inheritance Flashcards
where might you find 23 pairs of chromosomes and what are the exceptions
nucleus of human cells
gametes - sperm and egg cells have 23 single chromosomes
what is sexual reproduction, what process does it involve, and what will offspring look like
- involves the fusion if male and female gametes (fertilisation)
- meiosis
- genetic information is mixed, variation in offspring
what is asexual reproduction,what process foes it involve, and what will offspring look like
- only one parent
- mitosis
- no fusion of gametes, no mixing of genetic information - clones (genetically identical offspring)
where does meiosis occur
reproductive organs (ovary/testes)
purpose of meiosis and what does it produce
producing gametes for sexual reproduction
- egg and sperm, pollen and egg
- one cell produces 4 genetically different gametes, each with half the normal number of chromosomes
stages of meiosis
- all chromosome pairs are copied
- cell divides into 2, one pair each
- cell divides again, single chromosomes
what happens after meiosis in sexual reproduction
- gametes fuse (fertilisation), cell has normal number of chromosomes
- cell divides (mitosis), clump of identical cells (embryo) formed
- cells differentiate and embryo develops e.g nerve/muscle cells
advantages of sexual reproduction
- variation: increased survival of change in environment
- these individuals breed and pass survival genes on - natural selection
what is selective breeding
where individuals with survival genes are bred
- increases food quality and yield
advantage if asexual reproduction
- only one parent/no mate: faster as less energy and time needed
- fast: extremely useful in favourable conditions, offspring produced rapidly
disadvantage of asexual reproduction
- no variation: could all die in unfavourable conditions
what organisms can reproduce by both methods
malaria
fungi
plants
how do malarial parasites reproduce
life in mosquito vector: sexually
life in human host: asexually
how does fungi reproduce
spores (become new fungi) can be produces asexually and sexually
how can plants reproduce
- sexually to produce seeds
- asexually e.g
• strawberry plants grow runners which form new plants when they hit soil
• bulb division: bulb produces buds, becomes offspring
what is dna
genetic material found in chromosomes
structure of dna
two strands, polymers (made up of nucleotides) twisted in double helix
what is a gene
small section of dna on a chromosome that each codes for a particular sequence of amino acids to make a specific protein/characteristic
how are chromosomes linked to sex
22/23 chromosome pairs contain genes determine inherited characteristics, one pair contains gene that determines sex, labelled XX (female) or XY (male)
how is sex inherited
in punnett square, parents XX and XY genotypes means average 50% offspring are female and 50% are male
what is a genome
entire set of genetic material in an organism
advantages of understanding human genome
- identify genes linked to diseases e.g Alzheimer’s
- understand and treat inherited disease e.g cystic fibrosis
- trace past human migration patterns to discover ancestry
what determines a protein
sequence order of amino acids determines shape, which determines function
structure of nucleotide
phosphate group attached to sugar molecule, always the same
sugar is attached to one of four bases, a, c, g, t, which pair complimentarily: A links with T, C links with G
what determines the order of amino acids in a protein
sequence of bases in the gene for that protein
the cell reads the bases as triplets (e.g ATG), each triplet codes for a specific amino acid in the protein
what and where is first stage of protein synthesis
transcription: nucleus
sequence of bases of gene is copied into a complementary, single strand, template molecule: mRNA
this passes out of nucleus and into cytoplasm
what and where is second stage of protein synthesis
translation: cytoplasm
- mRNA attaches to a ribosome
- carrier molecules (tRNA) bring amino acids to ribosome
- ribosome reads triplets of bases on the mRNA to join correct amino acids in correct order
- complete protein chain folds into its unique shape
what is a mutation in coding dna and how might it change a protein
a random change to a base of dna.
