Patterns of Inheritance, 6.2 Flashcards
What is the genotype?
Genetic make up of an organism
What is the phenotype?
Visible characteristics
What can gene mutations be caused by?
- Physical agents - x-rays, gamma rays, UV
- Chemical - tobacco smoke, mustard gas
- Biological - viruses, food contaminants
When do chromosome mutations occur?
During meiosis
What is deletion?
Part of a chromosome is lost
What is inversion?
Section of the chromosome breaks off and is reinserted in the opposite direction
What is translocation?
Part of a chromosome reinserted on a different chromosome
What is duplication?
Piece of a chromosome is duplicated
What is non-disjunction?
One pair of chromosomes fails to separate so zygote has an extra chromosome
What are the different types of chromosome mutations?
Deletion, inversion, translocation, duplication, non-disjunction
What does Aneuploidy mean?
Chromosome is not a multiple of the haploid number for that organism
What is Polyploidy?
Diploid gamete is fertilized by a haploid gamete. Causes a triploid zygote
What causes genetic variation?
Sexual Reproduction - meiosis, crossing over in prophase 1, the fusion of gametes
What is variation?
Differences between individuals
What two factors cause variation?
Genetic and enviromental
What are some examples of environmental variation?
Accents. Losing a limb. Piercings. Scars.
What is epigenetics?
Environmental interacting with genes
What are some examples of epigenetics?
Genes put in certain modes where they might react a certain way. Plants responding to light. Magnesium deficiency in plants - grow up to be chlorotic.
What is meant by the term monogenic?
Determined by a single gene
What is an allele?
Version of a gene
What does homozygous mean?
True breeding. Identical alleles at a particular gene locus. (RR, rr)
What does heterozygous mean?
Different alleles at a particular loci (Rr)
What is meant by dominant?
Only 1 copy required for the phenotype to show
What is meant by recessive?
Two copies needed for the phenotype to show
What can we use to show a monohybrid cross?
A Punnett Square
What did Gregor Mendel do?
Looked at pea plants. Cross fertilized - looked at characteristics. Sometimes the trait was unchanged. Came up with the foundations of inheritance.
What is meant by the term dihybrid?
Involves two gene loci
What are multiple alleles?
Characteristics for which there are 3 or more alleles in the populations gene pool
Name some examples of multiple alleles.
Human blood groups. Coat colour in rabbits
What did Gregor Mendel observe in pea plants that suggested dihybrid inheritance?
The peas could be round or wrinkled and yellow or green
Define Loci
Specific linear position of a particular gene on a certain chromosome
Define Pure Breeding Strain
Group of organisms in which a certain features is unaltered for generations indicating that organisms are homozygous for that feature.
What are the four blood groups? And how many alleles are they determined by?
A, B, AB and O. Determined by 3 alleles
What does the blood group gene code for?
Codes for an isoagglutinogen, I, on the surface of erythrocytes. I(A), I(B), I(O)
What is the order of dominance for the blood group alleles?
I(A) and I(B) are dominant to I(O). I(A) and I(B) are codominant.
What are the different coat colours in rabbits? Say which is dominant to which?
- Wild C, dominant to all
- Albino c, recessive to all
- Chinchilla, C(ch), dominant to himalayan
- Himalayan, C(h), dominant to albino
What does blood type A and B have the blood type O doesn’t?
Antigens
Which blood group can receive blood from which blood group?
- Type O to everyone, universal donor
- Type B to Type B, specific antigens
- Type A to Type A, specific antigens
- Type AB can receive from all blood groups
What is meant by sex linked?
Any gene that is carried on the X or Y chromosome
What are normal chromosomes called?
Autosomes
What do sex chromosomes determine?
The gender
What is the difference between X and Y and what is the impact of this?
Y is shorter than X, they are not fully homologous. There are fewer genes on the Y. The X may not have any partner alleles on the Y.
What happens if a female has an abnormality on an X chromosome?
The other X chromosome will have normal functioning allele
What happens if a male has an abnormality of the X chromosome?
There may not be a Y allele that matches up. The male will therefore suffer from a genetic disease. They are functionally haploid for X linked genes
Define linkage
Two or more genes located on the same chromosome
Define autosomnal linkage
Linked genes which are carried by an autosome
What are some examples of problems/diseases caused by sex linkage?
Hemophilia A. Colour Blindness.
What is Hemophilia A?
Where a person is unable to clot blood fast enough. Injuries cause bleeding or internal hemorrhage
How is Hemophilia caused?
- X chromosome codes for blood clotting protein (factor 8)
- A recessive abnormal allele with altered DNA will not code for the blood clotting allele
- In a male there will be no dominant functioning factor 8 on the Y chromosome
- He will suffer from hemophilia
What is colour blindness caused by?
- Protein for colour vision on X but not on Y
- A mutated allele may result in colour blindness
- Many suffer from red-green colour blindness
What is an example of sex linkage in cats?
