GENETICS IGENETICS ICHROMOSOMESCHROMOSOMES

A. CHROMOSOMESA. CHROMOSOMES

Chromosomes are Chromosomes are found in the found in the nucleus of the cellnucleus of the cell

CHROMOSOMESCHROMOSOMES

CHROMOSOMES CHROMOSOMES within a cell are within a cell are arranged in pairs from the arranged in pairs from the largest largest to the smallest, followed by sex-to the smallest, followed by sex-chromosomes chromosomes

– As you can see, we As you can see, we have: have: twotwo # #11 chromosomes,chromosomes,twotwo # # 22 chromosomes,chromosomes,twotwo # # 33 chromosomes,chromosomes,and so on for all and so on for all the pairs.   the pairs.  

B.B. AUTOSOMESAUTOSOMES

The first The first 22 pairs22 pairs are called are called AUTOSOMESAUTOSOMES, and , and are shared by both are shared by both the male and the the male and the female. female.

C. SEX CHROMOSOMESC. SEX CHROMOSOMES

Chromosomes in Chromosomes in pair #23pair #23 are are called sex-called sex-chromosomes. chromosomes.

FEMALESFEMALES– A A womanwoman has has

two Xtwo X sex- sex-chromosomeschromosomes

XX XX

MALESMALES A A manman has has oneone XX

sex-chromosome sex-chromosome and and one Yone Y sex- sex-chromosome. chromosome.

XYXY

D. KARYOTYPESD. KARYOTYPES

WHAT’S A KARYOTYPE?WHAT’S A KARYOTYPE?

KaryotypeKaryotype

A karyotype is a photograph of A karyotype is a photograph of chromosomes grouped in order in pairs.chromosomes grouped in order in pairs.

Karyotyping is a test to examine Karyotyping is a test to examine chromosomes in a cell, which can help chromosomes in a cell, which can help identify genetic problems as the cause identify genetic problems as the cause of a disorder or disease. of a disorder or disease.

This test can This test can Count the number of ChromosomesCount the number of Chromosomes Look for structural changes in the Look for structural changes in the

chromosomeschromosomes

SINGLE CHROMOSOMESINGLE CHROMOSOMEKARYOTYPEKARYOTYPE

PAIRED CHROMOSOMESPAIRED CHROMOSOMESKARYOTYPEKARYOTYPE

Karyotypes of a Karyotypes of a male and femalemale and female

F. Determining sexF. Determining sex

A. A. FERTILIZATIONFERTILIZATION LifeLife begins when a begins when a

spermatozoaspermatozoa and an and an ovumovum uniteunite to form one to form one single cell called a zygote, single cell called a zygote, which as of that moment, which as of that moment, will undergo a series of will undergo a series of divisions (mitosis) that will divisions (mitosis) that will result in the birth of an result in the birth of an infant. infant.

This process is known as This process is known as fertilizationfertilization, and it takes , and it takes place in the female's place in the female's uterine tubes. uterine tubes.

Humans have 23 Humans have 23 pairs of pairs of chromosomeschromosomes

1-22 are 1-22 are homologous and homologous and are called are called autosomes autosomes

Pair 23 are the sex Pair 23 are the sex chromosomes and chromosomes and determine your sexdetermine your sex

Fertilization happens when an egg cell and sperm unite Note: Egg and sperm not shown to scale

                                          

                         

Most of our cells contain 46

What determines if What determines if you are a male or you are a male or female? female?

XY = maleXY = male XX = femaleXX = femaleHuman Female Karyotype

As a result of As a result of chromosome chromosome separation during separation during meiosis, each meiosis, each gamete contains gamete contains one sex one sex chromosome and chromosome and one of each pair 1-one of each pair 1-2222

F. GAMETESF. GAMETES(SEX CELLS)(SEX CELLS)

All egg cells contain 1 X chromosomeAll egg cells contain 1 X chromosome

50% of sperm cells contain an X 50% of sperm cells contain an X chromosomechromosome

The The otherother 50% contain a Y chromosome 50% contain a Y chromosome

So, what determines the sex of the So, what determines the sex of the zygote?zygote?

What about twins?What about twins? Identical twins come Identical twins come

from one fertilized egg from one fertilized egg that splits early in the that splits early in the pregnancy and pregnancy and develops into more develops into more than one fetus. This is than one fetus. This is different because not different because not only do the fetuses only do the fetuses share the same share the same placenta, but they also placenta, but they also share the same genetic share the same genetic material. That is why material. That is why they are identical (they they are identical (they have the same hair have the same hair color, eye color, sex, color, eye color, sex, and blood type). and blood type).