Each human chromosome consists of a single DNA molecule. Humans have 23 pairs of chromosomes, for a total of __________.
Chromosomes are numbered 1 through 23. Chromosome pairs 1 through 22 are called
___________________________. Human males and females share these chromosomes, and the genes they contain, in common.
Chromosome pair number 23 are the sex chromosomes. Males have an __________, females have ____________.
A _____________________ is a picture of all the chromosomes in the nucleus paired up and in order from 1 to 23. It can be used to diagnose a genetic disorder.
Mendel’s laws and other laws of inheritance all apply to humans. However, since researchers cannot control human matings, they must analyze patterns of inheritance within families using pedigrees.
A pedigree is a family tree that records and traces a ______________ trait through several generations. The traits examined in human pedigrees are generally diseases or disorders caused by either recessive or dominant alleles. Ordinary non-disease traits such as earlobe shape, cleft chins, widow’s peak, and others can also be traced to illustrate how alleles get inherited.
Symbols: male female parents female male showing trait female showing trait parents with children male carrier (of a recessive trait) female carrier (of a recessive trait)
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Types of human inheritance:
Autosomal traits are those controlled by genes located on the autosomes. Autosomal dominant traits are inherited by receiving two dominant alleles or one dominant and one recessive allele.
Autosomal recessive traits are inherited by receiving two recessive alleles.
Sex-linked traits are mainly inherited on the X chromosomes. Although sex-linked traits can be dominant, the sex-linked disorders discussed in class are sex-linked recessive.
Genes on which chromosomes?
Chromosomes # 1 -22 X chromosome
Genotype to show trait
(use A, a)
AA, Aa X a X a , X a Y
Who can inherit the trait?
Males and females equally
Males and females equally
How do they inherit it?
Recessive allele from each parent
Are there carriers? Who can be a carrier?
Yes, males or females
No carriers possible since expression of trait is dominant
Males inherit recessive allele from mother only; females inherit a recessive allele from both parents
Can pass to both
Can pass to daughters, but not to sons
Can males pass allele for trait to sons? daughters?
Can pass to both
Can females pass allele for trait to sons? daughters?
Can pass to both Can pass to both Can pass to both
Examples
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Example 1: Autosomal inheritance. The pedigree below shows the inheritance of tongue rolling in a family. The individuals shown by the shaded symbols cannot roll their tongues. The half-shaded symbols are carriers. Carriers have inherited one allele for a trait but do not show it. They can pass the trait to their offspring, as seen in this pedigree.
I
II
III
Is no tongue rolling dominant or recessive? What are the genotypes for each family member?
If the married couple in the second generation have another child, how probable is it that child could not roll its tongue? What chance is there the child could roll its tongue but be a carrier for no tongue rolling? (Hint: put the parents in a Punnett square and solve.)
Example 2. The pedigree below shows another type of autosomal inheritance. The shaded symbols show persons with Huntington’s disease, a serious neurological disorder.
Is Huntington’s disease a dominant or recessive trait? Explain.
Write in the genotypes for each family member on the chart.
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Example 3: The pedigree below is for a recessive sex-linked trait such as hemophilia, colorblindness, or Duchenne muscular dystrophy. Determine the carriers and label all the genotypes.
If couple C D have another child what chance is there that the child will have hemophilia?
If the child is male, what is the chance he will have hemophilia?
If the child is female, what is the chance she will have hemophilia?
Chromosomal Disorders:
Chromosomal disorders lack an inheritance pattern because they are caused by “mistakes” that occur during meiosis. Sometimes a pair of homologous chromosomes can fail to separate resulting in gametes with the wrong number of chromosomes. This is called nondisjunction.
Examples of
Chromosomal
Disorders:
Down Syndrome Turner Syndrome Kleinfelter’s Syndrome
What causes the inheritance of the disorder?
Blood Typing: (Study the chart!!)
What blood types are possible if mom has A+ blood and dad has B+ blood?
If mom has B- and the baby has A+ blood, what are the possible blood types for dad?
What blood types can be given to a man in need of a blood transfusion if he has B- blood?
A person with O+ blood can donate blood to which blood types?
If blood clumps in Anti-A serum but not in Anti-B serum or Anti-Rh serum, what is the blood type?
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