The Basics of Genetics and Inheritance Patterns

Genetics and inheritance patterns from genetics can be a very interesting study. In human genetics the traits we inherit from our parents come from the chromosomes were receive. In standard inheritance we receive 23 chromosomes from each parent. Chromosomes are made up from many genes and different versions of the gene are called alleles. These alleles can be dominant or recessive. On occasion an extra chromosome can be inherited or a chromosome can be missing.

Dominant and recessive genes:

A dominant chromosome is just that. When this dominant gene is passed it will take precedence over a recessive gene that is received. In general, a trait of brown eyes is considered a dominant gene while blue eyes come from a recessive gene. In this example the brown eyed trait will be referred to as "B" and the blue eyed trait as "b". If both parents pass a "B" gene the offspring will have two "B" alleles and brown eyes. With one parent passing the "B" and the other passing "b" the child will still have brown eyes as brown is the dominant gene. For blue eyes, both parents must pass the recessive "b" allele. An interesting note is that two brown eyed parents may have a blue eyed child. This will occur if both parents have a recessive blue trait and both pass this recessive trait to their offspring.

Sexual determination:

There are two chromosomes that determine the sex of the child. These are the X and Y chromosomes. A female has two X chromosomes and can only pass an X chromosome to their child. A male has both an X and Y chromosome. The chromosome the father passes is the one that determines whether the child will be male or female. The understanding of this is significant because in older times the lack of a male heir to royalty was blamed on the mother. The wives of Henry the VIII might have faired better had this been known at the time.

Blood types:

In blood types there are three possible alleles. These are A, B, and O. A and B blood alleles are dominant while the O allele is recessive. When two different dominant alleles are passed it is referred to as co-dominance. In this example an "A A" combination produces "A" blood type, "A O" will produce an "A" blood type as "O" is recessive. The same follows with the passing of a "B" blood type while one parent passing "A" and one passing "B" will result in the "A B" blood type. For a child with "O" blood type both parents must pass the "O" allele.

Genetic anomalies:

On occasions extra chromosomes can be passed. Sometimes a chromosome can be missing. The most common cause of Turner's syndrome is the lack of one X chromosome with the female child only having one X. Trisomy is a condition where three sets of a gene are passed instead of the usual two. Down's syndrome is an example where three sets of the 21^st chromosome are passed to the child.

There are also extra traits that can be passed on the X or Y chromosomes. There are many factors that can go into the actual genetic make up of an individual including genetic mutations and environmental changes. This makes the inheritance patterns of genetics a very interesting area of study.

　

References:
http://www.marchofdimes.com/professionals/14332_1209.asp
http://kidshealth.org/teen/diseases_conditions/genetic/turner.html
http://www.dartmouth.edu/~cbbc/courses/bio4/bio4-1997/01-Genetics.html
http://anthro.palomar.edu/mendel/mendel_3.htm
http://www.bioweb.uncc.edu/1110Lab/notes/notes1/lab7.htm