Chapter 2 mendelian inheritance
2.1 Mendel’s study of pea plants
Mendel studied the pea plants for 8 years. He did not immediately receive recognition for his
findings. Only around the 1900 his work was rediscovered.
Mendel chose pea plants as his experimental organism
He did hybridization experiments, In which he crossed parent to create hybrids. The male gametes
produced within pollen grains that form in anthers. Female gametes produced within ovules
that from in ovaries. Mendel used self-fertilization and cross-fertilization.
Mendel studied seven characteristics that bred true
General characteristics of organisms = characters. A specific property of a character = traits/ variant.
Mendel started with a true-breeding line = variety that continues to produce same trait after
generations.
2.2 Law of segregation
Mendel followed the outcome of a single character for two generations
Mendel used an empirical approach = no hypothesis, but analyses of mathematical relationship. His
first proposal was that one variant is dominant to the other. His data were consistent with a
particulate theory of inheritance genetic traits are inherited as units that remain unchanged. He
proposed genes segregate.
Mendels 3:1 ratio is consistent with law of segregation
Mendel’s law of segregation states: 2 copies of a gene segregate during process that gives rise to
gametes. The phenotypic ratio in F2 = 3:1, the genotypic ratio = 1:2:1.
Punnett square can be used to predict outcome of crosses and self-
fertilization experiments
The genotypes of the parents must be known. The possible gametes should be formed and the
square can be filled in. The square shows the genotypic ratio.
2.3 Law of independent assortment
To formulate this second law, two-factor crosses needed to be done. Two characters studied.
Mendel also analyzed crosses involving two different characters
Because of independent assortment, 4 kinds of gametes could be produced in a two factored cross.
The occurrence of non parental variants contradicted the linked-assortment hypothesis. The law of
independent assortment: 2 different genes will randomly assort their alleles during process that
gives rise to gametes. The phenotypic ratio becomes 9:3:3:1 in a heterozygote plant. When offspring
receives nonparental variant genetic recombination.
Multiplication and forked-line methods can be used to solve independent
assortment
Any cross bigger than 2 factor will be a lot of work to make in a Punnett square. Each gene can have
their own punnet square, multiply the three phenotypic outcomes together.
Modern geneticists are often interested in relationship between molecular
exoression and outcome of traits
Recessive alleles ca be loss-of-function alleles.
, 2.4 Studying inheritance patterns in humans
A pedigree is specifically organized. Vertical lines connect generations, horizontal lines connect
parents. Males are square and females round. The filled in figures are the diseased. Sometimes
figures are also partly filled in, this indicates the individual is a carrier of the disease. However many
times the pedigree is based on the phenotypes and carriers are not mentioned.
2.5 Probability and statistics
The product rule can be used to calculate problems with independent outcomes.
Probability is the likelihood an outcome will occur
Probability = number of times particular outcome occurs / total number of possible outcomes. The
deviation between observed and expected outcomes = random sampling error.
Product rule is used to predict probability of independent outcomes
First use a Punnett square to calculate individual probability of affected offspring. Multiply the
outcomes with each other. The rule can also be used to calculate the chance of a specific genotype.
2.1 Mendel’s study of pea plants
Mendel studied the pea plants for 8 years. He did not immediately receive recognition for his
findings. Only around the 1900 his work was rediscovered.
Mendel chose pea plants as his experimental organism
He did hybridization experiments, In which he crossed parent to create hybrids. The male gametes
produced within pollen grains that form in anthers. Female gametes produced within ovules
that from in ovaries. Mendel used self-fertilization and cross-fertilization.
Mendel studied seven characteristics that bred true
General characteristics of organisms = characters. A specific property of a character = traits/ variant.
Mendel started with a true-breeding line = variety that continues to produce same trait after
generations.
2.2 Law of segregation
Mendel followed the outcome of a single character for two generations
Mendel used an empirical approach = no hypothesis, but analyses of mathematical relationship. His
first proposal was that one variant is dominant to the other. His data were consistent with a
particulate theory of inheritance genetic traits are inherited as units that remain unchanged. He
proposed genes segregate.
Mendels 3:1 ratio is consistent with law of segregation
Mendel’s law of segregation states: 2 copies of a gene segregate during process that gives rise to
gametes. The phenotypic ratio in F2 = 3:1, the genotypic ratio = 1:2:1.
Punnett square can be used to predict outcome of crosses and self-
fertilization experiments
The genotypes of the parents must be known. The possible gametes should be formed and the
square can be filled in. The square shows the genotypic ratio.
2.3 Law of independent assortment
To formulate this second law, two-factor crosses needed to be done. Two characters studied.
Mendel also analyzed crosses involving two different characters
Because of independent assortment, 4 kinds of gametes could be produced in a two factored cross.
The occurrence of non parental variants contradicted the linked-assortment hypothesis. The law of
independent assortment: 2 different genes will randomly assort their alleles during process that
gives rise to gametes. The phenotypic ratio becomes 9:3:3:1 in a heterozygote plant. When offspring
receives nonparental variant genetic recombination.
Multiplication and forked-line methods can be used to solve independent
assortment
Any cross bigger than 2 factor will be a lot of work to make in a Punnett square. Each gene can have
their own punnet square, multiply the three phenotypic outcomes together.
Modern geneticists are often interested in relationship between molecular
exoression and outcome of traits
Recessive alleles ca be loss-of-function alleles.
, 2.4 Studying inheritance patterns in humans
A pedigree is specifically organized. Vertical lines connect generations, horizontal lines connect
parents. Males are square and females round. The filled in figures are the diseased. Sometimes
figures are also partly filled in, this indicates the individual is a carrier of the disease. However many
times the pedigree is based on the phenotypes and carriers are not mentioned.
2.5 Probability and statistics
The product rule can be used to calculate problems with independent outcomes.
Probability is the likelihood an outcome will occur
Probability = number of times particular outcome occurs / total number of possible outcomes. The
deviation between observed and expected outcomes = random sampling error.
Product rule is used to predict probability of independent outcomes
First use a Punnett square to calculate individual probability of affected offspring. Multiply the
outcomes with each other. The rule can also be used to calculate the chance of a specific genotype.
