MENDELIAN INHERITANCE

• Gregor Mendel, the father of genetics bred pea plants to understand how inheritance worked.

• Why did he choose pea plants?

• Essentially, he studied how traits were passed down.

Trait: a particular __________ of an inherited

characteristic

Mendel performed his experiments on seven Hereditary characteristics of the pea plant: flower colour, flower position, stem length, seed shape, seed colour, pod shape, and pod colour.

Definitions! true-breeding organism: an organism that produces

offspring that are genetically ___________ for one or more traits when _____-pollinated or when crossed with another true-breeding organism for the _______ traits

hybrid: the offspring of two __________ true breeding plants

Cross: breeding of two organisms with _____ _____________ traits

Definitions!

P generation: the _______ used in a cross

F1 generation: the offspring of a _______________cross

F2 generation: the offspring of an _______________cross

Definitions!!!

Monohybrid: the offspring of _____ different true breeding plants that differ in ______ one characteristic

Monohybrid cross: a cross designed to study the inheritance of ______ ____trait

Mendel’s Experiments

• Mendel only crossed plants that differed in ______ ______characteristic, which became his P generation.

• Mendel conducted a ___________ cross.

– The hybrid offspring of the P-generation cross were the F1 generation (F stands for filial). The F1 generation differed from each other in only one characteristic, making them ________________.

Mendel’s Experiments • Mendel used the plants from the F1 generation

and self-pollinated them. This became the F2 generation. What did he see?

• This meant that the trait for white flowers had

been _________ in the F1 generation.

• He recorded the numbers of the F2 generation plants according to their traits. He then calculated the ratios of the traits for each characteristic

What did Mendel find?

• Mendel found a ________.

• F1 generation: only _____ of the two traits was present.

• F2 generation: _______ traits were present—the missing trait had _____________. This _______ the “blending” theory.

Mendel’s Conclusions • Traits must be passed on by discrete heredity

units (factors) • Even though they might not be ___________,

they can be ________ on • He called the factor that was expressed in the F1

generation the _____________ factor • He called the hidden factor in the F1 generation

but was expressed in the F2 generation the ____________ factor

The First Law of Mendelian Inheritance

• For each characteristic (such as flower colour), an organism carries ___ factors (genes): ____ from each parent.

• Parent organisms donate _____ ____copy of each gene in their gametes.

Alleles

• A locus is like the __________ of a gene and we have two forms of these (one from mom and one from dad)

• Each form of a gene is called an ________

• The alleles an individual can inherit for a particular characteristic can be the ______ or _____________.

Alleles

• This leads to different _____ of a characteristic

• If the two alleles of a particular gene are the same, the individual is ____________ for that allele

• If the two alleles of a particular gene are different, the individual is _____________ for that allele

Alleles

• The set of alleles that an individual has is its __________. An individual’s genotype includes all forms of an individual’s genes, even if some of these genes remain __________.

• In contrast, the traits of an individual make up its ___________. The alleles that are ____________ determine an individual’s phenotype.

Dominant vs. Recessive

• In heterozygous individuals, which allele is expressed? – A _________allele is an allele that expresses its

phenotypic effect ___________ it is present in the individual.

– A recessive allele is expressed only when ______ alleles are of the recessive form.

• This explains why all the plants in the F1 generation of Mendel’s experiment were all purple plants

Dominant vs. Recessive

Geneticists use letters to represent alleles

– Uppercase for ___________ alleles

– Lowercase for __________ alleles

Homozygous Heterozygous

Phenotypes

• Can you tell by looking at a purple pea plant whether it is TT or Tt?

• Whenever an individual has at least _____ copy of the dominant allele, that allele is expressed.

Punnett Squares

• a diagram that summarizes ______ __________ ______________ of each allele from each parent;

• a tool for determining the ___________ of a single offspring having a particular _____________

Punnett Squares

• Punnett squares are valuable mathematical tools for geneticists. Punnett squares are used to __________ the probability of different genotypes and phenotypes that may result from a given cross.

• They are a graphic summary of every possible combination of maternal and paternal alleles.

Test Crosses

• A cross used to determine whether the genotype of an individual expressing a dominant trait is ____________________________

Test Crosses

• It is always performed with an _________ genotype and a ___________ individual

– If all the offspring display the ___________ phenotype, then the individual in question is ______________dominant

– If the offspring displays both dominant and recessive phenotypes, then the individual is ________________