Chapter 6 - Section 1 Human Inheritance

Vocabulary Multiple Alleles – three or more forms of a gene that code for a single trait Sex Chromosomes – a pair of chromosomes carrying genes that determine whether a person is male or female Sex-linked Gene – genes found on the X or Y chromosomes Carrier – a person who has one recessive allele and one dominant allele for a trait

Gold Keys Some human traits are controlled by single genes with two alleles, and others by single genes with multiple alleles. Still other traits are controlled by many genes that act together The sex chromosomes carry genes that determine whether a person is male or female. They also carry genes that determine other traits Many of an organism’s characteristics are determined by an interaction between genes and the environment.

General Notes Even though a gene may have multiple alleles, a person can carry only 2 of those alleles. Human blood is an example of gene controlled by multiple alleles Hair, skin eye color are examples of traits controlled by multiple genes Girls sex chromosomes are XX, boys are XY – sex of a baby is determined by which allele the father passes on

Colorblindness is a trait controlled by a recessive allele on the X chromosome. More men have colorblindness than women because if they receive an X chromosome from their mother that has the recessive allele there is nothing on the father’s Y chromosome to mask that trait. Environment plays a part in how a genetic trait is shown. Example – height is genetic but nutrition also plays a part in how tall a person will become