Chpts 12, 13 & 14 Flashcards Preview

Human Bio- Sem 2 > Chpts 12, 13 & 14 > Flashcards

Flashcards in Chpts 12, 13 & 14 Deck (75):

Define allele frequency

How often each allele of a gene occurs in the gene pool for that population


Define mutation

Variations in offspring that do not resemble either parent or have never occurred before in the history of the family


Define gene mutation

Changes in a single gene so that the traits normally produced by a gene are changed or destroyed


Define chromosomal mutations

All or part of a chromosome is affected


When do gene mutations occur

During the replication of DNA molecule before cell division
Any subtle alteration of DNA can produce changes in usual characteristics of species
Can be passed from generations as mutation is copied each time DNA molecule reproduces


Can mutations be a good thing?

Sometimes mutations result in better traits suited to a particular environment so it can contribute to human survival


Why do mutations occur

Can occur without any known cause or influenced by mutagenic agents such as:
Mustard gas, formaldehyde, some antibiotics, ionising radiation (UV light, x-rays, etc)
Women who are pregnant are especially advised to avoid x rays as radiation can cause mental retardation, skeletal malformations or a small head in child


Explain somatic mutation

Mutations in body cells (somatic cells)
Only the individual with the somatic mutation is affected
Each time the mutant body cell divides, it is passed to daughter cell
Doesn't affect reproductive cells, hence mutation lost when individuals dies
Involved in cancerous growths


Explain germline mutation

Occurs in gametes (reproductive cells) and can be passed on
Involved in which mutation occurs not usually affected, however, person produces gametes with changed DNA
If conception occurs with mutated DNA, embryo naturally aborted early in pregnancy
Diseases such as phenylketonuria (PKU) can arise through mutation during gamete formation


List the diseases of genetic mutation

Duchenne muscular dystrophy, cystic fibrosis, Tay-sachs disease


Explain duchenne muscular dystrophy in genetic mutation

Mutation in mother can be inherited by sons or can occur in male zygote so child develops disease
Results in wasting of leg muscles and later, the arms, shoulders, chest
Apparent ages 3-5
Death occurs usually before 20-25 as respiratory muscles begin to fail


Explain cystic fibrosis in genetic mutations

Mutation in gene on chromosome number 7 which has code for 1480 amino acids that make up protein to regulate passage or chloride ions across cell membrane
Recessive allele- has to be inherited by both parents
Symptoms: salty tasting skin, persistent coughing, wheezing, pneumonia, digestive and other problems


Explain Tay Sachs disease in genetic mutations

Lethal recessive condition resulting from a missing enzyme that causes accumulation of fatty substance in nervous system
Death occurs early childhood
A baby with 2 recessive alleles for TSD develops disease in first few months-- mental and physical disabilities


Explain lethal recessive alleles

Result in Death of embryo, foetus or child
People who inherit two such alleles would die before alleles are passed on to next generation
Proportion of lethal recessive alleles in gene pool gradually reduces


Explain chromosomal mutations

There are five different types:


Explain deletion

Part of a chromosome is lost


Explain duplication

Section of chromosome occurs twice as part of chromatid breaks off and joins onto wrong chromatid


Explain inversion

Breaks occur in chromosomes once broken pieces join back in, but the wrong way around
Changes order of genes and can disrupt homologous chromosome pairing in meiosis


Explain translocation

Part of a chromosome breaks off and is re-joined to the wrong chromosome


Explain non-disjunction

During meiosis, a chromosome pair doesn't separate so one daughter cell has extra chromosome, one daughter cell missing a chromosome - called anelploidy


Explain trisomy

Result of non-disjunction
Failure of one or more chromatids to separate in second meiosis division - too many or missing one


Explain monosomy

Individual missing a chromosome
Have one copy instead of usual two


List diseases of chromosomal mutation

Down syndrome
Patau syndrome
Klihefelters syndrome
Cri-du-chat syndrome
Turners syndrome

All can be detected before birth via amniotic fluid or from placenta


Explain Down syndrome in chromosomal mutations

Child has 3 of chromosome 21 instead of normal 2
Affected gamete carries extra chromosome 21 and gives it to embryo
Down syndrome symptoms occur if only part of an extra chromosome 21 is attached to other 2 (partial trisomy)


Explain patau syndrome in chromosomal mutations

Extra chromosome 13 produces individuals with mental retardation, a small head, extra finger, cleft lip or palate, malformed eyes or ears
Can come from mother or father
Extra chromosome appears in each body cell
Occurs in 1 out of 5000 live births --> 80% of these children die within first month


Explain klihefelters syndrome in chromosomal mutation

Individuals with trisomy XXY (extra X)
Normal as boys but develop disease as adults
Small testes won't produce sperm, breasts enlarged, sparse body hair, can occasionally be retarded


Explain cri-du-chat syndrome in chromosomal mutations

Type of partial trisomy- missing portion of chromosome 5
Problems with larynx and nervous system

