Mendelian Inheritance

Question 1

What was Mendel’s success based on?

Answer 1

1. Used a self-fertilising plant
2. CHose traits that had clear cut alternative forms
3. Started his experiments with pure-breeding lines
4. Did reciprocal crosses to eliminate maternal effects
5. Analysed a large number of plants
6. All plants were planted under same conditions

Question 2

The ratio for 2 genes

Answer 2

9:3:3:1

Question 3

How many gametes are there for 3 genes?

Answer 3

2^3 gametes

Question 4

What are the ultimate source of new alleles?

Answer 4

Mutations

Question 5

What is incomplete dominance?

Answer 5

Situation where F1 phenotype is halfway between those of parents

Question 6

Describe familial hypercholesterolemia

Answer 6

Causes very high levels of LDL at a young age: caused by a mutation in the gene that codes for LDL receptor.

Homozygous FH patients may have heart attacks in their 20s. Heterozygous individuals have 50% of the LDL recpetors

Question 7

What are the phenotypic/genotypic ratios in incomplete dominance?

Answer 7

Genotypic and phenotypic: 2:1:1

Question 8

What is the explanation of the round & wrinkled peas?

Answer 8

INCOMPLETE DOMINANCE

in round peas, the dominant allele is a wt for an enzyme that catalyses the conversion from unbranched to branched starch: high levels of glucose lets water in. Wrinkled peas the enzyme is not functional

Question 9

What is codominance?

Answer 9

2 alleles at a locus produce different and detectable gene products in heterozygote

Question 10

What is an example of codominance?

Answer 10

Human blood groups

Question 11

What is overdominance?

Answer 11

Heterozygotes are more vigorous than both the corresponding homozygotes

Question 12

What are examples of overdominance?

Answer 12

Sickle cell anemia: confers heterozygote advantage

Question 13

What are lethal alleles?

Answer 13

Alleles that cause an organism to die only when present in the homozygous state: causes the ratio to be 2:1 instead of 3:1

Question 14

What is epistasis?

Answer 14

Interaction of genes: effect of one gene pair masks or modifies the effect of another gene pair

Question 15

How are the RBCs in heterozygotes for sickle cell anemia?

Answer 15

Are likely to rupture when infected by plasmodium preventing the propagation of the parasite

Question 16

Examples of epistasis

Answer 16

1. Agouti mice
2. Bombay pedigree

Question 17

What is the Bombay pedigree?

Answer 17

When there is no fucose transfer, there is no H substance: when the H substance is not present the A and B antigens can not be expressed so the phenotype will be O

Question 18

What is pleiotrophy?

Answer 18

One gene has effects on multiple phenotypes

Question 19

What are examples of pleiotrophy?

Answer 19

1. Cystic fibrosis: multiple systems affected
2. Marfan syndrome
3. Parphyria variegata

Question 20

What is penetrance?

Answer 20

the % of individuals that show at least some degree of expression of the genotype

Question 21

What is expressivity?

Answer 21

The range of expression of the phenotype [can be the result or both genetic background differences or environmental effects]

Question 22

What is incomplete penetrance with variable expressivity?

Answer 22

Identical known genotypes produce a broad range of phenotypes

Question 23

What are modifier genes?

Answer 23

Gene interacting with non-allelic gene modifying the phenotype associated with the expression of alleles of the gene in a milder way

Question 24

Sex-limited inheritance

Answer 24

Specific phenotype linked to one sex

Question 25

Sex-influenced inheritance

Answer 25

Sex influences expression of phenotype but not limited to one sex or another i.e. hormones

Question 26

How is pattern baldness controlled?

Answer 26

Sex-influenced: in BB women is reduced and occurs later in life, Bb women not affected men are affected

Question 27

Sex-limited trait

Answer 27

expressed in one sex but not the other- due to anatomical and physiological limitations