Bio 15 - Genetics Flashcards
What is a chromosome ?
A complex of DNA and proteins (including histone proteins)
What is a gene ?
A sequence of DNA that codes for a protein or polypeptide
What is a locus ?
The position of a gene on a DNA molecule
What is meant by a homologous pair of Chromosomes ?
Humans inherit 46 chromosomes - 23 maternal and 23 paternal.
A given chromosome from maternal origin has a counter-part from paternal origin which codes for the same product.
What is an Allele ?
Any homologous pair of chromosomes having a pair of genes (allele) which codes for the same product (ie. hair colour)
Describe Homozygosity ?
When both alleles coding for a gene are identical
Describe Heterozygosity
When the alleles coding for a gene are different
What is the genotype ?
The set of genes possessed by a particular organism.
What is the phenotype ?
The expression of the genotype (may also have environmental influences!)
Explain dominant and recessive alleles ?
In a heterozygous genotype, the expressed gene is the dominant allele while the other is the recessive.
This is also known as Mendel’s law of dominance.
What is the convention for symbolising dominant and recessive genes ?
A - dominant
a - recessive
Explain incomplete or co-dominance ?
Each individual carries two alleles, while populations may have many or multiple alleles.
Sometimes these genes aren’t strictly dominant or recessive.
There may be degrees of blending (incomplete dominance) or two alleles may be equally dominant (co-dominant). E.g. ABO blood types
What happens to the phenotype when two dominant alleles are present ?
The contributions of both alleles do not overpower each other, the phenotype is a result of the expression of both alleles.
Describe the genotype, antigens and antibodies present in the Phenotype Blood group A ?
Describe the genotype, antigens and antibodies present in the Phenotype Blood group B ?
Describe the genotype, antigens and antibodies present in the Phenotype Blood group AB ?
Describe the genotype, antigens and antibodies present in the Phenotype Blood group O ?
What is the universal donor ?
O negative - no antigens !
What is the universal recipient ?
No antibodies
Describe Rhesus factors ?
Coded for by different genes at different loci to A and B antigens
What %age of the population are Rh+ ?
85%
What is erythroblastosis fatalis ?
If and Rh- woman has been exposed to Rh+ blood, she will then have antibodies in her blood.
If her fetus is Rh+ antibodies may cross the placenta and cause the fetus erythrocytes to agglutinate.
What is Mendels first law of segregation ?
In gametogenesis, homologous chromosomes separate during the first meiotic division, therefore alleles coding for the same trait are segregated.
What is Mendel’s second law of independent assortment ?
Different chromosomes separate independently of each other, e.g. paternal and maternal chromosomes don’t all end up in seperate spermatocytes
Each chromosome in a homologous pair separates independently of any other chromosome in other homologous pairs
What is “crossing over” ?
When homolgous chromosomes exchange parts
What is linkage in terms of genetics ?
The propensity for some genetic traits to refrain from assorting independently
What is a “double crossover” ?
When two crossovers happen in a chromosomal area being studied.
Why is sex linkage an exception to Mendel’s law ?
Some traits follow the inheritance of the sex chromosomes.
Describe human sex chromosomes ?
1 pair
XX = Female XY = Male
What are autosomes ?
The remaining 22 pairs of homologous chromosomes that are not sex linked
Describe 3 well-known, sex-linked traits ?
- Haemophilia
- Colour-blindness
- Muscular Dystrophy
What is a Barr body ?
Every female has a condensed, inactivated X chromosome in the somatic cells (aka a Barr body)
Describe a First Fillial (F1) and its significance
If two parents, one AA and the other aa, each parent can only form one type of gamete (A or a) with respect to that allele.
Therefore, the F1 generation must either by hybrids or homozygous
What is a population ?
It includes all members of a species which occupy a more or less well defined area and have demonstrated the ability to reproduce from generation to generation.
What is a gene pool ?
A sum of all the unique alleles for a given population
Describe a way in which evolution can be viewed ?
As a changing of gene frequencies within a population over successive generations
What does the Hardy-Weinberg law predict ?
The outcome of a randomly mating population of sexually producing diploid organisms who are not undergoing evolution.
What are the five conditions that must be met for the Hardy-Weiberg law to be applied ?
- Random mating - no preferences !
- No mutations
- Isolation - no mixing populations !
- Large population size
- No selective pressures ie. no one allele must have reproductive advantage
What is the Hardy-Weinberg equation ?
