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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