One of the genes for coat colour. Allele C(O) produces ginger fur. Allele C(B) produces black fur. They are codominant. Cats with genotype X(CO) X(CB) are tortoise shell (can only occur in females)
What is meant by inactivation of X chromosomes in female mammals?
A mechanism that prevents twice the number of X-linked genes being present. In every cell one of the X chromosomes is inactivated.
How are males represented in a pedigree chart?
With a square
How are females represented in a pedigree chart?
With a circle
What does the shading of a square or a circle represent in a pedigree chart?
Presence of a disease
What is meant by codominance?
Both alleles present in the genotype contribute to the phenotype
How does codominance occur?
When there are 3 phenotypes because neither allele is dominant over the other
Describe the snapdragon plants as an example of codominance.
- C(R) for red, all functional enzymes
- C(W) for white, no functional enzymes
- C(R) C(W) for pink, some functional enzymes
- There are 3 different phenotypes
Describe the coat colour in shorthorn cattle as an example of codominance
- C(R) for red
- C(W) for white
- C(R) C(W) for roan
What is an example of a lethal allele?
The effect of codominanc in Manx cats which have no tails. The gene S controls the development of the embryo spine: S(N) S(N) - normal, S(N) S(A) - abnormal no tail, S(A) S(A) - spine not developed they die.
What is meant by the term polygenes?
2 genes at different loci can combine to affect one single characterstic
What can polygenic inheritance be affected by?
More than one gene. Affected by the environment.
Define Epistasis
Interaction of non-linked gene loci where on masks the expression of the other
How does epistasis reduce genetic variation?
Reduces the number of phenotypes produced in the F2 generation
What does antagonistic mean?
They have the opposite effects to each other
How does recessive epistasis work?
The homozygous presence of a recessive allele a the first locus prevents the expression of another allele at a second locus
What is the term to describe the gene masked by another gene in epistasis?
Hypostatic
What does complementary epistasis mean?
Genes working together to code for two enzymes that work in succession catalysing sequential steps of a metabolic reaction
Describe mice coat colour as an example of epistasis
Gene locus C/c determines colour - CC & Cc will produce colour. cc will be albino. A/a - determines what colour. AA/Aa - greyish. aa - black. If you get cc the colour protein is dysfunctional and you won’t get colour despite what A/a is
What is the Chi-Squared test?
A statistical test to find out if the difference between observed and expected data or significant or due to chance
How do we get the expected and the observed results?
Expected - prediction. Observed - carry out the experiment and get the actual result.
What is a null hypothesis?
There is no statistically significant difference between the observed and the expected data. Any difference is due to chance.
What is the formula for the chi-squared test?
x(^2)=the sum[ (O-E)^2/E ]
When can we use the chi-squared test?
- Data is in categories not continuous
- Strong biological theory to predict values
- Large sample size
- Raw data
- No zeros
What are the steps of using the chi-squared test?
- Determine the value of x(^2)
- Determine the degrees of freedom
- Compare our value with the critical value
- Reject or accept the null hypothesis
What is Natural Selection?
Mutations and migration introduce new alleles into a populations. Some individuals will be better adapted to survive than others die to genotypes and phenotypes.
What will happen to allele frequencies over time?
They will change this is evolution
What is stabilising selection?
Leading to a constancy within the population. Intermediate phenotypes selected. reduces genetic variation.
When does stabilising selection occur?
When organisms environment remains unchanged.
What is an example of stabilising selection in humans?
Have a birth mass close to 3.5kg as babies are more likely to survive. Their offspring then inherit this.
What is directional selection?
Occurs when an environment change favours a new phenotype results in a change in the population.
What is an example of directional selection?
If the environment gets colder it would be an advantage to be larger. More large animals would survive and reproduce. Overtime there will be a gradual shift and the optimum would move.
What is disruptive selection?
Favours the extreme phenotypes and selects against the intermediate phenotypes
What is genetic drift?
If a population descends from a small group of parents
What is intraspecific variation?
Differences within species
What does variation rely on?
Mutations and selection pressures
What is interspecific variation?
Differences between different species
How will a random change affect a large population?
Small effect. Genetic drift will also have a small impact. Allele frequency will remain stable.
How will a random change affect a small population?
Large effect. As does genetic drift. On populations genetic diversity.
What is a gene pool?
The total information from all the genes and alleles of the breeding individuals in a population at a particular time
Why can the gene pool composition change?
Relative proportions of alleles vary from one generation to the next
What is meant by a genetic bottleneck?
A sharp reduction in population size due to environmental catastrophes. As the population increases again it less genetically diverse.
Why is it thought that the cheetah has a low genetic diversity?
Because only a few survived the ice age.
What is the impact of a genetic bottleneck?
