1. Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison-Wesley What Is a Gene? A gene is a section of DNA that contains instructions for making a protein. An organism’s genetic makeup is its genotype. The traits an organism exhibits are known as its phenotype.

2. Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison-Wesley Genes are found on chromosomes A chromosome consists of a single long strand of DNA and small proteins called histones around which the DNA is wrapped. Genes are sections of chromosomes.

3. Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison-Wesley Chromosomes Most cells have two of each kind of chromosome. These cells are diploid, and their matched chromosomes are called homologous chromosomes. Sperm and egg cells contain only one of each kind of chromosome. These cells are haploid.

4. Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison-Wesley Chromosomes Humans have 46 chromosomes (23 pairs). One pair—the sex chromosomes — determines the sex of the person. Females have two X chromosomes. Males have one X and one Y chromosome. All the other chromosomes are autosomal chromosomes.

5. Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison-Wesley Karyotype analysis

6. Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison-Wesley The Structure of DNA A molecule of DNA consists of two strands and looks like a spiraling ladder. It is often called a double helix. The “side” of the ladder consists of alternating molecules of deoxyribose sugar and phosphate. The “rungs” are a series of paired nitrogenous bases.

7. Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison-Wesley The Structure of DNA Only four bases are used in DNA: A (Adenine) G (Guanine) C (Cytosine) T (Thymine) Which bases pair up together?

8. Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison-Wesley DNA Replication (DNA copying) During replication, The two strands of the DNA molecule unzip Each strand serves as a template for making a new partner, following the base-pairing rules Each new DNA molecule contains one old strand and one new strand Each new DNA molecule is identical to the original

9. Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison-Wesley DNA Replication Old strand New strand

10. Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison-Wesley Transcription and Translation DNA provides instructions for cells to build proteins through the processes of transcription and translation. In transcription, DNA is used as a template for making RNA. In translation, this RNA is used to assemble a protein.

11. Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison-Wesley Transcription and Translation

12. Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison-Wesley Transcription In eukaryotes, transcription occurs in the cell nucleus. The two strands of DNA separate. One strand serves as a template for constructing the RNA transcript. RNA uses uracil (U) instead of thymine (T). Otherwise, transcription follows the same base- pairing rules as DNA replication. So, which base pairs with G and which pairs with A?

13. Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison-Wesley Transcription The RNA molecule made during transcription is called messenger RNA (mRNA).

14. Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison-Wesley Translation Translation occurs at ribosomes. mRNA is translated into protein by “reading” triplets of nucleotides called codons. Each codon represents an amino acid. These are strung together to make a protein..

15. Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison-Wesley Translation

16. Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison-Wesley Meiosis: Genetic Diversity Meiosis is a special form of cell division used to make haploid cells, such as eggs and sperm. What does haploid mean? In meiosis, one diploid parent cell divides into four haploid daughter cells. Something to think about: Is the “norm” for meiosis 4 cells or is it 1 large cell? During sexual reproduction, sperm and egg join to restore the diploid chromosome number.

17. Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison-Wesley Meiosis Parent cell FemalesMales

18. Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison-Wesley Mendelian Genetics Gregor Mendel’s work explained hereditary patterns. His experiments breeding pea plants demonstrated the existence of dominant and recessive traits. Dominantrecessive

19. Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison-Wesley Mendelian Genetics Mendel postulated that heritable factors (genes) that determine traits consist of two separate alleles. Half of the sex cells an individual produces carry one allele, and the other half carry the second allele. Allele= an alternative form of a gene (one member of a pair) that is located at a specific position on a specific chromosome This is Mendel’s principle of segregation. Can anyone explain this…help?

20. Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison-Wesley Mendelian Genetics When two homozygotic (WW or ww) pea plants are bred, the offspring inherit one W (round pea) allele and one w (wrinkled pea) allele. These Ww plants are called heterozygotes. All of the heterozygotes express dominant characteristics—they are round pea plants. In the second generation, self- fertilizing Ww plants produce a 3:1 ratio of round pea to wrinkled pea plants.

21. Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison-Wesley Inheritance: Beyond Mendelian Genetics In incomplete dominance, the combination of two alleles in a heterozygote produces an intermediate trait. Sickle Cell Disease

22. Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison-Wesley Inheritance: Beyond Mendelian Genetics In codominance, the combination of two alleles in a heterozygote results in the expression of both traits. Blood type is an example of codominance. Three alleles—A, B, and O—can result in blood types A, B, AB, or O. The AB blood type shows codominance.

23. Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison-Wesley Inheritance: Beyond Mendelian Genetics Polygenic traits are determined by more than one gene. They tend to show more of a continuum than traits determined by a single gene. Examples: human eye color, skin color, and height

24. Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison-Wesley Inheritance: Beyond Mendelian Genetics Pleiotropy occurs when a single gene affects more than one trait. Examples: sickle cell anemia in humans a single allele in cats that leads to white fur, blue eyes, and deafness

25. Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison-Wesley Inheritance: Beyond Mendelian Genetics Sex-linked traits are determined by genes found on sex chromosomes (X and Y in humans). Sex-linked genes occur more often on the X chromosome. Consequently, men, who have only one X chromosome, are more likely than women to exhibit recessive sex- linked traits such as red–green color- blindness and hemophilia.

26. Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison-Wesley The Human Genome The human genome consists of 23 pairs of chromosomes. The Human Genome Project sequenced the entire human genome. Over 99.9% of the 3 billion base pairs in the human genome are identical in all humans.

27. Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison-Wesley The Human Genome Humans have about 30,000 genes. Most of the bases in the genome consist of “junk DNA” with no known function. The chromosomes differ in the number of genes they carry.

28. Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison-Wesley Genetic Mutations Genetic mutations: Occur when the sequence of nucleotides in an organism’s DNA is changed May result from errors in DNA replication or from exposure to mutagens (UV light, X-rays, chemicals) May have no effect, some effect, or very dramatic effects In egg or sperm cells may be passed down to offspring Are the ultimate source of genetic variation

29. Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison-Wesley Science and Society: Genetic Counseling A pedigree is a family tree that shows which relatives are and are not affected by a particular genetic disease. Medical tests can determine if a person is a carrier of a disease allele. Amniocentesis and chorionic villus sampling can determine if a fetus has a genetic disease.