B6 Flashcards
1st stage: transcription
takes place in the nucleus
-the base sequence of a gene is copied into a complimentary template molecule
-the mRNA now passes out of the nucleus and into the cytoplasm
2nd stage: translation
-the mRNA molecule attaches to a ribosome
-amino acids are now brought to the ribosomes on carrier molecules
-the ribosomes now reads the triplets of bases on the mRNA and uses this to join up the correct amino acid in the correct order
what are template molecules
-mRNA
- single stranded molecules
- they are a copy of a nucleuotide
what are the 2 types of cell division
meiosis: results in the formation of four genetically non identical daughter cells
-used in sexual reproduction
mitosis:
results in the formation of 2 genetically identical daughter cells
used in asexual reproduction
what is sexual reproduction
process of reproduction where the nuclei of 2 gametes (sec cells) fuse to form a zygote (a process known as fertilisation) to create genetically different offspring
what are the key features of sexual reproduction
-two parents
-male and female gametes fuse
- offspring are non identical
- cells divid by meiosis
what is asexual reproduction
Asexual reproduction is the process of reproduction that forms genetically identical offspring from only one parent. Asexual reproduction is common in single-celled organisms and some plants.
what are the key features of asexual reproduction
- no gamete fusion
- offspring are clones
- cells divide by mitosis
- only one parent
meiosis
-each cell has a pair of each chromosome (diploid cell)
- during meiosis each pair of chromosomes replicate and split in 2
- there are now 2 identical cells and the diploid cell spilts again
- haploid cell is created where there are 4 genetically different gametes that each have half the number of chromosomes found in the larger cells
- during sexual reproduction the gametes fuse to make the normal amount of chromosomes (46)
-once the cells have combined they now divide asexually by mitosis
- as soon as the cell reaches a certain size it starts to differentiate (become specialised)
advantages of sexual reproduction
artificial selection - Humans can speed up artificial selection through selective breeding of plants and animals.
This depends on genetic variation.
This process has many benefits, including boosting food production and breeding fast horses.
Variation in offspring- increases the chances of a population being able to survive environmental change by natural selection.
This is because some individuals are likely to be adapted to the new conditions.
means things can evolve
what plants can reproduce sexually or asexually
strawberry plants
fungi
malaria parasites
advantages of asexual reproduction
if an organism can reproduce either way they normally reproduce asexually if conditions are good
because:
-it’s quicker
-no mate - more efficient, less time + energy
- lots of identical offspring - if conditions are good, identical offspring is favourable
what is a genome
the entire genetic material of an organism
in the genome there are lots of levels of organisation:
whats is inside a genome
DNA- double helix polymer, which means it is a polymer (a large molecule made up of many different sub units) made up of two strands forming a twisted, ladder shape.
- a gene = a small section of DNA.
Genes code for a sequence of amino acids, which combine to give a specific protein.
Chromosomes
Long strands of DNA are coiled up to form chromosomes.
Chromosomes contain many genes.
Human body cells contain 23 pairs of chromosomes, one of each pair coming from each parent.
what is the organisation of genetic material
the nucleus of eukaryotic cells contain chromosomes made from DNA molecules
Each chromosome contains a large number of genes.
Each gene tells how a specific protein should be made.
what can the understanding of genomes help us understand more of
Human evolutionary and migratory history
Investigating human evolutionary history, including how humans migrated in the past
what is DNA
DNA is a polymer made up of two long strands of small units that repeat throughout the structure, called nucleotides. Each of these is made up of a sugar, a phosphate and a base attached to the sugar.
DNA structure
The two long strands within each DNA molecule are held together by attractions between opposite bases.
Each base has one other specific base with which it pairs:
T pairs with A.
G pairs with C.
The sugar and phosphates of nucleotides form the long strands.
nucleotides
A nucleotide is made up of a phosphate and a base attached to the sugar.
The sugar and phosphates of nucleotides form the long strands.
The attraction between opposite bases holds the two strands together.
each nucleotide has a different base and there are 4 different nucleotides
what is a codon
Each amino acid is coded for by a specific sequence of three bases (called a codon)
what does the order of based on the DNA tell us
the order for combining amino acids to create particular proteins.
how can we change the protein made by a gene
by altering the sequence of bases in that gene.
what is a mutation
A mutation is a permanent change in the nucleotide sequence of DNA
Occasionally, a mutation may change the structure or shape of a protein. All genetic variants arise from mutations.
when do mutations occur
Mutations happen continuously and normally only slightly affect proteins or don’t affect them at all.
what are undesirable changes caused by mutations
The outcome of a mutation is almost always detrimental to protein function.
For example, in enzymes, the substrate may no longer be able to bind to the active site. In structural proteins, their strength may be reduced.
Some regions of DNA do not encode protein sequences.
The term given to these sections is non-coding DNA.
can mutations give a survival advantage
More rarely, a mutation may give a survival advantage, such as resistance to an antibiotic in bacteria.
These mutations can be beneficial and represent the foundation of evolution by natural selection.
what are alleles
Alleles are different forms of the same gene.
Humans have pairs of every gene and in one gene, each half of the pair may have different alleles.
People’s characteristics are determined by the alleles that they have. Alleles can either be dominant or recessive:
what is a dominant allele
A dominant allele is always expressed, regardless of the identity of the other allele
It only needs one copy present to be expressed (BB or Bb).
It is represented by a capital letter, e.g. B.
If B is the allele for brown eyes:
When a person has a copy of the B allele, they will have brown eyes, no matter what other allele is present.
what is a recessive allele
A recessive allele is only expressed if the other allele is also recessive.
It is represented by a lowercase letter e.g. b
It needs two copies to be present to be expressed (bb).
If b is the allele for blue eyes:
A person can only have blue eyes if both of their alleles are b.
what terms do we use when talking about the inheritance of characteristics
genotype and phenotype
what are genotypes
Genotype refers to the combination of alleles an organism has.
If the two alleles are different, we say that the person is heterozygous (Bb).
If the two alleles are the same, we say that the person is homozygous (BB or bb).
what is a phenotype
A phenotype is an observed characteristic of an individual.
The phenotype is determined by the interaction between the genotype and environment.
Earlobes being attached or free is an example of a phenotype, where the alleles present will determine a characteristic, unless the environment interferes.
what is monohybrid inheritance
refers to the inheritance of traits determined by a single gene.
what are punnet squares
Punnett squares are diagrams that help us to visualise the outcome of a monohybrid cross. In these diagrams, a capital letter shows a dominant allele.
The alleles of the parents are drawn along the top and side of a grid.
The pairs of alleles that the offspring could have are then filled in to the grid
what is discontinuous variation
variation controlled by genes alone and is inherited
what is continuous variation
characteristics you inherit but environment can influence
genes you can measure
what are acquired characteristics
characteristics caused by environment
features acquired during life
not coded for in DNA
cant be passed on or inherited
why do not identical twins look similar
comes form different genes inherited from parents
genes are mixed up so offspring looks similar but different from parents
