B18: Continuity and Variation Flashcards
What does DNA mean?
Deoxyribonucleic acid
What is DNA?
The nucleic acid that contains all genetic information
What is a gene?
- A section on a chromosome that is responsible for a particular feature.
- It is the basic unit of inheritance
what is a chromosome?
threads of DNA in the nucleus that are surrounded by proteins(histones), and that carry genes.
What is an allele?
alternate form of a gene that occupies the same position on a particular chromosome and controls the same character
What is a genotype?
The combination of of alleles present in genome of organism.
What is a phenotype?
the observable characterisitc of an organism, ie physical appearance
examples of phenotypes
colour of eyes
colour of hair
colour of lowers
height
What is a dominant allele?
An allele that, if present, will always produce the same phenotype, even if its paired allele is different
What is a recessive allele?
Allele that can only produce a phenotype if its paired allele is identical
What is a dominant trait?
It is a trait that is seen in an individual with with one or two dominant alleles
What is a recessive trait?
A trait that is results only when two recessive alleles are present, or when no dominant allele is present in a particular position on a chromosome
What is codominance?
Give an example
A characteristic where both alleles are expressed in a phenotype of a heterozygote, that is , no allele dominates over the other
an example of codominance is sickle cell or the ABO blood groups
what is an autosome?
A chromosome that is not a sex chromosome
What is a locus?
The specific location of a gene on a chromosome.
if R is the allele for red flowers and W is the allele for white flowers and both alleles pair during fertilization, what will the be colour of the offspring if these genes are codominant and why?
offspring will be pink because both the red and white alleles of the gene with be expressed
What is a homozygote?
An organism that carries 2 copies of the same allele for a particular trait in a genome.
What is a heterozygote?
An organism that carries 2 different alleles for a particular trait
homozygous means:
alleles of a gene are identical
heterozygous means:
the alleles of a gene are different
when are recessive alleles expressed?
only when they are homozygous
when are dominant alleles expressed?
Dominant alleles are always expressed. It does not matter if they are homozygous or heterozygous
What is a carrier?
A person carrying an allele that is not expressed (recessive allele in heterozygotes) but is capable of passing on allele to offspring.
What is linkage?
When 2 or more genes are located on the same chromosome and are always inherited together, unless crossing over occurs in meiosis.
What is sex-linkage?
A characteristic which is controlled by a gene which is located on a sex chromosome (either X or Y).
What are examples of codominance?
- Sickle-cell anaemia. - Roan cattle. - Human blood groups.
What evidence is there in a family pedigree diagram to suggest that there is a sex-linked disease in the family?
When a higher majority of one sex has possessed the disease than the other throughout the family history.
why are men generally not carriers for sex linked traits and women are?
because in men sex linked traits are generally on the X chromosome and will be expressed whether they are recessive or not. Women have two X chromosomes so they can be a carriers if they have a recessive allele.
which parent determines the sex of the offspring? why?
the male determines the sex of the offspring because nly the male gamete can pass on the ‘y’ chromosome
What is the nature of sex-linked inheritance?
- If condition is Y-linked, only males will inherit the disease. - If the condition is X-linked, both females and males can inherit the disease, but females need to inherit 2 faulty X chromosomes in order to acquire disease whilst males only need 1. - Males cannot be carriers of the disease as they only have 1 X chromosome, so they either have the disease or they don’t.
What evidence is there in a family pedigree to indicate the condition is recessive?
When 2 unaffected individuals produce an affected offspring. This indicates that both parents were carriers of the disease.
most sex linked traits are on the X chromosome because ___________
the Y chromosome is very short and has very few genes, so most genes are only represented by one allele which is on the X chromosomes.
What is monohybrid inheritance?
Inheritance of a characteristic controlled by a single gene.
describe mitosis
- chromosomes shorten and thicken and duplicate themselves and become visible
- each chromosome becomes a pair of sister chromatids joined by a centromere.
- the centrioles duplicate and migrate to opposite poles of the cell
- the nuclear membrane disintegrates and spindle fibres are formed between the centrioles.
