3.2 DNA and Inheritance, Natural selection Flashcards
What is an allele?
an alternative version of a gene that cause difference in inherited characteristics such as hair colour
What is an anticodon?
part of tRNA that is complementary to a codon on mRNA
What is a chromosome?
a long, coiled molecule of DNA that carries genetic information in the form of genes
What is codominance?
two different alleles both being expressed in the phenotype
What does the term codon mean?
sequences of 3 bases on mRNA which corresponds to a specific amino acid
What is deoxyribonucleic acid (DNA)?
double stranded polymer arranged in a double helix
made up of DNA nucleotides that carry the genetic code
What does dominant mean?
an allele that is always expressed in the phenotype when in the genotype, denoted by a capital letter
What is evolution?
the change in inherited traits within a population over time
modelled by natural selection
What is a gene?
a section of DNA that codes for a specific sequence of amino acids that forms a protein and is responsible for a particular trait (phenotype)
What is a genome?
the complete genetic material of an organism
What is a genotype?
all of the alleles present in an organism
What is a haploid?
a ell that contains half the amount of genetic information
human gametes have 23 chromosomes
What does heterozygous mean?
when an organism has two different alleles of a gene e.g. Bb
What does homozygous mean?
when an organism has two of the same alleles e.g. BB, bb
What is meiosis?
a form of cellular division that produces gametes, genetically different haploid cells
4 daughter cells produced over two divisions involving two parent CELLS only occurs in the reproductive and used to produce gametes
What is mitosis?
a form of cellular division that produces gametes, genetically identical diploid cells from a single parent CELL
2 daughter cells produced over one division, occurs everywhere in the body and used for growth and repair of cells/tissues
What is mRNA?
has a complementary sequence to a sequence of bases on DNA (gene)
made up of codons (3 bases on mRNA)
produced in the nucleus during transcription and travels to the ribosomes for translation (protein synthesis)
What is a mutation?
A mutation is a change in the sequence of bases in DNA.
which may result in genetic variations that can produce a slightly different protein and therefore a different phenotype if the mutation occurs in a gene
example being addition, substitution and deletion
What is natural selection?
a change in the environment causes an organism with a mutated allele to be at an advantage
they are more likely to survive
reproduce and pass n their advantageous, mutated allele to their offspring
this happens over many generations and results in the mutated allele becoming more frequent in the population at the expense of the previous dominant allele
What is a phenotype?
an organisms visual characteristics e.g. hair colour
What is protein synthesis?
the formation of a sequence of amino acids and then protein form a gene
involves transcription, the production of mRNA in the nucleus and translation
the production of the sequence of amino acids from mRNA forming a polypeptide chain in the ribosome
What does the term recessive mean?
an allele that is only expressed in the phenotype when present with another recessive allele in the genotype (homozygous)
denoted by a lower case letter e.g. b
What is a ribosome?
an organelle that is the site of protein synthesis, specifically translation
What is RNA?
a single stranded polymer of RNA nucleotides; adenine, uracil, cytosine and guanine, with it being the same as DNA but uracil replaces thymine
two main types, mRNA and tRNA
What are sex chromosomes?
a pair of chromosomes that determine the sex of an individual
in humans this is the 23rd pair and is XX in females and XY in males
What is transcription?
- The two strands of the DNA helix are unzipped by breaking the weak hydrogen bonds between base pairs. This unwinding of the helix is caused by an enzyme (helicase).
- The enzyme RNA polymerase attaches to the DNA just before the gene.
- RNA polymerase moves along the DNA strand. Free RNA nucleotides are attracted to (and form hydrogen bonds with) the exposed DNA strand nucleotides by complementary base pairing.
- RNA polymerase then catalyses the formation of covalent bonds between the RNA nucleotides to form a strand of mRNA.
- The newly formed strand of mRNA is now ready to leave the nucleus and travel to the ribosome.
What is translation?
- The mRNA strand travels through the cytoplasm and attaches to the ribosome. The strand passes though the ribosome.
- For every three mRNA bases the ribosome lines up one complementary molecule of tRNA. We call every three bases on mRNA a codon. The complementary three bases on the tRNA are an anticodon.
- tRNA molecules transport specific amino acids to the ribosome. The ribosome allows two tRNA molecules to sit next to each other; the ribosome catalyses the formation of a covalent bond (peptide bond) between the two amino acids.
- Used tRNA molecules exit the ribosome and collect another specific amino acid.
5.A chain of several hundred amino acids forms in the correct order according to the original DNA is then made. This is called a polypeptide –> protein
What is tRNA?
a form of RNA that is involved in translation
has a complementary anticodon to a codon on mRNA and brings a specific amino acid with is to the ribosome
What does the term variation mean?
the differences between individuals due to genes, the environment or a combination of both
What is a diploid?
an organism with a full set of chromosomes
diploid human cells contain 46 chromosomes
What are the 4 DNA nucleotides?
adenine (A)
thymine (T)
cytosine (C)
guanine (G)
What are the 4 DNA nucleotides made up of?
a phosphate molecule and deoxyribose sugar
Monohybrid cross
a cross between two organisms that is used to investigate the inheritance of a single gene
What are mutagens?
chemicals that increase the frequency of mutations in DNA
Describe the structure of DNA
double stranded
arranged in a double helix
paired bases
A - T, C - G
What is the role of enzyme helicase?
unzip the DNA helix by breaking the weak hydrogen bonds between the base pairs
What is the role of the enzyme polymerase?
attaches to the DNA just before the gene
RNA polymerase moves along the DNA strand
so that free, RNA nucleotides are attracted to (and form hydrogen bonds with) the exposed DNA strand nucleotides by complementary base pairing.
What two observations was Darwin’s theory based on?
all living things/organisms show variation
all living things tend to ever-reproduce
What can we deduce from Darwin’s theory?
- Variation occurs due to mutations. These occur randomly and continuously.
- Some individuals within a population will have features (specialisations) which make them more able to survive in the environment - they might be able to get more food, or have features which mean they can cope with the temperature better.
- These individuals with better specialisations are more likely to survive to reproduce.
- They will pass on their advantageous alleles to the next generation.
- Therefore the offspring will tend to inherit the advantageous characteristics.
- Less favourable alleles tend to become less common in the population.
- This repeats for many generations.
- Over time, the specialisations which help organisms to survive will become more common and the characteristics of a species will change. We end up referring to them as a different species.
What is an antibiotic?
chemicals that kill bacteria and do not usually harm animals
by targeting structures such as bacterial cell walls, which animals do not contain
How has natural selection occurred in response to the overuse of antibiotics? Example penicillin
- Originally, none of the bacteria were resistant and penicillin was not used
- Doctors began to use penicillin, which killed the bacteria
- A chance mutation gave some bacteria resistance to the antibiotic
- These bacteria were better adapted to an environment in which penicillin was used
- They survived in greater numbers. As there are fewer non-resistant bacteria there is less competition for resources.
- So the resistant bacteria reproduce rapidly and passed on the resistance allele
- This was repeated with each generation of bacteria
- The proportion of bacteria with the resistance allele increased until most had the allele
name the type of organism that makes antibiotics
fungi
penicillium
bacteria
