Introduction to inheritance
Defining key terms
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Genes
Genotype
Alleles
Mutation
Multiple alleles
Co-dominance
Dominant Allele
Recessive Allele
Homozygous dominant
Heterozygous
Homozygous recessive
Phenotype
Modification
• Genotype The genetic constitution of an organism
• Phenotype The expression of this genetic constitution and its interaction with the environment
• Gene A section of DNA that is a sequence of nucleotide bases that usually determines a single characteristic
• Alleles Are one of more alternative versions of the same gene
• Locus The position of a gene on a chromosome
Condition in which the alleles of a particular gene are identical. Can be homozygous recessive
• Homozygous or homozygous dominant
• Heterozygous Condition in which the alleles of a particular gene are different
• Dominant allele The allele that is always expressed in the phenotype
• Recessive allele the allele that is only expressed in the phenotype in the presence of another identical a
• Co-dominance Two alleles that both contribute to the phenotype
• Multiple alleles A gene that has more than two possible alleles, eg blood groups ABO
• Homologous A pair of chromosomes that have the same gene loci and therefore determines
the same features
chromosomes
Reproductive cell containing haploid number that fuses with another gamete at
• Gamete
fertilisation
• Haploid (n) Cells that contain only a single copy of each chromosome eg gametes
• Diploid (2n) Cells that contain 2 sets of chromosomes
• Sex linked gene A gene that is carried on one of the sex chromosomes
Gregor Mendel
• http://www.youtube.com/watch?v=YxKFdQo10rE
Simple genetic questions - answers
1a = Bb
1b = bb
1c =
Bb x bb
B b
b
b
B
b
b
Bb
bb
b
Bb
bb
results = 2 Bb (brown hair): 2 bb (blonde hair)
= 1:1 or 50%/50% or 0.5:0.5
Simple genetic questions - answers
2a = PP x pp
P P
note – P is not a good letter to use when hand writing quickly
p
All offspring are
Pp = Pink
p
P
P
p
Pp
Pp
p
Pp
Pp
2b = Pp x Pp
P
p
P
PP
Pp
P p
P p
p
Pp
pp
3 Pink: 1 blue
So chances of a blue flower = 25%
Simple genetic questions - answers
3a = a carrier Cc x a normal woman CC
when hand writing quickly
Cc x CC
C c
C
C
Chance of having a CF child = 0%
3b = Carrier Cc x Carrier Cc
C c
C c
So chances of a CF child = 25%
note – C is not a good letter to use
C
C
C
CC
Normal
CC
Normal
c
Cc
Carrier
Cc
Carrier
C
c
C
CC
Normal
Cc
Carrier
c
Cc
Carrier
cc
CF
sufferer
Simple genetic questions - answers
3c = a CF sufferer cc x a normal man CC
note – C is not a good letter to use when hand writing
quickly
cc x CC
c c
C
C
So,
Chance of having a CF child = 0%
C
C
c
Cc
Carrier
Cc
Carrier
c
Cc
Carrier
Cc
Carrier