3 inheritance (b) Flashcards
3.19, 3.20-3.27, 3.38, 3.39
what is the genome?
- the entire DNA of an organism
what is a gene?
- a section of a molecule of DNA that codes for a specific protein
what does the nucleus contain?
- chromosomes
where are genes located?
- on chromosomes
P2 structure of a DNA molecule:
- two strands coiled to form a double helix
P2 what are DNA strands linked by?
- A- adenine
- T- thymine
- C- cytosine
- G- guanine
P2 structure of a RNA molecule:
- single stranded
P2 what does a RNA molecule contain instead of thymine?
- U- uracil
what is genetic variation?
- eye colour
- blood type
what is environmental variation?
- lifestyle
- diet
- climate
what are most phenotypic features the result of?
- polygenic inheritance
what is an allele?
- version of a gene
how many alleles do you have of each gene?
- two
- they are dominant or recessive
what does the dominant allele do?
- will always be represented by the bigger letter
what does the recessive allele do?
- will always be represented by a little letter
homozygous dominant meaning?
- both dominant alleles are present TT
homozygous recessive meaning?
- both recessive alleles are dominant tt
heterozygous meaning?
- the two different forms of alleles are present Tt
genotype meaning?
- any combination of allele, Tt, TT, tt
phenotype meaning?
- outward appearance of an individual (actual appearance)
what is polygenic inheritance?
- most characteristics are controlled by many genes
what is monogenic inheritance?
- a characteristic controlled by one gene
P2 what is codominance?
- some alleles are both expressed in the same phenotype
what are the female chromosomes?
- XX
what are the male chromosomes?
- XY
Darwin’s theory of evolution by natural selection:
M= random mutation
V= causes variation in the population
A= new mutation means some individuals have an advantage
P= pass on allele
S= several generations
what does increased resistance in antibiotics mean?
resistance to antibiotics can increase in bacterial populations, which can lead to infections being difficult to control
differences between DNA and RNA:
DNA:
- double stranded
- thymine
- no uracil
- long
- deoxyribose
RNA:
- single stranded
- no thymine
- uracil base
- short
- ribose
P2 what happens in transcription?
- DNA unzips by enzymes
- mRNA forms using complimentary base pairings
- mRNA bases are formed with a sugar phosphate backbone and bound with RNA polymerase
- mRNA leaves the nucleus and delivers instructions to ribosomes
P2 what happens in translation?
- mRNA arrives at the ribosome
- mRNA has codons
- the ribosome moves along the mRNA strand
- tRNA brings amino acids to the codon
- the anticodon on the tRNA binds with the codon on the mRNA
- an amino acid it produced
what does mitosis produce?
two genetically identical daughter cells
when does mitosis occur?
during growth, repair, cloning and asexual reproduction
how many cells does meiosis produce?
4 genetically different haploid cells
what does meiosis produce?
gametes (sex cells)
what does haploid mean?
23- half the number of chromosomes
what does diploid mean?
46- number of chromosomes in a human cell
how many cell divisions in mitosis?
1
how many cell divisions in meiosis?
2
what can variation within a species be because?
genetic, environmental or both
what is a mutation?
a rare, random change in genetic material that can be inherited
P2 how can insertion affect a phenotype?
- A new base is randomly inserted into the DNA sequence
- An insertion mutation changes the amino acid that would have been coded for by the group of three bases in which the mutation occurs
- Remember – every group of three bases in a DNA sequence codes for an amino acid
- An insertion mutation also has a knock-on effect by changing the groups of three bases further on in the DNA sequence
P2 how can deletion affect a phenotype?
- A base is randomly deleted from the DNA sequence
- Like an insertion mutation, a deletion mutation changes the amino acid that would have been coded for by the group of three bases in which the mutation occurs
- Like an insertion mutation, a deletion mutation also has a knock-on effect by changing the groups of three bases further on in the DNA sequence
P2 how can substitution affect a phenotype?
- A base in the DNA sequence is randomly swapped for a different base
- Unlike an insertion or deletion mutation, a substitution mutation will only change the amino acid for the group of three bases in which the mutation occurs; it will not have a knock-on effect
P2 what can your risk of mutations be increased by?
- exposure to ionising radiation (gamma rays, x-rays, ultraviolet rays)
- chemical mutagens (chemicals in tobacco)
P2 effect of mutations on phenotype (none):
Most mutations do not alter the protein or only alter it slightly so that its appearance or function is not changed
P2 effect of mutations on phenotype (some):
- However, a small number of mutations code for a significantly altered protein with a different shape
- This may affect the ability of the protein to perform its function.
- For example:
If the shape of the active site on an enzyme changes, the substrate may no longer be able to bind to the active site
A structural protein (like collagen) may lose its strength if its shape changes
P2 effect of mutations on phenotype (large):
- new allele (and its resulting phenotype) gives the individual a survival advantage over other members of the species
- For example:
A bird develops a mutation leading to a change in feather colours
This makes it more attractive to birds of the opposite sex
Which causes the bird to breed more frequently and have more chances of passing on the mutated phenotype to the next generation - Mutations can also lead to harmful changes that can have dramatic effects on the body - for example, sickle cell anaemia in humans
