Inheritance Flashcards
What are polygenic traits
Phenotypes/ traits determined by multiple interacting genes
Eg height determined by 50 genes
What is mendels 1st law in meiosis
2 copies of each gene are seperated into diff gametes
What is mendels second law
Copies of each gene segregate independantly from other genes
Unless linked
Are dominant and recessive alleles expressed in the F1 or F2 generation
Dominant - F1
Recessive - reappear in F2 eg if suppressed by dominant
What are linked genes
Genes on the same chromosome which would not be independantly assorted (inherited together)
In a mono hybrid cross of 2 heterozygotes, what is the genotype ratio and phenotype ratio of offspring
AA= 1 Aa= 2 as = 1. 1:2:1
Phenotype - 3:1. (3 expressed)
What is the genotype ratio in a dihybrid cross
9:3:3:1
If a polygenic trait individual has AAbbCCddEE (tall) what would their gametes be
A b C d E
What would you use instead of punnet squares to determine the offspring of 2 polygenic individuals
Probability instead
Remembering the 1:2:1 ratio of probability of homozygous and heterozygous
How would you work out the probability of eg offspring with AABBCcDDee
AA - 1/4 BB - 1/4 Cc- 1/2 DD- 1/4 ee- 1/4. Multiples = 1/512 probability
Remember 1/4= AA 1/2 = Aa 1/4 = aa
How would fractions differ if you were working out phenotype proportion eg of AbCDe
A= 3/4 (dominant is 3:1) b = 1/4 C = 3/4 D = 3/4 e = 1/4
Recessive is 1/4 chance vs 3/4 for dominant phenotype
Which are more likely - disorders that are single trait or polygenic
Polygenic is more common - more genes involved
What is the ratio in polygenic crosses of genes are not linked
Still 1:2:1 or 3:1
Are populations alleles distributed equally. Ie are dominant always 50% and recessive 50%
No, sometimes In populations it can be 80% dominant and 20% recessive frequency
What is the hardy weinberg principle
Allele frequency’s and genotype will always stay the same in next generation - no alleles disappear
Will always be p2 + 2pq + q2 = 1
What is the hardy Weinberg equation
P2 + 2pq + Q2 = 1
P + Q = 1
P2 = AA genotype
2PQ = heterozygous genotype
Q2 = aa genotype
Why is heterozygous 2PQ?
Because in the genotype ration it’s 1:2:1 and in the cross there are 2 heterozygous individuals
Where does hardy Weinberg principle not apply
Gene flow - movement of Individuals
Genetic drift - small populations - inbreed
Non random mating - eg liked characteristics
Natural selection
All these contribute to genotype frequencies varying
Give some recessive single gene disorders
Cystic fibrosis - CFTR gene
Sickle cell anemia - HBB gene
Albinism
Give some examples of dominant single gene disorders
Polydactyly
Dwarfism
What is the female and male symbols on a pedigree analysis
Male = square Female = circle
If affected = coloured
Why do recessive phenotypes show horizontal patterns on pedigree analysis
Horizontal due to parents not likely affected but carriers
The recessive then become apparent in F2 generation
Why is dominant disorders in pedigree charts called vertical patterns
Every generation is likely to have a person affected due to dominant
Why are men most likely affected by x linked disorders
Only have 1 copy of X and Y doesn’t have all the genes for the disorder
The allele on X is always expressed
Give some X linked disorders that are recessive most likely found in males
Haemophilia and red green colour blindness
If a male was affected by a dominant x linked disorder, who is likely to get it
The affected males pass it to all the females but not sons because sons don’t get X from father
Which offspring get X from which parents
Males get X from mother (could be any X)
Daughters get X from father and mother
What disorders can come from Y linked disorders?
Some to do with male fertility eg testes development
What is a pseudoautosomal disease
Disorders that are from the PAR region of X and Y so can be either linked but depends on where mutation is
Why do some females get both variations of phenotypes eg for colours if the gene is x linked
Because 1 x is inactivated and some parts of the body could have other X inactivated. It can vary = varying colours eg in cats
How do you work out whether a population is in hardy Weinberg equilibrium
Compare the expected genotype values with the observed values of the offspring
If equal = 1:2:1
What is a reciprocal cross
Where the sex linked genotypes are reversed in the second cross to show the sex link
