genetics and inheritance

Question 1

Explain codominance and multiple alleles with reference to the inheritance of the ABO blood group phenotypes – A, B, AB, O, gene alleles IA, IB and i.

Answer 1

Codominance– alleles that are both expressed if they are present together in a heterozygous organism eg. sickle cell anaemia, AB blood group phenotype.

Question 2

Describe the determination of sex in humans – XX and XY chromosomes.

Answer 2

• inheritance of sex is controlled by sex chromosomes
• each of us has 1 pair of sex chromosomes (XX - email; XY - male)
• All female gametes carry an X chromosome while half of the male gametes carry the X chromosome and half carry a Y chromosome
• The sex of offspring in humans is decided by which tupe of male gamete fuses with the female gamete

Question 3

factors that may increase the rate of mutation

Answer 3

• Radiation
  -Chemicals

Question 4

Difference between continuous and discontinuous variation and examples of each (characteristics)

Answer 4

Discontinuous variation: Characteristic concerned is 1 or 2 or more discrete types with no intermediate forms e.g. human ABO blood grouping, tall or dwarf. rolling of tongue
Continuous variation: Results in a continuous distribution of values e.g. height in human, body weight, skin colour

Question 5

Difference between continuous and discontinuous variation and examples of each (how many genes)

Answer 5

discontinuous variation: controlled by one gene with 2 alleles
continuous variation: controlled by a number of genes = polygenes – effect of any one of these genes make a very insignificant effect on the phenotype, but the combined effect of all the genes in the poly gene is to produce infinite variety among the offspring

Question 6

Difference between continuous and discontinuous variation and examples of each (varieties)

Answer 6

Discontinuous variation: clear-cut differences in an inherited characteristic with no intermediate form & no overlap between both phenotypes
Continuous variation: no clear-cut differences with an infinite varieties

Question 7

Difference between continuous and discontinuous variation and examples of each (environment)

Answer 7

Discontinuous variation: unaffected by environmental conditions/ factors
Continuous variation: affected by environmental conditions/factors

Question 8

genetic basis of continuous variation and discontinuous variation

Answer 8

continuous variation: many additive genes control a characteristic
discontinuous variation: one or few genes control a characteristic

Question 9

Law of segregation

Answer 9

during meiosis, pairs of alleles have to separate so that each cell has 1 allele per pair
allele pairs separate independently during the formation of gametes

Question 10

Law of independent assortment

Answer 10

during meiosis, the separation of one pair of alleles is independent of the separation of another pair of alleles.
the inheritance of 1 character has no effect on the inheritance of another

Question 11

Explain how the environment may affect the phenotype as a form of epigenetics, including how diet affects the differentiation of honey bees.

Answer 11

Phenotype = genotype + influences of the environment
Colony of honey bees: 3 phenotypes (drones, workers, queen); 2 genotypes
Drones are the community’s males – develop from unfertilised egg (genotype is haploid)
Queen and workers - develop from fertilised eggs and have identical genotypes
Queen – a much larger organism (differs from her worker only by diet she is fed in the larval stage) 🡪 her protein-rich food is not given to the larvae that will be workers, makes a significant difference in their phenotypes