Inheritance

Question 1

What are polygenic traits

Answer 1

Phenotypes/ traits determined by multiple interacting genes

Eg height determined by 50 genes

Question 2

What is mendels 1st law in meiosis

Answer 2

2 copies of each gene are seperated into diff gametes

Question 3

What is mendels second law

Answer 3

Copies of each gene segregate independantly from other genes

Unless linked

Question 4

Are dominant and recessive alleles expressed in the F1 or F2 generation

Answer 4

Dominant - F1

Recessive - reappear in F2 eg if suppressed by dominant

Question 5

What are linked genes

Answer 5

Genes on the same chromosome which would not be independantly assorted (inherited together)

Question 6

In a mono hybrid cross of 2 heterozygotes, what is the genotype ratio and phenotype ratio of offspring

Answer 6

AA= 1 
Aa= 2 
as = 1.    1:2:1 

Phenotype - 3:1. (3 expressed)

Question 7

What is the genotype ratio in a dihybrid cross

Answer 7

9:3:3:1

Question 8

If a polygenic trait individual has AAbbCCddEE (tall) what would their gametes be

Answer 8

A 
b
C
d
E

Question 9

What would you use instead of punnet squares to determine the offspring of 2 polygenic individuals

Answer 9

Probability instead

Remembering the 1:2:1 ratio of probability of homozygous and heterozygous

Question 10

How would you work out the probability of eg offspring with AABBCcDDee

Answer 10

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

Question 11

How would fractions differ if you were working out phenotype proportion eg of AbCDe

Answer 11

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

Question 12

Which are more likely - disorders that are single trait or polygenic

Answer 12

Polygenic is more common - more genes involved

Question 13

What is the ratio in polygenic crosses of genes are not linked

Answer 13

Still 1:2:1 or 3:1

Question 14

Are populations alleles distributed equally. Ie are dominant always 50% and recessive 50%

Answer 14

No, sometimes In populations it can be 80% dominant and 20% recessive frequency

Question 15

What is the hardy weinberg principle

Answer 15

Allele frequency’s and genotype will always stay the same in next generation - no alleles disappear

Will always be p2 + 2pq + q2 = 1

Question 16

What is the hardy Weinberg equation

Answer 16

P2 + 2pq + Q2 = 1

P + Q = 1

P2 = AA genotype

2PQ = heterozygous genotype

Q2 = aa genotype

Question 17

Why is heterozygous 2PQ?

Answer 17

Because in the genotype ration it’s 1:2:1 and in the cross there are 2 heterozygous individuals

Question 18

Where does hardy Weinberg principle not apply

Answer 18

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

Question 19

Give some recessive single gene disorders

Answer 19

Cystic fibrosis - CFTR gene
Sickle cell anemia - HBB gene
Albinism

Question 20

Give some examples of dominant single gene disorders

Answer 20

Polydactyly

Dwarfism

Question 21

What is the female and male symbols on a pedigree analysis

Answer 21

Male = square 
Female = circle 

If affected = coloured

Question 22

Why do recessive phenotypes show horizontal patterns on pedigree analysis

Answer 22

Horizontal due to parents not likely affected but carriers

The recessive then become apparent in F2 generation

Question 23

Why is dominant disorders in pedigree charts called vertical patterns

Answer 23

Every generation is likely to have a person affected due to dominant

Question 24

Why are men most likely affected by x linked disorders

Answer 24

Only have 1 copy of X and Y doesn’t have all the genes for the disorder

The allele on X is always expressed

Question 25

Give some X linked disorders that are recessive most likely found in males

Answer 25

Haemophilia and red green colour blindness

Question 26

If a male was affected by a dominant x linked disorder, who is likely to get it

Answer 26

The affected males pass it to all the females but not sons because sons don’t get X from father

Question 27

Which offspring get X from which parents

Answer 27

Males get X from mother (could be any X)

Daughters get X from father and mother

Question 28

What disorders can come from Y linked disorders?

Answer 28

Some to do with male fertility eg testes development

Question 29

What is a pseudoautosomal disease

Answer 29

Disorders that are from the PAR region of X and Y so can be either linked but depends on where mutation is

Question 30

Why do some females get both variations of phenotypes eg for colours if the gene is x linked

Answer 30

Because 1 x is inactivated and some parts of the body could have other X inactivated. It can vary = varying colours eg in cats

Question 31

How do you work out whether a population is in hardy Weinberg equilibrium

Answer 31

Compare the expected genotype values with the observed values of the offspring

If equal = 1:2:1

Question 32

What is a reciprocal cross

Answer 32

Where the sex linked genotypes are reversed in the second cross to show the sex link