Introduction to Genetics

Biology 1-2

Genetics

Genetics is the study of heredity and inheritable traits. Gene-a discreet unit of hereditary

information consisting of a DNA sequence.

Law of Segregation

The law of segregation explains how traits are passed to offspring and which traits will show. 1. There are alternate forms of genes.

Alternate forms of genes are called alleles. Alleles create variation in a trait.

2. For each inherited characteristic, an organism has two genes, one from each parent.

Law of Segregation cont’d

3. If the two alleles differ, one is fully expressed in the organism’s appearance. The other allele has no noticeable effect on the organism’s appearance.

The dominant allele is the one that is fully expressed.

There is no intermediate form or mixing when the alleles are different.

The recessive allele is covered up by the dominant allele.

Only shows when there are two recessive alleles together.

Law of Segregation cont’d

4. Each sperm or egg carries only one allele for each inherited trait.

When the sperm or egg form, each gets one allele for each trait.

When the sperm an egg meet, the resulting offspring ends up with two alleles for each trait.

Homozygous dominant-two dominant alleles. Homozygous recessive-two recessive alleles. Heterozygous-one dominant and one recessive

allele. The dominant trait shows, hiding the recessive trait.

Law of Segregation cont’d

Genotype-the genetic makeup of an organism. What genes the organism has.

Phenotype-the expressed traits of an organism. The physical appearance of an

organism. Genotype creates the phenotype.