genetics

Objectives:

1. Understand what genes are and how they work to create living things

2. Describe patterns of inheritance

3. Understand how inheritance is predicted

Essential Questions:

How do genes work to create living things?

How are genes inherited?

Key Terms:

Alleles - A form of a gene

Polygenic - many genes (more than one)

Genotype - a combination of alleles of a specific gene

Phenotype - the appearance of a trait

Dominant - inheriting a single copy of an allele

Recessive - inheriting two copies of an allele

Multiple Alleles - three or more forms of alleles

Sex-linked traits - traits controlled by the genes on a sex chromosome

Chromosome - A structure of nucleic acids and proteins

Genes decode particular proteins. Different types of genes are called alleles. Organism’s alleles determine the organism's traits. Most organism’s traits are polygenic which means they are determined by many different genes in different chromosomes. There are different alleles of genes that determine traits. Sexually reproducing organisms have two alleles of each gene. An organism can inherit two of the identical alleles or two different alleles this combination is called a genotype. If an organism inherits two dominant alleles it becomes a dominant phenotype. If an organism inherits two recessive alleles then, it becomes a recessive phenotype. Organisms with two identical alleles are called homozygous. Heterozygous is when an organism inherits two different alleles. Dominant alleles are more than recessive alleles so, a heterozygous will show the dominant trait. Scientist use something called Punnett squares to show all possible alleles combinations. Punnett squares can be used to determine things like cystic fibrosis but can’t be used to predict the genotype or phenotype of an offspring. The pedigree chart is used to trace the inheritance of a trait back to many generations. In pedigree charts, females are represented by circles and males are represented by squares. Some genes don’t have just one dominant allele and one recessive allele some are in between with a combination of both this is called incomplete dominance. For example, if two snapdragons reproduce one that is red which is dominant and the other white which is recessive. In a normal case, the offspring would be red because red is the dominant trait but, incomplete dominance gives the offspring a mix of both the dominant and recessive traits so the offspring would be pink. Co-dominance may also happen in alleles this means that and offspring can have both of its parents traits but instead of having a mix of both they have each one completely. In humans and animals sex chromosomes determine a person's sex. There are two human sex chromosomes X and Y. XX chromosomes are female and XY are male. X chromosomes are much bigger and contain more genes than Y chromosomes. Traits that are determined by the genes on a sex chromosome are called sex-linked traits.