Mendelian Inheritance
7 Phenotypes studies by Mendel
• Pea plants used to figure out how traits are inherited
• Have clear dichotomous characteristics e.g. round or wrinkled seeds, purple or white
petals, axial or terminal flowers, inflated or pinched pods, long or short stems, green
or yellow pods
• Complete dominance – no blending of characteristics
• True breeding – peas are a self-fertilising plant. Can isolate ones that are true
breeding. The same characteristic is passed onto all offspring
How to cross pea plants: crossing or selfing
Left plant = male, right = female. Remove anthers so it can’t self-fertilise and to know which
is male and female.
Crossing True Breeding Lines
• F1 always had smooth seeds
• No blending of characteristics
• One characteristics always dominant
, Mendel’s First Law: The Law of Segregation
• Heredity determined by paired unit factors (Genes)
• In formation of gametes, the genes separate so that
each gamete is equally likely to contain either one
• SS or ss = homozygous
• Ss = heterozygous
• S = dominant. s = recessive
• Monohybrid cross
•
Law of Segregation in F2
• 3 genotypes, 2 phenotypes
• Genotypes = 1:2:1 (SS: Ss: ss)
• Phenotypes = 3:1 (dominant: recessive
i.e. smooth: wrinkled)
• S- = if we don’t know what the second
allele is i.e. if it is homozygous dominant or
heterozygous dominant
Mendel’s Dihybrid Crosses
• Mendel was studying genes on different
chromosomes
• Only 7 chromosomes in pea
7 Phenotypes studies by Mendel
• Pea plants used to figure out how traits are inherited
• Have clear dichotomous characteristics e.g. round or wrinkled seeds, purple or white
petals, axial or terminal flowers, inflated or pinched pods, long or short stems, green
or yellow pods
• Complete dominance – no blending of characteristics
• True breeding – peas are a self-fertilising plant. Can isolate ones that are true
breeding. The same characteristic is passed onto all offspring
How to cross pea plants: crossing or selfing
Left plant = male, right = female. Remove anthers so it can’t self-fertilise and to know which
is male and female.
Crossing True Breeding Lines
• F1 always had smooth seeds
• No blending of characteristics
• One characteristics always dominant
, Mendel’s First Law: The Law of Segregation
• Heredity determined by paired unit factors (Genes)
• In formation of gametes, the genes separate so that
each gamete is equally likely to contain either one
• SS or ss = homozygous
• Ss = heterozygous
• S = dominant. s = recessive
• Monohybrid cross
•
Law of Segregation in F2
• 3 genotypes, 2 phenotypes
• Genotypes = 1:2:1 (SS: Ss: ss)
• Phenotypes = 3:1 (dominant: recessive
i.e. smooth: wrinkled)
• S- = if we don’t know what the second
allele is i.e. if it is homozygous dominant or
heterozygous dominant
Mendel’s Dihybrid Crosses
• Mendel was studying genes on different
chromosomes
• Only 7 chromosomes in pea
