1. Inherited Change and
Gene Technology
The passage of information
from parent to offspring
ALBIO9700/2006JK

2. • Locus – position on the chromosome
in which the gene resides
*plural: loci
• Alleles – a particular variety of the
same gene
ALBIO9700/2006JK

3. • Homozygous – 2 identical alleles of a
gene
• Heterozygous – 2 different alleles of a
gene
ALBIO9700/2006JK

4. • Genotype – alleles possesed by an
organism
• Phenotype – observable
characteristics/physical traits of an
organism (resulting from interaction
between genotype and environment)
ALBIO9700/2006JK

5. • Dominant – when effect on the phenotype of a
heterozygote is identical to its effect in a
homozygote
• Recessive – only expressed when no dominant
allele is present
• Codominant – both alleles have an effect on
the phenotype of a heterozygous organism
ALBIO9700/2006JK

6. Genetic Diagram (monohybrid
crosses)
• Let N be the dominant allele for normal pigment.
• Let n be the recessive allele for albino.
Parent phenotype Heterozygous Normal Heterozygous
Normal
Parent genotype Nn X
Nn
Gametes N n
N n
Possible offspring
genotype NN Nn Nn
nn
Offspring phenotype Normal Normal Normal
Albino
ALBIO9700/2006JK

7. Genotypes of parent
N n
NN Nn
N
Genotypes
Normal Normal
of parent
Nn nn
n
Normal Albino
Ratio of phenotype 3 normal : 1 albino
ALBIO9700/2006JK

8. Genetic Diagram (dihybrid crosses)
• Let A be the dominant allele for purple stem and a
recessive green
• Let D be the dominant allele for cut leaves and d
recessive smooth
Parent phenotype Heterozygous Heterozygous
Parent genotype AaDd X AaDd
Gametes AD Ad aD
ad
ALBIO9700/2006JK

9. Genotypes of parent
AD Ad aD ad
AADD AADd AaDD AaDd
AD Purple, Purple, Purple, Purple,
cut cut cut cut
AADd AAdd AaDd Aadd
Ad
Purple, Purple, Purple, Purple,
Genotype cut smooth cut potato
s of
AaDD AaDd aaDD aaDd
parent
aD Purple, Purple, Green, Green,
cut cut cut Cut
AaDd Aadd aaDd aadd
ad Purple, Purple, Green, Green,
cut smooth Cut smooth
Ratio of phenotype 9 purple,cut:3 purple,smooth:3 green,cut:1 green,smooth
ALBIO9700/2006JK

10. • Sex linkage – related to genes that are
carried on an X chromosome but not on a
Y chromosome
• Codominance ?
• Multiple alleles – the existence of 3 or
more alleles of a gene (eg. determination
of A, B, and O blood groups)
ALBIO9700/2006JK

11. Test Crosses
• Involves crossing an organism showing
the dominant phenotype with one which is
homozygous recessive to find out if the
dominant genotype is hetero- or
homozygous.
ALBIO9700/2006JK