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Genetics and Prenatal Development

Genetics and Prenatal Development. The Beginning of Life Conception. The Human Cell. The human body is comprised of over 200 different kinds of cells which are the smallest self-contained structures Cell membrane: the outside layer of the cell

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Genetics and Prenatal Development

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  1. Genetics and Prenatal Development • The Beginning of Life • Conception

  2. The Human Cell • The human body is comprised of over 200 different kinds of cells which are the smallest self-contained structures • Cell membrane: the outside layer of the cell • Cytoplasm: is comprised of specialized structures • Mitochondria: are the powerhouses that process nutrients and provide the cell’s energy • Endoplasmic reticulum, Golgi apparatus, and ribosomes: produce proteins • Neucleus: The inner part of the cell

  3. The Nucleus • Chromosomes • Genes • Deoxyribonucleic acid (DNA)

  4. Chromosomes • Rod shaped structures found in the center of the nucleus of every cell in the body. • Each sperm and each ovum contains 23 chromosomes. • The chromosomes contain the DNA and genes. • The fertilized egg (zygote) and all the body cells that develop from it (except the sperm cells and the ova) contain 46 chromosomes.

  5. Chromosomes • 22 of the pairs are called autosomes and are numbered from largest to smallest. • The autosomes are not involved in determining sex. • The 23rd pair are the sex chromosomes: • XX in females • XY in males

  6. KaryotypeA photograph of a cell’s chromosomes arranged in pairs according to size

  7. A Portion of a DNA Molecule

  8. DNADeoxyribonucleic Acid Nucleotides are the building blocks of DNA They contain 4 nitrogen-carbon-hydrogen basis that bond to form specific pairs: adenine can only pair with thymine cytosine can only pair with guanine The combination of base pairs cannot vary

  9. DNAWhat Can Vary: 1- Which side of the ladder each base comes from 2- The order in which the base pairs occur along the ladder 3- The overall number of base pairs These variations account for differences between species. All organisms use just these 4 bases, but with different numbers and arrangements

  10. DNA There are 3.12 billion base pairs in human DNA The DNA in each normal human being is about 99.9% the same as every other normal human being Only .1% accounts for the biological contribution to all our individual differences in physical and psychological characteristics

  11. DNASingle Nucleotide Polymorphisms (SNPs) • A large portion of the .1% individual difference takes the form of single nucleotide polymorphisms. • SNPs (snips) are nucleotide variations that occur on average about every 1,250 base pairs

  12. DNA • They determine the nature of each cell in the body and how it will function. • At each level of the spiral or rungs of the ladder are particular chemical pairs. The arrangement of these pairs along the DNA molecule determines which kind of proteins will be formed in the cell.

  13. Genes • The basic unit of genetic information • They determine the nature and the function of the cell. • The human genes (about 120,000) are referred to as the human genome. • A genome is the full set of genes in each cell of an organism.

  14. Proteins Proteins are molecules that perform an array of crucial functions in the human body: Enzymes:break down and altar biochemicals Hemoglobin:binds with oxygen allowing it to be transported to cells throughout the body Collagen:in bones and connective tissues Hormones:regulate physical growth

  15. Genes and Protein Synthesis • A nuclear enzyme attaches to a segment of DNA causing nucleotide bonds to separate. • Transcription occurs resulting in messenger RNA (mRNA). • Transfer RNA (tRNA) initiates translation into amino acid. • Ribosomes move along the RNA bonding amino acids into polypeptide chains which make proteins.

  16. 1- Transcription: the transfer of information from an DNA molecule into an RNA (ribonucleic acid) molecule. 2- Messenger RNA (mRNA): a type of RNA synthesized from DNA; attaches to ribosomes to specify the sequence of amino acids that form proteins. 3- Translation: the transfer of information from an RNA molecule into a Polypeptide, in which language of the nucleic acids is translated into that of amino acids.

  17. Celera GenomicsThe Human Genome Project • In June 26, 2000, they both made an announcement that the “correct alphabetical order of the 3.12 billion letters” of the human genome had been mapped. • It will be many years before the incredibly complex functions of the genome in making and maintaining a living human being are fully understood.

