Inheritance Flashcards
Definition of a gene
A gene is a section of a molecule of DNA that codes for a specific protein.
Definition of DNA
DNA is a molecule composed of two strands coiled to form a double helix carrying the genetic instructions used in the growth, development and functioning of all known living organisms.
Name the 4 bases that pair strands of DNA
- Adenine (A)
- Thymine (T)
- Cytosine (C)
- Guanine (G)
Adenine pairs with…
Thymine
Cytosine pairs with…
Guanine
What three things is a nucleotide made up of?
- phosphate group
- sugar
- nitrogenous base
3 differences between DNA and RNA
- nitrogenous bases
- strands
- sugar
- size
- in RNA, uracil replaces thymine as the nitrogenous base (AUCG)
- RNA is single stranded, DNA is double stranded
- DNA is contains deoxyribose sugar, RNA contains ribose sugar
- RNA is made up of a smaller number of nucleotides
1 similarity between DNA and RNA
Phosphates are the same
Transcription
- A section of the DNA helix is untwisted and unzipped.
- The template strand of DNA is copied into a new molecule of messenger RNA. The bases on the mRNA nucleotide match with their complementary base pair on the template DNA strand (give eg).
- The new mRNA molecule leaves the nucleus through the nuclear pores into the cytoplasm and onto the ribosome.
Translation
- At the ribosome, the bases on the mRNA are read in threes to code for a single specific amino acid.
- This amino acid is brought to the ribosome by a tRNA molecule.
- The codons on the mRNA connect to the anticodons on the tRNA.
- The amino acids join together to form a polypeptide chain which then folds to reveal a unique 3D structure (a protein).
Definition of an allele
An alternative form of a gene
Definition of a dominant allele
Alleles which will always be expressed in the phenotype when they are present.
Definition of a recessive allele
Alleles that can be masked by a dominant one, so they will only be expressed in the phenotype in the absence of a dominant allele.
Definition of homozygous alleles.
Both alleles are the same, for example BB (homozygous dominant) or bb (homozygous recessive).
Define heterozygous alleles
The alleles are different, for example Bb
Definition of a phenotype
The physical appearance of an individual regarding a particular characteristic
Definition of a genotype
The genetic makeup of an individual regarding a particular characteristic
Define codominance
When both alleles are expressed in the same phenotype because neither allele is dominant over the other.
What is a monohybrid cross
the study of the inheritance of one characteristic.
What are pair of chromosomes is female.
XX
What pair of chromosomes is male
XY
Definition of genetic variation
The difference in DNA sequence of individual offsprings from the same parent or species.
Causes of genetic variation
- fertilisation
- meiosis
- mutations
Explain how meiosis results in genetic variation.
The chromosomes are shuffled during the process resulting in random chromosomes ending up in each of the cells.
Explain how fertilisation results in genetic variation
The random fertilisation of an egg cell by a single sperm out of over millions of sperm cells with produce genetically distinct zygotes.
Explain how mutations result in genetic variation
Genetic variation may result from mutation involving a change in DNA sequence to produce new alleles for a specific trait.
Name and explain the 5 stages of MITOSIS
Interphase: nuclear membrane breaks, DNA replicates
Metaphase: chromosomes line up at the equator, spindle fibres from centrioles join the chromosomes
Anaphase: sister chromatids pulled apart, each side of the cell has a full set of chromosomes.
Telophase: duplicated genetic material is separated into two genetically identical daughter cells
Cytokinesis: physical process of cell division.
Uses of mitosis
- growth
- repair
- cloning
- asexual reproduction
Describe the 3 stages of meiosis
- Cell makes copies of its chromosomes, meaning it now has double the genetic information needed
- The cell splits into two cells meaning each cell contains the normal amount of genetic information (46 chromosomes) and is therefore diploid.
- The two cells both splint into two cells to produce 4 genetically different cells with 23 chromosomes.
Use of meiosis
Production of gametes for sexual reproduction
Definition of a haploid cell
One copy of each chromosome (no, of chromosomes is 23)
Definition of a diploid cell
Two copies of each chromosome (no, of chromosomes = 46)
Give 3 examples of genetic variation
Eye colour
Hair colour
Blood type
Etc
Give three examples of environmental factors that may cause variation
Resource availability (food) Environmental conditions (weather) Biological factors (pathogens)
Definition of a genetic mutation
A rare and random change in DNA sequence coding for new alleles for a gene.
Name the 3 types of mutations that can occur
Beneficial mutation (changes to DNA sequence that make organism better adapted to the environment) Detrimental mutations (changes to DNA sequences that abrogate normal function of a trait) Neutral mutations (no effect on functioning of a specific trait)
Why do changes in DNA affect proteins?
- for protein synthesis to occur, DNA sequence needs to be transcribed and translated
- when mutations change DNA base, base sequence of complementary mRNA transcript will also change.
- modified mRNA transcript will be translated o code for different AAs, changing the structure of the polypeptide chain.
- function of protein is altered.
Why do meiosis produce genetically different cells?
The chromosomes are shuffled during the process, resulting in random chromosomes ending up in each of the four cells.
name the 4 stages of natural selection/evolution
- variation
- survival + reproduction
- rate of passing
- evolution
definition of evolution
the change in the frequency of a phenotype in a population over many generations
describe the variation stage in natural selection
- individuals in a species show a wide range of variation caused by differences in genes.
describe the survival and reproduction stage of natural selection
- individuals with characteristics most suited to the environment have a higher chance of survival and more chances to reproduce
describe the rate of passing stage of natural selection
- the advantageous characteristics are passed onto their offspring at a higher rate than those with characteristics less suited to survival.
describe the evolution stage of natural selection
- over many, generations, these beneficial characteristics become more common in the population so the species changes (evolves)
name the 4 stages of antibiotic resistance
- mutation
- death
- reproduction
- result
describe the mutation stage of antibiotic resistance
- a random mutation occurs in the DNA of individual bacterial cells. the mutation protects the bacterial cell from the effects of the antibiotic- it becomes antibiotic resistant
describe the death stage of antibiotic resistance
- bacteria without the mutation die when an antibiotic is present
describe the reproduction stage of antibiotic resistance
- antibiotic resistant bacteria survive and can reproduce with less competition from non-resistant bacterial strains. the genes for antibiotic resistance are passed onto more offspring
describe the result stage of antibiotic resistance
- over time the whole population becomes antibiotic resistant because the antibiotic resistant bacteria are best suited to their environment.
describe insertion mutations
A new base is randomly added/inserted into the DNA sequence
describe deletion mutations
A base is randomly removed/deleted from the DNA sequence
describe substitution mutations
A base in the DNA sequence is randomly swapped for a different base
give two ways of increasing the likelihood of mutations
Gamma rays, x - rays and ultraviolet rays - all types of ionising radiation which can damage bonds and cause changes in base sequences
Certain types of chemicals - for example chemicals such as tar in tobacco
