Why do I Look This Way? Elementary Genetics

Chromosomes Chromosomes carry the genetic information of the individual. Each chromosome is made of a single strand of DNA Humans have 23 pairs of chromosomes

Gender  You have two chromosomes that determine your gender Males have XY  Females have XX

Here are the gender possiblilities  From mother XX from father XY gender X X Female X Y Male X X Female X Y Male

Where are the chromosomes located?  Sex cells have half as many chromosomes. The chromosomes are in the nucleus of each in the nucleus of each cell. Every cell has the cell. Every cell has the exact same ones. exact same ones. When the cells duplicate (mitosis), they make exact copies of the chromosomes. (mitosis), they make exact copies of the chromosomes.

Sex Cells  Duplicate through MEIOSIS  Have half as many chromosomes as other cells  Are called “eggs” in females  Are called “sperm” in males  Must join to begin life

Why is sexual reproduction important?  Keeps species from dramatically overpopulating  Insures that parents are old enough to care for young  Makes individuals that are not identical  Allows elimination of weak traits

traits  Some traits are dominant while others are recessive  You inherit one chromosome from each parent (each with a trait marker)  You will exhibit the trait which is dominant

Eyes, for example:  Brown eyes are dominant over blue  Your mother could have blue eye if she has bl bl  Your father might have brown eyes if he has BR bl You could get:  bl BR You would have BR eyes  bl bl You would have bl eyes  bl BR You would have BR eyes  bl bl You would have bl eyes

OR:  Your mother might have brown eyes if she has BR bl  Your father might have brown eyes if he has BR bl You could get:  BR BR You would have BR eyes  BR bl You would have BR eyes  bl BR You would have BR eyes  bl bl You would have bl eyes

Just a note:  While it its generally true that brown eye genes are dominant over green eye genes which are both dominant over blue eye genes, variations can occur. Because many genes are required to make eye color pigments, there is a way called genetic compensation to get brown or green eyes from blue-eyed parents.

The double helix structure was discovered due to the work of three scientists:  Rosalind Franklin  James Watson  Francis Crick