Mendelian genetics and punnett squares


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Mendelian genetics and punnett squares


Population genetics

Mendelian genetics and punnett squares

Hardy-Weinberg equilibrium

Inheritance patterns

Independent assortment of genes and linkage

Evolution and natural selection

Genetic disorders

Down syndrome (Trisomy 21)

Edwards syndrome (Trisomy 18)

Patau syndrome (Trisomy 13)

Fragile X syndrome

Huntington disease

Myotonic dystrophy

Friedreich ataxia

Turner syndrome

Klinefelter syndrome

Prader-Willi syndrome

Angelman syndrome

Beckwith-Wiedemann syndrome

Cri du chat syndrome

Williams syndrome

Alagille syndrome (NORD)


Polycystic kidney disease

Familial adenomatous polyposis

Familial hypercholesterolemia

Hereditary spherocytosis

Huntington disease

Li-Fraumeni syndrome

Marfan syndrome

Multiple endocrine neoplasia

Myotonic dystrophy


Treacher Collins syndrome

Tuberous sclerosis

von Hippel-Lindau disease


Polycystic kidney disease

Cystic fibrosis

Friedreich ataxia

Gaucher disease (NORD)

Glycogen storage disease type I

Glycogen storage disease type II (NORD)

Glycogen storage disease type III

Glycogen storage disease type IV

Glycogen storage disease type V


Mucopolysaccharide storage disease type 1 (Hurler syndrome) (NORD)

Krabbe disease


Niemann-Pick disease types A and B (NORD)

Niemann-Pick disease type C

Primary ciliary dyskinesia

Phenylketonuria (NORD)

Sickle cell disease (NORD)

Tay-Sachs disease (NORD)



Wilson disease

Fragile X syndrome

Alport syndrome

X-linked agammaglobulinemia

Fabry disease (NORD)

Glucose-6-phosphate dehydrogenase (G6PD) deficiency


Mucopolysaccharide storage disease type 2 (Hunter syndrome) (NORD)

Lesch-Nyhan syndrome

Muscular dystrophy

Ornithine transcarbamylase deficiency

Wiskott-Aldrich syndrome

Mitochondrial myopathy

Autosomal trisomies: Pathology review

Muscular dystrophies and mitochondrial myopathies: Pathology review

Miscellaneous genetic disorders: Pathology review


Mendelian genetics and punnett squares


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Victoria S. Recalde, MD

Evan Debevec-McKenney

Tanner Marshall, MS

Justin Ling, MD, MS

Genetics is the science that studies inheritance, or the way parents transmit certain traits to their descendants.

And Mendelian genetics, refers to Gregor Mendel—an Austrian monk—who studied inheritance by experimenting on pea plants.

He cross-pollinated the flowers of different plants together, took the seeds the developed from the pairing, planted those seeds, and took careful notes on the types of peas that resulted in the subsequent generations. As a monk he was just trying to find his inner peas (peace)!

Now in addition to having lots and lots of peas in his garden, he helped to formulate two important laws; the law of segregation and the law of independent assortment.

So to start out - Mendel took plants with violet flowers and plants with white flowers and crossbreed them.

This original group of flowers are called the P generation, as in “parent,” and then when he obtained some peas, he planted them and got more plants and the flowers in this offspring generation was called F1, or filial one.

It turned out that the F1 generation consisted of all violet flowers, so he called the violet trait “dominant,” while the white trait which appeared to be lost in the F1 generation, was called “recessive.”

Next, Mendel let the violet flowers in the F1 generation cross-pollinate amongst themselves, and when they formed peas - he planted them again.

He got more plants and the flowers from that second generation of plants he called filial two or F2.

It turned out that some of the plants in this F2 generation had white flowers whereas other plants had purple flowers! In fact, the ratio was about 3 violet flowering plants for every 1 white flowering plant.

Based on this experiment, Mendel drew a few conclusions.

First, since the F1 violet flowers had some offspring plants that produced violet flowers and other offspring plants that produced white flowers, it meant that the F1 plants must have contained both of these elements.

The inheritable elements of pea plants are its the gametes, so that meant that the gametes of the F1 plant, contained either the dominant violet trait or the recessive white trait.

The F2 plants are created with one gamete from each parent.

And Mendel worked out that the white flowering plants resulted when they receive both white flower elements, and that plants that had at least one violet flower element from either parent would produce violet flowers.

Mendel didn’t know this at the time, but the “element” he was referring to were segments of DNA called genes that encoded flower color.

These genes were located on specific parts of chromosomes, called loci.

Different versions of a gene are called alleles, and in the case of the flowers there were two alleles - a white and violet allele for flower color.

A helpful way to visualize Mendel’s experiment is to use a Punnett square.


Mendelian genetics is the study of how genes are passed from parents to their offspring. Genes are inherited in pairs, one gene from each parent. Punnett squares are a tool used by geneticists to predict the possible combinations of genes that could be inherited from a particular mating. To use a Punnett square, you first need to determine the genotypes of each parent. Then you can use the Punnett square to predict the possible genotypes of their offspring.


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