Mohamed Abu-Bakr MohamedM.B.B.CH

M.SC.DEGREE IN PAEDIATRICSAssistant lecturer of pediatric , AUCH

Clinical geneticist & metabolic diseases specialist

2016

Introduction to human genetic

Human body

Different systems

Different organs

Millions of cells

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Definitions

Genome:-the total number of genes contained in one cell.

Genotype:-complete genetic structure of an individual.

Phenotype:-the physical appearance of an individual that is produced by the interaction of his genes & environment.Allele:-alternative forms of a gene that occupy a specific locus on a specific gene

• Karyotype:-systematic arrangement of chromosomes into homologous pairs

• Autosomal chromosome in humans, the 22 pairs of chromosomes that are not the sex chromosomes (XX or XY)

• Sex chromosomes :-pair of chromosomes involved in sex determination; in males, the XY chromosomes; in females, the XX chromosomes

Cell cycle & Cell divison

Diploid (2N) – cell that contains both chromosomes of a homologous pair

human bodycells 46

Homologous Chromosomes pair of chromosomes that have same size and shape

• human body cells have

23 homologous pairs

Haploid (N) – cell that has only one chromosome of each homologous pair

ovum & sperm human sex

cells23

Cell cycle

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Cell Cycle

• The cell cycle is a sequence of cell growth and division.

• The cell cycle is the period from the beginning of one division to the beginning of the next.

• The time it takes to complete one cell cycle is the generation time.

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Cells divide when they reach a certain size. NO (nerve and red blood cells)

Stages in eukaryotic cell cycleInterphase1-First gap phase2-Synthesis phase3-Second gap phase

M phase1-cell divison2-Cytokinesis

Cell Cycle

Interphase

G1 phasecell grows to mature size

S phaseCell’s DNA copies

G2 phaseCell prepares for cell division

Interphase

Why cells divide?

Replace old, damaged or dead cellsGrowth of organism (multicellular)

Or organs

Eukaryotic Cell Division

2 kinds of cell divisionMitosis- Process in which 2 new cells with

identical genetic material are made from the parent cell (1 diploid cell divides to produce 2 new diploid cells)Meiosis- Process in which gametes (sex cells) are

made in which they recieve half of the genetic information

Mitosis divison

Mitosis division of chromosomes

4 EventsProphaseMetaphase AnaphaseTelophase

1st step in Mitosis: Prophase (preparation phase)

The DNA recoils, the chromosomes condense the nuclear membrane disappears

Two pairs of centrioles migrate to each pole of the cell and release spindle fibers that radiate throughout the cell and attach to the centromere of each chromosome

2nd step in Mitosis:metaphase (organizational phase)

The chromosomes line up the middle of the cell with the help of spindle fibers attached to the centromere of each replicated chromosome.

3rd step in Mitosis: Anaphase (separation phase)

• Chromatids of each chromosome split and are pulled apart to opposite poles of the cell

4th step in Mitosis: Telophase

The chromosomes, along with the cytoplasm and its organelles and membranes are divided into 2 portions. This diagram shows the end of telophase.

After Mitosis: Cytokinesis

The actual splitting of the daughter cells into two separate cells is called cytokinesis and occurs differently in both plant and animal Cells.

Cell Cycle

Meiosis divison

Meiosis Interphase

Meiosis is preceded by interphase. The chromosomes have not yet condensed.

Meiosis Prophase I

The chromosomes are completely condensed.

In meiosis (unlike mitosis), the homologous chromosomes pair with one another

crossing over may occur

Crossing Over Between Homologous Chromosomes

Meiosis Metaphase I

The nuclear membrane dissolves

the homologous chromosomes attach to the spindle fibers.

They are preparing to go to opposite poles.

Meiosis Anaphase I

The chromosomes move to opposite ends of the cell.

Meiosis Telophase I & CytokinesisThe cell begins to divide into two daughter cells.

Meiosis Prophase II

The cell has divided into two daughter cells.

Meiosis Metaphase IIAs in Meiosis I, the chromosomes line up on the spindle fibers.

Meiosis Anaphase II

The two cells each begin to divide. As in Meiosis I, the chromosomes move to opposite ends of each cell.

Telophase II & Cytokinesis

With the formation of four cells, meiosis is over.

Each of these germ cells carries half the number of chromosomes of somatic cells.

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Why we study cell division?!!!

Gametogensis

Male Spermatogenesis1- spermatogenesis occur in seminiferous tubules.2- process started at puberty.3-continuos process without any pauses till end of life.4- mitosis primary spermatocyte.5-1st meiotic secondary spermocyte.6-2nd meiotic spermatid.7- duration of process69-75 days.

Female oogenesis

1- process occur in ovary.

2-mitosis start during intra-uterine life primary oocyte

3-then 1st meiotic start after birth and arrested at prophase I then resumed at puberty when ovulation occurred

4- 2nd meiotic occur after ovulation and arrested at metaphase II until fertilization occur with formation of mature ovum

5- duration of process12-45 years

Gametes sex cells (sperm and egg)

human sperm cells

human egg cell

cell that results fromthe fusion of gametes

• forms when sperm fertilizes

the egg

Zygote

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