DNA stands for deoxyribonucleic acid DNA is a type of nucleic acid Nucleic acids are polymers of nucleotides Nucleotides are composed of 3 parts: Nitrogenous 1 Deoxyribose Sugar (adenine)

There are 2 types of nitrogenous base:  PYRIMIDINES PURINES

Alternating phosphate and sugar 
groups form the backbone of DNA

DNA uses the nucleotides containing A, G, C, 
and T DNA molecules are helical in structure, and 
two DNA strands coil around each other.

The two strands in DNA are held together by hydrogen bonds 
between nitrogenous bases on adjacent strands. Base pairing occurs between A and T,(2 H-bonds) and 
between G and C (3 H-bonds)

The two strands are said to run antiparallel. Each strand of the DNA molecule has a free phosphate 
group at one end and a free sugar (deoxyribose) at the 
other end. The two strands 
are said to run 
antiparallel. Every nucleotide 
pair is composed 
of a purine facing 
a pyrimidine

DNA Model Building - Kit

Review

It involves two stages of cell division. Meiosis Meiosis is the process by which sex cells, or gametes, are formed. It involves two stages of cell division. In meiosis, the chromosome number of 
the daughter cells is half that of the 
parent cell.

Each gamete will contain both the same 
number and the same kind of chromosomes. The number of chromosomes in a gamete is 
called the haploid chromosome number, or n; The number of chromosomes in all other cells is 
twice the haploid number and is called the 
diploid number, or 2n.

You receive 23 chromosomes 
from your father and 23 from 
your mother. You have 23 pairs of 
chromosomes called 
homologous chromosomes The genes in homologous 
chromosomes deal with the 
same traits.

` Human Karyotype

Meiosis involves two 
divisions. Meiosis II

The nuclear membrane begins to dissolve The centriole splits, move to 
opposite poles,spindle  fibres are 
formed. Homologous pairs come together 
(form tetrad) This process is referred to as 
synapsis.

Sometimes the intertwined chromatids 
exchange segments (crossing over)

The homologous 
chromosomes attach themselves to 
the spindle fibres and 
line up along the 
equatorial plate.

Homologous pairs of chromosomes move toward opposite poles Homologous pairs of 
chromosomes move 
toward opposite 
poles. The process is 
known as 
segregation.

Membrane begins to 
form around each 
nucleus. Unlike in mitosis, the 
chromosomes in the 
two nuclei are not 
identical.

During meiosis II, pairs of 
chromatids will separate and 
move to opposite poles. Prophase, metaphase anaphase 
and telophase are all very similar. Four haploid daughter cells are 
produced from each meiotic 
division.

The formation of sex cells during 
meiosis is referred to as gametogenesis.

Abnormal Meiosis: Nondisjunction Meiosis is not always perfect. Nondisjunction occurs when two 
homologous chromosomes move to the 
same pole during meiosis. This is a problem if it happens during the 
formation of sex cells.

In humans, gametes with 22 and 24 chromosomes 
can form (This results in a zygote containing 47, or 
45 chromosomes) If the zygote has three homologous chromosomes 
it is referred to as trisomy. If the zygote has only one of the chromosomes it is 
called monosomy.

Down syndrome (Trisomy 21) Individuals with Down syndrome have an extra 
chromosome number 21. This results in a person has too much genetic information. People with Down syndrome share several common traits: - a round, full face; - enlarged and creased tongue; - short height; - large forehead. It has been estimated that 1 in 600 babies is born with 
Down syndrome.

OTHERS: Edwards syndrome - trisomy of chromosome 18. - almost every organ system affected 1:10,000 live births. 
Generally do not live more than a few months. Patau syndrome - trisomy 13. - serious eye, brain, circulatory defects as well as cleft 
palate. 1:5000 live births. Rarely live more than a few 
months.

Turner syndrome is a monosomic disorder that produces a female with a single X chromosome. When the egg with no X chromosome is fertilized 
by a normal sperm cell with an X chromosome, a 
zygote with 45 chromosomes is produced. (More 
often it is a sperm with no X or Y) Individuals with Turner syndrome: - appear female - do not develop sexually - tend to be short - have thick widened necks.

About 1 in every 3000 
female babies is a Turner 
syndrome baby. Most Turner syndrome 
fetuses are miscarried 
before the 20th week of 
pregnancy.

Klinefelter syndrome is caused by either the sperm or egg with 2 chromosomes The child inherits two X chromosomes—
characteristic of females—and a single Y 
chromosome—characteristic of males. The child appears to be a male at birth 
but at sexual maturity, he begins 
producing high levels of female sex 
hormones.

Males with Klinefelter 
syndrome are sterile. It has been 
estimated that 
Klinefelter syndrome 
occurs, on average, 
in 1 of every 500 
male babies.

Triple X syndrome or Trisomy X - additional X chromosome in each of a female's cells. - typically causes no unusual physical features. - Most females with triple X syndrome have normal 
 sexual development Triple X syndrome is associated with: - an increased risk of learning disabilities and delayed 
 development of speech and language skills. - delayed development of motor skills - weak muscle tone (hypotonia),  behavioral and emotional difficulties

XYY syndrome - extra copy of the Y chromosome in each of a 
 male's cells. - typically causes no unusual physical features. - normal sexual development XYY syndrome is associated with: - risk of learning disabilities - delayed development of motor skills - weak muscle tone - involuntary movements (motor tics) - behavioral and emotional difficulties

- some diagnosed with autistic spectrum disorders. Occurs in about 1 in 1,000 newborn boys.

Produce a Karyotype

The Miracle of Life 55 min