- Loss of some advantageous alleles
- Disproportionate frequency of harmful alleles
- Lowers the populations chance of survival
- Fertility can be affected
- Population will no longer be representative of the population it originated from
What is the founder effect?
Small sample of an original population establishes in a new area - its gene pool is not as diverse.
- Through migration
- Special case of genetic bottleneck
What are the impacts of the founder effect?
- Loss of genetic variation
- Could only get recessive alleles
What is discontinuous variation?
When phenotype classes are distinct and discrete - fall into separate categories
How is discontinuous usually determined?
- By the alleles of a single gene locus, one gene contributes (monogenic)
- Sometimes the alleles of two genes interact to govern a single characteristic (eg epistasis)
What is continuous variation?
Smooth gradation between many intermediates - phenotypes which exist in a range
What are some examples of continuous variation?
Foot size, height, skin colour, heart rate, cob length, leaf length, tail length
How is continuous variation usually determined?
- Many alleles involved (polygenic) more than one gene contributes to the phenotype
- The greater the number of gene loci contributing the more continuous the variation
Does environment have a greater effect on the expression of polygenetic or monogenetic characteristics?
Polygenes - eg everyone has the genetic potential for height but if you don’t have the right nutrition you won’t grow to your full height
What is a population?
Members of a species living in the same place at the same time and are able to interbreed.
What factors affect allele frequencies?
- Population size
- Mutation rate
- Migration
- Natural selection
- Changes to the environment
- Non-random mating
- Genetic drift
- Gene flow
What does a population need to survive?
Genetic variation
What is meant by subspecies?
If populations are different but can still interbreed
What is speciation?
If two populations of the same species have become so genetically different thy can no longer interbreed and produce offspring. Two new species.
How can the proportions of alleles and genotypes in a population be calculated?
The Hardy-Weinburg equation
What can you deduce from the Hardy Weinburg equation?
The frequency of those carrying a recessive allele for a genetic disorder
What are the assumptions of the Hardy Weinburg Principle?
- Population is large enough to make a sampling error negligible
- Mating occurs randomly
- No selective advantage for any genotype
- No mutation, migration or genetic drift
What is the equation for Hardy Weinburg? What does each part mean?
p(^2) + q(^2) + 2pq = 1. p = frequency of dominant allele. q = frequency of recessive allele
How do two populations become isolated?
Geographical or reproductive. Mutations which occur in one population may not occur in the other.
How does geographical isolation occur?
Separated geographically eg by rivers, lakes, mountains, volcano
From geographical isolation how does speciation then occur?
- The isolated populations are subject to different selection pressures in the two environments.
- Undergo independent changes to the allele frequencies.
- 2 groups do not meet and cannot interbreed
- Each population adapts to its environment
What is allopatric speciation?
Formation of two different species as a result of geographical isolation
What is reproductive isolation?
Biological and behavioral changes within a species lead to reproductive isolation. A mutation could lead to some organisms in a population changing behavior.
How can genetic changes cause reproductive isolation?
Prevent gamete fusion. Make zygotes less viable. Lead to infertile hybrid offspring.
How could mating be affected by mutation?
- Different courtship behavior
- Mate at different times
- Animal genitalia or plant flower structure different
What is sympatric speciation?
Still in the same splace
What is artificial selection?
Selective breeding of organisms. Humans choosing desired characteristics. Selection pressures from humans.
What are some examples of desirable characteristics in plants?
High yield. Pest and disease resistance. Improved appearance. Grow under harsh conditions. Good flavour
What are some examples of desirable characteristics in animals?
Docility. Ability to be trained. High yields of milk, meat and wool. Pets - looking cute.
What happens as a result of artificial selection?
Genetic diversity in the gene pool of the selected breed is reduced
What is interbreeding depression?
When two related individuals are crossed the chances of getting two copies of a recessive harmful allele are increased.
How do breeders introduced more variety?
They out cross individuals to two different varieties - hybrid vigour
Why is hybrid vigour important?
Maintains a resource of genetic material. The resulting F1 are heterozygous - more genetic diversity
What can be the impact of decreased genetic variety from artificial selection?
Increased widespread susceptibility to disease. An entire crop could be wiped out for example.
What are examples of gene banks?
Rare breed farms. Wild populations. Botanic gardens and zoos. Seed bank. Sperm bank. Frozen embryos.
Why is artificial breeding unethical?
- Domesticated animals docile but wouldn’t be able to survive in the wild
- Livestock animals have less fat so would succumb to low temps
- Pedigree dogs are more susceptible to disease
- Coat colours would fail as camouflage
What are some examples of issues that pedigree dogs might have?
- Boxer, cancer, heart disease
- Labrador, Chronic skin itchiness, shoulder pain
- German Shepard, heart disease, skin infections
- Bulldog, breathing problems, hip and elbow problems
Why do allele frequencies change?
Natural selection, evolution
