Chapter 5 Science Notes
Test 11/27
Key concepts and ideas to understand:
Boy or Girl?
- Sex chromosomes carry genes that determine gender (boy or girl). They also can carry genes
that determine other traits.
-A female has an XX genotype. A male has an XY genotype.
-When two parents create an offspring, there is always a 50% chance of the offspring being a
girl and 50% chance of the offspring being a boy.
-Here is a Punnett square showing that shows this.
Dad (XY)
Mom (XX)
Sex-linked traits
-There genes for some traits are carried on the X and Y chromosome. They are called sexlinked genes.
-Some examples of traits carried on the X chromosome are hemophilia (when someone bleeds
very easily) and red-green colorblindness (difficulty seeing the colors red or green).
-Sex-linked genes can be either on the X or the Y chromosome, depending on the disorder.
Hemophilia and red-green colorblindness are on the X chromosome.
-So, boys (XY) are more likely to get these disorders because they have only 1 X chromosome.
If that chromosome has the trait, then they will have the disorder. The boys get the X from their
mom only.
-Girls have X X, so if one X has the trait, the other good X can balance it out. A girl has to get
the disorder from both her mom and her dad to show the trait.
Genetic Disorder-Section 2
-A genetic disorder is an abnormal (not normal) condition inherited through the genes.
-Genetic disorders can be caused by mutations or a different structure or number of
chromosomes.
-Some examples of genetic disorders are sickle-cell anemia, hemophilia (a sex-linked disorder),
and cystic fibrosis.
Here is an example from our book about hemophilia
Testing-Section 2
-Doctors use pedigrees, karyotyping, and genetic testing to trace and diagnose genetic
disorders.
-A pedigree is like a family tree for a trait. It lets us see which family members have a genetic
trait. Here is a pedigree from our book:
-A karyotype is a picture of an organism’s chromosomes. Here is a karyotype. This person has
46 chromosomes. The 23rd pair of chromosomes are the gender chromosomes. The person
has 2 X chromosomes so they are a girl.
← 23 pair
XX
girl
Advances in Genetics-Section 3
-Sometimes we want plants with special features or animals with a unique trait. Selective
breeding, cloning, and genetic engineering are three ways we can create organisms with special
traits.
-selective breeding (like hybridization and inbreeding) are used when we want to select
organisms with the best traits to become parents. This often happens with crops and flowers.
-cloning produces and organisms that is genetically identical to itself. People put leaves of
African violets into water and create an identical plant to the one they got the leaf from. Dolly the
sheep was a clone of her mother. She was created from her mother’s cell and was an exact
copy of the sheep she came from.
-genetic engineering is when genes from one organism are transplanted into another organism.
This is sometimes done with crops and medicines.
Using Genetic Information-Section 4
-We use the genetic information to identify people and to help understand disorders.
-A genome is an organisms full set of DNA
-The Human Genome Project was completed in 2003. The purpose was to figure out the
locations of the the genes by identifying the entire sequence of human DNA (the A, T, G, C
letters)
-DNA fingerprints are small fragments of DNA that are in unique lengths and patterns for each
person. These are what help identify people in crimes. They are called “fingerprints” because
everyone’s is unique.