Why do I Look This Why do I Look This Way?Way?

Elementary GeneticsElementary Genetics

ChromosomesChromosomesChromosomes carry Chromosomes carry the genetic information the genetic information of the individual.of the individual.

Each chromosome is Each chromosome is made of a single made of a single strand of DNAstrand of DNA

Humans have 23 Humans have 23 pairs of pairs of chromosomeschromosomes

GenderGender You have two chromosomes that determine You have two chromosomes that determine

your genderyour gender

Males have XYFemales have XXFemales have XX

Here are the gender Here are the gender possiblilities possiblilities

From mother From mother XXXX from father from father XXYY gender gender

XX XX FemaleFemale

XX YY Male Male

XX XX Female Female

X X Y Y MaleMale

Where are the Where are the chromosomes located?chromosomes located?

Sex cells have half as many Sex cells have half as many chromosomes. chromosomes.

The chromosomes are 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 duplicateWhen the cells duplicate (mitosis), they make exact (mitosis), they make exact copies of the chromosomes.copies of the chromosomes.

Sex CellsSex Cells

Duplicate through MEIOSISDuplicate through MEIOSIS Have half as many chromosomes as Have half as many chromosomes as

other cellsother cells Are called “eggs” in femalesAre called “eggs” in females Are called “sperm” in malesAre called “sperm” in males Must join to begin lifeMust join to begin life

Why is sexual Why is sexual reproduction reproduction important?important? Keeps species from dramatically Keeps species from dramatically

overpopulatingoverpopulating Insures that parents are old enough to Insures that parents are old enough to

care for youngcare for young Makes individuals that are not identicalMakes individuals that are not identical Allows elimination of weak traitsAllows elimination of weak traits

traitstraits

Some traits are dominant while others Some traits are dominant while others are recessiveare recessive

You inherit one chromosome from each You inherit one chromosome from each parent (each with a trait marker)parent (each with a trait marker)

You will exhibit the trait which is You will exhibit the trait which is dominantdominant

Eyes, for example:Eyes, for example: Brown eyes are dominant over blueBrown eyes are dominant over blue Your mother could have blue eye if she has Your mother could have blue eye if she has

bl blbl bl Your father might have brown eyes if he has Your father might have brown eyes if he has

BRBR blbl You could get: You could get: blbl BR BR You would have You would have BRBR eyes eyes bl bl bl bl You would have You would have blbl eyes eyes bl bl BR BR You would have You would have BRBR eyes eyes bl bl bl bl You would have You would have blbl eyes eyes

OR:OR: Your mother might have brown eyes if Your mother might have brown eyes if

she has she has BRBR blbl Your father might have brown eyes if he Your father might have brown eyes if he

has has BRBR blbl You could get: You could get:

BR BR BR BR You would have You would have BRBR eyes eyes BR BR bl bl You would have You would have BRBR eyes eyes bl bl BR BR You would have You would have BRBR eyes eyes bl bl bl bl You would have You would have blbl eyes eyes

Just a note:Just a note:

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

The double helix structure was The double helix structure was discovered due to the work of discovered due to the work of three scientists:three scientists: Rosalind Rosalind

FranklinFranklin James James

WatsonWatson Francis Francis

CrickCrick