3.2.4 Predicting Genetic Inheritance

Question 1

Family pedigree diagrams are usually used to trace, what?

Answer 1

the pattern of inheritance of a specific characteristic (usually a disease) through generations of a family

• This can be used to work out the probability that someone in the family will inherit the genetic disorder

Question 2

In a family pedigree chart, how are males and females represented

Answer 2

Males are indicated by the square shape

females are represented by circles

Question 3

Affected individuals are represented by what colour?

Answer 3

Red

Question 4

Unaffected individuals are represented by what colour?

Answer 4

Blue

Question 5

Horizontal lines between males and females show, what?

Answer 5

that they have produced children (which are shown underneath each couple)

Question 6

What is Monohybrid inheritance

Answer 6

Monohybrid inheritance is the inheritance of characteristics controlled by a single gene

Question 7

How can Monohybrid inheritance be determined

Answer 7

using a genetic diagram known as a Punnett square

Question 8

What does a Punnett Square diagram show?

Answer 8

the possible combinations of alleles that could be produced in the offspring

Question 9

Is a dominant allele shown using a capital letter or lower case

Answer 9

a capital letter

Question 10

Is the recessive allele shown using upper case or lower case

Answer 10

lower case

Question 11

The height of pea plants is controlled by, what?

Answer 11

a single gene that has two alleles: tall and short

Question 12

The tall allele is dominant and is shown as, what?

Answer 12

T

Question 13

The small allele is recessive and is shown as, what?

Answer 13

t

Question 14

The term ‘pure breeding’ indicates, what?

Answer 14

that the individual is homozygous for that characteristic

Question 15

All of the offspring of the first cross have the same, what?

Answer 15

genotype, Tt (heterozygous), so the possible combinations of offspring bred from these are: TT (tall), Tt (tall), tt (short)

Question 16

There is more variation in the second cross, with a , what?

Answer 16

3:1 ratio of tall : short

Question 17

The F2 generation is produced when the offspring of the F1 generation (pure-breeding parents) are allowed to do what?

Answer 17

interbreed

Question 18

The heterozygous plant will be, what?

Answer 18

tall with the genotype Tt

Question 19

The short plant is showing the recessive phenotype and so must be, what?

Answer 19

homozygous recessive – tt

Question 20

How to determine the parental genotypes

Answer 20

1. Select a letter that has a clearly different lower case, for example, Aa, Bb, Dd

• Side tings (You may be asked to comment on the ratio of different allele combinations in the offspring, calculate percentage chances of offspring showing a specific characteristic or just determine the phenotypes of the offspring)

Question 21

Completing a Punnett square allows you to predict the probability, of what?

Answer 21

of different outcomes from monohybrid crosses

Question 22

Most characteristics are a result of what?

Answer 22

multiple genes interacting, rather than a single gene

Question 23

Characteristics that are controlled by more than one gene are described as being

Answer 23

polygenic

Question 24

Polygenic characteristics have, what?

Answer 24

phenotypes that can show a wide range of combinations in features

Question 25

The inheritance of these polygenic characteristics is called, what?

Answer 25

polygenic inheritance

Question 26

Why is Polygenic inheritance difficult to show using genetic diagrams

Answer 26

because of the wide range of combinations

Question 27

Give an example of Polygenic inheritance

Answer 27

eye colour

Question 28

Exam Tip

Answer 28

You will NOT be expected to explain the polygenic inheritance of characteristics using a genetic diagram, you just need to be aware that many characteristics are controlled by groups of genes and that this is known as polygenic inheritance.

If you are asked to use your own letters to represent the alleles in a Punnett square, try to choose a letter that is obviously different as a capital than the lower case so the examiner is not left in any doubt as to which is dominant and which is recessive.