genetics & inheritance Flashcards
definition of a gamete?
sex cells
definition of a chromosome?
thread like structures of DNA, carrying genetic information in the form of genes. located in nucleus of the cell
definition of a gene?
a section of DNA found on chromosomes that codes for a specific protein/a trait
definition of an allele?
different versions/variations of a particular gene
definition of a dominant allele?
an allele that’s always expressed, even if only one copy is present
definition of a recessive allele?
an allele that’s only expressed if two copies are present (therefore no dominant allele present)
definition of homozygous?
if the two alleles of a gene are the same
definition of heterozygous?
if the two alleles of a gene are different
definition of a genotype?
the combination of alleles that control each characteristic
definition of a phenotype?
the observable characteristics of an organism, or the genotype that is expressed
true or false: some characteristics are controlled by a single gene
true, the inheritance of these single genes is monohybrid inheritance
what’s an example of monohybrid inheritance?
fur colour in mice, red-green colour blindness in humans
do we have two alleles for each gene, and why?
- yes
- 2 copies of each chromosome, 2 copies of each gene, therefore 2 alleles for each gene
- 1 of the alleles inherited from mother, other from father
a dominant allele needs to be inherited from ___ parent in order for the characteristic to show up in the phenotype
a dominant allele needs to be inherited from one parent in order for the characteristic to show up in the phenotype
a recessive allele needs to be inherited from ____ parents in order for the characteristic to show up in the phenotype
a recessive allele needs to be inherited from both parents in order for the characteristic to show up in the phenotype
what do homozygous dominant and homozygous recessive mean?
homozygous dominant: having two copies of the dominant allele
homozygous recessive: having two copies of the recessive allele
what letters are given to dominant and recessive alleles when completing genetic diagrams?
dominant: capital letter
recessive: same letter but lower case
what does polygenic mean?
characteristics that are controlled by more than one gene
(most characteristics are a result of multiple genes interacting, rather than a single gene)
what can the phenotypes of polygenic characteristic show?
a wide range of combinations in features
what does polygenic inheritance mean?
the inheritance of polygenic characteristics
why do we not usually use genetic diagrams for polygenic inheritance?
because it’s difficult to show due to the wide range of combinations
e.g. eye colour: while it’s true brown eyes dominant to blue eyes, not as simple as this as eye colour’s controlled by several genes. this means there’s several different phenotypes beyond brown & blue, like green & hazel
how can the inheritance of characteristics be determined?
using Punnet squares
what do punnet squares show?
the possible combinations of alleles that could be produced in the offspring
what do F1 and F2 mean?
first generation and second generation
what are family tree diagrams/pedigrees usually used for?
to trace the pattern of inheritance of a specific characteristic (usually a disease) through generations of a family
—> this can be used to work out probability that some1 in family will inherit the genetic disorder
3.21B what is codominance?
- when two alleles cross that are both dominant
- when this happens the organism may show multiple phenotypes
how do you represent codominance on a punnet square?
use same capital letter for each allele & add another letter to top right-hand corner to represent their differences
—> both alleles are dominant, therefore both need 2 be represented by capital letter
3.14 what is a genome?
the entire DNA of an organism
3.14 what is a gene?
a section of a molecule of DNA that codes for a specific protein
3.16B describe a DNA molecule
two strands coiled to form a double helix, the strands being linked by a series of paired bases: adenine (A) with thymine (T), and cytosine (C) with guanine (G)
what are nucleotides
nucleotides consist of a sugar (deoxyribose), a phosphate & a nitrogenous base (nitrogenous base are A, C, G or T)
3.16B what does adenine always pair with?
thymine
3.16B what does cytosine always pair with?
guanine
what type of bond joins the nucleotides together?
covalent bonds between the sugar of one nucleotide & the phosphate group of the next nucleotide
3.17B how does RNA differ from DNA?
