Biology



Biology

Rendell/Walz

Chapter 7 Human Inheritance

7-1

|Key Words |Notes |

|Fruit fly |Drosophilia melanogaster |

| |Perfect organism for genetic studies |

| |Used by Thomas Hunt Morgan for genetic studies |

| |8 chromosomes in diploid cell |

|Colchicine |Poison breaks down microtubules |

| |Prevents cells from completing mitosis |

| |Causes cells to be trapped in metaphase |

|Karyotype |Diagrammatic representation of individual chromosomes cut from a photograph and |

| |grouped together. |

|Human karyotype |22 pairs of homologous chromosomes – autosomes |

| |numbered from 1 – 22 from largest to the smallest |

| |1 pair of sex chromosomes – X and Y |

|X X |Female |

|X Y |Male |

|Human reproductive cells |sperm and egg |

| |produced by meiosis |

| |haploid (23 chromosomes) |

|Zygote |Formed when egg and sperm unite (fertilization) |

|Pedigree |Diagram that follows the inheritance of a single gene through several generations in |

| |a family. |

|Human traits |Formed when egg and sperm unite (fertilization) |

|Polygenic traits |Inherited by action of genes that have dominant and recessive alleles. |

|Multiple alleles |traits determined by more than one gene |

| |Examples: height, skin color, eye color |

| |None of the genes is dominant |

| |Active allele and inactive allele |

| |Active alleles affect phenotype; inactive alleles do not. |

| |Environmental conditions also affect phenotype of polygenic traits. Ex. Nutrition , |

| |disease, exercise affect height and weight. |

| |Type of gene that is determined by more than 2 alleles. |

| |Example: ABO blood group |

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7-2

|Key Words |Notes |

|Determination of sex |chromosomal |

| |depends on sex chromosome individual inherits |

| |XX = female |

| |XY = male |

|Sex-linked genes |genes located on the sex chromosomes. |

|Sex-linked inheritance |Males are more likely than females to exhibit a recessive gene on the X chromosome. |

| |Colorblindness, hemophilia, Duchenne Muscular Dystrophy |

|Sex-linked disorders | |

|Colorblindness |Caused by recessive allele |

| |Carried on X chromosome |

|Hemophilia |Genetic disorder |

| |Clotting factor protein is not produced. |

| |Small cuts can present serious problems. |

| |Carried on X chromosome |

|Duchenne Muscular Dystrophy |Genetic disorder |

| |Carried on the X chromosome |

| |Recessive allele produces a defective protein that causes muscles to weaken and break|

| |down, eventually causing death. |

|Sex-linked disorder and males |Males have one X chromosome |

| |Recessive traits on the X chromosome are not masked by another allele. |

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7-3

|Key Words |Notes |

|Autosomal genetic disorders |Autosomes are chromosomes that are not sex chromosomes. |

| |Majority of human genes are carried on autosomes |

| |Therefore, the majority of genetic disorders are carried on autosomes. |

| |Examples: albinism, cystic fibrosis, Tay-Sachs Disease, PKU, Huntington Disease |

|Albinism |Genetic disorder |

| |Recessive allele on chromosome 11 |

| |Unable to produce melanin – the pigment responsible for human skin color |

| |Have no color in hair or skin |

| |Sensitive to light |

|Cystic Fibrosis |Most common fatal genetic disease. |

| |Recessive allele on chromosome 7 |

| |Makes a defective cell membrane protein that interferes with the movement of chloride|

| |ions into and out of the cell. |

| |Chloride ions build up inside cell and cause water form surrounding liquid to enter |

| |cells. |

| |Result ( surrounding liquid becomes thick and heavy, and clogs the lungs and |

| |breathing passageways. |

|Tay-Sachs Disease |Fatal genetic disorder |

| |Recessive allele |

| |Common in Jewish families of Eastern European ancestry. |

| |Rapid breakdown of nervous system beginning by age 2 or 3. |

|Sickle Cell Anemia |Blood disorder |

| |Characterized by crescent, or sickle-shaped, red blood cells. |

| |Recessive allele produces an alternate form of hemoglobin |

| |Hemoglobin is the red blood cell protein. |

|PKU |Phenylketonuria (PKU) |

| |Recessive allel |

| |Can cause severe mental retardation. |

| |There is a test and treatment for the disorder |

|Huntington Disease |Rare genetic disorder |

| |Caused by dominant allele on chromosome 4 |

| |Nervous system begins to break down |

| |Most patients die within 15 years after symptoms appear. |

|Chromosome Number Disorder |Nondisjunction ( “not coming apart” |

|nondisjunction |Abnormal number numbers of chromosomes are produced on sex cells. |

| |If sex cell produces a zygote, a genetic disorder results. |

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7-3 continued

|Turner Syndrome |Nondisjunction |

| |Sex chromosomes fail to separate in meiosis can result in Turner syndrome |

| |Only females are affected |

| |Sex organs do not fully develop – therefore, females cannot have children |

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|Klinefelter Syndrome |Nondisjunction |

| |Produces males whose cells contain an extra chromosome |

| |Symbolized as 47 XXY |

|Down Syndrome |Nondisjunction |

| |Trisomy ( cells contain three copies of a chromosome |

| |Extra copy of chromosome 21 |

| |Heart and circulatory problems |

| |Weakened immune system |

| |Mental retardation |

|Chromosome deletions |Pieces of chromosomes break off and get lost in meiosis |

|Chromosome translocations |Pieces of broken chromosomes become reattached to another chromosome |

|Prenatal Diagnosis |Amniocentesis |

|Detecting genetic disorders before birth |Involves withdrawing a small amount of fluid from the sac surrounding the fetus. |

| |Chorionic villus sampling |

| |Tissue surrounding fetus is removed and examined |

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