Genetics the scientific study of heredity.

Many of your physical traits resemble those of your parents Many of your physical traits resemble those of your parents. These are physical or behavioral characteristics that vary from one individual to another. Heredity can be defined as the passing of genetic traits from parents to offspring. Question: Which one of the president’s daughters looks more like their mother? Traits

Gregor Mendel Gregor Mendel was an Austrian monk and a scientist who performed experiments with garden peas. Mendel studied seven pea plant traits, each with two contrasting characters. He crossed plants with each of the seven contrasting characters and studied their offspring.

Mendel’s Crosses Each original pair of plants is the P (parental) generation. The offspring are called the F1, or “first filial,” generation. The F1 hybrid plants all had the character of only one of the parents.

Mendel’s Seven Traits Mendel's first conclusion was that biological inheritance is determined by factors that are passed from one generation to the next. He called these factors genes. Each of the traits Mendel studied was controlled by one gene that occurred in two contrasting forms that produced different characters for each trait.

Principle of Dominance The different forms of a gene are called alleles. Mendel’s second conclusion is called the “Principle of Dominance.” which states that some alleles are dominant (expressed) and others are recessive (masked).

Mendel suggested that the alleles segregate from each other during the formation of the sex cells, or gametes. Gamete Formation

Try writing your own PUN for extra credit.

Mendel’s Principles 1) Genes are passed from parents to their offspring. 2) If two or more forms (alleles) of the gene for a single trait exist, some forms of the gene may be dominant and others may be recessive. 3) In most sexually reproducing organisms, each adult has two copies of each gene. These genes are segregated from each other when gametes are formed. 4) The alleles for different genes usually segregate independently of one another.

Probability, Ratios and Punnett Squares The likelihood that a particular event will occur is called probability. Probability can be used to predict the outcomes of genetic crosses. Punnett squares are diagrams used to predict and compare the genetic variations that will result from a cross.

Punnett Square Practice To determine the phenotype of an offspring you must first recognize its genotype. We have discussed two types of alleles, Dominant (B) and Recessive (b) We have also discussed Heterozygous (Bb) and Homozygous (BB) or (bb) alleles Punnett squares provide a means for determining the phenotypic outcome resulting from the combination of gametes The basic construction of a simple punnet square is to the left of this explanation. Punnett Square Practice

List the phenotype and genotype outcomes for each cross below using the Punnett Square. Practice Problems Heterozygous dominant x Homozygous recessive Hh x hh ( H = white, h = green ) homozygous recessive x homozygous recessive bb x bb ( B = Black, b = brown) Heterozygous dominant x homozygous dominant Tt x TT ( T = tall, t = short )

Probability and Predicted Averages • Probabilities predict the average outcome of a large number of events. • In genetics, the larger the number of offspring, the closer the resulting numbers will get to expected values. Cat example from class. Mom and Dad were BbxBb had 25 kittens of black and white color

Incomplete Dominance When one allele is not completely dominant over another it is called incomplete dominance. In incomplete dominance, the heterozygous phenotype is between the two homozygous phenotypes.

Codominance In codominance, both alleles contribute to the phenotype (like spots!). Heterozygous chickens are speckled with both black and white feathers. The black and white colors do not blend to form a new color, but appear separately.

Multiple Alleles •An individual can’t have more than two alleles. (Only two parents….) However, more than two possible alleles can exist in a population. •A rabbit's coat color is determined by a single gene that has at least four different alleles. - Blood types in humans (A, B, and O)

Polygenic Traits Traits controlled by two or more genes are said to be polygenic traits. •Skin color in humans is a polygenic trait controlled by more than four different genes. Scientists do not believe they have identified all the genes responsible for eye color.

REVIEW The name of the scientist responsible for forming the foundations of genetics is __________. Why did this scientist chose garden peas to perform his experiments? Heredity can be defined as ________ Genetics can be defined as _______ What is difference between dominant and recessive traits? Explain the difference between the P, F1 and F2 generations. What type of genetic characteristics can be observed in each one? The difference between a gene and an allele is? Homozygous is? What is codominance? What is incomplete dominance?

Sex-Linked Traits

LOL Some traits are linked on the sex chromosomes. These are typically on the X chromosome This means that even if it is a recessive trait, it will show up in a male individual. Examples: male pattern baldness, hemophilia and specific color patterns in chickens

X linked codominant traits Some of these traits are linked on the X chromosome and you need two for the trait to show up. Calico cats are always female This is a codominant X- linked trait The calico coloring is completely random Cloned calico cats have a different coloring than that of the cat they were cloned from.

Pedigrees Pedigrees show how traits are passed through families We draw pedigrees by going backwards from the trait that we want to trace First you show which people have the trait Then you figure how the trait was passed from parent to offspring Key: Blank = no trait Filled in = affected Squares = MALE Circles = FEMALE

Hemophilia in the Royal Family

Two Factor Hybrid Cross For a two-factor F1 hybrid cross, the Punnett square predicts a 9 : 3 : 3 : 1 ratio in the F2 generation.