Name comes from crying noise of baby in infants when born


Explain turners syndrome in chromosomal mutations

Chromosomes with only one set of X chromosomes
Females short in stature, lack secondary sexual characteristics and are infertile


Define DNA sequencing

The determination of the precise order of nucleotides in a sample of DNA

Used to show whether a person will develop inherited disease, identifies point mutations
(Diseases include spastic paraplegia, sickle-cell anaemia, cystic fibrosis, some cancer forms)


Explain the synthesis of DNA in DNA sequencing

when building a sequence each new nucleotide is bonded to hydroxyl group (OH) of previous nucleotide
In DNA sequencing synthetic nucleotides that lack this OH group can be added to a growing strand
This synthetic nucleotide is added to the section of DNA and stops the enlongation of the sequence as there is no OH group for the next nucleotide to attach to
Allows strands to be compared


Explain electro gel phoresis

Scientists have developed techniques to cut the DNA at specific base sequences, leaving pieces of varying lengths

Used when piece of DNA found in a fossil- determines age and where it falls on scale
Can determine hereditary diseases
Used in forensic science (body fluids, hair piece)


List steps involved in electro gel phoresis to create DNA profile or fingerprint

1. DNA pieces are placed on a bed of semi-solid gel
2. Electric current passed through electrodes on either end
3. DNA which is negatively charged, moves through gel toward positive electrode
4. The smaller piece moves faster than the larger ones, resulting in a pattern of bands like a barcode


Explain polymerase chain reaction (PCR)

Technique used to amplify a single copy or a few copies of a particular DNA sequence
Easy and cheap tool
Useful for diagnosing or monitoring genetic diseases, forensics-fingerprints/profiles, DNA based phylogeny (evolution family trees), DNA cloning for sequencing


List basic steps of PCR

1. Initial denaturing for 2 minutes at 94 degrees- heats the double stranded DNA template strand to the point that the stand starts denaturing and hydrogen bonds between nucleotide pairs are broken hence DNA strands separated
2. Continued denature for 30 seconds at 94
3. Anneal primers for 30 seconds at 55- primer is stable within this temperature range to bind to each of the single stranded DNA template strands. Taq polymerase stable enough to now bind to the primer DNA sequence
4. Extension/enlongation- extend DNA for 1 minute at 74- the taq polymerase is at ideal temperature around 70-75, so allows for synthesis and enlongation of strand accurately and rapidly
5. Repeat 25-30 times (doubles each time)


Why can take polymerase be used in PCR

it doesn't break down when heated and has allowed procedure to be simplified and automated, so PCR sample can be heated and cooled alternately


What is the recombinant DNA technique

Amplifies gene or DNA segments and inserts them into bacterial cells creating a TRANSGENIC ORGANISM


List the steps of recombinant DNA technique

1. Isolate gene of interest
2. Gene is inserted into a vector and cloned
3. Vector now has a segment of DNA that is variable of replicating on its own
4. Cloning of the vector then occurs so that numerous copies of the DNA are available to insert into host cells


Define ligase

An enzyme capable of combining isolated gene and plasmid together
Joins at sticky ends


Define phage

A virus that infects bacteria


Define plasmid

Small circular strand of DNA distinct from the main bacterial genome
Composed of only a few genes and is able to replicate independently within a cell


Define restriction enzyme

Enzyme that cuts a stand of DNA at a specific sequence of nucleotides
A plasmid is cut with the same type of restriction enzymes

Produces sticky ends


Define sticky ends

The overhanging ends produced by a staggered cut of a sequence of nucleotide bases

Also called cohesive ends


List the diseases that have been assisted through genetic engineering

Haemophilia A


Explain diabetes and genetic engineering

Human gene that has code for insulin production introduced into bacterial cells
Bacteria become insulin factories and are cultured in vats where they produce insulin
Insulin produced by bacteria is identical to human insulin as human gene is engineered into bacteria
Yeast cells commonly used as culture medium
No side effects unlike older methods


Explain haemophilia A and genetic engineering

Disease where blood clotting factor VII is in poor supply or missing- people can die during bleeding injures if blood doesn't clot
Cultured in mammalian cells
Previously donors required which caused risk of disease transmission - genetic engineering overcame this issue
Free of other plasma proteins so no immune response or allergic reaction caused


Define gene therapy

The treatment of a disease by replacing, manipulating or supplementing non-functional genes in cells and tissues


How did gene therapy help with cystic fibrosis

Cystic fibrosis is a single gene disorder
Before lungs get too severely damaged, gene therapy can be used to make new cells in the body
Lungs won't become damaged as quickly therefore people will disease can live longer and disease on set may be later


Define cell replacement therapy

The replacement of damaged cells with healthy ones


What is the primary objective of tissue engineering

To restore healthy tissues or organs for patients and thus eliminate the need for tissue or organ transplants or artificial implants


List the ways variations arise in populations

Random assortment
Crossing over
Random fertilisation


Explain random assortment affecting variations in populations

Huge number of possible combinations as chromosomes during meiosis come from male and female parents


