Story of Us : part 1 Flashcards
what is the full form of DNA?
deoxyribonucleic acid
what is the function of DNA?
- stores the genetic information
- controls cell activities
what is genetic information comprised of?
- instructions for building all proteins within an organism
how is DNA found in eukaryotes?
- within the nucleus
- as linear (straight) chromosomes
how is DNA found in prokaryotes?
- in the cytoplasm
- in the form of a circular chromosome and many small plasmids
what is the structure of DNA?
- double helix shape (two strands wrapping around each other)
- made up of building blocks called nucleotides
what are nucleotides comprised of?
- a sugar (deoxyribose)
- a phosphate
- a nitrogenous base
what are the four types of base and its pairs?
- adenine - thymine
- cytosine - guanine
how are the nucleotides joined together?
- by covalent bonds between the sugar of one nucleotide and the phosphate group of the next nucleotide - forming the sugar phosphate backbone
what will always be the same for the bases?
- the number of A’s and T’s
- the number of C’s and G’s
what is RNA?
- a type of nucleic acid called ribonucleic acid
what is the structure of RNA?
- the RNA nucleotides are joined to form a single strand
- the nucleotides are joined by a covalent bond between the sugar of one nucleotide and the phosphate of the next
how does RNA differ from DNA?
- RNA is single stranded while DNA is double stranded
- RNA has a sugar called ribose while DNA has a sugar called deoxyribose
- RNA has the base uracil (U) while DNA has the base thymine (T)
what are the two types of RNA you need to know?
- messenger RNA
- transfer RNA
describe the messenger RNA.
- mRNA
- formed in the nucleus of the cell
- it copies the sequence of bases of a section of DNA in a process called transcription
- mRNA carries the code for building a specific protein from the nucleus to the ribosomes in the cytoplasm
describe the transfer RNA.
- tRNA
- found in the cytoplasm
- the tRNA picks up specific amino acids from the cytoplasm and brings them into position on the surface of a ribosome where they can be joined together in specific order to make a specific protein
- process is called translation
what is a gene?
- a length of DNA which codes for a protein
- this means it provides info on the sequence of amino acids in a protein (like an enzyme)
what do the proteins coded by genes do?
- these proteins then control chemical reactions, growth, colouration and all inheritable characteristics
- this is why a gene codes for a characteristic
how are the codes for the proteins read?
- universally
- the code is universal
- bacteria read it in the same way that animal cells and plant cells read it
in DNA, what do the sequence of three bases code for?
- a specific amino acid
what do we refer to every three bases as in a chain of amino acids in a protein?
- a codon
what is DNA wrapped in?
- structures called chromosomes
how many of each chromosome does a person have?
- two of each chromosome
- one of each pair comes from the father, the other from the mother
why do we say chromosomes are homologous?
- genes controlling a specific characteristic are situated at the same point on each chromosome
what is there in every diploid nucleus?
- there is a pair of genes for each characteristic
what can genes have?
- different versions called alleles, which code for different forms of a protein
what is the genome?
- one copy of all an organism’s DNA
- in humans this is all the DNA that makes up the 23 pairs of chromosomes found in all diploid body cells
what are all the diploid body cells?
- all cells except sex cells or gametes which only have half of a person’s genome (haploid)
how many chromosomes do human body cells contain?
- two copies of each of their 23 chromosomes, this is a diploid cell
- some cells (and organisms) only contain one copy of each chromosome - they are called haploid
which is the “sex” chromosome?
- the 23rd chromosome
- it determines your sex
- if you have two X chromosomes you are biologically female, if you have 1 X and 1 Y you are biologically male
which cells are haploid?
- human gametes
- this is so, when they fuse, they can form a diploid offspring
what does growth and reproduction require?
- cell division
what are the two types of cell division?
- mitosis and meiosis
what does the cell division of mitosis produce?
- genetically identical daughter cells which are diploid - they have one pair of each chromosome in each nucleus
- mitosis is used for growth, repair and asexual reproduction
what does the cell division of meiosis produce?
- produces haploid gametes (sperm, eggs, pollen) which are not genetically identical
- meiosis is only used to produce gametes for sexual reproduction
what is variation in offspring produced by?
- genetic variation in gametes produced by meiosis
- random fertilisation of ova (egg cells) by male gametes
what is important in order for evolution to occur?
