Aim: How are human traits inherited?

HW #9

Chapter 14 text

Read pages 340-343

Construct a pedigree of your family starting with your grandparents showing how a particular trait is expressed. Include a key.

Pedigree Chart

Poll the class to determine what traits are present

Characteristic Present Absent

Dimples

Freckles

Widow’s peak

Earlobes(attached)

Tongue Roller

Cleft chin

Hair above knuckles

Hitchhiker’s thumb

Brown eyes

Autosomes and Sex chromosomes

• There are no pairs of chromosomes in the sperm or egg of sexually reproducing organisms.

• Fertilization restores the 2n number, each parent contributing one chromosome to restore the pair.

A circle represents a female.

A square represents a male.

A horizontal line connecting a male and female represents a marriage.

A vertical line and a bracket connect the parents to their children.

A half-shaded circle or square indicates that a person is a carrier of the trait.

A completely shaded circle or square indicates that a person expresses the trait.

A circle or square that is not shaded indicates that a person neither expresses the trait nor is a carrier of the trait.

Section 14-1

Figure 14-3 A Pedigree

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Human Pedigree Chart

caused by

Section 14-1

includeincludeinclude

Concept Map

AutosomolDisorders

Recessive alleles

Dominant allelesCodominant

alleles

Albinism Galactosemia Tay-Sachs disease

Huntington’s disease

Sickle cell disease

Cystic fibrosis

Phenylketonuria AchondroplasiaHypercholes-

terolemia

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recessive, dominant or co-dominant alleles on one of the 22 pairs of chromosomes

Dominant Allele on chromosome 4

• The clinical features of achondroplasia include the following:

• Short stature • Rhizomelic (proximal) shortening of the

arms and legs with redundant skin folds on limbs

• Limitation of elbow extension • Trident configuration of the hands • Genu varum (bow legs)

Traits can be carried on

Autosomal chromosomes (1 – 22)

Or

The sex chromosomes (X, Y)

HD is an autosomal dominant condition

• Anyone with 40 or more CAG repeat sequences will develop HD and their children will have a 50 per cent risk of developing HD.

• Evidence suggests that the huntingtin protein in people with HD tends to break into pieces, which then clump together. These protein clumps build up inside the nuclei of brain cells, which either impairs their functioning or kills them.

Aim: How are Sex-linked Traits inherited in the Human Population ?

Examples of Sex-linked Traits:

Red-green colorblindnessMale Pattern Baldness

HemophiliaDuchenne Muscular Dystrophy

Hemophilia is a disorder caused by an error in a person’s genetic code.

Carried on the X chromosome

Pedigree of Queen Victoria's Descendants

showing a sex linked trait

Key

The inheritance of Colorblindness

Parent phenotypes: normal vision Father X colorblind Mother

Genotypes:

X

X

X Y Offspring phenotypes

Parents’ phenotypesNormal Vision Father X Normal vision Mother

(no colorblindness Mother' family)

Parents’ Genotype:

X

X

X YOffspring Phenotypes