6.3 - Patterns of inheritance

Question 1

What is variation ?

Answer 1

• The term variation refers to the differences between living organisms.

Question 2

How can variation be ?

Answer 2

• It can be between different species or within a single species.

Question 3

What are the two types of variation ?

Answer 3

• Continuous
• Discontinuous

Question 4

What factors cause variation ?

Answer 4

• Genetic
• Environmental

Question 5

What is continuous variation ?

Answer 5

• Is when the individuals within a population vary within a range - there are no distinct categories e.g. humans can be in a range of height not just tall or short
• more examples, waist circumference fur length

Question 6

What is Discontinuous variation ?

Answer 6

• This is when there are two or more distinct categories - each individual falls into one of these categories.
• ## E.g Blood group - A,B, AB or O

Question 7

Explain how variation can be influenced by your genes

Answer 7

• Different species have different genes
• Individuals of the same species have the same genes but different alleles.
  EXAMPLE:
• Human blood group -there are three different blood
  group alleles, which result in four different blood groups.
• Inherited characteristics that show continuous variation are usually influenced by many genes
  these characteristics are said to be polygenic.
• Human skin colour is polygenic- it comes in loads of different shades of colour.
• Inherited characteristics that show discontinuous variation are usually influenced by only one gene
  (or a small number of genes). Characteristics controlled by only one gene are said to be monogenic.
  EXAMPLE:
  Violet flower colour - can only be purple or white

Question 8

What is variation in phenotype referred to as ?

Answer 8

Phenotypic variation.

Question 9

How can sexual reproduction cause variation ?

Answer 9

• Meiosis makes gametes with a unique assortment of alleles through crossing-over and the independent assortment of chromosomes.
• The random fusion of gametes during fertilisation also increases genetic variation in the offspring.

Question 10

What is genotype ?

Answer 10

all of the alleles that an organism carries on its chromosomes

Question 11

What is phenotype ?

Answer 11

the characteristics displayed by an organism.

Question 12

How can the environment cause variation ?

Answer 12

• Variation can also be caused by differences in the environment, e.g. climate, food, lifestyle.
  Characteristics controlled by environmental factors can change over an organism’s life.

Question 13

What are examples of variation in the environment

Question 14

What is intraspecific variation ?

Answer 14

• Organisms of the same species have different characteristics

Question 15

What is monogenic inheritance ?

Answer 15

• Monogenic inheritance is the inheritance of one gene.
• ratio 3:1

Question 16

What is a dominant allele ?

Answer 16

• A dominant allele is an allele that , when present is always expressed in the phenotype.

Question 17

Define phenotype

Answer 17

• The phenotype is the expression of the genotype and its interaction with the environment

Question 18

What is dihybrid inheritance ?

Answer 18

• Dihybrid inheritance is the inheritance of two genes.

Question 19

What is the phenotypic ratio of offspring

Answer 19

• 9:9:3:1