Genetic crosses

Question 1

What is a gene?

Answer 1

A gene is a sequence of nucleotides that codes for the production of a specific protein molecule (polypeptide)

Question 2

What does locus refer to in genes?

Answer 2

• Locus refers to the position of a gene on a chromosome
• each gene can exist in two or more different forms called alleles

Question 3

What does homologous mean? Give an example

Answer 3

• homologous means having similar or corresponding parts, structures or positions
• Homologous structures or organs indicate a common evolutionary origin
• a common example is the forelimbs of vertebrates = all derived from the same ancestral tetrapod structure

Question 4

What are chromosomes? How many pairs of chromosomes doe humans have?

Answer 4

• a chromosome is a thread-like structure made up of a single DNA molecule that contains all or some of the genetic information of an organism (contains genes)
• humans have 23 pairs of chromosomes and the chromosomes in each pair are called homologous chromosomes

Question 5

What are alleles?

Answer 5

Alleles are alternative forms of a gene occupying a position on a chromosome

Question 6

What makes up a persons genotype?

Answer 6

• the alleles that a person has make up their genotype
• the genotype is the collection of alleles that determine an organisms characteristics

Question 7

What does the term phenotype refer to?

Answer 7

• the characteristic (observable effect) caused by the genotype, is the phenotype

Question 8

What is a recessive allele?

Answer 8

A recessive allele is an allele that affects the phenotype of the organism only if a dominant allele is NOT present (e.g. Ff, ‘f’ is recessive & ff = recessive)

Question 9

What is a dominant allele?

Answer 9

A dominant allele is an allele that affects the phenotype of the organism unless (e.g. Ff, ‘F’ is dominant & Ff = dominant FF = dominant)

Question 10

What does incomplete dominance refer to?

Answer 10

incomplete dominance is when a dominant allele, or form of a gene, does not completely mask the effects or a recessive allele, and the organism’s resulting physical appearance shows a blending of both alleles

Question 11

What does homozygous refer to?

Answer 11

• homozygous refers to having two identical copies of alleles in the DNA sequence that encodes for a particular trait
• e.g. FF and ff

Question 12

What does heterozygous refer to?

Answer 12

• heterozygous refers to an individual having two different alleles for a specific trait
• e.g. Ff