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Biology µGCSE:

Codominance
+ Sex-linked Inheritance

 

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10 minutes maximum! (can you do it in 5?)

1+2: In some flowering plants there is one gene for flower colour but neither allele is dominant to the other. When red flowered plants RR are crossed with white flowered plants WW all the offspring are Pink, as shown in the genetic diagram.

  male gametes
W W
female
gametes
R RW RW
R RW RW
 

1. When two of the pink flowers RW are crossed with each other what will be the possible phenotypes and genotypes of the offspring?

  • A. All Pink
  • B. 2 Red : 2 White
  • C. 3 Red : 1 white
  • D. 1 Red : 2 Pink : 1 White
2. Which statement best describes the alleles for flower colour?
  • A. Red allele is dominant to the white allele
  • B. The red and white alleles are codominant
  • C. The white allele is sex linked
  • B. White allele is dominant to the red allele

3-6: In humans there are 4 different blood groups, A, B, AB and O. The alleles for Blood group A, IA and B, IB are co-dominant.  Both IA and IB alleles are dominant to the allele for blood group O, IO.

 
3. How many different alleles are there for human blood groups?
  • A. One
  • B. Two
  • C. Three
  • D. Four
4. In determining the phenotype of a person for blood groups, ....
  • A. IA is dominant over IB
  • B. IO is dominant over IA
  • C. IO is recessive to both IA and IB
  • D. IB is dominant over IA

5. A woman is heterozygous for blood group A and her husband is blood group O. Which of the following is the correct genotype of the couple?

  Genotype
Woman Man
A IAIA IOIO
B IAIO IOIO
C IAIB IOIO
D IOIO IAIO
6. The man claims that a child born to the woman is his son. The child has blood group AB.  Which of the following statements cannot be true?
  • A. The boy’s genotype is IAIB
  • B. The woman is the child’s mother
  • C. The man is the child’s father
  • D. The boy’s phenotype is blood group AB

7-9.  Red green colour blindness is a sex- linked characteristic.

Roy and Mary had 5 children. Use the pedigree chart to answer the questions.

Inherited colour blindness diagram

7. What is Mary’s phenotype?
  • A. Carrier female with normal vision
  • B. Colour blind female
  • C. Normal vision male
  • D. Colour blind male
8. Alison has two children with a man who does not have colour blindness.

Which of the following statements about Alison is not true?

  • A. She is red green colour blind
  • B. She is heterozygous for the colour-blind gene
  • C. Two of her brothers are red green colour blind
  • D. She received the recessive allele for colour blindness from her mother.
9. What is the chance that Alison’s daughter will be a carrier for red green colour blindness?
  • A. 0%
  • B. 25%
  • C. 50%
  • D. 100%

10. The allele for colour blindness may have been caused by a mutation. A mutation is ...

  • A. a frequent random change in genetic material that can be inherited.
  • B. a rare random change in genetic material that cannot be inherited.
  • C. always bad, causing harm to the organism.
  • D. a rare random change in genetic material that can be inherited.