Chapter 2 Patterns of inheritance Flashcards
Definition of genotype?
Genetic makeup of an organism
Definition of phenotype?
Visible characteristic of an organism
Genome definition?
Total DNA content of a cell or an individual organism
What is meant by polygenic?
Determined by several genes
What are some physical mutagenic agents?
- X-rays
- Gamma rays
- UV light
What are some chemical mutagenic agents?
- Nitrous acid
- Mustard gas
- benzopyrene (tobacco smoke)
What are some biological mutagenic agents?
- Some viruses
- Transposons (remnants of viral nucleic acid)
- Food contaminants such as mycotoxins from fungi
What are the 5 types of chromosome mutations that occur during meiosis?
- deletion
- inversion
- translocation
- duplication
- non-disjunction
What is the chromosome mutation inversion?
A section of a chromosome breaks off, turns 180 degrees and join again. Some genes may be too far away from their regulatory nucleotide sequences to be properly expressed
What is the chromosome mutation deletion?
Deletion - part of a chromosome (containing genes and regulatory sequences) is lost
What is the chromosome mutation translocation?
A piece of one chromosome breaks off and become attached to another chromosome.
What is the chromosome mutation duplication?
A piece of a chromosome may be duplicated. Too many of certain proteins may disrupt metabolism
What is the chromosome mutation non-disjunction?
One pair of chromosomes/ chromatids fails to separate, leaving one gamete with an extra chromosome.
What is meant by aneuploidy?
When a chromosome number is not an exact multiple of the haploid number for that organism (e.g. trisomy).
What is meant by polyploidy?
When a diploid gamete is fertilised by a haploid gamete or 2 diploid gametes are fused, resulting in more than 2 sets of chromosomes.
What does genetic variation result from during meiosis?
- Allele shuffling during crossing over in prophase 1 (swapping of alleles between non-sister chromatids)
- Independent assortment of chromosomes during metaphase 1/ anaphase 1
- Independent assortment of chromatids during metaphase 2/ anaphase 2
What is meant by monogenic?
Determined by a single gene
What is meant by dihybrid?
Involving 2 gene loci
What is an allele?
Different versions of the same gene
What is co-domidance?
Where both alleles present in the genotype of a heterozygous individual contribute to the individual’s phenotype
What are some examples of codominance?
- ABO blood group (phenotypes - A,B,AB,O, where A and B are codominant and O is recessive)
- Coat colour in rabbits
- Sickle-cell anaemia (codominant if type of haemoglobin is the phenotype)
- Flower colour
What are some examples of multiple alleles?
- ABO blood group
- coat colour in rabbits
What are autosomal chromosomes?
All chromosomes except sex chromosomes
How many genes does the X chromosome carry?
1000
What are some examples of sex-linked characteristics?
- Haemophilia A (blood is unable to clot)
- Red-green colour blindness
- Duchenne muscular dystrophy
What is autosomal linkage?
Two genes are located on the same autosome and are more likely to be inherited together because they are less likely to be separated during crossing over.
When there is autosomal linkage between two genes, how many possible combinations of alleles are there in the gametes?
2
What is epistasis?
Interaction of non-linked genes where one masks the expression of the other
What is meant by complementary and antagonistic epistasis?
Antagonistic epistasis refers to when a gene is inhibiting expression of another. Complementary epistasis refers to when a gene is encouraging expression of another.
Which is the epistatic gene?
The gene that is suppressing/ affecting another gene
Which is the hypostatic gene?
The gene that is being suppressed/ affected in epistasis
What is meant by recessive epistasis?
Presence of a homozygous recessive genotype prevents the expression of the second gene
What is meant by dominant epistasis?
Presence of a homozygous dominant or heterozygous genotype prevents the expression of the second gene
What is an example of:
a) recessive epistasis
b) dominant epistasis
c) complementary epistasis
a) Salvia plant flower colour
b) Feather colour in chickens
c) Coat colour in mice
What is the chi-squared test used for?
To find out if the difference between observed and expected data is significant or due to chance.
What is discontinuous variation?
Genetic variation producing discrete phenotypes - two or more non-overlapping categories
What is continuous variation?
