Inheritance

Question 1

How genotype is linked to phenotype

Answer 1

basic:
- genotype refers to the
genetic makeup,
commonly used in ref to the
paired alleles carried by an organism
- that give rise to a phenotype, which is
a physical manifestation of a genetic trait

explanation:
- phenotype depends on the different combination of alleles at each gene locus
- may depend on
interactions between 2 or more genes
- a range of phenotypes may also be controlled by the
combined effect of multiple genes

Question 2

dominant inheritance
(interaction between alleles at one gene locus)

Answer 2

• when genotype consists of either 1 or 2 copies of the dominant allele of a gene
• organism displays the dominant phenotype, as a result of
  the presence of a protein
• as effect of recessive allele is masked by that of dominant allele in a heterozygote

Question 3

recessive inheritance (interaction between alleles at one gene locus)

Answer 3

• when genotype consists of 2 copies of recessive allele of gene
• organism displays the recessive phenotype, as a result of
  the lack of protein
  (- which could result in lethality if protein is critical to embryonic development )

Question 4

incomplete dominance (interaction between alleles at one gene locus)

Answer 4

• when genotype has 2 incompletely dominant alleles
• organism displays an intermediate phenotype

Question 5

co-dominance (interaction between alleles at one gene locus)

Answer 5

• when genotype has 2 co-dominant alleles,
• organism simultaneously expresses the phenotypes of both types of homozygotes

Question 6

epistatic gene interaction (interaction between 2 or more genes)

Answer 6

allele(s) of epistatic gene mask the effect of alleles of hypostatic gene

Question 7

combined effect of multiple genes / polygenes

Answer 7

• genes act of phenotype in an additive manner
• and effects of single genes are too slight to be detected
• effect: leads to continuous variation of trait in phenotype

Question 8

effect of temp on coat /fur colour in Himalayan rabbits

Answer 8

• Himalayan rabbits are homozygous for Ch allele of tyrosinase gene
• which codes for a heat-sensitive form of enzyme tyrosinase
• which is needed for melanin production resulting in black fur
• however, heat-sensitive tyrosinase is active only when air temp is below 33 ºC
• thus black fur only grow in parts of the body that are cool enough (e.g. extremities)

Question 9

Effect of diet on differentiation in honey bees

Answer 9

• queen bees and workers bees have the same mount of genetic material
• but are phenotypically different;
• in which workers are infertile while queen is fertile
• due to difference in diet of bee larvae;
• in which larvae destined to be workers are switched to a diet containing honey and pollen
• while those destined to be the queen is fed with royal jelly
• high content of protein in royal jelly stimulate formation and maturation of the female repro system

Question 10

how chi-squared test results can support a sample being an example of (autosomal) linkage

Answer 10

• X^calc > X^crit
• probability that chance alone is reason for difference between observed and expected results is less than 5%
• observed results do not fit expected 9:3:3:1 phenotypic ratio (i.e. Mendelian inheritance)
• with there being a larger no of parental phenotypes than recombinant phenotypes

Question 11

explaining the mode of inheritance

Answer 11

• autosomal or sex-linked
  
  • sex-linked: father with disease would produced daughters that all have the disease
  • autosomal: prove that it is not sex-linked
• recessive or dominant
  
  • recessive: both parents which have the disease should have children which all have the disease
  • dominant:
    
    • prove that it is not recessive
    • no skipping of generations

use specific context for evidence
e.g. if given pedigree,
II-6 who has red hair has a daughter, III-5 who does not have red hair