Explain crossing over affecting variations in populations

Piece of chromatid being broken off and attaching to a different chromatid
Results in changed sequence of alleles along resulting chromosomes


Explain non disjunction affecting variations in populations

One or more members of a chromosome pair fail to separate
Gametes have less or more than correct chromosome number


Explain random fertilisation affecting variations in populations

Any sperm can fertilise any egg, hence many combinations


Explain mutations affecting variations in populations

Permanent changes in DNA of a chromosome that can result in new characteristics
If occurs in gamete, it will be passed on to next generations


What is the most important source of variation

They produce new and different alleles in the gene pool. If this can help individuals to survive, it will cause composition of gene pool to change
Favourable alleles can help a species to survive


What are the six factors that cause changes to allele frequencies within a gene pool

Natural selection
Random genetic drift
The founder effect
Genetic disorders


Explain natural genetic drift

Random non-directional variation in allele frequency
Occurs in small, isolated populations (do not move by choice) populations stay around the same size
Not related to the environment
Breeding only occurs within certain populations


How does random genetic drift and natural selection differ

Random genetic drift:
•a non-directional change
•likely in a small population
•not related to the environment
•chance occurrence


Explain founder effect

Occurs when a small group move away from its original population Roma totally new area and establishes a community, which expands
Not related to the environment


Explain migration

The gene flow from one population to another
If immigration to a certain country brings alleles that are not already in that population, through interbreeding, there will be a change in allele frequencies


How can gene flow be a good thing, with example

It brings favourable genes and protects the population


Explain barriers

Barriers to gene flow can cause variation or changes in allele frequencies within a population
Barriers stop interbreeding
As no two environments are the same, the environmental pressures acting in the populations will change the allele frequencies within each population
There are:
Sociocultural barriers (economic status, educational background, social position, religion)
Geographical barriers (mountain ranges, oceans, lake systems, deserts, expansive eye sheets)


Explain genetic diseases

Diseases can result in changes to allele frequencies in a gene pool
An allele causing an inherited, fatal disease would be expected to be gradually eliminated from a population as people with allele would die and not pass to next generation, however, some diseases continue to persists
Examples of diseases: Tay Sachs and thalassemia


Explain how some genetic diseases are a survival advantage

Sickle cell anaemia trait provides degree of immunity to malaria which is prevalent in areas sickle cell allele is found
Allele therefore maintained in areas where malaria is present


Explain natural selection

Mutations cause variation within a gene pool
Different selection pressures/environmental pressures act on each gene pool and favour one set of alleles at the expense of others
The chosen allele frequency will increase within gene pool and be passed on to next generation


Explain natural selection in humans

The environment of early humans had a profound effect upon the characteristics that were selected
There are many features of the human body that appear to correlate with the environments in which they occur
Relates to body stature,skin colour, speciation and disease


Explain body stature in cold climates

Individuals with long bodies and short limbs have a smaller surface area in relation to body volume
Therefore lose less heart and have a survival advantage in cold climates


Explain body stature in hot climates

Individuals with short bodies and long limbs have a larger surface area in relation to body volume, therefore lose more heat and have survival advantage in hot climates


Explain skin colour in cold climates

Individuals with light skin colour have selective advantage in cold as light skin provides better absorption qualities of UV light
This helps body produce more vitamin D for bodily processes
Generally live further away from the equator


Explain skin colour in hot climates

Individuals with dark skin have a selective advantage in hot climates. Dark skin contains a lot more melanin which protects the skin against UV light, therefore less light absorbed and they are less likely to suffer skin cancer

Live closer to the equator


Explain sickle cell anaemia for natural selection in humans

Occurs in different parts of the world hence another example of natural selection
Results when someone is homozygous for sickle cell allele, symptoms include clogged blood vessels, pneumonia, heart disease
If person is heterozygous, no signs of illness present unless O2 concentrations low
Sickle shape of cells due to mutation of gene responsible for production of normal haemoglobin (carry iron) - causes substitution of one amino acid (valine) for another (glutamic acid) during formation of haemoglobin
This affects functioning of red blood cells- affected haemoglobin called "haemoglobin S" which cells that carry it, collapse when O2 conc. low
If homozygous carries of sickle cell die then it won't be passed to next generation and over time frequency of allele decreases, however, still prevalent in some areas (malaria areas) -- heterozygous for sickle cell have survival advantage and can reproduce and pass on allele, homozygous with no sickle cell are susceptible to malaria
Malaria is a selective agent for sickle cell allele


Define speciation for natural selection in humans

The process of a new species developing


List the process of speciation

1) VARIATION: a range of variations exists within the population which share a common gene pool
2) ISOLATION: a barrier forms dividing populations into two, of which each have separate gene pool
3) SELECTION: different selection pressures act on each population over generations. This brings change in gene frequencies of gene pool. Leads to evolution of separate subspecies
4) SPECIATION: over time changes in each gene frequency may be enough to stop interbreeding - this is when two different species exist


Why are chromosomal mutations worse than gene mutations

Chromosomal mutations effect a large number of genes whereas genetic mutations effect a single gene