6.2.6 codominance

Question 1

define codominant

Answer 1

where both alleles present in genotype of a heterozygous individual contribute to individual’s phenotype

Question 2

what is the phenotype of heterozygotes different from

Answer 2

phenotype of homozygotes

Question 3

example of codominant inheritance

Answer 3

= coat colour in shorthorn cattle

• single gene for coat colour has 2 alleles: CR (red) & CW (white)
• cattle that are homozygous for red-coat allele (CR) have red coat
• cattle homozygous for white-coat allele (CW) have white coat
• heterozygous cattle (genotype CRCW) have red/white hairs = roan coat

Question 4

what happens if red/white (roan) shorthorn cattle are interbred

Answer 4

all offspring are roan

Question 5

what happens if red/white (roan) shorthorn cattle are mated

Answer 5

= offspring will show 3 phenotypes in ratio 1 white : 2 roan : 1 red

Question 6

example of codominant inheritance in humans

Answer 6

• MN blood groups
• ABO blood groups
• sickle cell anaemia

Question 7

describe how MN blood groups are an example of codominant inheritance in humans

Answer 7

• controlled by single gene with 2 alleles: GM and GN
• gene codes for certain protein on surface of erythrocytes
• GM allele codes for 1 version of protein
• GN allele codes for slightly different version of protien
  = animals are codominant

Question 8

phenotype of children of couple where one is blood group M and other blood group N

Answer 8

will all have blood group MN

Question 9

probability of inheritance of MN blood group system in children of couple who are both heterozygous & have blood group MN

Answer 9

1 group M : 2 group MN : 1 group N

Question 10

codominance of ABO blood groups

Answer 10

• alleles IA and IB are codominant
• individual genotype of IAIB expresses both and has both types of isoagglutinogen protein on their erythrocytes
• inheritance of blood groups also show dominance as IA and IB are both dominant to allele IO

Question 11

codominance of sickle cell anaemia

Answer 11

• caused by mutation in gene that codes for beta-globin chain of haemoglobin
• mutate allele (HbS)
• normal allele (HbN)
• in heterozygous people, at least half of haemoglobin in RBC is normal and half is abnormal = heterozygous people don’t suck from sickle cell anaemia

Question 12

codominant inheritance in plants

Answer 12

• some types of camellia have red flowers & some have white
• if these are crossed, the offspring will have red/white spotted flowers
• both alleles for gene for petal pigment (PR and PW) are expressed in phenotype of heterozygotes