Genetics & Inheritance

Question 1

What is a gene?

Answer 1

• section of DNA which codes for a specific polypeptide

Question 2

What is a genotype?

Answer 2

• the genetic constitution of an organism, all the alleles an organism processes

Question 3

What is a genepool?

Answer 3

• all the alleles within an interbreeding population

Question 4

In genetic crosses, the observed phenotypic ratios obtained in the offspring are often not the same as expected ratios.

Suggest two reasons why.

Answer 4

• small sample size
• fertilisation of gametes is random
• sex-linkage
• epistasis
• selection advantage

Question 5

What is a phenotype?

Answer 5

• is the expression of its genetic constitution and its interaction with the environment

Question 6

Define gene linkage

Answer 6

• genes on the same chromosome

Question 7

What is a multiple allele?

Answer 7

• more than 2 alleles for the same gene

Question 8

Define locus

Answer 8

• different alleles for the same gene are found at same position of a homologous chromosome

Question 9

What is meant by the term homozygous?

Answer 9

if two copies of a gene are the same allele

Question 10

What is meant by the term heterozygous?

Answer 10

if two copies of a gene are different alleles

Question 11

What is a dominant allele?

Answer 11

• it will always be expressed in the phenotype regardless whether the organisms genotype is homozygous or heterozygous

Question 12

What is a recessive allele?

Answer 12

• it will only be expressed in the phenotype if the genotype is homozygous

Question 13

What is meant by codominant?

Answer 13

equally expressed within phenotype

Question 14

State three causes of genetic variation

Answer 14

• mutation
• crossing over
• independent segregation
• random mating

Question 15

how do multiple alleles of a gene arise?

Answer 15

• mutations
• which are at different positions on the gene

Question 16

What does the hardy weinberg principle predict?

Answer 16

‘The allelic frequencies of a particular gene from one generation to the next will remain constant’
if there is no:
- migration
- gene mutations
- selection for or against a particular allele
ALSO should be a large population and mating should be random

Question 17

Define epistasis

Answer 17

• the allele of one gene affects or masks the expression of another in phenotype

Question 18

What are the rules for dominant alleles

Answer 18

• affected offspring must have at least one affected parent
• unaffected parents only have unaffected offspring
• if both parents are affected and have an unaffected offspring, both parents must be homozygous

Question 19

What are the rules for recessive alleles

Answer 19

• unaffected parents can have an affected off spring if they are heterozygous

Question 20

Male off spring are more likely than females to show recessive sex-linked characteristics. Explain why.

Answer 20

• recessive allele is always expressed in males
• females need two recessive alleles

Question 21

Explain how a single base substitution causes a change in the structure of a polypeptide

Answer 21

• change in primary structure
• change in hydrogen/ionic/disulphide bonds
• alters tertiary structure