Download Genetics-KEY

National 5 Biology
Key Area 5:
Variation and Inheritance
National 4 Biology
Key Area 4
Genetic Information
By the end of the lesson you
will be able to …..
• Give reasons why the actual phenotype
ratio is different from the predicted.
• Use the Genetics specific vocabulary
confidently
Actual figures vs. predicted
figures in a cross
•50% of gametes
contain the P
(purple) allele
•50% of gametes
contain the p
(white) allele.
Predicted phenotypic ratio =
3 dominant: 1 recessive
This cross was repeated and 100 offspring were produced.
Predicted figures
•75 purple
•25 white
Actual Figures
•71 purple
•29 white
This cross was repeated and 100 offspring were produced.
Predicted figures
•75 purple
•25 white
Actual Figures
•71 purple
•29 white
Actual figures vs. predicted
figures in a cross
•In reality, there is often a
difference between the actual
phenotypes shown in F2 and the
predicted phenotypes shown in F2.
•This is because fertilisation is a
random process or the sample size
could be too small.
Genetics Language!
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Phenotype
Genotype
Allele
Dominant
Recessive
Homozygous
Heterozygous
True-Breeding
In the following example, name
a) the characteristic
b)the phenotype for each flower
Phenotype and Genotype Example
White
White
Black
White
Black
Black
1. What characteristic do you think we are looking at?
2. What is the phenotype for each guinea pig?
3. What is DOMINAT allele?
4. What is the recessive allele?
5. What is the genotype for each guinea pig?
6. Using “heterozygous” and “homozygous”, describe
each guinea pig
Word
Meaning
Phenotype
The physical appearance of an organism
Genotype
The genes (or alleles) that an organism possesses. Usually
written as letters.
Alleles
Dominant
Recessive
Homozygous
Heterozygous
True-breeding
Different forms of the same gene.
An allele that always expresses itself whether it is partnered
by a recessive allele or by another like itself.
Describes the variant of a gene for a particular characteristic
which is masked or suppressed in the presence of the dominant
variant. A recessive allele will only be expressed in the
phenotype if it is paired with another recessive gene
This describes a genotype in which the two alleles for
the characteristic are identical.
This describes a genotype in which the two alleles for a
particular characteristic are different
Describes an organism that on being crossed with a member of
the same strain always produces more organism of exactly
the same strain