Inheritance

Question 1

What is the genotype?

Answer 1

The genetic constitution of an organism

Question 2

What is the phenotype?

Answer 2

The expression of the genetic constitution and its interaction with the environment - observable characteristics

Question 3

What is a gene?

Answer 3

A length of DNA that codes for a polypeptide or functional RNA

Question 4

What is a locus?

Answer 4

the position of a gene on a particular DNA molecule - there are 2 loci in a pair of homologous chromosomes that each carry one allele of a gene

Question 5

What are homozygous and heterozygous alleles?

Answer 5

in a diploid organism, the alleles at a specific locus may be either homo or heterozygous

homo = the allele on each of the chromosomes is the same
hetero = 2 different alleles

Question 6

Which alleles express themselves in the phenotype?

Answer 6

• in heterozygotes the dominant allele is always expressed in the phenotype over the recessive allele
• recessive alleles are only expressed in homozygous recessives

Question 7

What is co-dominance?

Answer 7

• when 2 alleles both contribute to the phenotype, leading to either a blend of both features, or both features being represented

Question 8

What is monohybrid inheritance?

Answer 8

the inheritance of a single gene

Question 9

When 2 F1 generations are crossed, what is the ratio of the F2 generation?

Answer 9

3:1

Question 10

What is the typical ratio produced in dihybrid inheritance?

Answer 10

9:3:3:1

Question 11

How do you write alleles with co-dominance?

Answer 11

using subscript

Question 12

What are multiple alleles and give an example

Answer 12

when a gene has more than 2 types of alleles, however as there are only 2 chromosomes, only 2 of the alleles can be expressed - eg. blood types in humans are IA, IB and IO

Question 13

What types of alleles are the blood groups?

Answer 13

IA and IB are codominant
IO is recessive

Question 14

What are the genotypes of the different blood groups?

Answer 14

A= IAIA or IAIO
B= IBIB or IBIO
AB= IAIB
O= IOIO

Question 15

What are the F1 and F2 generations?

Answer 15

F1 = offspring produced by the first cross of pure breeding organisms
F2 = offspring produced from a cross between 2 heterozygous F1

Question 16

Why are expected ratios not always the same as observed ratios?

Answer 16

random fusion of gametes so the ratio is not always constant - based on probability and therefore due to chance

Question 17

What is sex-linkage?

Answer 17

When a gene is carried on the X or Y sex chromosomes

Question 18

Example of a sex-linked disease and is it dominant or recessive?

Answer 18

haemophilia - recessive condition