Cell ReproductionNotes Day 1

Warm Up

Where are your genes located?

http://people.na.infn.it/~nicodem/research/cell_genes.jpg

•DURING MOST OF THE CELL’S LIFE, DNA FORMS A TANGLED MASS CALLED CHROMATIN.•CHROMATIN LOOKS LIKE A PLATE OF SPAGHETTI.•RIGHT BEFORE A CELL DIVIDES, THE CHROMATIN FORMS INTO CHROMOSOMES (X-SHAPED).

MOST OF THE TIME ONCE IN A WHILE

CHROMATIN CHROMOSOMES

Cell Division• Chromosomes = Tightly coiled, rod-shaped DNA• Chromosomes are made of chromatin• Human body produces 2 trillion cells per day & 25

million per second• Cells are formed by cell division of older cells

1. When a cell divides, DNA is first copied & then distributed

2. Each cell ends up with a complete set of DNA

Chromosome Number

• Each human somatic cell has 2 copies of 23 different chromosomes – Total 46– Somatic = any cell that is NOT a sex cell– (also called body cells or autosomes)

Sets of Chromosomes

• Each pair is made up of 2 homologous chromosomes– Homologous chromosomes = chromosomes that are similar

in size, shape, & genetic content– Each homologue comes from one of the parents

• One from mom• One from dad

Cells Can Be Diploid or Haploid

• Diploid = a cell that contains 2 sets of chromosomes (2n)

• Haploid (monoploid) = a cell that contains only 1 set of chromosomes (1n or n)

Chromosomes Determine Your Gender

• Humans have 23 pairs of chromosomes• 22 pairs are autosomes (chromosomes NOT

directly involved in determining sex)• 1 pair are sex chromosomes (contain genes

that WILL determine the sex)– X & Y chromosomes

X & Y Chromosomes

• Male = XY• Female = XX• Male (dad) can donate an X or a Y to

offspring• Female (mom) can ONLY donate an X

So-Which parent determines the sex of the baby?

MALEXY

Gametes

• Gametes are reproductive cells– Males = sperm (n = 23)– Female = egg (n = 23)

• Combine in fertilization to make a: – Zygote (2n = 46)

Karyotype• Karyotype = a photo of the chromosomes in a

dividing cell that shows the chromosomes arranged by size.

Karyotype cont’d

• Each of an individual’s 46 chromosomes has thousands of genes so the presence of all chromosomes is essential for normal functioning– Humans who are missing a chromosome don’t

survive– Humans with more than two copies of a

chromosome, called trisomy, may survive but will not develop properly.

What is wrong?

The Cell Cycle

• Repeating sequence of cell growth and division during an organism’s life

• 90% of cell life is spent in INTERPHASE

• Then it may go into MITOSIS & CYTOKINESIS

INTERPHASE(divided into mini-phases)

• G1(first growth) phase = Cell grows rapidly

• S (synthesis) phase = DNA copied

• G2 (2nd growth) phase = Nucleus prepares to divide

http://publications.nigms.nih.gov/insidethecell/ch4_interphase_big.html