Inheritence Flashcards
Def of autosomal allele
All chromosomes except the X & Y
Dihybrid cross
Inheritance of two genes at the same time
Height and petal colour are controlled by separate genes on different chromosomes
Height gene: tall (T) and short (t)
Petal Colour: red (R) and white (r)
1) draw the possible gamete’s produced by heterozygous plant
2) show the results of crossing over 2 heterozygous plants
3) list the 4 possible phenotypes and the ratio they are found in of the offspring
1) possible gametes
TR Tr tR tr
2) draw a dihybrid cross with the 4 gamates on the top and the bottom.
(See notes for more info)
3) possible phenotypes
Tall & Red - TTRR , TTRr, TtRR, TtRr
Small & White - ttRr, ttRR
Tall & White - TTrr, Ttrr
Small & Red - ttrr
Ratio of phenotypes is 9:3:3:1
Coat texture and colour are controlled by separate genes on different chromosomes
Texture : rough (R) and smooth (r)
Colour: black (B) and white (b)
1) show the results of crossing over a rough, black male (RrBb) and smooth,black female (rrBb)
2) list the 4 possible phenotypes and the ratio they are found in of the offspring
Males gamates= RB, Rb, rB, rb
Female gametes = rB, rb
1) Use dihybrid cross (see notes for more info)
2) rough, black - RrBB, RrBb
Rough, white - Rrbb
Smooth, black - rrBB, rrBb
Smooth white - rrbb
Ratio = 3:1:3:1
Def of epistasis
Alleles of one gene are needed for expression of a second gene
(The relationship between genes where the allele of one gene affects the expression of different gene)
Def of genotype
All the alleles that an organism carries on its chromosome
Def of Phenotypes
Observable characteristics of an organism which result of the genotype as well as environmental factors
Def of dominant allele
Only 1 allele is required for the characteristic to be expressed in the phenotype.
Def of recessive
The characteristic is only expressed if there is no dominant allele present in order for the phenotype to be expressed
Def of Codominant
Both alleles are expressed equally and contribute to the phenotype, with there being a blend of the 2 characteristics or both seen together
Def of allele
An alternative form of a gene
Def of locus
The specific position of the gene on the chromosome
Def of monohybrid inheritance
When a phenotype or trait is controlled y a single gene
Draw a monohybrid cross
E.g if the colour of peas
Is green (G) and yellow (g)
And parents are green homozygous
And yellow homozygous
See notes for cross
A ratio of 3:1 green: yellow
Def of sex linkage alleles
The expression of an allele depends on the gender of the individual as the gene is located on a sex chromosome
Def of autosomal linkage
Two or more genes are on the same autosomal chromosome.
autosomal - a gene that is not on the sex chromosomes
Def of epistasis
When one gene locus affects the other gene locus
(One gene loci can either mask or suppress the expression off another gene locus)
Recessive epistasis occurs when ….
The presence of a recessive allele prevents the expression of another allele at a second locus.
Recessive epistasis gives the ration 9:3:4
Dominant epistasis occurs when …
A dominant allele at one locus completely masks the alleles at a second locus.
Dominant epistasis gives a ratio of 12:3:1
How would you use X2 test to compare observed phenotypes and expected?
https://www.gstatic.com/education/formulas2/553212783/en/chi_squared_test.svg
X2 = sum of (observed - expected)^2
———————————-
Expected value
Def of allele frequency
The number of times an allele appears within a population’s gene pool
Def of gene pool
All the different variations of genes in individuals that make up a population
Def of population
A group of organisms of the same species occupying a particular space at a particular time that can potentially interbreed
What are the hardy-Weinberg laws
p +q =1
p^2 + 2pq + q^2 = 1
Where p = frequency of dominant allele
q = frequency of recessive allele
pq= frequency of heterozygous
What is hardy-Weinberg principle
A mathematical model, which predicts that allele frequencies will not change from generation to generation
What conditions must be met for Hardy-Weinberg principle to be true
1) population is large
2) mating is random
3) no mutations occur
4) no immigration or emigration of the population
5) all genotypes are equally fertile so that no natural selection takes place
in genetic crosses, suggest why observed phenotypes are not the same as expected ratios
4 marks
- Small sample size
- Linked genes
- Random fertilisation of gametes
- Selectional advantages
what is meant by term phenotype
The observable characteristics due to an individual’s genotype and environmental interactions
What is genetic diversity
The measure of the variation of alleles within a population
Def of gene pool and allele frequency
Gene pool = Total number of alleles in a given population
Allele frequency = number of alleles for a particular trait in a population
outline evidence that suggests all modern humans are descended from a relatively small number of people
There is much less genetic variation within the human population than would be expected for a population of 8 billion
*explain why this event is referred to as a genetic bottleneck
Genetic bottleneck means a large proportion of a population dies out leaving a small population with less genetic diversity (less variation/ fewer alleles)
what is the founder effect
When a population is descended from a very small starting population following genetic bottleneck or migration to a new location
-this results in low genetic diversity
Why is genetic diversity important in a population
Variation means there will always be some organism within population with ideal combination of alleles to survive and reproduce
- allows species to adapt to any environmental change
- ensure survival of species
Def of speciation
The process by which new species arise after a population because separated and cannot interbreed
Stages a population must go through to become a new species
1) reproductive isolation
a single population becomes divided and prevented from interbreeding
2) natural selection
different selection pressures act on each population causing new varieties each with slightly different alleles and phenotypes
3) genetic drift
over time each variety acquires different random mutations & chromosomes rearrangement = genetically distinct
4) speciation
each variety eventually becomes different species when they can no longer interbreed
5) change in allele frequency
Frequency of alleles changes, increasing if selected for and decreasing if selected against
What are the 2 types of speciation
Allopathic speciation
- process of new species arising because of physical/geographic barrier separating them
Sympatric
- process of new species arsing when 2 populations within same area become reproductively isolated
Def isolating mechanism
A factor that prevent varieties/ sub-populations from interbreeding
Def of genetic drift
Variation in allele frequency of small populations due to chance/ random mutations and different selection pressures
