Download Topic 16.2: Inheritance

Topic 16.2: Inheritance
Inheritance and genetic material Part 2
1
objective
Define homozygous
State that two identical homozygous individuals that
breed together will be pure-breeding
Define heterozygous
State that a heterozygous individual will not be purebreeding
Define dominant allele
Define recessive allele
Interpret pedigree diagrams for the inheritance of a
given characteristic
Use genetic diagrams
Use Punnett squares in crosses which result in more
than one genotype to work out
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The chromosome structure
If the person received two identical alleles
from the parent for a particular
characteristic so this organism is said to be
HOMOZYGOUS (having two identical alleles
of a particular gene)
If the person received two different alleles
from the parent for a particular
characteristic so this organism is said to be
HETEROZYGOUS(having two different alleles
of a particular gene)
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The chromosome structure
Dominant allele: a strong one , that is
expressed in the phenotype (physical
features) if it is present , of an organism
whether the organism is homozygous or
heterozygous
Recessive allele: a weak one, that is only
expressed when there is no dominant allele
of the gene present
The organism which has the recessive
phenotype is always homozygous
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Monohybrid inheritance
Cross between organisms which show variation
of only one characteristic
Example a black animal is crossed with a white
one, if all the offspring is black, the allele for black
is said to be dominant and it is represented by a
capital letter B
while the allele for white is recessive and is
represented by a small letter b
Remember: each individual receives two alleles
for each characteristic, one from the father and
one from the mother
So what is dominant and what is recessive?
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Results of simple cross
Case 1: If two homozygous individuals with
different phenotypes are crossed, what is the
result ?
Parent phenotype Red
white
Genotype
RR
rr
Gamete
F1 genotype
Phenotype
Phenotype ratio
Genotype ratio
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Results of simple cross
Case2: if two heterozygous organisms with the
same phenotype:
Parent phenotype Red
Red
Genotype
Rr
Rr
Gamete
F1 genotype
Phenotype
Phenotype ratio
Genotype ratio
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Results of simple cross
Case3: if a heterozygous dominant and
homozygous recessive are crossed
Parent phenotype Red
white
Genotype
Rr
rr
Gamete
F1 genotype
Phenotype
Phenotype ratio
Genotype ratio
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