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
/ FemaleX Y
/ MaleHuman 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
/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
/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