Inheritance, variation and evolution

sexual reproduction

fusion of male and female gametes (fertilisation), mix of genes- variation.

gametes

sex cell- only have half of genetic variation, 23 chromosomes

asexual reproduction

one parent, no mixing- no genetic variation, identical clones

cell cycle- mitosis

duplicates each of the 46 chromosomes and creates an x shape. line up towards the centre of the cell, then cell fibres pull cells to opposite sides (poles). cytokinesis- cell splits and creates 2 identical daughter cells with 46 chromosomes each

meiosis

replicate DNA and form x shape. they make a line and cell fibres pull chromosomes to each side of the cell. the DNA crosses over. the cell splits into two different halves, the DNA is different. the chromosomes again line up towards the centres, and each arm is pulled to either side of the cell to make 4 genetically unique cells (gametes) with 23 chromosomes in them each.

pros and cons of asexual reproduction

pros: quick, only one parent needed, identical offspring (w/ favourable conditions), time and energy efficient

cons: no genetic variation, endangers species, less chance of adapting

pros and cons of sexual reproduction

pros: lots of genetic variation, population can adapt (evolution), survival advantages, selective breeding

cons: more time and energy (finding mates)

both types of reproduction

malarial parasites: asexually in the human host, sexually in the mosquito

fungi: asexually by spores, sexually for variation

plants: produce seeds sexually, reproduce asexually (eg. strawberry plants, daffodil bulbs)

DNA made up of

double helix, polymer, 2 strands, stored inside the nucleus of a cell.

sex chromosomes

xx: female

xy: male

gene

small section of DNA that codes for a protein (small section of a chromosome). combined amino acids makes a unique protein.

genome

entire set of genetical material/makeup of an organism. genes can be inherited (disease). can trace migrations of ancestors. eg. BB, Bb, b. they determine the phenotype

alleles

a variant form of a gene to produce different types of a characteristic. we get 2 alleles for each gene- one from each parent.

homozygous & heterozygous

homo: 2 of the same allele inherited from parents

hetero: 2 different alleles inherited from parents

genotype & phenotype

genotype: collection of alleles

phenotype: different characteristics

structure of dna

double helix, polymer. one strand for example, has monomers- aka. nucleotide. they contain a sugar, phosphate and a base. ATCG

protiens

code together from sequences of 3 bases. (codons). they are unique as they are folded together creating different shapes for different functions. mainly for enzymes (biological catalysts), hormones (carry messages) and structural protiens (strength to tissues and cells). made from 20 amino acids

protein synthesis

1. transcription

2. translation

mRNA

messenger RNA

1. shorter than DNA

2. only a single strand

3. uses uracil (U) instead if thymine (T)

transcription

the DNA unwinds and hydrogen bonds break exposing one strand (template). mRNA is built using complementary base pairing (AU, TA, CG, GC). then the mRNA leaves the nucleus through a nuclear pore

translation

mRNA attaches to a ribosome. tRNA brings amino acids and matches the anticodon to the mRNA codon. amino acids link together with peptide bonds and forms a polypeptide (protein)

genetic variation influences phenotypes

coding DNA: mutations change the protien. can work better or worse eg. cystic fibrosis

non coding DNA: controls when and how much a gene is used, mutations can turn them on and off eg. insulin production

mutations

changes in the DNA base sequence. carcinogens and radiation (x-rays or gamma rays) increase the risk. they happen spontaneously in our cells.

types of mutation

substitution- one base is randomly changed with another

insertion- extra base is inserted into the sequence

deletion- one base is deleted

polydactyly

baby born with extra fingers or toes- dominant

cystic fibrosis

disorder of cell membrane, releases mucus- recessive

embryo screening

look at genes carrying genetic disease

pros: reduce suffering, saves money, saves time

cons: implies people with genetic disorders are undesirable, future screening- designer babies

chromosomes in the body

there are 23 pairs of chromosomes

22 pairs control characteristics only

one pair carries the sex gene. female: xx, male: xy

genetic variation is due to

genes they have inherited (genetic causes)

conditions they have developed in (environmental causes)

a combo of genetics and environment

beneficial mutations

survival of the fittest- charles darwin

mutations→ more likely to survive→ more reproduction.

useful traits passed onto offspring- natural selection

evolution

inheritance of certain characteristics in a population (over multiple generations) could change the species itself- charles darwin. all current species must have evolved from other species.

selective breeding

breeding the best plants/ animals together for better offspring- then repeating to keep getting better offspring

characteristics chosen for

disease resistance

animals producing more meat or milk

domestic dogs with more gentle traits

large or unusual flowers

cons selective breeding

reduces gene pool of population (collection of alleles). small gene pool could lead to inbreeds; prone to disease or have inherited defects. less variation- new pathogens could rid most of the population

genetically modified

take a desirable gene from something, then transfer it to another organism to gain the same trait, aka. GM. can work between different species.

