Understanding Inheritance

Traits

Detached Earlobes

Tongue rolling

Dimples

Cleft Chin

Cross Left thumb over right

See Colours Red and Green

Straight Hair Line vs Widows Peak

Key Terms Selective breeding Artificial breeding Pure Bred Gregor Mendell Traits Self-fertilization vs. Cross Fertilization Monohybrid cross Dihybrid cross P generation F1 and F2 generation Dominant vs. recessive traits Genotype vs. Phenotype Heterozygous and Homozygous alleles

Early Genetics Selective breeding was the earliest form of understanding about genetics Selective breeding (a form of artificial breeding) is when people breed certain animals or plants in order to produce a desired offspring For example: Horses that developed strong muscles were bred with other horses that had strong muscles in order to make race horses.

Early Genetics Pure bred horses are used by horse breeders to produce offspring that are quicker, stronger, and more durable for races.

Early Genetics Prior to the 1850’s and 1860’s people did not understand how genetics worked. In the 1600’s, live sperm was discovered using a microscope. It was believed that a tiny person was inside the sperm and that this person would develop inside the mother In the 1800’s, scientists realized that people inherit their characteristics from both parents. However, they believed in blended inheritance (i.e. if mother has blond hair and father has black, the child will have brown hair.

Gregor Mendel – The Pioneer of Genetics

Gregor Mendel: The Pioneer of Genetics Gregor Mendel was the first to conduct a scientific experiment on inheritance Mendel discovered inheritance by studying garden peas

Gregor Mendel’s Observations Gregor Mendel noticed that some garden pea plants were tall while others are short, some pea plants had different flower position…

Gregor Mendel’s Observations … some pea plants were round while others were wrinkled, and some pea pods were full while others flat Mendel referred to these characteristics as traits.

Gregor Mendel’s Observations Mendel also noticed that pea plants could self- fertilize and cross-fertilize. Self-fertilization means that a plant is able to reproduce with itself and produce offspring. Cross-fertilization means that a plant reproduces with another plant to produce an offspring (sexual reproduction).

Cross-Fertilization Vs. Self-Fertilization

Mendel’s Experiment Mendel used pea plants that self-fertilize for his experiment. This meant that the offspring made by that plant will be the same as the parent This is referred to as true breeding or pure breeding. Mendel then selectively fertilized a pure bred green pea plant with a pure breed yellow pea plant. In Genetics this is called a cross. (a.k.a cross fertilization)

Mendel’s Experiment Cross Fertilization

Before we look at the results let us clarify some key terms

Key Terms Since Mendel was only examining the colour of the pea pod, it is called a monohybrid cross. If for instance Mendel was examining both the colour and the size of the pea plant, then it would be called a dihybrid cross.

Key Terms In a test cross (cross pollination) the parent generation is called P generation The first offspring is called F1 generation The children of the F1 generation is the F2 generation. …And so forth…

Back to the results of Mendel’s Experiment

Mendel’s Results When Mendel cross fertilized pure bred green pea plants with pure bred yellow pea plants The offspring were all green pea plants.

Mendel’s Experiment Through this experiment Mendel realized that some traits (i.e green coloured pea plants) are dominant to other traits (i.e. yellow coloured pea plants). The green coloured allele for pea plants is therefore dominant to the yellow coloured allele. The yellow coloured allele is therefore recessive.

Mendel’s Experiment (Part 2) Mendel then crossed two of the F1 generation pea plants from the original experiment and… The result was that ¾ of the offspring were green and ¼ were yellow

Genotype vs. Phenotype Alleles are often represented using upper-case letters and lower-case letters. Recall Mendel’s experiment: Which colour allele is dominant?

Genotype Since the green allele is dominant, we can represent it using the letter G. On the other hand, the yellow allele is recessive and we can represent it using the letter g. Remember each trait has 2 alleles: This makes it possible to have 3 different combinations: 1. GG 2.Gg 3. gg

Let us look at a different example

Genotype vs. Phenotype

Genotype vs. Phenotype Genotype refers to the combination of alleles and the phenotype refers to the physical characteristics (e.g. observable traits) produced by the alleles.

Genotype If the gene contains two dominant alleles (e.g. GG) we call this genotype homozygous dominant. If the gene contains two recessive alleles (e.g. gg) we call this genotype homozygous recessive. If the gene contains one dominant and one recessive allele (e.g. Gg) we call this genotype heterozygous.

Genotype vs. Phenotype

homework Pg.207 # 4, 6, 9, 11