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Genetics by Mr. Chipps

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Tim Chipps

on 27 January 2012

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Transcript of Genetics by Mr. Chipps

Heredity- The passing of traits from parent to offspring
Alleles- the different forms of a trait that a gene may have
Genetics- the study of how traits are inherited through the interactions of alleles
Gregor Mendel- the "Father of Genetics"; gained information about inheritance of traits through work with pea plants
Mendel's work with pea plants- Mendel crossed two plants with different alleles for a certain trait. He discovered that the first generation offspring did not express one of the parental traits, but in the second generation, that trait was restored.
Dominant and Recessive Traits
When two traits are crossed, and one trait covers up the other trait, the trait that covers up the other trait is "dominant", while the trait that was covered up is "recessive".
Making Predictions about Genetics based on probability
Probability- a branch of mathematics that helps predict the chances that something will happen.
Punnett Square
A tool used to predict the resulting genotype of and phenotype of offspring when two parents of known genotypes mate.
Genotype- letters that represent the genetic makeup of an organism.

Phenotype- the way an organism looks and behaves as a result of its genotype
Homozygous vs. Heterozygous
Most organisms contain 2 alleles for each trait.

Homozygous- an organism with two alleles that are the same for a certain trait.

Heterozygous- an organism with two alleles that are different for a certain trait
Practice Making a Punnet Square-

Turn to page 131 in your book.
Tutorial on how to make a Punnett Square
3 Main Principles of Heredity
1. Traits are controlled by alleles on chromosomes.

2. An allele's effect is dominant or recessive.

3. When a pair of chromosomes separates during meiosis, the different alleles for a trait move into separate sex cells.
Incomplete Dominance
When the offspring of 2 homozygous parents show a "blended" phenotype.
Multiple Alleles
When a trait is controlled by more than two alleles, it has more than 3 phenotypes possible.
Polygenic Inheritance
When a group of gene pairs acts together to produce a trait.

- eye color, height, hair color are examples
Impact of Environment on Gene Expression
These can be
internal
or
external
-

internal example-
chemicals in male birds can turn on a gene for brightly colored feathers during mating season
external example-
people can carry a gene that makes them have a greater risk of cancer. Decisions they make can help reduce their risk.
Sex Determination
Grab a ruler, and try the mini lab on pg. 136. Record results from at least 5 of your classmates, and answer the analysis questions.
- Eggs always have one x chromosome.
- Sperm can have either an x chromosome or a y chromosome
- If offspring end up with a genotype of xx, the offspring is a girl.
- If offspring end up with a genotype of xy, the offspring is a boy.
Sex- Linked Disorders
An allele inherited on a sex chromosome is called a sex-linked gene.

An example of a sex-linked gene is color blindness. It is inherited on the x chromosome.
Pedigrees
A pedigree is a visual tool used to follow a trait through generations of a family

Boxes- Males

Circles- Females

Filled in circle or square- trait is seen in that person

Half-filled in circle or square- indicates that the person is a carrier, but does not have the trait (they are heterozygous)
Full transcript