Chapter 14

Human Heredity

14.1 Human Chromosomes

A karyotype shows the complete diploid set of chromosomes.– Grouped in pairs– In order of decreasing size

• Sex Chromosomes – pair 23 (determine gender0

• Autosomal Chromosomes (autosomes) – pairs 1-22

• Normal Male 46, XY• Normal Female 46, XX

Normal Male Karyotype

Transmission of Human Traits• Patterns of Inheritance

– Simple autosomal dominance (trait has two possible phenotypes carried on the autosomal chromosomes)

• Rh blood groups (+ or -)

• Widows peak

• Freckles

– Polygenic (multiple genes influence the trait)

• Hair color, eye color, height

– Codominance and Multiple alleles

• Blood types

– Sex-Linked Inheritance (genes located on the sex chromosomes)

• Colorblindness

• Hemophilia

Autosomal Inheritance

• Appear in both sexes equally• Carried on autosomal chromosomes

• Autosomal Dominant – A single, abnormal gene causes the disorder

• Disorder: Huntington’s disease

• Example:– HH – affected– Hh – affected– hh - normal

• Autosomal Recessive – Must have two abnormal genes to show the disorder.

– A patient having one abnormal gene is called a carrier. • Example:

– AA – normal– Aa – normal (carrier)– aa – affected

• Disorders: Tay Sachs disease, Cystic Fibrosis, Sickle Cell disease

Polygenic inheritance – several genes influence a character.

– Can be located on the same chromosome, or different chromosomes.

– These characters have degrees of intermediate conditions between each extreme.

Order of dominance: brown > green > blue.

Multiple Alleles – genes with three or more alleles.

– Ex: blood type in humans (IA, IB, i)

– IA IB genotype produces blood type AB (codominant)

– The allele i is recessive, therefore genotype ii results in blood type O.

Blood Type Punnett Square Example

• What blood types are possible in the children of a man with blood type O and a woman with blood type AB?– Parent Genotypes:

– Possible Children:

Blood Type example:

• A woman with type A blood is claiming that a man with type B blood is the father of her child who is type O. Is it possible that this man is the father?

Sex-Linked Inheritance

• Sex-Linked Recessive– Hemophilia (X-linked)

• Impairs the blood’s ability to clot

• Genoypes: female XhXh, male XhY

– Color blindness (X-linked)

• 1 in 20 men, 1 in 2000 women

• red/green color blindness is the most common

• Genotypes: female XbXb, male XbY

• In order for sex-linked traits to be expressed in females, they must inherit the recessive allele from both parents.

Sex Linked Example Punnett Square

• A man who is color blind marries a woman who is not (homozygous dominant). What are the possible genotypes and phenotypes of their children?– Parent genotypes:

– Possible children:

Human Pedigrees

• Pedigree – family history showing how traits are inherited over several generations.

Read the following passage, which describes the family shown in Pedigree I.Write the name of each person below the correct symbol in Pedigree I.Although Jane and Joe Smith have dimples, their daughter, Clarissa, doesnot. Joe’s father has dimples, but his mother, and his sister, Grace, do not.Jane’s father, Mr. Renaldo, her brother, Jorge, and her sister, Emily, do nothave dimples, but her mother does.

Examine Pedigree I, which traces the dimples trait through three generations of a family. Blackened symbols represent people with dimples.

Pedigree Analysis Practice

• Is it possible that this pedigree is for an autosomal recessive trait?

Practice cont.

• Is it possible that this pedigree is for an autosomal recessive trait?

Practice cont.

• Is it possible that this pedigree is for an autosomal dominant trait?

Practice cont.

• Is it possible that this pedigree is for an autosomal dominant trait?

14.2 Chromosomal Disorders

• Trisomy 21 – Down Syndrome• 47 XXY – Kleinfelter Syndrome• 45 X – Turner Syndrome

• Occur due to nondisjunction– Chromosomes fail to separate during meiosis

– Leads to an abnormal number of chromosomes