3.3.1 Loci, gene linkage and sex linkage Quiz: Pearson Edexcel Biology, Unit 3

The 20 questions

1. What term describes the specific position of a gene on a chromosome?

   • Allele
   • Chiasma
   • Locus
   • Centromere

2. What term describes genes located on the same chromosome that are inherited together?

   • Epistasis
   • Sex linkage
   • Autosomal linkage
   • Codominance

3. Which process during meiosis breaks the linkage between genes on the same chromosome?

   • DNA replication
   • Crossing over
   • Independent assortment
   • Random fertilisation

4. Sex-linked genes in humans are usually located on which chromosome?

   • The Y chromosome only
   • Chromosome 21
   • The X chromosome
   • Mitochondrial DNA

5. Haemophilia is an example of which type of condition?

   • Y-linked
   • Autosomal dominant
   • Mitochondrial
   • X-linked recessive

6. A carrier woman (X^c X) for colour blindness has a colour-blind husband (X^c Y). What is the probability that a son is colour blind?

   • 1
   • 0
   • 1/2
   • 1/4

7. Why are males more likely to express X-linked recessive phenotypes than females?

   • One Y chromosome
   • No X chromosome
   • One X chromosome
   • Two X chromosomes

8. Recombinant gametes are produced most frequently when linked genes are located where?

   • Far apart
   • On different autosomes
   • On different centromeres
   • Close together

9. A recombination frequency of 4% indicates that two linked genes are what?

   • Completely unlinked
   • Far apart
   • Close together
   • On separate chromosomes

10. What proportion of a father's daughters will inherit his X-linked allele?

    • 50%
    • 100%
    • 25%
    • 0%

11. Which offspring phenotypes are most common in a test cross involving linked genes?

    • Recombinant phenotypes
    • Mutant phenotypes
    • Equal phenotype proportions
    • Parental phenotypes

12. A test cross yields a 46:4:4:46 phenotypic ratio. What is the percentage of recombinants?

    • 4%
    • 46%
    • 8%
    • 92%

13. What term describes a locus having two different alleles on homologous chromosomes?

    • Heterozygous
    • Homozygous
    • Hemizygous
    • Epistatic

14. A female carrier of haemophilia (X^H X^h) has a normal husband (X^H Y). What is the probability that a daughter is affected?

    • 1
    • 0
    • 1/2
    • 1/4

15. Why are Y-linked inherited traits expressed only in biological males?

    • Y alleles are recessive
    • Females lack X chromosomes
    • Males lack X chromosomes
    • Females lack Y chromosomes

16. To which of his children does a father pass an X-linked allele?

    • Sons only
    • Firstborn child
    • Daughters only
    • All children

17. How many alleles of a given gene does a diploid cell carry at one locus?

    • Two
    • Three
    • Four
    • One

18. A 50% recombination frequency between two loci indicates that the genes behave as what?

    • Tightly linked
    • Epistatic
    • Sex-linked
    • Unlinked

19. Why might a female heterozygous for an X-linked recessive allele not express the trait?

    • Autosomal linkage
    • Histone methylation
    • X-chromosome inactivation
    • Gene duplication

20. A recessive X-linked allele is written X^r and the normal allele X^N. Which genotype describes a female who expresses the condition?

    • X^r X^r
    • X^r Y
    • X^N Y
    • X^N X^r

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