Mendelian Genetics

Objectives SWBAT explain the key terminology used in Mendelian Genetics. SWBAT apply the principles of Mendelian Genetics to solve heredity problems using Punnett Squares.

Key Points Different forms of the same gene are called alleles. When gametes are produced, alleles segregate from each other, so that each gamete carries one copy of the gene. Genes for different traits segregate independently. Punnett squares can be used to predict and compare genetic crosses

Gregor Mendel’s Peas An Austrian monk named Gregor Mendel helped discover two basic principles of heredity. 1. Genes exist in more than one form. The different forms of a gene are called alleles. 1.Some alleles are dominant and others are recessive.

The Principle of Dominance An organism with a dominant allele for a particular trait, will always exhibit that particular trait. The recessive will be silent. Example using Mendel's Pea Plants : The allele for yellow seeds (Y) is dominant over the allele for green seeds (y). If the plant had one copy of each allele, Yy, the plant’s seeds would be yellow.

Segregation When gametes are produced, alleles segregate from each other, so that each gamete carries one copy of the gene.

Biology Check-Up The human trait for large (E) and small (e) eyes is controlled by the same. 1.Different forms of the same gene is called an __________ 2.We can say that an individual’s genetic combination of this trait is Ee. If we know that large eyes is dominant over small eyes, what size eyes will this individual have? Why?

Punnett Squares Punnett Squares can be used to predict and compare genetic variation. We used a Punnett Square when we cross two individuals. Example:

Key Words Genotype – the actual combination of Alleles Aa or aa or AA Phenotype – the actual trait that is created This is what you see!!! Homozygous – Pure Bread AA or aa Heterozygous – Hybrid Aa

You can get a huge amount of information from one Punnett Square!

The allele for webbed fingers (W) is dominant over the allele for normal finders (w).

Let’s cross Ww x Ww

Step 1: Apply the Law of Segregation Ww x Ww W W w w

W W w w Step 2: Fill in the square. WW w W W w ww

W W w w WW w W W w ww We have created 3 different Genotypes Genotypic Ratio 1:2:1 Homozygous Dominant Homozygous Recessive Heterozygous

We have created 2 Phenotypes. W W w w WW w W W w ww Webbed Normal Phenotypic Ratio 3:1

W W w w WW w W W w ww What is the expected percentage of individuals that will express a heterozygous genotype?

W W w w WW w W W w ww What percentage of individuals will show the normal phenotype?

W W w w WW w W W w ww What percentage of individuals will express the homozygous dominant phenotype?

Lets try another one… Use the same trait, Webbed (W) and non-webbed (w), but this time cross homozygous dominant with homozygous recessive.

Lets try another one… What is the expected percentage of individuals that will express the heterozygous genotype?

Lets try another one… What percentage of individuals will express the normal phenotype?

Lets try another one… What percentage of individuals will express the webbed phenotype?

Independent Assortment Gene of different traits can segregate independently during the formation of gametes. This is why we are all so different!!!