- the cromatids pairs line up around the equator of the cell and then each sister chromatid separates and is pulled towards the opposite poles of the cell
- once the chromatids reach the poles they are now chromosomes. The spindles disintegrate and the cell constricts along the equator.
- nuclear membrane reapears around each new set of chromosomes and the cell divides forming to identical daughter cells.
- The chromosomes now become long , thin and invisible
- Each daughter cell has the diploid number of chromosomes
Describe Meiosis(reduction division)
what is the genetic diagram used for?
It uses the phenotype and genotype of the parents to predict the characterstics of the offspring
observe the punnet square below.
What percentage of the off spring could be
- albino
- have normal pigmentation
25% albino
75% normal pigmentation
what is the punnet square?
A diagram that is used to predict an outcome of a particular cross or breeding experiment
eg.
what is the name of this diagram. Use it to predict the possible genotypes of the offspring
Punnet Square
possible genotypes are: TT, Tt; tT, TT, tt,
this means: 25% chance of TT; 50% chance of Tt, 25% chance of tt
observe the punnet square below.
What percentage of the off spring could be
- albino
- have normal pigmentation
- Albino - 50%
- Normal pigmentation - 50%
which form of reproduction results in variation?
meiosis
what is mitosis?
A type of cell division where two genetically identical cells known as clones, are formed
importance of mitosis
- maintains the diploid number of chromosomes of a species
- ensures daughter cells have the same combination of genes
- important for growth and repair of damaged tissues
- imporant in asexual reproduction
what is meiosis?
a type of cell division where 4 genetically diferent cells are formed, each with the haploid number(n) of chromosomes.
importance of meiosis
- the way in which gametes are formed for sexualreproduction
- leads to variation among offspring to ensure survival by adapting to changing environmental conditions.
another name for meiosis
reduction division
why is the number of chromosomes so important in cell division?
each species has it own number or chromosomes
where does mitosis occur
all cells except gametes
where does meiosis occur
only in the reproductive organs (testes and ovaries)
how does genetic variation arise in a species
- sexual reproduction
- mutation
genotype + environmental influences = __________
phenotype
what is artificial selection
process by which organisms with desired traits are selected and bred by humans
What is natural selection?
natural process by which organisms that are better adapted to their environment tend to flourish and produce more offspring
what is a pedigree chart?
shows how a specific trait is passed down among family members. It helps to predict possible genoptypes and phenotypes of future offspring.
points to know when constructing a pedigree diagram
- female are represented by circles and males represented by squares
- females drawn before males(circle before square)
- the shading represents one trait being studied
in order to solve pedigree charts we need to know to construct ___________
punnette squares
When interpreting a Pedigree chart what 4 points are important to remember
- is the trait autosomal dominant?
- is the trait autosomal recessive?
- is the trait sex linked dominant?
- is the trait sex linked recessive?
Why are pedigree charts important?
The information they provide helps genetic councellors identify potental risks for future offspring developing a genetic disorder, eg in sickle cell disease.
What is variation ?
It is the differences between individuals
What are the two main types of variation ?
- Continuous - e.g. Height, where there is a smooth range of measurements
- Discontinuous - e.g. Blood group, where there are distinct categories with no values in between
Why are there differences between individuals ?
- there are differences in genes they inherit
- and the conditions in which they develop ( environmental causes )
What happens when a mutation occurs in a body cell ?
It will affect only those cells produced by mitosis from the affected cell. This type of mutation is not inherited. Mutations in body cells can give rise to cancer of the cells that are affected.
What happens when a mutation occurs during meiosis in a gamete ?
It will affect all the cells in the individual which develops from the gamete. This means that the mutation is inherited.
What was Darwin’s theory ?
- there will be a struggle for existence because organisms over reproduce, resources will be limited
- Some will be better adapted to their environment than others because they vary
- those who are best adapted to survive reproduce in great numbers, the less well adapted do not reproduce as much
What is the anagram to help remember natural selection ?
M - MUTATION in individual
V - result in natural VARIATION
A - individual has an ADVANTAGE over others, extinction of species unable to compete
R - surviving individuals REPRODUCE
P - advantage alleles for mutation are PASSED on
S - repeated over SEVERAL generations
what is the phenotype of an organism determined by?
