New predators may have evolved or migrated to the area.
3. A new disease arises and there are no resistant alleles to it.
4. They have to compete with a species which has advantageous mutations for the same food source.
5. A catastrophic event can wipe out a species.
6. Destruction of habitat

Question 30

How to bacteria become resistant

Answer 30

• Bacteria reproduce at a fast rate.
• Mutations during reproduction can result in new genes, such as the gene for antibiotic resistance. This the creation of a new strain.
Exposure to antibiotics creates a selection pressure, as those with antibiotic
resistant genes survive and those without die.
• As a result those with antibiotic resistance can reproduce and pass on the advantageous gene to their offspring.
• This population of antibiotic resistant bacteria increases.
• Bacterial diseases spreads rapidly because people are not immune to these new resistant bacteria and there is no treatment for it.

Question 31

What is MRSA

Answer 31

• Called a ‘superbug’ as it is resistant to many different types of antibiotics
• Common in hospitals: spreads when doctors and nurses move to different patients

Question 32

How do you slow the development of antibiotic resistance

Answer 32

Antibiotics should not be given for viral or non-serious infections
2. Specific antibiotics should be given for specific bacteria
3. Patients should complete their course of antibiotics - if they do not some bacteria may survive and mutate to become antibiotic resistant.
4. Antibiotics should be used less in agriculture - farmers currently use them to prevent their livestock dying from disease, but this overuse leads to antibiotic resistant bacteria which are then transterred to humans when they consume the meat.

Question 33

How to slow the transmission of bacteria

Answer 33

Maintain high standards of hygiene in hospitals
2. Medical staff and visitors should wash hands regularly
3. Medical staff should wear disposable clothing or clothing that is regularly sterilised