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9.4 Human Chromosomes and Genes

9.4 Human Chromosomes and Genes. Pages 196-199. Introduction. No one else in the world is completely like you! Genes have a lot to do with why you are different.

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9.4 Human Chromosomes and Genes

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  1. 9.4 Human Chromosomes and Genes Pages 196-199

  2. Introduction No one else in the world is completely like you! Genes have a lot to do with why you are different. Even identical twins are different. Why? The environment influences human characteristics and no two people have the same environment.

  3. Human Genome All of the DNA in the human species makes up the human genome. The DNA consists of about 3 billion base pairs and is divided into thousands of genes on 23 pairs of chromosomes.

  4. Chromosomes and Genes Each species has a characteristic number of chromosomes. The human species has 23 pairs.

  5. Autosomes Autosomes are chromosomes that contains genes for characteristics that are unrelated to sex. Of the 23 pairs of chromosomes, 22 pairs (1-22) are autosomes. These autosomes are the same in males and females. The majority of human genes are located on autosomes.

  6. Sex Chromosomes The remaining pair of chromosomes in humans are the sex chromosomes. Females have two X chromosomes. Males have an X and Y chromosome. In females one X chromosome is inactivated and known as the Barr body. The X contains 2000 genes, the Y contains fewer than 100 genes. Virtually all of the X genes are unrelated to sex.

  7. Only the Y gene contains genes that determine the sex of the organism. A single Y chromosome gene is called SRY (sex-determining region gene), it triggers an embryo to develop into a male. Without the Y chromosome, an individual develops into a female, so you can think of female as the default sex of the human species. http://highered.mcgraw-hill.com/sites/9834092339/student_view0/chapter13/x_inactivation.html

  8. Human Genes Humans have an estimated 20,000 to 22,000 genes. However, human cells use splicing and other process to make multiple proteins from the instructions encoded into a single gene. Of the 3 billion base pairs in the human genome, only 25% make up the genes and their regulatory elements. The functions of many other base pairs are still unclear. (will you be the person to solve the mystery?)

  9. The majority of human genes have two or more possible alleles. Differences in the alleles account for the considerable genetic variations among people. In fact, most human genetic variation is the result of differences in individual DNA bases within alleles.

  10. Lesson Review Questions Due today Question 2 and 3

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