G.M vs G.E

gm: DNA modifications, selective breeding/ radiation/ gene insertion, less controlled, eg. cross breeding

ge: direct and precise DNA modifications, gene splicing, highly targeted, eg. bacteria producing insulin

genetic engineering examples

drugs in sheep milk- extract and used to treat disease

bacteria which produce insulin and harvested to treat disease

improving quality and size of crops, or making them resistant to diseases, insects or herbicides

pros and cons of gm crops

pros: desirable characteristics, more nutritious, resistant to diseases, more food for less money, important for poorer countries eg. golden rice contains beta-carotene which prevents blindness

cons: don’t know how it could affect health, plants could spread to wild and change the whole ecosystems

transferring gene

find the gene we want, cut it out and isolate it using enzymes. insert gene into the vector (virus or bacterial plasmid). introduce vector to the organism. the cells of the organism will take up the vector and useful gene, then create a protein

cloning animals

get a sperm cell and an egg cell from an organism to fertilise it. one the egg is fertilised it will start to develop into an unspecialised embryo. we use a glass rod to split the embryo in half, then transport the embryo into host mothers. when the animals are born, we will gain two identical offspring.

cons of cloning animals

because we use a sperm and egg cell, we can’t control what characteristics they might have. we can overcome this by adult cell cloning

adult cell cloning

(can choose characteristics) remove a cell from the adult animal (eg. skin cell). then remove the nucleus from the cell and take an unfertilised egg from the same species. remove the nucleus from the cell and replace it with the adult nucleus. then you give an electric shot to the embryo which divides the cell then given to the host mother.

cloning plants

pros: predictable characteristics

take a cutting, dip in rooting powder which contains plant hormones- encouraging root growth

tissue culture: using cells to form identical new plants. good for plant preservation or commercially in nurseries

theory of evolution by natural selection

individual organisms within a particular species show a wide range of variation for characteristics

characteristics most suited to environments are more likely to survive

the favourable characteristics are passed on to offspring

it was gradually accepted because

challenged religious ideas about God’s creation

insufficient evidence at the time

inheritance and variation discovered 50 years later

speciation

how new species form.

a geographical barrier would separate interbred organisms from each other so mutations would not be able to spread. overtime, two populations would change. if the two populations of snails mix, they would be so different that they can’t produce offspring

gregor mendels ideas

carried out breeding experiments on plants. he observed that units are passed on to the offspring. later on, chromosome behaviour during cell division was observed. mendels units behaved in similar ways. units were actually genes inside of chromosomes. this helped develop gene theory

fossils

remains of organisms from millions of years ago which are found in rocks

fossil formation

form when parts of organisms have not decayed- not enough oxygen, not enough water, temp is too cold.

form when parts of the organism are slowly replaced by minerals during decay

form by preserved traces of animals eg. footprints or burrows and roots

early fossils

soft bodied organisms mainly dominates early earth. the fossils have been destroyed naturally by rocks so it is hard to find out how earth has started.

extinction

fossils show extinction

they become extinct by: catastrophic events (eg. astroid), environmental changes, new diseases/ predators, new species compete with it for resources (eg. food, water)

bacteria reproduction

can reproduce rapidly so they evolve rapidly

MRSA antibiotic resistance

mutations of bacterial pathogens produce new strains. some may be resistant to antibiotics so they aren’t killed. they survive and reproduce so the population of the resistance strain rises. it will then spread to people who aren’t immune and there is no effective treatment

reducing amounts of antibiotic resistance

• not overprescribing antibiotics

• completing the course of treatment

• agricultural use of antibiotics should be restricted

categories of class systems

kingdom

phylum

class

order

family

genus

species

binomial system

two names. genus then species

three domain system

archaebacteria- extreme conditions

true bacteria- human digestive system

eukaryota- protists, fungi, plants and animals

classification data

it can be used to make evolutionary trees. this data in living organisms includes DNA, in extinct organisms scientists use fossils