6.2 Patterns of inheritance Flashcards
define genotype
Genetic makeup of an organism
define phenotype
visible characteristic of an organism
define mutagen
agents which increase the rate of mutation
What are the three types of mutagens
physical agents
chemical agents
biological agents
Give examples of chemical mutagens
mustard gas
nitrous acid
aromatic amines
Give examples of physical mutagens
X-rays
gamma rays
UV light
Give examples of biological mutagens
viruses
food contaminants
What is a persistent mutation
can be transmitted through many generations without change
What is a random mutation
they are not directed by a need on the part of the organism in which they occur
What are the 5 types of chromosome mutations
deletion
inversion
translocation
duplication
non-disjunction
Describe deletion chromosomal mutation
part of a chromosome containing genes and regulatory sequences is lost
Describe inversion chromosomal mutations
A section of chromosome may break off, turn 180 degrees then join again
Why are inversion mutations harmful
although all the genes are still present some may now be too far away from their regulatory nucleotide sequences to be properly expressed
Describe translocation chromosomal mutations
a piece of one chromosome breaks off and then becomes attached to another chromosome
Describe duplication chromosomal mutations
a piece of chromosome may be duplicated and overexpression of genes may be harmful
Describe non-disjunction chromosomal mutations
one pair of chromosomes or chromatids fails to separate leaving one gamete with an extra chromosome.
When fertilized by a normal haploid gamete the resulting zygote has one extra chromosome
Define aneuploidy
the chromosome number is not an exact multiple of the haploid number as chromosomes or chromatids may fail to separate during meiosis - trisomy
Define polyploidy
if a diploid gamete is fertilised by a haploid gamete the resulting gamete the zygote will be triploid - have 3 sets of chromosomes
How dos sexual reproduction contribute to evolution
Genetic variation causes by random fusion of gametes, independent assortment of chromosomes during metaphase 1+2 and allele shuffling during prophase 1
Give examples of variation caused by environmental factors
speaking with an accent
scars
tattoos
Give examples of variation caused by genetic factors
eye colour
blood group
Give examples of variation caused by both environmental and genetic factors
skin colour
weight
height
Define heterozygous
having different alleles at a particular gene locus on a pair of homologous chromosomes
Define homozygous
True-breeding
having identical alleles at a particular gene locus on a pair of homologous chromosomes
define monogenic
determined by a single gene
define sex-linked
gene present on one of the sex chromosomes
define autosome
the pairs are fully homologous - they match in length and contain the same genes at the same loci
why are the sex chromosomes slightly homologous
so that they can pair up during meiosis
How is XX different to XY in terms of alleles
If a female has one abnormal allele on one of her X chromosomes she will probably have a functional allele on the other X chromosome
Whereas f a male inherits the abnormal allele on the X chromosome he will suffer from a genetic disease
Define codominance
where both alleles present in the genotype of a heterozygous individual contribute to the phenotype of an organism
Give an example of codominance
Red and white cows, when they mate can produce roan offspring
Humans can have AB blood types
Give examples of sex linkage
Males suffer from haemophilia A whereas females dont
Theyre are only female tortoise shell cats
Define multiple alleles
characteristic for which there are three or more alleles in the populations gene pool
give an example of a characteristic with multiple alleles
blood group
define autosomal linkage
gene loci present on the same autosome that are often inherited together
what is the mendeleian ratio for monohybrid inheritance
3:1
What are recombinant genes
when there is crossing over between two non-sister chromatids during prophase 1
What increases the chance of recombinant genes
the further the 2 gene loci are away from each other
describe inheritance of autosomally linked genes with no crossing over
they are always inherited as one unit
define dihybrid
involving two gene loci
what is the ratio in a dihybrid cross
9:3:3:1
When in autosomal linkage may there be more than the expected phenotypes
because the genes had crossed over
what can we deduce from dihybrid crosses
The alleles of two genes are inherited independently of each other so each gamete has one allele for each gene locus
during fertilisation any one of an allele pair can combine with any one of another allele pair
How does epistasis differ from dihybrid crosses
although 2 gene loci are involved with epistasis there is only 1 phenotype expressed
Define epistasis
interaction of non-lined gene loci where one masks the expression of the other
What are some examples of genes working antagonistically
recessive and dominant epistasis
Define recessive epistasis
the homozygous presence of a recessive allele at the first locus prevents the expression of the other
what are the second gene loci called in epistasis
they are said to be hypostatic to those at the first locus
What is the ratio of recessive epistasis
9:3:4
Define dominant epistasis
The presence of a dominant allele at the first locus prevents the expression of another allele at the second gene loci
Give an example of recessive epistasis
inheritance of flower colour in salvia
What is the ratio for dominant epistasis
12:3:1
13:3
Give examples of dominant epistasis
feather colour in chicken
why might there be a ratio of 13:3 in dominant epistasis
when the first dominant allele may prevent colour from being present in chicken
but in the second gene some alleles also may prevent colour being deposited as well
basically only two phenotypes able to be expressed white or coloured
How may genes work in a complimentary fashion?
