3.2.4 Predicting Genetic Inheritance Flashcards
Family pedigree diagrams are usually used to trace, what?
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
In a family pedigree chart, how are males and females represented
Males are indicated by the square shape
females are represented by circles
Affected individuals are represented by what colour?
Red
Unaffected individuals are represented by what colour?
Blue
Horizontal lines between males and females show, what?
that they have produced children (which are shown underneath each couple)
What is Monohybrid inheritance
Monohybrid inheritance is the inheritance of characteristics controlled by a single gene
How can Monohybrid inheritance be determined
using a genetic diagram known as a Punnett square
What does a Punnett Square diagram show?
the possible combinations of alleles that could be produced in the offspring
Is a dominant allele shown using a capital letter or lower case
a capital letter
Is the recessive allele shown using upper case or lower case
lower case
The height of pea plants is controlled by, what?
a single gene that has two alleles: tall and short
The tall allele is dominant and is shown as, what?
T
The small allele is recessive and is shown as, what?
t
The term ‘pure breeding’ indicates, what?
that the individual is homozygous for that characteristic
All of the offspring of the first cross have the same, what?
genotype, Tt (heterozygous), so the possible combinations of offspring bred from these are: TT (tall), Tt (tall), tt (short)
There is more variation in the second cross, with a , what?
3:1 ratio of tall : short
The F2 generation is produced when the offspring of the F1 generation (pure-breeding parents) are allowed to do what?
interbreed
The heterozygous plant will be, what?
tall with the genotype Tt
The short plant is showing the recessive phenotype and so must be, what?
homozygous recessive – tt
How to determine the parental genotypes
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)
Completing a Punnett square allows you to predict the probability, of what?
of different outcomes from monohybrid crosses
Most characteristics are a result of what?
multiple genes interacting, rather than a single gene
Characteristics that are controlled by more than one gene are described as being
polygenic
Polygenic characteristics have, what?
phenotypes that can show a wide range of combinations in features
The inheritance of these polygenic characteristics is called, what?
polygenic inheritance
Why is Polygenic inheritance difficult to show using genetic diagrams
because of the wide range of combinations
Give an example of Polygenic inheritance
eye colour
Exam Tip
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.
