Science - Biology - Inheritance, Variation and Evolution - B6 Flashcards
what does DNA stand for ?
deoxyribonucleic acid
what is DNA ?
the chemical that all of the genetic material in a cell is made up from
what does DNA do ?
have all of the information to put an organism together and make it work
what does DNA determine ?
what inherited characteristics you have
where is DNA found ?
in the nucleus
what really long structures are DNA found in ?
chromosomes
what does DNA form in a chromosome ?
the arms of a chromosome
what number do chromosomes come in ?
pairs
DNA is a polymer - what does this mean ?
it is made up of a large molecule built from a chain of smaller molecules
what shape do the 2 strands of DNA form ?
double helix
what is a gene ?
a small section of DNA found on a chromosome
what does a gene do ?
tell cells what order to put the amino acids together
what do amino acids form ?
proteins
how many types amino acids are used in DNA ?
20
does DNA determine what proteins the cell produces, and therefore determines what cell is produced ?
yes
what is a genome ?
the entire set of genetic material in an organism
what does understanding the human genome tell scientists ?
- it helps them identify genes in the genome which are linked to different types of disease
- knowing which genes are linked to inherited diseases helps us understand them better and could help us develop treatment
- genomes can trace the migration of certain populations around the world - scientists can work out when and where populations went
how did the human genome change ?
it is mostly identical in all humans
but as different populations migrated away from Africa they developed tiny differences in their genomes
what are nucleotides ?
strands of polymers made up of lots of repeating units which help form DNA
what does a nucleotide consist of ?
- a sugar
- a phosphate group
- one of 4 different bases
how many types of nucleotides are there ?
4
what are the 4 different bases ?
A
T
C
G
what do the 4 different bases join to ?
a sugar
what forms the backbone to the DNA strands ?
the sugars and phosphate groups in the nucleotides
what does the order of bases determine ?
the order of amino acids in a protein
how many bases is each amino acid coded by ?
3
what do amino acids join together to make up ?
proteins
what does the base A always pair up with ?
T
what does the base C always pair up with ?
G
what do the non - coding parts of DNA do ?
switch genes on and off
control whether or not a gene is used
where are proteins made ?
in the ribosomes in the cytoplasm
what do ribosomes do to make up proteins ?
- use the code in DNA
how does the cell get the code needed to make up proteins from DNA in the nucleus to the ribosomes ?
mRNA
why can’t DNA move out of the cell nucleus ?
it is too big
what is mRNA ?
a molecule which acts as a messenger between the DNA and the ribosome by carrying the code between the 2 and by acting as a template
what do carrier molecules do in mRNA ?
bring the correct amino acids to the ribosomes in the correct order
what do amino acids do when they have been assembled ?
folds into a unique shape which allows the protein to perform the task it is meant to do
what are proteins used for ?
- enzymes
- hormones
- structural proteins
what is a mutation ?
a random change in an organisms DNA
they can sometimes be inherited
how do mutations occur ?
- continuously
- randomly
- when a chromosome isn’t replicated properly
how can the chances of a mutation be increased ?
- when exposed to some types of radiation
- when exposed to certain substances
what do mutations do ?
change the sequence of the DNA bases in the gene which produces a genetic variant
as the sequence of DNA bases codes for the sequences of amino acids which make up proteins, mutations can lead to cell changes
what is a genetic variant ?
a different form of the gene
do mutations have an effect on the protein ?
most of the time no
what could happen if a mutation changes a proteins shape ?
- if an enzyme’s active site is changed its substrate may not be able to bind to it
- structural proteins like collagen could lose their strength if their shape has changed
what are the 3 ways DNA can change the DNA base sequence ?
- insertions
- deletions
- substitutions
what are insertions ?
where a base is inserted into the DNA base sequence where it shouldn’t be
what can insertions cause ?
amino acids to change, as they have a knock-on effect so the bases further on in the sequence can be altered
what are deletions ?
where a random base is deleted from the DNA base sequence
what are substitutions ?
where a random base in the DNA sequence is changed to a different base
what is sexual reproduction ?
where genetic information from 2 organisms is combined to produced offspring which are genetically different to either parent
what are gametes ?
things produced by the mother and father in sex
what is the female gamete ?
egg
what is the male gamete ?
sperm
how many chromosome does each gamete contain in humans ?
