Biology

Rendell/Walz

Chapter 7 Human Inheritance

7-1

Key Words

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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

7-2

Key Words

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Notes

Determination of sex /
  • chromosomal
  • depends on sex chromosome individual inherits
  • XX = female
  • XY = male

Sex-linked genes
Sex-linked inheritance
Sex-linked disorders /
  • 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 /
  • 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.

7-3

Key Words

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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 /
  • Nondisjunction  “not coming apart”
  • Abnormal number numbers of chromosomes are produced on sex cells.
  • If sex cell produces a zygote, a genetic disorder results.

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

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

Detecting genetic disorders before birth /
  • Amniocentesis
  • Involves withdrawing a small amount of fluid from the sac surrounding the fetus.
  • Chorionic villus sampling
  • Tissue surrounding fetus is removed and examined