[3.7] Genetics, Populations, Evolution & Ecosystem

Question 1

What is meant by the term genotype?

Answer 1

• Genetic constitution of an organism.

Question 2

What is meant by the term phenotype?

Answer 2

• The expression of the genetic constitution (genotype) of an organism and its interaction with the environment.

Question 3

What are alleles and how do they arise?

Answer 3

• Variations of a particular gene (same locus) -> arise by mutation (changes in DNA base sequence).

Question 4

How many alleles of a gene can be found in diploid organisms?

Answer 4

• 2 as diploid organisms have 2 sets of chromosomes (chromosomes are found in homologous pairs).
  
  • But there may be many (more than 2) alelles of a single gene in a population.

Question 5

Describe the different types of alleles.

Answer 5

DOMINANY ALLELE

• Always expressed (shown in the phenotype).

RECESSIVE ALLELE

• Only expressed when 2 copies present (homozygous recessive) / NOT expressed when dominant allele present (heterozygous).

CODOMINANT ALLELES

• Both alleles expressed / contribute to phenotype (if inherited together).

Question 6

What is meant by the terms homozygous and heterozygous?

Answer 6

HOMOZYGOUS

• Alleles at a specific locus (on each homologous chromosome) are the same.

HETEROZYGOUS

• Alleles at a specific locus (on each homologous chromosome) are different.

Question 7

What do monohybrid and dihybrid crosses show?

Answer 7

MONOHYBRID CROSS

• Inheritance of one phenotypic characteristic coded for by a single gene.

DIHYBRID CROSS

• Inheritance of two phenotypic characteristics coded for by two different genes.