- different base triplets can enconde for same amino acid, so most of the time will not change the sequence and wont effect shape or function of protein
- sometimes it can encode a different amino acid, changing sequence so changing shape and function of protein
what can a mutation that changes shape and function of protein lead to
- active site of enzymes can change shape, no longer bind to substrate
- change shape of structural proteins, e.g collagen, loses strength and becomes useless
what do non-coding dna regions do
tell genes when to produce proteins
what can a mutation in a region of non-coding lead to
effects how genes are switched on and off
e.g protein produced when it shouldnt have been & cell is not meant to have
- can lead to uncontrolled mitosis which leads to cancer
what is an allele
different versions of a gene, meaning each copy codes for different characteristic
what is the genotype of someone and how is it written
combination of alleles present
two letters eg EE, Ee, ee
eg
ee: their genotype is ee
what is the phenotype of someone
the characteristics caused by their alleles
eg
ee: their phenotype is dry earwax
Ee: their phenotype is wet earwax, as E (wet earwax) is dominant and e (dry earwax) is recessive
EE: their phenotype is wet earwax
define homozygous
having two copies of the same allele for a gene, eg ee or EE
organism is homozygous for the earwax allele
define heterozygous
having two different alleles for a gene, eg Ee
organism is heterozygous for the earwax allele
what is cystic fibrosis
disorder of cell membrane, controlled by a single gene (two alleles, C and c)
how does cystic fibrosis occur
must have genotype cc, as alleles of defective cell membrane are recessive
both parents must be carriers, so offspring can inherit one recessive defective cell membrane allele (c) from each parent
what is a carrier
someone with one defective allele and one normal allele
eg someone with genotype Cc is heterozygous and a carrier of cystic fibrosis allele
how to use punnett square
- write genotypes of gametes for each parent (eg Cc - half of gametes are C and half are c, put into top of columns)
- intersections show how gametes combined during fertilisation
punnett square for two carriers of cystic fibrosis allele
most likely
- 25% of offspring will be carriers, they are heterozygous for cystic fibrosis allele
- 50% of offspring will be unaffected, they are homzygous for C allele
- 25% of offspring have cycstic fibrosis, they are homozygous for c allele
what is polydactyly
inherited disorder where person has extra fingers or toes
how does polydactyly occur
must have genotype PP or Pp as allele of polydactyly is dominant
how to treat inherited disorders
embryo screening
gene therapy
what is embryo screening
testing embryos to see if they have the alleles for inherited disorders, them implanting those which dont to produce healthy offspring
issues of embryo screening
- expensive, argument that money should be spent elsewhere in healthcare
- unethical, lots of embryos created but only little implanted, lots destroyed
- unethical, we may be able to screen embryos to produce offspring with desire features
what is gene therapy
experimental
correcting faulty alleles to treat inherited disorders
how can you tell if an inherited disorder is caused by a dominant or recessive allele from a family tree diagram
if offspring has disorder and at least one parent has disorder, allele is dominant
if offspring has disorder and neither parents do, allele is recessive and parents must be carriers
how to find chance that two parents without CF have another child with CF
- both parents must be heterozygous as first child has cc genotype
- punnett square: when two carriers reproduce, probability of cc is 25%
whos work led us to our understanding on genetics and what did he do
mendel
- carried out thousands of breeding experiments on pea plants to see how characteristics were passed on between generations
- disproved theory that characteristics were blended when inherited
what conclusion did mendel reach
- characteristics are determined by “hereditary units” (genes)
- units do not change when passed on to offspring
- some characteristics could be masked then reappear - recessive genes
what happened to mendels discoveries
forgotten, as scientists still believed characteristics were blended during inheritance
why was mendels work accepted after his death
- late 1800s, scientists looked at how chromosomes behave during cell division
- realised behaviour was similar to mendels units (genes)
- realised genes must be located on chromosomes
- mid 1900s, structure of dna was determined, scientists able to find out how genes work
what is variation
differences in characteristics of individuals in a population
causes of variation with examples
- genetic: inherited alleles, eg hair and eye colour
- environment: eg colour of flowers depends on soil pH, language of humans
- genetic and environmental: eg height, alleles determine max height, however calcium in diet (develops bones) determines whether height is reached
cause of genetic variation
mutations (random changes to dna)
- often does not affect phenotype
- can have small influence on phenotype, slightly altering characteristics
- can lead to a new phenotype, changing a characteristic
benefits of mutations
can lead to a new phenotype.
- new phenotype can be beneficial if environment changes, eg becoming resistant during virus outbreak
what is the theory of evolution
all living things have evolved from simple life forms that first started to develop over 3 billion years ago
what is evolution
the change in the inherited characteristics of a population over time through natural selection
what is natural selection
- organisms within a species have wide phenotypic variation due to alleles inherited from parents
- if environment changes, organism with most suited characteristics are more likely to survive
- these organisms can reproduce, offspring could inherit alleles for desired characteristic, more likely to survive and reproduce
- over generations, characteristic will become more common within species, species has evolved
what led to darwins theories
- saw huge variety of organisms on round-the-world expedition
- studied geology and fossils showed todays organisms are similar to extinct species
- experimentation and discussion
what is darwins theory
theory of evolution by natural selection
- organisms in a species have a wide range of variation in characteristics
- organisms with characteristics most suited to environment are more likely to survive and breed
- these beneficial characteristics are passed on to next generation
why was darwins theory controversial
- challenged strong belief that god made all animals and plants
- scientists felt he had little scientific evidence
- people didnt understand that characteristics are inherited
who challenged darwin and what did he suggest
lamark
- when a characteristic is regularly used, it becomes more developed, and this strengthened characteristic passes onto offspring
why was lamark incorrect
most often, changes that occur during the organisms lifetime cannot be passed onto offspring
who else contributed to discovery of evolution and what did he do
wallace
- studied how animals evolved to have warning colouration, and independently developed the same theory as darwin, together published discovery
- studied speciation
describe evolution of bacteria
extremely rapid as they reproduce rapidly
preventions of bacteria disease and limits
- antibiotics in medicine and farming
- strains have evolved to become antibiotic-resistance
how does antibiotic resistance occur
- mutation can mean a bacterium in a population becomes resistant to antibiotics
- antibiotic used on population, non-resistants die
- resistant survives and reproduces without competition
- population of resistant strain rises
how to reduce development of antibiotic resistant strains of bacteria
- doctors should prescribe antibiotic appropriately (no viruses)
- patients complete course of antibiotics so no bacteria can survive and mutate
- restrict use in of antibiotics in farming
problem of trying to develop new antibiotics
- long time and expensive
- new resistant bacteria constantly emerging, we cannot keep up
what is speciation
development of new species
stages of speciation
- a geographical barrier, eg a river changing course, separates population
- over time, natural selection will result in different alleles on either side due to different factors eg food sources
- no interbreeding between two groups, so mutations cannot spread
- over many generations, two groups will begin to change
- if groups mix, eg river changes course again, phenotypes are so different that they can no longer reproduce to make fertile offspring
- snails are now two different species
what is a fossil
remains found in rocks of organisms from millions of years ago
how can fossils form
- when parts of organisms have not decayed due to conditions
- when parts of organisms are replaced by minerals during decay
- preserved traces of organisms eg footprints
why is it difficult to determine how life on earth began
there are few fossils of early life
- early forms of life were soft-bodied, with no shell or skeleton.