- RNA single stranded, DNA double stranded
- RNA has sugar ribose while DNA has sugar deoxyribose
- RNA has base uracil (U) while DNA has base thymine (T)
3.18B what is a codon?
the sequence of three bases in DNA that codes for a specific amino acid
3.18B what is messenger RNA/mRNA?
- formed in nucleus of cell
- copies sequence of bases of a section of DNA in transcription
- carries code for building a specific protein from nucleus to ribosomes in cytoplasm (acts as messenger)
3.18B what is tRNA?
- found in cytoplasm
- picks up specific amino acids from cytoplasm & brings them into position on surface of ribosome where they can be joined together in specific order to make a specific protein (translation)
3.18B describe transcription
- 2 strands of DNA helix unzipped by breaking weak hydrogen bonds between base pairs. this unwinding of the helix caused by enzyme helicase
- enzyme RNA polymerase attaches to DNA just before the gene
- RNA polymerase moves along DNA strand. free RNA nucleotides are attracted to (and form hydrogen bonds w) the exposed DNA strand nucleotides by complementary base pairing
- RNA polymerase then catalyses formation of covalent bonds between RNA nucleotides to form strand of mRNA
–> bc opposite base bonds w exposed DNA bases, strand of mRNA is opposite copy of DNA strand - complementary copy - newly formed strand of mRNA now ready to leave nucleus & travel to ribosome
3.18B describe translation
- the mRNA strand travels through cytoplasm & attaches to ribosome, passes through ribosome
- for every 3 mRNA bases the ribosome lines up 1 complementary molecule of tRNA. (every 3 bases on mRNA is a codon, complementary 3 bases on tRNA is an anticodon)
–> bc there are 3 mRNA bases for each tRNA molecule, we call this the triplet code - tRNA molecules transport specific amino acids to ribosome. ribosome allows 2 tRNA molecules to sit next to each other; ribosome catalyses formation on a covalent bond (peptide bond) between 2 amino acids
- used tRNA molecules exit ribosome & collect another specific amino acid
- chain of several hundred amino acids formed in correct order according to og DNA then made - called a polypeptide
–> after translation, polypeptide finally folded into correct shape & becomes protein
3.22 what type of inheritance are most phenotypic features the result of?
polygenic inheritance, rather than single genes
3.34 what is mutation?
a rare, random change in genetic material that can be inherited (or from topic notes: a change in the sequence of bases in DNA)
3.35B how can a change in DNA affect the phenotype of an organism?
by altering the sequence of amino acids in a protein:
- replacement of a single base pair w a different pair
- addition or deletion of one or more base pairs
this will normally alter the shape & function of the protein
3.36B what effect do most genetic mutations have on the phenotype?
most genetic mutations have no effect on the phenotype, some have a small effect and rarely do they have a significant effect
3.37B how can the incidence of mutations can be increased?
by exposure to ionising radiation:
- gamma rays
- x-rays
- ultraviolet rays
and some chemical mutagens:
- e.g. chemicals in tobacco
3.38 explain Darwin’s theory of evolution by natural selection
- variation occurs due to mutations. these occur randomly & continuously
- some individuals within pop. will have features (specialisations) which make them more able to survive in the environment
- these individuals w better specialisations more likely to survive to reproduce
- they’ll pass on their advantageous alleles to next generation
- therefore the offspring will tend to inherit advantageous characteristics
- less favourable alleles tend to become less common in pop
- repeats for many generations
- over time, specialisations which help organisms survive will become more common & characteristics of species will change
3.39 understand how resistance to antibiotics can increase in bacterial populations, and appreciate how such an increase can lead to infections being difficult to control
- originally, none of bacteria resistant & penicillin not used
- doctors began to use penicillin, which killed bacteria
- a chance mutation gave some bacteria resistance to the antibiotic
- these bacteria better adapted to an environment in which penicillin used
- they survived in greater no.s. as there are fewer non-resistant bacteria there is less competition for resources
- so resistant bacteria reproduce rapidly & pass on resistance allele
- this repeats w each generation of bacteria
- proportion of bacteria w resistance allele inc until most had the allele