Variation that produces phenotypic variation where the quantitative traits vary by very small amounts between one group and the next
What are some factors affecting allele frequencies within populations?
- population size
- mutation rate
- migration
- natural selection
- changes to the environment
- genetic drift
- founder effect
- non-random mating
What are the 3 main types of natural selection?
Stabilising, directional and disruptive
What is disruptive/ diversifying selection?
Selection pressure toward the extremes creates two modal values. It favours extreme phenotypes.
What is stabilizing selection?
Natural selection leads to constancy within a population. Intermediate phenotypes are favoured.
What is directional selection?
An environmental change favours one extreme, resulting in a change in population mean.
What is an example of stabilizing selection?
Human birth weight
What is an example of directional selection?
Antibiotic resistance
What is an example of disruptive selection?
Rabbits are black, white or agouti. Black and white rabbit have advantages so agouti is less common.
Definition of gene pool?
All the genes and alleles of the breeding individuals in a population at a particular time.
What is genetic drift?
Neither allele has an advantage/ disadvantage, so evolution is down to chance and occurs due to random events such as natural disasters or diseases rather than selection pressures.
What is a genetic bottleneck?
A sharp reduction in size of a population due to environmental catastrophes, which also reduces genetic diversity. As the population expands it is less genetically diverse than before.
What are possible causes of genetic drift?
A genetic bottleneck or the founder effect.
What is the founder effect?
When a small sample of an original population establishes in a new area. It’s gene pool is not as diverse as that of the parent population.
What is the definition of population?
Members of a species living in the same area at the same time, that can interbreed.
What does the Hardy-Weinberg model assume?
- Mating in the population occurs at random
- The population is experiencing no selection
- The population is large enough to make sampling error negligible
- The population has no mutation, migration or genetic drift
What are the 2 equations that show allele frequencies determine genotype frequencies?
p^2 +2pq + q^2 = 1
p + q = 1
What is speciation?
The splitting of a genetically similar population into 2 or more populations that undergo genetic differentiation and eventually reproductive isolation, leading to the evolution of 2 or more new species.
What is allopatric speciation?
Formation of 2 different species from one original species, due to geographical isolation.
What is sympatric speciation?
Formation of 2 different species from one original species, due to reproductive isolation, while the populations inhabit the same geographical location.
What is geographical isolation?
Occurs when physical barriers divide a population so isolated populations experience different selection pressures and each population becomes adapted to their environment (allopatric speciation).
What is reproductive isolation?
Biological or behavioural changes preventing 2 populations from successfully breeding together (sympatric speciation).
Examples of changes leading to reproductive isolation?
- Change in chromosome number may prevent gamete fusion, make zygotes less viable or produce infertile hybrid offspring
- Changes in courtship behaviour, e.g. time of year mating occurs
- Changes in animal genetalia or flower structure
What is artificial selection?
Selectively breeding organisms; involves humans choosing desired phenotypes and interbreeding those phenotypes individually.
What is the selecting agent for artificial selections?
Humans
What is a negative affect of artificial selection?
Interbreeding depression - The genetic diversity in the gene pool of the selected breed is reduced so the chances of an individual inheriting 2 copies of a recessive harmful allele are increased.
What can breeders do to avoid interbreeding depression?
Hybrid vigour - Outcross individuals belonging to two different varieties, to obtain individuals that are heterozygous at many gene loci.
What are gene banks and some examples?
They store genomes, but in their organisms, e.g.
- rare breed farms
- seed banks
- sperm banks
- wild populations of organisms
- botanic gardens
- zoos
What are some ethical considerations of artificial selection?
- domesticated animals retain many juvenile characteristics, making them less able to defend themselves and easy pray
- Livestock are selected to have less fat so might succumb to low temperatures during winter if not housed
- Some dog breeds have susceptibility to disease
- Some coat colours of dogs would fail to camouflage them
- Some selected dog traits might put them at a selective disadvantage if they had to survive in the wild
What is the selecting agents for natural selection?
Environment
What is the phenotypic ratio likely to be if two genes are autosomally linked?
A higher proportion will have the same genotypes to parents. Alleles are not completely re-mixed.