23
what happens during fertilisation ?
the egg and sperm cell fuse together to form a cell with the full number of chromosomes
what is the fusion of gametes known as ?
fertilisation
why does the offspring inherit features from both parents ?
it recieves a mixture of chromosomes from its mum and dad which causes variation
what does sexual reproduction involve the fusion of ?
female and male gametes
what is the sperm version of a gamete in a flowering plant ?
pollen
how does asexual production happen ?
mitosis
what is asexual reproduction ?
there is only 1 parent, no fusion of gametes and no genetic variation between the parent and offspring
the offspring and the parent are identical in asexual reproduction - what are they ?
clones
how do you make gametes ?
meiosis
how many cell divisions does meiosis involve ?
2
where does meiosis happen in humans ?
reproductive organs
describe the steps of meiosis ?
- before cell divides it duplicates its genetic information, forming 2 armed chromosomes which are identical, after replication chromosomes arrange themselves into pairs
- in the first division pairs line up in the centre of the cell
- the pairs are then pulled apart so each cell has 1 copy of each chromosome - some of the fathers - some of the mothers
- in the 2nd division chromosomes line up again in the centre of the cell - arms of the chromosomes are pulled apart
- you get 4 sets of gametes with only 1 set of chromosomes in it
why are the gametes produced genetically different from the others ?
the chromosomes get shuffled up during meiosis and each gamete only gets 1 of them - at random
what happens to the cells when the embryo starts to develop ?
they differentiate into different types of specialised cell that make up a whole organism
what are the advantages of sexual reproduction ?
- offspring will have a mixture of 2 sets of chromosomes - the organism inherits genes from both parents giving variation
what are the advantages of variation ?
it increases the chance of species surviving a change in environment as some of the varied organisms may be able to survive in the new environment whilst others are killed off
what is natural selection ?
individuals with characteristics which make them better adapted to the environment are more likely to breed successfully and pass the genes for the characteristics on
what is used to speed up natural selection ?
selective breeding
what is selective breeding ?
where individuals with a desirable characteristic are bred to produce more offspring that also have the desired characteristic
why can we use selective breeding to increase food production ?
- breeding animals that have lots of meat
- breeding cows which have a high milk yield
what are the advantages of asexual reproduction ?
- needs 1 parent so it uses less energy because organisms don’t have to find a mate
- identical offspring can be produced in favourable conditions
give an example of how asexual production can be used successfully ?
- dandelion plants can grow quicker and spread faster if grown in a good environment and because all offspring have the same genes as the parent they’re all likely to survive in these conditions
give examples of when organisms can reproduces both asexually and sexually ?
- malaria = reproduces sexually when in mosquito and asexually when it is in human host
- fungus = spores
- plants = runners, bulbs
how many pairs of chromosomes are in every human body cell ?
23
how are the 23rd pair of chromosomes labelled ?
xx
xy
what do the 23rd pair of chromosomes determine ?
your sex
what sex has xy characteristics ?
male
what sex has xx characteristics ?
females
what chromosome causes male characteristics ?
y
what is the % chance of a sperm cell getting a y chromosome ?
50 %
what is the % chance of the eggs getting an x chromosome ?
100 %
what depends on whether the individual is male or female ?
the sex chromosomes it recieves - its sex inheritance
what can genetic diagrams be used to show ?
sex inheritance
what are genetic diagrams ?
models that are used to show all the possible genetic outcomes when you cross together different genes or chromosomes
what is probability ?
the measure of how likely something is to happen
what are alleles ?
an alternative version of a gene
how many alleles to gametes have ?
1
how many alleles do all the other cells in an organism - apart from gametes have ?
2
why do all cells except for gametes get 2 alleles?
we inherit half our alleles from our mother and half from our father
what represents alleles in genetic diagrams ?
letters
what does homozygous mean ?
if an organism has 2 alleles that are the same for a particular gene
what does heterozygous mean ?
if an organism has 2 alleles that are different for a particular gene
what is a dominant allele ?
the allele for the characteristic that is shown
what is the recessive allele ?
the allele for the characteristic which isn’t shown
how can an organism display a recessive characteristic ?
both its alleles must be recessive