Biology 6

Meiosis= non-identical cells

Mitosis= identical cells

Sexual reproduction= fusion of male & female gametes

-sperm & egg cell in aminals

-pollen & egg cells in flowering plants

Sexual reproduction = mixing genetic info --> variet in offspring

-formation of gametes involves meiosis

Asexaul reproduction= one parent & no fusion of gametes

-no mixing of genetic info

-genetically identical offspring (clones)

-mitosis involved

Meiosis halves number of chromosomes in gametes & fertilisation restores to full number

-new cell divides by mitosis

-number of cells increase

-during development cells diffrentiate

Cells in reproductive organs divide by meiosis

-copies of genetic info made

-cell divide 2x= 4 gametes (each with single set of chromosomes)

-gametes genetically different

Gametes

Advantages (sexual reproduction):

-variation of offspring

-survival advantage (natural selection)

-natural selection sped up= increase to food production

Advantages (asexual reproduction):

-one parent need                                                 -faster than sexual rep

-time & energy efficient (no mate)                       -many identical offspring

Some organisms do both depending on circumstances:

-Malaria parasites reproduce asexually in host but mosquito reproduce sexually

-fungi reproduces asexually by spores but reproduce sexualy for variation

-plants produce seed sexually but strawberries & bulbs of daffodils reproduce asexually

DNA= chemical genetic material inside of nucleus

-DNA= polymer made of 2 strands formed into double helix

-contains chromosomes

Gene=small section of DNA on chromosome

-gene codes in sequence of amino acid---> specific protein

Genome= entire genetic material of organism

-human genome studied & important to medicine

Limited:

-search for genes linked to diseases

-understanding & treating inherited disorders

-tracing human migration pattern from past

DNA polymer made of different nucleotides

-each nucleotide consists of common sugar & phosphate group 

DNA contains four bases (A,C,G & T)

Sequence of three bases= code for particular amino acid

-order controls order amoino acid assembled to produce protein

Long strand consist of alternating sugars & phosphate sections

-attached to each sugar is 1/4 bases

DNA polymer= repeating nucleotides units

-gametes          -gene          -dominant     -homozygous      -genotype

-chromosomes  -allele         -recessive      -heterozygous    -phenotype

Some characteristics controlled by single gene

-each may have different forms (alleles)

Alleles (genotype) operate a molecular level to develop a characteristic expressed (phenotype)

Dominant allele always expressed

Recessive is only expressed if 2 copies present

Homozygous= two alleles present are same

Heterozygous= alleles are different

Characteristics result of multiple genes interacting

Some disorders are inherited (caused by certain alleles)

-Polydactyly(extra fingers or toes)= dominant allele

-Cystic fibrosis (disorder of cell membranes)= recessive allele

Human body cells contain 23 pairs of chromosomes

-22 pairs control characteristics

-1 pair carries genes that determine sex

Female= same sex chromosomes (**)

Male= different sex chromosomes (XY)

Variation= differences in characteristics of individuals in a population because:

-genes are inherited

-conditions developed

-combination of genes & environment

There is extensive variation of a population

Mutations mostly don't affect the phenotype but some do

Mutations occur continuously

-if new phenotype is suited to environment --> rapid change in species

Evolution= change in inherited characteristics over time throught natural selection

Theory of evolution by natural selection

-all species evolved from simple life forms 

-developed more than 3 million yrs ago

Two populations of one species become different in phenotype can't interbreed

-forms 2 new species

Selective breed= process of breed animal/ plants for specific genetic characteristics

-involves choosing parents (with desired characteristics)= mixed population

-parents are bred together --> continues over mant generations

Characteristics chosen for usefulness/ appearance:

-Disease resistance 

-animals produce more meat or milk

-domestic dog have gentle nature

-large/ unusual flowers

S B--> interbreeding= prone to disease/ inherited defects

Plant cells GE to resist disease/ produce bigger & better fruits

Bacterial cells GE to produce useful substances 

Genetic Engineering (could help overcome inherited disorders):

-enzymes used to isolate gene required (gene inserted into vectors)

-vector used to insert gene into required cells

-genes transfered to organism at early stage of development (develop with desired characteristics)

Genetically modified crops= crops with genes modified

-resistant to insect attack/ herbicides

-increase yield

Could effect people when eating or organism (flowers & insects)

Tissue culture= small groups of cells from part of plant to grow identical new plants

-preserve rare plant species

Cuttings= method used to produce many identical new plants from parent plant

Embryo transplants= splitting apart developing animal embryo before specialised

-transplant embryo into host mothers

Adult cell cloning:

-nucleus removed from unfertilised egg cell

-nucleus from adult body cell (skin cell)  inserted into egg cell

-electric shock stimulates egg cell to divide (form embryo)

-embryo contains same genetic info as adult skin cell

-embryo (ball of cells) inserted into female to continue development

Charles Dawin observed through fossils and geology --> Theory of evolution by natual selection

-organisms show range of variation

-organism have characteristics suited to its environment

-characteristics enable organism to survive

Dawin published 'On the Origin of Species' (had controversy around ideas)

Ideas gradually accepted because:

-theory challenged idea of God creating everything

-insufficient evidence at the time

-mechanism of inheritanc & variation not know at the time

Jean - Baptiste Lamarck based ideas off organisms' change over lifetime can be inherited (this is wrong)

Alfred Russel Wallace proposed theory of evolution by natural selection

-prompted Darwin to publish book

Wallace gathered evidence of evolutionary theory

-focused on warning colouration of animals & theory of speciation

-allowed scientist now to understand theory of speciation

19th Century

Mendel carried out breeding experiments on plants

-inheritance of characteristics is determined by 'units' passed to descendants unchanged

Behaviour of chromosomes also observed

20th Century

Chromosomes & units behave similarly

-'units' now known as genes are in chromosomes

Structure of DNA determined & mechanism of gene function worked out

Gene theory developed by many scientists' work

Theory of evolution widely accepted

Evidence:

-characteristics passed to offspring in genes

-fossil records

-knowledge of how resistance to antibiotics evolves in bacteria

Fossils= remains of organisms from millions of years ago found in rocks

Fossils formed by:
-parts of organisms have not decayed (conditions needed for decay absent)

-parts of organisms replaced by minerals

-preserved traces of organisms (footprints, burrows etc)

Early forms of life soft bodies= few traces behind

-traces destroyed by geological activity= scientists cannot be certain how life begins

Fossils teach us how organsisms changed as life developed on Earth

Extinction = no remaining individuals of species still alive

Bacteria evolve rapidly as they reproduce quickly

Mutations of bacterial pathogens= new strains

-strains can be antibiotic resistant due to quick reproduction= population increase

-strain spreads= person not immune & no effective treatment

MRSA= antibiotic resistant

To reduce rate of development of antibiotic resistant strains:

-doctors should not provide unnecessary antibiotics (non serious or viral infections)

-patients should complete their course of antibiotics

-agricultural use of antibiotics restricted

Development of new antibiotics= expensive & slow (unlikely to keep up with new resistant strains)

Living things classified into groups depending on their structure & characteristics in system developed by Linnaeus

-classified things into KINGDOM, PHYLUM, CLASS, ORDER, FAMILY, GENUS & SPECIES

-organisms named by binominal system of genus & species

Evidence of internal structures become more developed (microscopes)

-understanding of biochemical processes progressed & new models of classification proposed

Evidence from chemical analysis--> 'three domain system' by Woese

-archaea (primative bacteris living in extreme environments)

-bacteria (true bacteria)

-eukaryota (includes protists, fungi & animals)

Evolutionary trees used to show how organisms relate