Download Genetics - Saint Demetrios Astoria School

Genetics
Heredity
- Heredity: the passing of traits from parent to offspring.
- Alleles: an alternative form that a gene may have for a single trait
An allele can be dominant, which describes a trait that covers over, or dominates, another form
of that trait, or an allele can be recessive, which describes a trait that is covered over, or
dominated, by another form of that trait and seems to disappear.
- Genetics: the study of how traits are inherited through the actions of alleles.
The father of Genetics is Gregor Mendel. He was an Austrian monk who studied mathematics
and science but became a gardener in a monastery.
- Purebred: organisms that always produces the same traits generation after generation.
- Hybrid: an offspring that was given different genetic information for a trait from each parent.
In order to predict the probability of certain traits in offspring that shows the different ways
alleles can combine, we use the Punnett square.
Mr. Saoulis
If a father has brown eyes (Bb) and a mother has blue eyes (bb). We use capital letters to
symbolize dominant genes, in this case a capital "B" for brown, and lower case letters to
symbolize recessive genes, in this case a little "b" for blue.
Fill in the Punnett square as shows above. The genotype is the genetic makeup of an
organism, which in the example given is:
BB = brown eyes, Bb = brown eyes, bb = blue eyes
The phenotype is the outward physical appearance and behavior of an organism as result of
genotype, which in the example given is:
BB = brown eyes, Bb = brown eyes, bb = blue eyes
- Homozygous: describes an organism with two (identical) alleles that are the same for a trait.
In the above example, a homozygous dominant would be a person with alleles BB (brown) and
homozygous recessive would be a person with alleles bb (blue).
- Heterozygous: describes an organism with two different alleles for a trait.
According to the example above, a heterozygous person would be someone with alleles Bb
(brown) giving the color eyes of the dominant trait, which is brown.
Mr. Saoulis
Mendel, as a gardener he was, focused on plants. After initial experiments with pea plants,
Mendel settled on studying seven traits that seemed to inherit independently of other traits: seed
shape, flower color, seed coat tint, pod shape, unripe pod color, flower location, and plant
height. The following table shows the dominant and recessive traits of the pea plants, but also
shows the phenotype of the offspring if we crossed two purebred, one parent homozygous
dominant and the the other homozygous recessive.
Mr. Saoulis