DNA
DNA is a nucleic acid made of two strands of nucleotides wound together in a spiral called a double helix

DNA
●
○ a sugar molecule known as deoxyribose
○ a phosphate group
○ and one or four different nitrogenous bases:
■ Adenine (A)
■ Thymine (T)
■ Guanine (G)
■ Cytosine (C)

DNA
The phosphate and sugar parts of the nucleotides form the backbone of each strand in the DNA double helix

DNA
The bases extend toward the center of the double helix.

DNA
Each base in one strand is matched with a complementary base in the other strand in accord with the base-pairing rules:
A pairs with T
G pairs with C

DNA
These structural characteristics of DNA are the same in all organisms.
The DNA of different organisms differs in the
of nucleotides, and these differences in nucleotide sequence are responsible for the inherited differences among organisms.

DNA
DNA -

DNA
In eukaryotic cells, each chromosome consists of DNA wrapped around special proteins.
The chromosomes are contained in the nucleus inside a nuclear membrane.

DNA

C HROMOSOMES
Chromosomes – tightly coiled packages of DNA; they are rod shaped and proteins hold them together.
Strands of DNA wrap around proteins called
Histones.

I MPORTANT W ORDS
Chromatid – each half of a chromosome; forms as
DNA copies itself before cell division
Centromere – holds the chromatids together until they separate

C HROMOSOMES
How many chromosomes do humans have?
Each species has a unique number of chromosomes.
46 chromosomes or 23 pairs.

T YPES OF C HROMOSOMES
2 Types of Chromosomes:
1. Sex Chromosomes – are the chromosomes that determine the sex of an organism.
Female: XX
Male: XY
2. Autosomes – all other chromosomes
●
Humans: 44 autosomal chromosomes

K ARYOTYPE : P ICTURE OF C HROMOSOMES .
W HAT DO YOU NOTICE ABOUT THE
ARRANGEMENT ?

C HROMOSOMES
Karyotype – is a picture of the chromosomes in a somatic (body) cell.
22 homologous pairs of autosomes.
2 sex chromosomes
Is this person male or female?
Male: XY
Normal or abnormal
Normal: 23 pairs

C HROMOSOMES
Notice that the chromosomes are organized in pairs.
These pairs are homologous chromosomes
Homologous chromosomes – two copies of each autosome
(maternal and paternal)
Homologous chromosomes are the same size, shape, and carry genes for the same trait.
Final pair is not numbered: Sex Chromosomes.

C OMPARE THE KARYOTYPES .
R ECORD YOUR OBSERVATIONS
K ARYOTYPE A K ARYOTYPE B

C OMPARISONS
K ARYOTYPE A
19 pairs: Not Human
Sex: Male (XY)
Sister chromatids are still attached at their centromeres (these are double copies of each chromosome).
This is a picture
BEFORE the cell divided!
K ARYOTYPE B
23 pairs: Human
Sex: Female (XX)
Single Copy of each chromosome.
This picture was taken
AFTER the cell divided!
Be prepared to analyze a karyotype regardless of when the picture of the chromosomes was taken.

H UMAN K ARYOTYPE :
M ALE

H UMAN K ARYOTYPE : F EMALE

C HROMOSOMES
Diploid – cells have two sets (maternal and paternal) of chromosomes.
●
Have all 46 chromosomes.
●
Represented by 2n (means a full set of DNA)
●
Somatic Cells (cells making up the body)
Haploid – cells have one set of chromosomes.
●
●
●
Have 23 chromosomes.
Represented by n (means a half set of DNA)
Gametes (reproductive cells : egg and sperm)

H APLOID C ELLS
Reproductive Cells
Gametes - sperm and egg cells; they have 23 chromosomes
Fertilization →23 in sperm
+ 23 in egg = 46 in zygote
Gametes are produced through Meiosis (cell division results in 4 genetically different cells)
More on this later.

D IPLOID C ELLS
Somatic Cells
Cells that make up the body of organisms.
Somatic Cells are produced through
Mitosis (cell division results in 2 genetically identical cells).

K ARYOTYPING A CTIVITY http://www.biology.arizona.edu/human_bio/act ivities/karyotyping/karyotyping.html
(online karyotyping lab)
Complete for homework due Friday:
Handwritten ON PAPER:
Answer the two questions for each patient
Answer 1 for the internet search question.

H OMEWORK
Carefully read pages 246-252
Summarize the reading in a sentence outline.
Write complete sentences in outline form to summarize the important points of the reading.

10/22/14

G OALS
Learning Objective:
Describe the structure, location, and functional role of chromosomes in eukaryotic cells.
Complete Karyotypes and Lab Questions = HW
Quiz on DNA structure, Chromosome, and Cell Cycle on Friday
Online Karyotyping Lab - Test Bonus Questions From here

I MPORTANT W ORDS chromosome tightly coiled packages of DNA chromatid each half of a chromosome; forms as
DNA copies itself before cell division chromatin string-like fiber of DNA and protein called chromatin

Chromosome vs. Chromatin
During interphase, DNA is combined with proteins and organized into a precise, compact structure, a dense string-like fiber called chromatin , which condenses even further into chromosomes during cell division.