After writing your 4 lines, share with the person sitting next to you. Do Now: Why would scientists want to know where genes are located on a chromosome? After writing your 4 lines, share with the person sitting next to you.

CHAPTER 14 – THE HUMAN GENOME 1. Genome – all the genetic material in an organism. (Mostly contained in the nucleus on the chromosomes.) 2. Humans – have 46 chromosomes or 23 pairs in the genome 3. How do we see and arrange these chromosomes? a. Cells photographed in mitosis; photographs enlarged , and then grouped in pairs. b. They are arranged in order from largest to smallest, except for the 23 pair. c. Other things that help arrange the chromosomes are the “bands” in them and where the centromere is located. d. The picture of this arrangement is called a Karyotype.

1. The 1st 22 pairs of homologous chromosomes are called autosomes. 2. The last pair are called sex chromosomes since they determine the organism’s sex. 3. The sex chromosomes here are XY (a male). XX is a female.

CHROMOSOMAL DISORDERS 1. The most common chromosomal disorder occurs in an error in meiosis when homologous chromosomes fail to separate. a. This is called Nondisjunction which means “ not coming apart” b. This causes too few or too many chromosomes to find their way into gametes. c. If these gametes join to form a new offspring, the child usually dies in the womb. BUT… d. The 3 most common nondisjunction disorders where the child lives are Down Syndrome, Klinefelter’s syndrome and Turner’s syndrome.

Klinefelter’s Syndrome

Turner’s Syndrome

Down Syndrome – also called trisomy 21 because there are 3 # 21 chromosomes. (autosomal disorder). a. This produces mild to severe mental retardation as well as increased susceptibility to many diseases. Klinefelter’s Syndrome – Nondisjunction of the sex chromosomes where there is an extra X chromosome (XXY). NOTE: If there is a Y chromosome then this is a male. Turner’s Syndrome – Nondisjunction where there is only one X chromosome (X0). These are females who are sterile because their sex organs fail to develop. These are females since they lack a Y chromosome. NOTE: The (Y) chromosome contains a sex-determining region that is necessary to produce male sexual development. See Fig. 14-12.

Sex-Linked Genes (X-Linked) 1. Sex-linked genes are genes that are only carried on the X chromosome Fig. 14-12 pg. 350 2. Since the Y chromosome is much smaller, it does not carry as many genes a the X chromosome. 3. Males have just one X chromosome, thus all X-linked alleles are expressed in males, even if they are recessive. 4. If an X-linked is recessive, then a female would need to have both recessive alleles to have the trait. 5. Two traits that are x-linked recessive are red-green colorblindness and male patterned baldness

Figure 14-13 Colorblindness Section 14-2 Father (normal vision) Normal vision Colorblind Male Female Daughter (normal vision) Son (normal vision) Mother (carrier) Question – could 2 people without colorblindness have a girl who is colorblind? How about a boy? Daughter (carrier) Son (colorblind)