DNA stands for deoxyribonucleic acid DNA is a

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: YRIMIDINES 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 Hbonds)

Each strand of the DNA molecule has a free phosphate group at one end 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

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 thehaploid chromosome number, or n; The number of chromosomes in all other cells is twice the haploid number and is called the diploid number, or 2 n.

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 ibres 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. 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 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 monosomy. has only one of the chromosomes it is called

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 20 th 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 exual development Triple X syndrome is associated with: - an increased risk of learning disabilities and delayed evelopment of speech and language skills. - delayed development of motor skills - weak muscle tone (hypotonia), ehavioral and emotional difficulties

XYY syndrome - extra copy of the Y chromosome in each of a ale'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