Describe a practical application of the Hardy-Weinberg equation ?
Prediction of how many people in a generation are carriers for a particular recessive allele.
What is a back cross ?
The cross of an individual (F1) with one of its parents (P) or an organism with the same genotype as the parent
What is a test cross ?
A specific type of back cross between an organism whose genotype for a certain type is unknown, and an organism that is homozygous recessive for that trait, therefore the unknown genotype can be determined from that of the offspring
Name two sources of genetic variability ?
Meiosis
Mutations
What happens during meiosis 1 ?
Crossing over occurs between the parental and maternal genes which leads to a recombination of parental genes yielding unique haploid gametes
What are mutations in terms of genetics ?
Rare, inheritable, random changes in the genetic material (DNA) of a cell
What are the 6 forms of genetic mutations ?
- Point mutation - single base pair
- Deletion - removal of a DNA sequence
- Inversion - reversal of DNA segment
- Translocation - chromosome breaks and re-attaches to another
- Duplication - repeated DNA sequence
- Frame shift mutation - deletion which is not a multiple of 3
What is a mutagen ?
Any substance or agent that can cause a mutation (N.B. Not the same as a carcinogen)
What are carcinogens ?
Agents that cause cancer
What is the Ames test ?
Widely used to screen chemicals used in foods or medications for mutagenic potential
What is Epistasis ?
When one gene masks the phenotype of another
Give an example of Epistasis ?
Pigmentation - E.g. one gene can turn On/Off, and another controls degree of pigmentation
What is Pleiotropy ?
When a single gene has more than one phenotypic expression
What is polygenic inheritance ?
Traits that cannot be expressed in just a few types, but rather as a range of values e.g. Height
What is Penetrance ?
The proportion of individuals in a population carrying a particular variant of a gene that also expresses the associated phenotype
What is expressivity ?
The variation in the degree of expression of a given trait
What is non-disjunction ?
Occurs when chromosomes do not separate properly and do not migrate to opposite poles as in normal anaphase of meiosis
Give an example of a condition resulting from a non-dis-junction mutation ?
Down’s - Trisomy 21
What is genetic linkage ?
Genes that reside on the same chromosome and are unable to display independent assortment because they are physically connected.
What is Phylogenetics ?
The use of mitochondrial DNA as a tool to determine how closely populations are related.
It also clarifies the evolutionary relationships among species
Describe mitochondrial DNA ?
It is circular, and is seen as the smallest chromosome in most species.
Mt DNA is inherited solely from the mother.
What do squares and circles represent on a pedigree diagram ?
Circle = female
Square = Male
What is DNA recombination ?
Involves DNA that contains segments or genes from different sources.
Restriction enzymes are used to cut out pieces of DNA
Describe restriction enzymes ?
They originate from bacteria and are extremely specific as they only cut DNA at specific recognition sites corresponding to nucleotide sequences,
They produce sticky and blunt ends when a double strand of DNA is cut.
What is a “sticky end” ?
The unpaired part of the DNA that is ready to bind with a complementary codon.
What is a restriction fragment ?
A piece of DNA that has been cut by a restriction enzyme.
The fragments are often inserted into plasmids which then be introduced into bacteria via transformation.
What is a plasmid (aka replicon) ?
A circular piece of DNA that is able to replicate independently of chromosomal DNA
What is the role of DNA ligase in DNA recombination ?
If the fragments and the plasmid are treated with the same restriction enzymes, the sticky ends are the same allowing the base pairs to join up.
This attachment is then stabilised by DNA ligase.
What is a health-related use for DNA recombination ?
Treating bacteria with recombinant DNA to produce Insulin
What is gel electrophoresis ? How does it work ?
A method of separating restriction fragments of differing lengths.
The fragments are passed through a gel which is electrified.
DNA is negatively charged, therefore will move towards the positive electrode.
Why is banding observed in gel electrophoresis ?
The shorter fragments move faster than the longer ones, and can be visualised as a banding pattern using autoradiography
What are introns in DNA ?
Non-coding regions of the DNA molecule
What is PCR ?
Polymerase chain reaction.
This can be used instead of bacteria to clone DNA.
DNA fragments are amplified using synthetic primers that intitate replication at specific nucleotide sequences
What are restriction endonucleases ?
Used to digest DNA in southern blotting to cut out specific pieces of DNA
