Unit 7: Inheritance and Evolution Flashcards
what is codominance?
Where both alleles are expressed in the phenotype
Give an example of a co-dominant genotype
Red flower - C^R C^R
What are multiple alleles?
There are more than two alleles of a particular gene
what are autosomes?
22 pairs of non-sex chromosomes
What are the sex chromosomes?
XX & XY
What are sex linked genes?
where the gene is carried only on one type
of sex chromosome (usually X)
how can you prove that an allele is recessive?
Two unaffected parents will have an affected child
- parents must therefore be heterozygous (carriers)
How can you prove that an allele is not sex linked when it is known to be recessive?
Unaffected parents who have an affected daughter
- Their father would pass on the dominant allele on the X so all daughters will be unaffected
How can you prove that an allele is dominant?
Two affected parents who have unaffected children
- Both parents must be heterozygous and pass on the recessive alleles
how can you prove that an allele is not sex linked when it’s known to be dominant?
2 affected parents will have an unaffected daughter
- The father would pass on the dominant allele on his X so all daughters would be affected
What is dihybrid inheritance?
refers to inheritance of two different characteristics
each characteristic is controlled by a different gene
what is a phenotype
appearance of a characteristic
what is a genotype
alleles present in an organism (e.g BB)
why may the observed and expected ratios in a dihybrid cross not be similar?
small sample size
random fertilisation of gametes
epistasis
linked genes
What are autosomal linked genes
genes present on the same chromosome at different loci
Why are there fewer combination of alleles in linked genes?
linked genes are inherited together and theres no independent assortment
- this leads to reduced variety of genes
Why is the number of recombinant alleles low?
because crossing over is rare
What is Epistasis?
when two or more genes interact to contribute to a phenotype
the allele of one gene affects/masks the expression of another at another locus
In what conditions does Epistasis occur?
in metabolic pathways controlled by enzymes coded for by different genes
What happens if the enzyme in epistasis is non functional?
the pathway comes to a halt
What is a species?
a group of organisms that can reproduce and produce fertile offspring.
What is a population?
a group of organisms of the same species occupying a particular space
What is a Gene pool?
all the alleles of all the genes of all the individuals in a population
What is Allelic frequency?
the number if times an allele of a particular gene occurs within the gene pool
What is the Hardy-Weinberg principle?
mathematical model which predicts that allele frequencies in a population will not change from generation to generation
What are the conditions for the Hardy-Weinberg principle?
- large and isolated population
- mating is random
- no mutations of the gene occurs
- no selection
Im a scenario where there are only 2 alleles for a gene what should the frequency of these alleles equal?
1.0
(100% of the population)
What is the equation for frequency of different genotype for an allele?
p^2 + 2pq + q^2 = 1.0
What does P^2 represent in the Hardy-Weinberg principle?
frequency of the dominant allele
What does q^2 represent in the Hardy-Weinberg principle?
frequency of the recessive allele
What is the Chi-squared test?
Determines a statistical difference between the expected and observed ratios from the result of a genetic cross
What is a null hypothesis?
assumes there will be no significant difference between observed and expected frequency
What is the equation for Chi-squared (X^2)
X^2 = sum ( (O-E)^2 / E )
If the X^2 is below the critical value..
the null hypothesis is accepted and there is NO significance
the probability that the difference is due to chance is more than 5%
If X^2 is above or the same as the critical value..
the null hypothesis is rejected and there is a significance
the probability that the difference is due to chance is less than 5%
How do you calculate the degree of freeodm?
number of categories - 1
What causes genetic variation?
- gene mutations
- crossing over
- independent segregation of chromosomes
- random fertilisation
What are the properties
of characteristics influenced by genetic factors not environmental ?
- controlled by two genes
- expressed as phenotypes with no intermediates
- represented as distinct groups on a bar chart/pie graph
What are the properties of characteristics that are significantly influenced by the environment?
- polygenic, controlled by many genes
- no separate categories, have range of intermediates
- produce a curve of normal distribution on graph
What are selection pressures?
preditation
disease
competiton
What is stabilising selection?
environment isn’t changing organisms with the mean characteristics are selected for
organisms with extremes (very high/low) are less likely to survive
What is directional selection?
environment is changing and selects for organisms with alleles for a phenotype towards the extreme range
What is Disruptive selection?
selects phenotypes at the two extremes at the expense of intermediate phenotypes
most important selection to bring out evolutionary change
What is speciation
the evolution of new species from existing ones
What is allopatric speciation?
a population splits into groups by geographical isolation which prevents breeding
different selection pressures occur in the new different environments and natural selection occurs resulting in new phenotypes
allelic frequenciesbecome different and organisms become two different species
What is sympatric speciation?
(no geographical isolation)
- involves disruptive selection
mutations cause organisms to not reproduce with organisms of the same species causing reproductive isolation
results in changes in courting behaviour
even though they live in the same habitat different gene pools occur
What is genetic drift?
By chance the allele of a particular gene is passed on to the offspring more often than
other alleles
has greater effect in small populations where there is a smaller variety of alleles in the gene pool, so
speciation occurs more rapidly