these most often did not form fossils, and ones that did form were destroyed by changes in crust
causes of extinction
- catastrophic events
- environmental changes
- new disease/predator
- outcompeted by new species
who began classification
linnaeus - developed classification system to classify species into categories based of structure and characteristics
what classification system did linnaes develop
- two kingdoms: plant and animal
- phylum
- class
- order
- family
- genus
- species
based on characteristics we can see
how to remember classification system
king phillip came over for good soup
how are species named
binomial system: using name of genus and species
what advances have been made since classification system was developed
- we can now use microscopes to look at internal structure
- we can analyse an organisms biochemistry, eg its dna, and look for similarities with other species
what is the current classification system and who created it
three-domain system
carl woese, compared biochemistry of different organisms
what is the current classification system
organisms split into three domains:
- archae: primitive bacteria, often found in extreme conditions eg hot springs
- true bacteria eg kind in human digestive system
- eukaryota: broad range including animals, plants, fungi, protists
what do evolutionary trees show
how closely related organisms are to each other
- intersections show common ancestors; the more recent, the more closely related.
what is selective breeding and give examples
breading certain organisms so genes for desired characteristics stay in population
dogs: gentle nature
crops: disease resistance eg wheat
animals: more meat/milk eg cows
plants: big/unusual flowers
process of selective breeding
- select organisms with desired characteristic from a mixed population
- breed together
- select offspring with desired characteristics from varied offspring
- breed together
- continue over several generations until all offspring have characteristic
issue with selective breeding and example
breeding closely related organisms causes inbreeding, which can result in some breeds being prone to disease or inherited defects
eg many dog breeds develop inherited disease eg joint problems
what is genetic engineering
transferring a gene for a desired characteristic from one organism’s genome to another, so it also has the characteristic
process of genetic engineering
- isolate wanted gene using enzymes
- transfer gene onto a vector: a virus or a bacterial plasmid
- desired gene transferred into cells of target organism
when is genetic engineering carried out
early stage of development eg embryo
to ensure all cells receive transferred gene, so develops with wanted characteristic
examples of genetic engineering
- bacteria: to contain human insulin gene, to produce insulin for type 1 diabetes
- gm crops: to increase size and yield, to create resistance to disease, hebicides, and insects
how can genetic modification be used medically and what are the issues
gene therapy - treating inherited disorders in humans
- long term effects unknown, eg gene is modified, we dont know effects on other genes
issues with gm crops
- potentially reduce biodiversity: harm to insects or wildflowers
- concern that we dont fully understand health effects of eating them
different ways to clone plants and when are they used
cuttings - a few clones
tissue culture - hundreds of clones
how to clone plants using cuttings
- gardeners cut small piece of plant and dip end in rooting powder, which contains plant hormone auxin
- plant develops roots and grows into genetically identical clone of original
how to clone plants using tissue culture
- all equipment sterilised to avoid unwanted microorganisms
- divide plant into hundreds of tiny pieces to get small groups of cells
- cells incubated with plant hormones
- plant can grow and develop into genetically identical clones of original
use of tissue culture
- in commercial plant nurseries as growers can produce thousands of clones with certain characteristics quickly and cheaply
- to preserve rare plant species
different ways to clone animals and what do we get from both
embryo transplant: uncertain we will get wanted characteristics
adult cell cloning: certain we will get wanted characteristics
how to clone animals using embryo transplants
- take sperm and egg cell from animal with wanted characteristic
- fertilise to get fertilised egg and allow to develop into early stage embryo, when cells have not specialised
- split embryo into two with glass rod
- transplant two embryos into host mothers to develop
- offspring will be identical clones
issue with embryo transplant
uncertainty that offspring will have wanted characteristics, as we start with sperm and egg
how to clone animals using adult cell cloning
- take cell from animal with wanted characteristic
- take nucleus to obtain genetic information
- take unfertilised egg cell from same species
- remove nucleus to obtain empty egg cell
- insert nucleus from original adult body cell into empty egg cell
- egg cell given electric shock to make it divide, forming embryo
- inserted into womb of host mother to develop when embryo has developed into ball of cells
- offspring will be clone of original adult body cell
