section 2: patterns of inheritance - topic 1: types and causes of variation

Question 1

what are the 3 types of variation?

Answer 1

continuous.
discontinuous.
phenotypic.

Question 2

what is continuous variation?

Answer 2

when the individuals in a population vary within a range.
^ there are no distinct categories.

Question 3

examples of continuous variation.

Answer 3

height.
waist circumference.
fur length.

Question 4

what kind of data is continuous?

Answer 4

quantitative.

Question 5

what is quantitative data?

Answer 5

data that has values that can be measured with a number.

(numerical data)

Question 6

what is discontinuous variation?

Answer 6

when there are 2 or more distinct categories - each individual falls into only 1 of these categories (there are no intermediates).

Question 7

examples of discontinuous variation.

Answer 7

blood group.
violet flower colour.
tongue-rolling ability.

Question 8

what kind of data is discontinuous?

Answer 8

qualitative.

Question 9

what is qualitative data?

Answer 9

data that doesn’t contain any numbers.

(non-numerical data)

Question 10

what is phenotypic variation?

Answer 10

the variation in an organisms phenotype.

Question 11

what is a phenotype?

Answer 11

the characteristics an organism displays.

Question 12

what is phenotypic variation influenced by?

Answer 12

genotype.
the environment.
genotype & the environment.

Question 13

what make up a genotype?

Answer 13

the genes and alleles an organism has.

Question 14

how does meiosis lead to genetic variation?

Answer 14

• 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.

differences in genotype result in phenotypic variation.

Question 15

example of a genotype affecting phenotypic variation.

Answer 15

human blood group.
- there are 3 different blood group alleles, which result in 4 different blood groups.

Question 16

what does it mean when characteristics are polygenic?

Answer 16

inherited characteristics that show continuous variation are usually influenced by many genes.

Question 17

are characteristics that are polygenic more likely to show continuous or discontinuous variation?

Answer 17

continuous.

Question 18

example of a polygenic characteristic.

Answer 18

human skin colour - it comes in loads of different shades.

Question 19

what does it mean when characteristics are monogenic?

Answer 19

inherited characteristics that show discontinuous variation are usually influenced by only one gene.

Question 20

are characteristics that are monogenic more likely to show continuous or discontinuous variation?

Answer 20

discontinuous.

Question 21

example of a monogenic characteristic.

Answer 21

violet flower colour.
- either coloured or white.
- controlled by 1 gene.

Question 22

what differences in the environment can affect phenotypic variation?

Answer 22

climate.
food.
lifestyle.

Question 23

examples of phenotypic variation caused by the environment.

Answer 23

etiolation.
chlorosis.

Question 24

what is etiolation?

Answer 24

this is when plants grow abnormally long and spindly because they’re not getting enough light.

Question 25

what is chlorosis?

Answer 25

this is when plants don’t produce enough chlorophyll and turn yellow.
^ caused by several environmental factors i.e. lack of magnesium in soil.

Question 26

how do the affects of genotype and the environment differ?

Answer 26

genotype - tends to influence the characteristics you’re born with.

environmental factors - can influence how some characteristics develop.

Question 27

what is most phenotypic variation caused by?

Answer 27

the combination of genotype and environmental factors.

Question 28

what type of variation does phenotypic variation caused by both genotype and the environment show?

Answer 28

continuous variation.

Question 29

examples of phenotypic variation caused by both genotype and the environment.

Answer 29

body mass in animals:
- partly genetic but also strongly influenced by environmental factors i.e. diet.
^ if your diet doesn’t contain enough of the right nutrients, your body mass is likely to be lower than that determined by your genes.
- varies within a range (continuous variation).

height of pea plants:
- they come in tall and dwarf forms (discontinuous variation) - determined by genotype.
- but the exact height of the tall and dwarf plant varies (discontinuous variation) because of the environmental factors.
^ i.e. light intensity, water availability.