Page 151 - Science Course 3 (Book 1)

Mo4-L3b: How DNA Changes Affect Traits?

The 46 human chromosomes contain between The effects of a mutation depend on where in the
20,000 and 25,000 genes that are copied during DNA sequence the mutation happens and the type
replication. of mutation. Some mutations in human DNA cause
genetic disorders.
Mutations can be triggered by exposure to X-rays,
ultraviolet light, radioactive materials, and some
kinds of chemicals.

There are several types of mutations.

Three types of mutations are substitution, insertion, and deletion.

Original Insertion Substitution Deletion
Three base pairs The yellow base pair Three base pairs have been
have been added. has been replaced removed. Other base pair
with a Blue pair will move in to take their
place.

In a deletion mutation, one or more nitrogen base is left out of the DNA sequence.

In an insertion mutation, one or more nitrogen bases is added to the DNA.

In a substitution mutation, one nitrogen base is replaced by a different nitrogen base.

Genetic Order

Defective Gene or Disorder Description
Chromosomes
PAH gene People with defective PAH genes cannot break down the amino
Phenylketonuria (PKU) acid phenylalanine. If phenylalanine builds up in the blood, it
poisons nerve cells.

CFTR gene In people with defective CFTR genes, salt cannot move in and
Cystic Fibrosis out of cells normally. Mucus builds up outside cells. The mucus
can block airways in lungs and affect digestion.

Chromosome 7, elastin gene People with Williams syndrome are missing part of chromo-
Williams Syndrome some 7, including the elastin gene. The protein made from the
elastin gene makes blood vessels strong and stretchy.

BRCA1, BRCA2 A defect in BRCA1 and/or BRCA2 does not mean the person
Breast Cancer and will have breast cancer or ovarian cancer. People with defective
Ovarian Cancer BRCA1 or BRCA2 genes have an increased risk of developing
breast cancer and ovarian cancer.
143