Download Chapter 7 Human Inheritance

Biology
Rendell/Walz
Chapter 7 Human Inheritance
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Key Words
Fruit fly
Colchicine
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Notes
Drosophilia melanogaster
Perfect organism for genetic studies
Used by Thomas Hunt Morgan for genetic studies
8 chromosomes in diploid cell
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
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XX
Female
XY
Male
Human reproductive cells
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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
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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.
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Type of gene that is determined by more than 2 alleles.
Example: ABO blood group
22 pairs of homologous chromosomes – autosomes
numbered from 1 – 22 from largest to the smallest
1 pair of sex chromosomes – X and Y
sperm and egg
produced by meiosis
haploid (23 chromosomes)
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Key Words
Determination of sex
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Notes
chromosomal
depends on sex chromosome individual inherits
XX = female
XY = male
Sex-linked genes
Sex-linked inheritance
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Sex-linked disorders
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genes located on the sex chromosomes.
Males are more likely than females to exhibit a recessive gene
on the X chromosome.
Colorblindness, hemophilia, Duchenne Muscular Dystrophy
Colorblindness
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Caused by recessive allele
Carried on X chromosome
Hemophilia
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Genetic disorder
Clotting factor protein is not produced.
Small cuts can present serious problems.
Carried on X chromosome
Duchenne Muscular Dystrophy
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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
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Males have one X chromosome
Recessive traits on the X chromosome are not masked by
another allele.
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Key Words
Autosomal genetic disorders
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Albinism
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Cystic Fibrosis
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Notes
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
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
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
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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
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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
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Phenylketonuria (PKU)
Recessive allel
Can cause severe mental retardation.
There is a test and treatment for the disorder
Huntington Disease
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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
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Nondisjunction  “not coming apart”
Abnormal number numbers of chromosomes are produced on
sex cells.
If sex cell produces a zygote, a genetic disorder results.
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Turner Syndrome
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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
Klinefelter Syndrome
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Nondisjunction
Produces males whose cells contain an extra chromosome
Symbolized as 47 XXY
Down Syndrome
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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
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Pieces of chromosomes break off and get lost in meiosis
Chromosome translocations
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Pieces of broken chromosomes become reattached to another
chromosome
Prenatal Diagnosis
Detecting genetic disorders before
birth
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Amniocentesis
 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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