Patterns of inheritance Flashcards
What is continuous variation
Individuals in a population vary within a range
What is discontinuous variation
When there are two or more distinct categories
Define allele
Different versions of genes
How does meiosis make gametes with a unique assortment of alleles
Through crossing over and independent assortment of chromosomes
What is variation in phenotype
Phenotypic variation
What is polygenic characteristics and what type of variation are they normally
A characteristic influenced by two or more genes typically continuous variation
What is monogenic characteristics and what type of variation are they normally
Characteristics controlled by only one gene typically monogenic
Define gene
A sequence of bases on a DNA molecule that codes for a protein resulting in a characteristic
Define genotype
The alleles and organism has e.g BB
Define phenotype
The characteristics the alleles produce e.g brown eyes
Define dominant
An allele whose characteristic only appears in the phenotype even when there is only one copy shown by a capital letter
Define recessive
An allele whose characteristic only appears on the phenotype if two copies are present shown by lower case letters
Define codominant and an example
Alleles that are both expressed in the phenotype - neither one is recessive. Such as sickle cell anaemia
Define locus
The fixed position of a gene on a chromosome. Alleles of a gene are found at the same locus on each chromosome in a pair
Define homozygote
An organism that carries two copies of the same allele
Define heterozygote
An organism that carries two different alleles
Define carrier
A person carrying an allele which is not expressed in the phenotype but that can be passed on to offspring
What is monogenic inheritance
Inheritance of a characteristic controlled by a single gene
What does monogenic crosses show
The likelihood of different alleles of that gene being inherited by offspring of particular parents
How to draw out a monogenic cross diagram steps
1) Parents genotypes
2) Gametes alleles
3) Possible genotypes of F1 offspring
4) Gametes alleles
5) Possible genotypes of F2 offspring
6) Phenotypes
7) Ratio in F2 offspring
What is dihybrid inheritance
The inheritance of two characteristics which are controlled by different genes
Expected phenotypic ratio of monogenic cross for F2 generation
3:1
Expected dihybrid ratio of monogenic cross for F2 generation
9:3:3:1
Expected phenotypic ratio of codominant cross for F2 generation
1:2:1
Why wont the expected ratios from different types of genetic crosses occur
Sex linkage, autosomal linkage or epistasis
What is a sex linked characteristic
When the allele that codes for the characteristic is located on a sex chromosome (X/Y)
Why are males more likely to show recessive phenotypes that are sex linked than females
They only have one X chromosome and only one allele for sex-linked genes. As they only have one copy they express the characteristic of this allele even if it is recessive. Such as colour blindness
What is an autosome
Any chromosome that is not a sex chromosome
What are autosomal genes
Genes located on autosomes
Genes on the same autosome are… and why
Linked - they will stay together during independent assortment of chromosomes in meiosis I and their alleles will be passed on to the offspring together unless crossing over splits them up before.
What does the closer the genes on an autosome mean
They are more closely linked as crossing over is less likely to split them up
Why won’t you see the expected phenotypic ratio of a cross that are autosomally linked
The two autosomally linked alleles are inherited together so there is a higher proportion of the offspring that will have their parents genotype and phenotype.
What is epistasis
When the allele of one gene masks the expression of the alleles of other genes such as hair colour and baldness
A dihybrid cross produces the phenotypic ratio of 9:3:4 in the F2 generation. What does this indicate about the genes involved
It involves a recessive epistatic allele
A dihybrid cross produces the phenotypic ratio of 12:3:1 in the F2 generation. What does this indicate about the genes involved
Crossing a homozygous recessive with a homozygoua dominant
What can the chi squared test be used for
To see if the results of an experiment support a theory
What is a null hypothesis
There is no significant difference between the observed and expected results - results are due to chance
How to work out the Chi-Squared Value
1) Work out the expected value for each phenotype
2) Record the actual number of offspring recorded
3) Subtract the expected result from the observed result
4) Square this number and divide by the expected result
5) Add all the numbers together to get the sum
X^2 = (O-E)^2 / E
What is the critical value
The value of X^2 that corresponds to a 0.05 (5%) level of probability that the difference between the observed and expected results is due to chance
When can the null hypothesis be rejected
If the X^2 value is larger or equal to the critical value then there is a significant difference
When can the null hypothesis be accepted
If the X^2 value is smaller than the critical value and then there is no significant difference
What are degrees of freedom
The number of phenotypes/classes
