b6

mitosis

produces genetically identical cells (asexual)

meiosis

produces genetically non-identical cells, leads to the formation of gametes

asexual reproduction

only one parent, no fusion of gametes therefore no mixing of genetic information, only mitosis is involved

where does meiosis happen in humans?

ovaries in females and testes in males

process of meiosis

parent cell with full number of chromosomes (46 in humans) copies its chromosomes, the chromosomes line up at the centre of the cell, cell divides twice to produce four cells. each cell has half the number of chromosomes (23) and all are genetically different, called gametes

advantages of sexual reproduction

if the environment changes variation gives a survival advantage by natural selection. natural selection can be speeded up by humans in selective breeding to increase food production

advantages of asexual reproduction

no time and energy wasted finding a mate, offspring produced faster than sexual reproduction, many identical offspring can be produced when conditions are favourable

life of the malarial parasite

the protist reproduces asexually in red blood cells in people. in the mosquito vector they reproduce sexually

sexual and asexual reproduction in a fungus

fungus reproduces sexually on the fruit but spores are made asexually

dna

polymer made of two strands that make a double helix, containing repeating units called nucleotides

chromosome

structure made up of dna tightly coiled around proteins

gene

small section of dna that codes for a specific order of amino acids to make a specific protein

genome

entire genetic material of an organism

advantages of understanding the human genome

search for genes linked to diseases, understand and treat inherited disorders, trace human migration patterns from the past

parts of a nucleotide

phosphate group, sugar, bass

the four bases

a + t , c + g

protein synthesis

a set of three bases on one strand of dna codes for a particular amino acid. the order of bases controls the order in which the amino acids are joined

in the nucleus, a copy of the dna base sequence is made - a template molecule (mRNA). the template molecule moves into the cytoplasm and attaches to a ribosome. carrier molecules (tRNA) bring specific amino acids to the template and add them to a growing chain. when a protein chain is complete, it folds into a unique shape, allowing the protein to do its job

coding regions in dna

code for proteins. genetic variants of the coding regions may code for protein with different activity

non coding regions in dna

can ‘switch’ genes on and off. genetic variants may alter how genes are expressed ( whether they are switched on or off)

mutation

change in the DNA sequence of a gene, when one or more base is added, removed or changed. they are random and happen spontaneously, or can be caused by radiation or chemicals (mutagens)

frameshift

caused by insertion and deletion mutations, changes every amino acid coded for after the mutation

effect of most mutations

most mutations have no effect, with no change or a slight change in the protein

alleles

different forms of a gene

genotype

combination of alleles present

phenotype

how the genotype is expressed (physical appearance)

polydactyly

inherited disorder caused by the presence of a dominant allele (extra fingers or toes)

cystic fibrosis

an inherited disorder of cell membranes caused by a recessive allele (cells in the airways and intestines that produces thick mucus)

gene therapy

the possibility of altering or repairing faulty genes or the alleles that cause disorders

embryo screening

used to check embryos for a genetic disorder. done by either using ivf to produce several embryos, testing and implanting one into the mother’s womb, or testing an embryo/foetus in the mother’s womb

sex determination

one pair of the 23 determines sex. females carry two x chromosomes, males carry one x one y chromosome

phenotype is developed from

the genome of an organism and the genome’s interaction with the environment

variation

differences in the characteristics of individuals of a species. comes from mutations

evolution

change in inherited characteristics in a species over time, happens through natural selection

how does a new species come about?

if two populations of a species become so different that they can no longer interbreed to produce fertile offpsring

causes of variation

genetic (inherited) , environmental, or a combination of both

theory of evolution by natural selection

all species evolved from simple life forms from 3 billion years ago

fossils

the ‘remains’ of organisms from millions of years ago found in rock

formation of fossils

if parts of organisms have not decayed (no oxygen or bacteria present), or when partd of organisms are replaced by minerals as they decay, or as preserved traces of organisms such as footprints

why did many early life forms not fossilise?

they were soft-bodied

extinction

when there are no remaining individuals of a species

causes of extinction

drought, climate change, natural disasters, new predators, new competitors, disease, habitat destruction

resistant bacteria

bacteria can evolve rapidly because they reproduce rapidly. mutations in bacteria can produce new strains. some strains can be resistant to antibiotics (eg MRSA)

selective breeding

humans breed plants and animals for wanted genetic characteristics

method for selective breeding

choose parents with desired characteristics (in this case chickens that produce large eggs), breed them together. select the offspring that produced the largest eggs and breed them, repeat over many generations

useful characteristics looked for

disease resistance in food crops, animals that produce more meat/milk, domestic dogs with a gentle nature, large or unusual flowers

selective breeding can lead to

inbreeding, where some breeds have inherited defects

genetic engineering

transferring genes from one living organism to another to give a desired characteristic

process of genetic engineering in plants

useful gene is removed from the nucleus of the cell, gene is inserted into the dna of an embryo cell from a crop plant

genetic engineering in humans

dna is taken out of the nucleus of a cell, gene for a human protein is inserted into a plasmid, plasmid is inserted back into its bacterium, which can now produce that human protein (eg for producing insulin)

using enzymes to genetically engineer

enzyme isolates the gene, gene is inserted into a vector (eg a virus), the vector inserts the gene into a cell (eg a plant embryo cell, that then divides and produces crops with that gene)

who developed the classification system

carl linnaeus

king philip came over for good soup

kingdom phylum class order family genus species

binomial system

genus and species

three domain system proposed by carl woese

archaea (primitive extremophile bacteria)

bacteria (true bacteria)

eukaryota (protists, fungi, plants, animals)

why was a new model proposed for classification?

evidence of internal structures became more developed with better microscopes, understanding of biochemical processes improved

cloning plants by cutting

cut off small shoot from plant with desired characteristics, dip in rooting powder and place it into soil. it will be genetically identical

tissue culture

a small group of cells are grown into a new organism in a medium that contains special nutrients eg glucose for respiration

embryo transplants for cloning

an embryo is split into several separate groups of cells, each is implanted into a separate host mother, each mother goes through a pregnancy

adult cell cloning

nucleus is removed from egg cell of A, nucleus from body cell of B is put into empty egg cell, electric shock is used to start the cell’s dividing, to form an embryo, which is implanted into a host mother. the baby will be a clone of B

darwin’s evidence for evolution

around the world expedition, years of experimenting and discussion with other scientists, knowledge of geology and fossils

lamarck

suggested that changes that occur in an organism in its lifetime can be inherited, but this is rare

alfred wallace

theory of speciation - development of new species. one population of a species can be separated into two or more by a geographical barrier, genetic variation in each population gives variation in characteristics

gregor mendel

carried out breeding experiments in pea plants. crossed pure-breeding plants and counted offspring, finding that traits are inherited in predictable patterns, determining that inheritance is determined by ‘units’ now known as genes, dominant/recessive passed unchanged from parents to offspring