Inheritance of Traits

The Relationship Among Genes and Chromosomes

Genes on chromosomes carry information for physical expression of traits.

Genetics Genetics: study of Heredity, or the passing of characteristics from parents to offspring. Traits: Inherited characteristics.

Gregor Mendel 1822-1884 Father of Genetics Austrian monk Botanist Mathematician Studied traits in garden peas Explained patterns of inheritance

Mendels Observations P generation = Parents white crossed with purple F1 generation = 1st generation of offspring: All purple F2 generation = 2nd generation of offspring: 75%purple, 25% white

Mendels Laws Law of Unit Factors 2 factors control each trait Alleles- alternate forms of genes plant height: tall or short flower color: white or purple

Allele Combinations Homozygous (purebreed) individuals have 2 of the same allele 2 tall alleles 2 white alleles Heterozygous (hybred) individuals have 2 different alleles 1 tall allele and 1 short allele 1 white allele and 1 purple allele

Mendels Laws 2. Law of dominance Only 1 of the 2 alleles is shown in an individual The dominant allele is always shown when it is paired with a recessive trait The recessive allele is hidden when with a dominant allele

Law of Dominance Purple: dominant White: recessive

Mendels Laws Law of Segregation Pairs of alleles separate during meiosis into gametes so that each egg or sperm has only 1 of each allele

Law of Segregation

Mendels Laws Law of Independent Assortment Which allele ends up in which gamete is independent of other alleles and random

Law of Independent Asssortment

Tail length is independent of fur color (tail length and hair color have nothing to do with each other)

Problem Solving Using the Punnett Square Use letter for the dominant trait Uppercase letter for dominant Lowercase letter for recessive Purple: P = dominant White: p = recessive Tall: ____ = dominant Short: ____ = recessive Tall: T = dominant Short: t = recessive

Problem Solving Using the Punnett Square Phenotype- physical expression of a gene purple, white, tall, short Genotype- genetic makeup in letters PP, Pp or pp, heterozygous or homozygous

Problem Solving Using the Punnett Square Set up Punnett square 2 parents are crossed (given genotype or phenotype) Possible parental gametes are determined Possible male gametes across head of each column Possible female gametes down head of each row

Punnett Square Cross 2 Heterozygous (hybrid) tall parents Tt x Tt

Results of Punnett Square Each square contains the possible genotype of offspring Expressed as percent, fraction or ratio Phenotypic results: dominant: recessive; 3:1 ¾tall, ¼ short; 75% tall, 25% short Genotypic results: Homozygous dominant: heterozygous: Homozygous recessive; 1:2:1 ¼ TT, ½ Tt, ¼ tt; 25%TT, 50%Tt, 25% tt

Round or wrinkled texture Monohybrid Cross One trait is observed Yellow or green pea color Round or wrinkled texture

Dihybrid Cross Two traits are observed Each parent donates two alleles to the offspring Texture Wrinkled or smooth Color Yellow and green