Theory question 104
Mendelian InheritanceA tall man and a tall woman have a child that is short.
(a)(i) State two factors that could be responsible for the height of their child. (ii) With the aid of a genetic diagram, give the genotypes of their offspring if the allele for tallness is T. (iii) Give the genotype of the child that is short.
(b)(i) Define the term genotype. (ii) List two factors that could cause variation in character within the same species.
(c)(i) Define the term allele. (ii) State two differences between genotype and phenotype.
Table columns: Genotype | Phenotype
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(a)(i) Heredity (both parents carry the recessive allele for shortness) and environmental factors such as poor nutrition or disease.
(ii) Both parents must be heterozygous: Tt x Tt. Gametes T, t and T, t. Offspring: TT, Tt, Tt, tt (3 tall : 1 short).
(iii) tt.
(b)(i) Genotype is the genetic make-up of an organism (the alleles it carries for a trait).
(ii) Any two: crossing over and independent assortment in meiosis; random fertilisation; mutation; environment (food, climate).
(c)(i) An allele is one of two or more alternative forms of a gene at the same position on a pair of chromosomes.
(ii) Genotype is the genetic make-up; phenotype is the observable characteristics. Genotype cannot be seen; phenotype can be seen or measured. Genotype is inherited; phenotype results from genotype acting with the environment.
Show parents, gametes and offspring in the genetic diagram.