Modern Genetics Human Inheritance Patterns of Inheritance Some

Modern Genetics Human Inheritance

Patterns of Inheritance • Some traits are controlled by a single gene with two alleles – One dominant, one recessive with 2 distinct phenotypes – Example: widow’s peak • Some traits are controlled by single genes with multiple alleles – Three or more forms of a gene that code for a single trait – Example: blood type • There are 4 main types of blood- A, B, AB and O. A and B are dominant, O is recessive. • The allele for A is written IA , B is written IB and O is written i. • Other traits are controlled by many genes – At least 4 genes control height in humans. The genes act together as a group to produce a single trait. – Skin color is another example of a human trait controlled by many genes

Sex Chromosomes • Sex chromosomes carry genes that determine whether a person is a male or a female. They also carry genes that determine other traits. • Girl or boy? – Sex chromosomes are the only chromosomes that do not always match. – If you are a girl, they do match XX – If you are a boy, they do not match XY

Sex Linked Genes • Genes on the X and Y chromosome are often called sex linked. – Red-green color blindness • Like other genes, sex linked genes carry dominant and recessive alleles. Any allele on an X chromosome, recessive or dominant, will produce that trait in a male. • Because males only have one X chromosome, they are more likely than a female to have a sex linked trait that is controlled by a recessive allele.

Colorblindness • Colorblindness is a sex linked trait controlled by a recessive allele on the X chromosome. • Many more males have the trait than females. • Carrier- a person who has one recessive allele for a trait and one dominant. – The carrier can pass on the trait, but does not have the trait.

Environment • The effects of your genes are often influenced by the environment- organisms surroundings. • Height is a good example: – A diet lacking protein, minerals or certain vitamins can prevent a person from growing as tall as might be possible • Environmental factors can also effect human skills, such a playing an instrument or muscle coordination.