B6- Inheritance, Variation and evolution

what is DNA

it is the chemical that all of the genetic material in a cell is made up from.

it contains coded information to put an organism together and make it work.

it determines inherited characteristics

what is a gene

a small section of DNA found on a chromosome.

each gene codes for a particular sequence of amino acids which are put together to make a specific protein

what is a genome

the entire set of genetic material in an organism

why is understanding the human genome important for sience and medicine

• identify genes that are linked to different types of disease.

• knowing what genes are linked to inherited diseases could help develop effective treatment.

• they can trace the migration of certain populations all over the world.

how does sexual reproduction work

• sexual reproduction is where genetic info from two organisms is combined to produce offspring which are genetically different.

• the mother and father produce gametes by meiosis - sperm & egg

• each gamete contains 23 chromosomes - half normal number

• the egg and sperm fuse together to form a cell with the full number of chromosomes

how does asexual reproduction work

• theres only one parent so the offspring are genetically identical to the parent

• happens by mitosis - an ordinary cell makes a new cell by dividing in two

• the new cell has exactly the same genetic material - a clone

• bacteria,some plants and some animals reproduce asexually

describe meiosis

1. before the cell divides it replicates its genetic information and the chromosomes arrange themselves into pairs

2. in the first division the chromosome pairs line up int he center of the cell

3. the pairs are then pulled apart so each new cell only has one coppy of each chromosome

4. this is repeated in the second division

5. 4 gametes are produced, each with only a single set of chromosomes.

what is the male and female genetic code

male: XY

female: XX

what does homozygous

if an organism has two alleles for a particular gene that are the same

what is heterozygous

if an organism has two alleles for a particular gene that are different

what is cystic fibrosis

a genetic disorder of the cell membrane. results in the body producing a lot of thick mucus in the air passage and in the pancreas.

the allele is a reccessive ‘f’

both parents must be a carrier of have the disorder

what is polydactyly

a genetic dissorer where a baby is born with extra fingers or toes.

it is caused by a dominant allele ‘D’ and can be inherited if one parent carries it

what is embryonic screening

during IVF it is possible to remove a cell from the embryo and analyse its genes to detect genetic dissorders

why are people against embryo screening

1. implies that people with dissorders are undesirable

2. expensive

3. it may become popular and every one does it to gain desirable characteristics.

why are people for embro screening

1. help stop suffering

2. treating the disorders costs the government money - tax

3. there are laws to stop it going too far

what is variation

variation is genetic and caused by a difference in genotype

what is a mutation

a rare, random change in an organisms DNA that can be inherited

most genetic variants have very little or no effect on the protein it codes for

some variants have small influence on the organisms phenotype - they alter the individuals characteristic

what is the theory of evolution

all of todays species have evolved from simple life forms that first started to develop over three billion years ago

survival of the fittest

charles darwin came up with the theory evolution by natural selection

• the organisms with the most suitable characteristics for the environment would be sucessful competitors and more likley to survive

• the succesful organisms are more likely to reproduce and pass on the successful characteristics.

• over time the beneficial characteristics become more common and the species evolves

what is speciation

over a period of time the phenotype of organisms change so much because of natural selection that a completley new species is formed

populations of the same species change to become reproductively isolated - they cant interbreed to produce fertile off spring

why do species become extinct

• the environment changes too quickly - destruction of habitat

• new preditors kill them all - humans hunting

• a new disease

• they cant compete with another species for food

• a catastrophic event kills them all

what is selective breeding

when humans artificially select the plants or animals that are going to breed so that the genes for particular characteristics remain in the population

how does selective breeding work

1. from existing stock, select the ones with the desired characteristics

2. breed them with eachother

3. select the best offspring and breed them together

4. continue this over several generations and the desirable trait gets stronger and stronger

what is the main dissadvantage to selective breeding

there is a reduce in the number of different alleles which can cause health problems from inbreeding.

if a new disease appears because there is not much variation in the population, if one gets killed the others are also likely.

what is genetic engineering

1. a useful gene is isolated from one organisms genome and is inserted into a vector

2. the vector is usually a virus or a bacterial plasmid

3. when the vector is introduced to the target organism the useful gene is inserted into its cells

examples of genetic engineering

1. bacteria modified to produce human insulin to treat diabetes

2. crops have been modified to improve the size and quality or make them disease resistant

3. sheep to produce substances like drugs in their milk to treat disease

3 ways that fossils form

1. gradual replacement

2. casts and impressions

3. preservation

how are fossils formed through gradual replacement

1. things like teeth, shells, bones - that dont decay easily can last a long time when buried

2. theyre eventually replaced by minerals as they decay, forming a rock like substance shaped like the original part

3. the surrounding sediments also turns to rock but the fossils stay distinct.

how are fossils formed through casts and impressions

1. fossils are formed when an organism is buried in soft material like clay which hardens around the organism as it decays and forms a cast

2. things like footprints can be pressed into the material when soft and leave an impression

how are fossils formed from preservation

1. in amber and tar pits there is no oxygen or moisture so decay microbes cant survive

why cant hypotheses abut how life began be proved

1. many early forms of life were soft bodied and soft tissue tends to decay completely

2. fossils formed millions of years ago may have been destroyed by geological activity

hoe does bacteria become antibiotic resistant

1. bacteria sometimes have random mutations in there DNA which can lead to changes in the bacteria’s characteristics meaning they are less affected by antibiotics

2. bacteria are rapid at reproducing so they can evolve quickly

3. if it is not impacted by the antibiotic it can live for longer and reproduce quicker which increases the population size.

what are the classification groups

• Kingdom

• Phylum

• Class

• Order

• Family

• Genus

• Species

what is the three domain system

1. ARCHAEA - primitive bacteria

2. Bacteria

3. Eukaryota - broad range of organisms : fungi, plans, animals, protists