- variation
what type of characteristic is variation?
- can be genetic, environmental or a combination of both
genetic characteristics
- following sexual reproduction, or mutation, organisms will have different versions of genes to another individual
environmental characteristics
- the environment might also affect the characteristics of an organism
both genetic and environmental characteristics
- usually both genetic and environmental factors contribute to the variation found in individuals of a species
what are the two main types of variation?
- continuous and discontinuous
continuous variation
- e.g. height, where there is a smooth range of measurements
discontinuous variation
- e.g. blood group, where there are distinct categories with no values in between
which type of variation is more heavily influenced by environmental factors?
- continuous variation
who was Gregor Mendel?
- in 1860, an austrian monk called gregor mendel noticed that the peas in the kitchen were two types, tall and dwarf
- he allowed the tall ones to self-pollinate (reproduce with themselves) for a number of generations and did the same with the dwarf ones
- he then assumed that both types were pure breeding
- he then crossed (bred) a tall pea plant with a dwarf pea plant
what does pure breeding mean?
- a group of identical individuals that always produce offspring of the same type when bred
what was gregor mendel’s method?
- he opened up the flowers of the tall plants when they were just emerging and cut out
the stamens, the male reproductive parts. - This would stop the pea plant from self-pollinating.
- He then covered the rest of the flower with a bag to stop insects pollinating the carpel,
the female part, with pollen from an unknown source. - When the flowers from a dwarf variety were ready he removed some pollen from one of
the stamens with a very fine paintbrush and brushed it onto the stigma of a carpel
protected by the bag.
what were the results of gregor medel’s experiment?
- the flower produced seeds and when these had dried out properly he planted them to see what was produced
- all of the seeds grew into tall plants, even though half the parents were dwarf plants
- he allowed these plants to self-pollinate, i.e. one plant acting as both parents
- surprisingly, tall parents gave rise to some dwarf plants
- when the offspring were counted he found that 839 were tall and 276 were dwarf
- he realised that this was a ratio of about 3 tall plants to 1 dwarf
label the flower.
onenote pictures
what is an allele?
- a version of a gene
what do the genes found on the chromosomes have?
- two different forms - called alleles
what sort of alleles will pure breeding plants have?
- only have alleles for one type - e.g. tall or dwarf
what are the two types of allele?
- dominant or recessive
what is a dominant allele?
- only needs one allele present to be expressed
what is a recessive allele?
- needs two alleles to be present to be expressed
what does heterozygous dominant alleles mean?
- one is recessive and the other is dominant
- the dominant allele overpowers the recessive allele
what does homozygous dominant alleles mean?
- two uppercase alleles
- the dominant allele overpowers
what does heterozygous recessive alleles mean?
- one dominant allele and one recessive
- the recessive allele overpowers the dominant allele
what does homozygous recessive alleles mean?
- both the same type of allele (lowercase)
- the recessive allele overpowers
fill in a punnet square to cross a Tt and Tt.
what is a genotype?
- a combination of alleles e.g. TT or Tt
what is a phenotype?
- what is expressed e.g. tall or dward
what are the punnett square rules?
- use one letter to represent a gene
- use the upper case to represent the dominant allele and the lower case to represent the recessive allele
- write the genotypes (allele combination) and phenotypes (characteristic of the parents
- write the alleles found in each gamete (separately to the parents’ genotypes)
- write the genotype and phenotype of each offspring
- finish with the probability of each phenotype in the offspring (fraction/% or ratio )
what is polygenic inheritance?
- where many characteristics are controlled by several genes which influence each other
- these characteristics are more likely to show continuous variation, e.g. skin colour in humans
what is cystic fibrosis?
- a disease that effects the lungs
- it affects the CFTR protein which causes mucus to be incredibly thick, so thick that it cannot be removed from the lungs
how much can cystic fibrosis reduce your life expectancy by?
- up to 30 years
is there a cure for cystic fibrosis?
no
is the cystic fibrosis gene dominant or recessive?
- recessive
- the heterozygous parents do not have the disease but do carry an allele - we refer to them as carriers
what is codominance?
- where both alleles are expressed and both take part in the characteristic
what can be used to determine the probability of inheriting a genetic disease?
- family trees/pedigree diagrams
show the likelihood of having a boy or a girl.
50:50