  18. Scientific Breakthroughs Greater insights into disease will be achieved Cures may be found Incurable diseases may be prevented There will be new insights into the evolutionary origins of humans

  19. Controversial Issues Will it be ethical for parents to have their children screened prior to birth and decide not to have a child with a genome that is merely undesirable ? What about employers not hiring people with bad genomes and insurance companies refusing to insure them?

  20. Cell Division and Reproduction When the cell is ready to divide and reproduce: the DNA staircase unwinds and the two long chains separate each chain attracts new biochemical material from the cell to synthesize a new and complementary chain Ultimately a new cell is formed

  21. Terms • Gametes: Sex cells (ovum or sperm) • Diploid cells: Cells having 2 copies of each chromosome • Haploid gametes: Gametes having 1 copy of each chromosome

  22. Meiosis • Meiosis takes place in the testicles and ovaries. • A diploid cell (having 2 copies of each chromosome) undergoes a special form of cell division to create haploid gametes (having 1 copy of each chromosome). • An egg and a sperm fuse together to form a new diploid cell called zygote (a process called fertilization)

  23. Mitosis • In the first step of mitosis, all chromosomes are copied, so that instead of 2 copies, the cell briefly has 4 copies of each chromosome. • Shortly afterwards, the cell divides in half, resulting in two cells each has a complete copy of the genetic information. • These cells grow larger and eventually undergo mitosis.

  24. Mitosis: each cell divides and duplicates itself exactly • Meiosis: How reproductive cells (ova and sperm) are produced • Results in gametes, cells that contain only 23 chromosomes

  25. In Males Meiosis takes place in the testes and involves 2 rounds of division Results in 4 fertile sperm cells By puberty, males begin producing many thousands of sperm cells on an ongoing basis, and they continue to do so through out their life span In Females Meiosis begins in the ovaries before birth and partly completes all of the roughly 400,000 ova a woman will ever have. It occurs in a two-stage process.. Results in one relatively big ovum and 2 small polar bodies that aren’t capable of being fertilized

  26. Mutation A mutation is an alteration in the DNA that typically occurs during mitosis and meiosis. In most cases mutation is maladaptive and the new cell simply dies or repairs and eliminates the mutation A small number of of mutations are viable – the cell survives

  27. Mutation In mitotic cell division, if a viable mutation occurs early in development, it will then be passed along to all cells replicated. In meiotic cell division, mutation only affects the ensuing gametes and stops there, Unless a mutated gamete happens to be involved in producing offspring – in which case the mutation can be passed along to the next generation and beyond.

  28. Gregor Mendel (1800s)

  29. Genotype The genetic makeup of a given individual Recessive Gene The gene pair that determines a trait in an individual only if the other member of that pair is also recessive Phenotype The traits that are expressed in the individual Dominant Gene One gene of a gene pair that will cause a particular trait to be expressed

  30. AllelesA pair of genes, found on corresponding chromosomes, that affect the same trait The child might inherit an allele for brown eyes (B) from the father and an allele for blue eyes (b) from the mother The child’s genotype for eye color would be Bb. What actual eye color will the child display? The allele for brown eyes is dominant (B). The allele for blue eyes is recessive (b). The dominant trait will be expressed as the phenotype

  31. Homozygous Referring to the arrangement in which the two alleles for a simple dominant- recessive trait are the same. Homozygous Individual (Eye Color) Could be BB or bb Heterozygous Referring to the arrangement in which the two alleles for a simple dominant-recessive trait differ. Heterozygous Individual (Eye Color) Could be Bb, or bB The chance for having blue eyes is 25%

  32. Incomplete Dominance Where people with a single recessive gene for a trait show some of the trait along with other normal manifestations. Example: Sickle-cell anemia

  33. Sickle-Cell Anemia • Occurs at its highest rate in individuals of black African ancestry. • People with a single recessive gene for the trait have a marked percentage of abnormal “sickle-shaped” red blood cells that interfere with oxygen transport throughout the body. • They also have normal (dominant) red blood cells aswell.

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