The determination of sex in domestic turkeys is different from that in humans. The sex chromosomes in turkeys are named Z and W. Male turkeys are ZZ and female turkeys are ZW. The gene for feather colour is located only on the Z chromosome. • The dominant allele codes for bronze feathers. • The recessive allele codes for brown feathers.

Mark scheme

Marking points from the official mark scheme (Oct/Nov 2022). The mark or mark type is shown in brackets.

1. [2]
2. dominant – allele always has effect on phenotype / allele expressed in homozygote and heterozygote / allele always expressed;
3. recessive - allele only has effect on phenotype if dominant allele absent / only expressed in homozygote ;
4. [5]
5. symbols ZB = allele for bronze feathers Zb = allele for brown feathers ;
6. parents phenotypes bronze male brown female
7. parents genotypes ZBZb X ZbW ;
8. gametes ZB Zb Zb W ;
9. offspring genotypes ZBZb ZBW ZbZb ZbW;
10. offspring phenotypes bronze male bronze female brown male brown female;
11. ecf for putting allele on W
12. ecf for incorrect symbols with no superscript
13. ecf for different letters for alleles
14. no sex chromosomes = no marks
15. [3]
16. 1 cross with brown female ;
17. 2 if all offspring bronze then male is, homozygous / ZBZB ;
18. 3 if (some offspring are bronze and) some are brown then male is, heterozygous / ZBZb ;