- genotype
- environmetal influences
The phenotype of an individual = (1)__________ + (2)_____________
- Genotype
- Environmental influences
examples of environmental influences
food
drugs
temperature
light
physical activity
which of the following is passed on to offspring?
- variation caused by genes(genotype)
- variation caused by environmental influences
variation cause by genes
this type of variation cannot be passed from generation to generation
variation caused by environmental influences
Definition of a species
group of organisms that closely resemble each other and are capable breeding to produce fertile offspring.
the 2 type of mutation are: (1)_________ and (2)____________.
chromosome mutation
gene mutation
changes in the stucture or number of (1)_________ is called (2)__________ mutation. Errors in the copying of (3) ___________ during its replication is called (4)_______________ . This is the only way that new alelles are formed:( 5)__________
- chromosomes
- chromosome
- DNA
- Genetic mutation
- Genetic mutation
New species are formed by (1)____________ and (2)____________.
- Geographical separation
- Behavioral(or ecological separation)
What does selective breeding mean ?
A means of producing animals and plants with desirable characteristics by choosing individuals to breed from and by repeating the process for many generations
examples of species formed by geographical separation include: (1)_______________. Examples of geographical barriers are (2)____________. Examples of behavioral or ecological separation are (3)_______________.
- Anolis lizards in different islands of the caribbean(Jamaica, Cuba, Hispaniola Puerto Rico)
- mountain range, deserts, oceans, rivers
- mating behaviors eg the Female cichlid fish only mates with males of a certain colour and as a result a new species of fish was formed
How is selective breeding performed ?
- selecting the desired organisms from the population and breeding them together
- look at the offspring for those with the best combination of desired features
- use only these individuals for breeding the next generation
- repeat the selection generation after generation
Techniques for selective breeding
- traditional selective breeding
- artificial insemination
- embryo transplantation
- cloning
- genetic engineering
What are Antibiotics?
There are chemicals that kill bacteria and do not harm animal cells
How do antibiotics kill bacteria and not animal cells?
They target cell structures such as cell walls, which animal cells do not have
How have antibiotics stopped working overtime ?
• originally, none of the bacteria was resistant to the antibiotic • doctors began to use the Antibiotic, which kills the bacteria • A chance mutation gave some bacteria resistance to the antibiotic • these bacteria are better adapted to an environment in which the antibiotic was used • they survive in greater numbers to reproduce and pass on the resistance allele • this was repeated with each generation of bacteria • The proportion of bacteria with resistant allele increased until most had the allele
What is genetic engineering?
The transfer of genes form one organism to another.
Examples of genetic engineering in medicine
- insulin: certain bacteria will produce insulin when the gene that codes for insulin is transfered into their DNA.
- Human Growth Hormone(HGH): certain bacteria will produce HGH when the gene that codes for insulin is transfered into their DNA.
- Hepatitis B vaccine: when the gene that codes for hepatitis B antigens is transfered into the DNA of yeasts, the yeast produce these antigens
Uses of Genetic engineering
- Genetic modification of crops to produce herbicide and pest resisitance; drought resistance; improved nutritional value such as increasing the amount of vitamin A in rice.
- Production of Medicines and vaccines such as insulin and Heptatitis B vaccines
- DNA testing (DNA fingerprinting)
- Gene therapy
Advantages of genetic engineering
- increased food yields
- increase nutritional value of foods
- increase plant resistance to pest
- produce safer vaccines
- produce larger quantity of drugs that are safer and purer
- avoids ethical concerns eg. using pigs and cows to produce insulin.
Disadvantages of genetic engineering
- raises moral and ethical issues eg. ‘designer babies’
- unpredictable environmental issues such as pestide resistant insects or herbicide resistant superweeds
- plants engineered to be toxic to a pest may also be toxic to useful organisms
- once a genetically modified organism is realeased into the environment it cannot be removed so any negative effects are irreversible
- unknown health risks from genetically modified plants and animals
- larger companies can use genetic engineering to get more profit as the expense of smaller companies and poorer countries.