epistasis
genes working to code for two enzymes that work in succession catalysing sequential steps for a metabolic pathway
Give an example of genes working in a complimentary action
coat colour in mice
allele C present means the mice will have a black coat and not albino
paired with allele A will create an agouti pattern
What are the ratios for complimentary gene action
9:7 - 2 phenotypes available for expression
9:3:4
9:3:3:1
What is the null hypothesis for the chi squared test
there is no statistically significant difference between the observed and expected data any difference is due to chance
Define discontinuous variation
where phenotype classes are distinct and discrete and discernible from eachother in a qualitative way
monogenic or epistasis involved
Give an example of discontinuous variation
blood group gender
Describe continuous variation
Where genetic variation shows a range with a smooth gradation between intermediates
polygenic
What are some examples of continuous variation
skin colour
height
tail length
Which variation is able to be influenced by the environment
continuous
Why might a 2:1 ratio be observed if 3:1 was expected
A pair of alleles may be lethal such as DD
Why can some alleles be said to be codominant
both alleles are expressed in the phenotype and neither is dominant or recessive to each other
By observing a graph how would you know that 2 genes are autosomally linked
the homozygous AB or ab are mostly produced from a heterozygous AaBb plant so for the alleles to be inherited together like this the 2 alleles must be on the same autosome
What is a phenotypic trait of a plant that is determined by plants
chlorosis
lack of magnesium in soil
Define speciation
the splitting of a genetically similar population into two or more populations that undergo genetic differentiation and eventually reproductive isolation leading to the evolution of two or more new species
Define allopatric speciation
formation of two different species from one original species due to geographical isolation
Define sympatric speciation
formation of two different species from one original species due to reproductive isolation while the populations inhabit the same geographical location
What are the different isolating mechanisms
geography
reproduction
Describe geographical isolation
populations separated by geographical features such as lakes experience different selective pressures and undergo independent allele changes and each population becomes adapted to its environment
describe reproductive isolation
biological or behavioural changes such as changes in time of activity or change in chromosome number or genitalia lead to speciation from reproductive isolation
How can change in the number of chromosomes lead to reproductive isolation
prevents gamete fusion
zygote is less viable
infertile hybrid offspring
Give example of evolution in action
tolerance to heavy metals in plants
antibiotic resistance
define stabilising selection
normally occurs when the organisms’ environment remains unchanged and the intermediate phenotype is favoured
eg babies with a birth mass closer to 3.5 are more likely to survive
define disruptive selection
where both of the extreme phenotypes are favoured and the intermediate is selected against
define directional selection
if the environment changes there will be a gradual shift over generations of the optimum value of a trait
when does genetic drift arise
after a genetic bottleneck or as a result of the founder effect
Define genetic bottleneck
when population size shrinks then increases again eg after a catastrophic event
What occurs after a genetic bottleneck
genetic diversity within the population will be reduced
loss of advantageous alleles or disproportionate frequency of harmful alleles putting the populations long term survival at risk
When might a genetic bottleneck be advantageous
if ones that survive have a particular advantage for example resistance to a particular pathogen it may improve the gene pool while also shrinking genetic diversity
Define the founder effect
if a new population is established by a very small number of individuals who originate from a larger population the new population is likely to experience loss of genetic diversity
Why might populations that are a result of the founder effect exhibit a loss of genetic diversity
The migrating populations will not be genetically representative of he parent population and so will have a small gene pool
What does the Hardy-Weinberg principle assume
population is large enough to make the sampling error negligible
mating occurs at random
there is no selective advantage for any genotype
no mutation, migration or genetic drift
What 2 equations are used in the Hardy-Weinberg principle
p+q=1
P2+pq+Q2=1
where p=dominant
q=recessive
What is the probability of gametes having two recessive or dominant alleles
p2
or
q2
What is the probability of gametes having heterozygous alleles
2pq
Define artificial selection
selective breeding of organisms where humans are the agents of selection by choosing the desired phenotype and interbreeding phenotypes individually
define inbreeding depression
when related individuals are crossed and the chances of inheriting two copies of a harmful recessive allele are increased
Define hybrid vigour
outcrossing individuals belonging to two different varieties to obtain individuals that are heterozygous at many gene loci
What is the problem associated with artificial selection i plants
Reduces the organisms genetic diversity so they are more likely to succumb to the same pathogen
e.g. if temperatures rise above 30C when wheat crops are flowering then their metabolism is disrupted and seeds do not form
What are some ethical considerations of artificial selection
domesticated animals may be less likely to be able to defend themselves and make them easy prey
lean animals may succumb in winter
desired traits in dogs may be disadvantageous in the wild
