Mendelian Genetics

By: Zinani Harriott, Taylor Bagen, & Felix Li

Mendel & Pea PlantsGregor Mendel• Austrian Monk• Used Pea Plants to find

answers• Creator of Laws of

Heredity• His findings were made

in 1866

Pea Plants• Cross pollinated 2

different kinds of plants

• Parental generation to make 1st generation

Heredity & Alleles & Traits

Heredity• passing on of

characteristics from one generation to the next

Traits• phenotypic characteristics

of an organism that can be inherited

Allele• A pair that is a form of a

gene on a chromosome

Dominant & Recessive

Recessive• the allele not expressed

in the heterozygous form (lowercase)

Dominant• gene has the same effect

when it is present as a single copy (heterozygous) as when it is present as two copies (homozygous) (UPPERCASE)

Law of Segregation and Independent Assortment

• Law of Segregation-states that during the forming of gametes, the alleles from separate heredity factors split up and result in the new offspring with one gamete from each parent

Ex.-a homozygous green pea pod (GG) and a homozygous yellow pea pod (gg) would create an offspring with the genotype (Gg). This is because the alleles separate, and the offspring receive one from each hereditary factor

• Law of Independent Assortment-states that two or more pairs of alleles separate from each other during gamete formation.

Ex.-the gene for color of pea pods, is a separate gene than the gene for wrinkled or smooth pea pods

Monohybrid crosses and Test crosses

• Monohybrid cross-a genetic cross for a single trait with two alleles

Ex.-a cross between a homozygous dominant green pea pod, and a homozygous recessive yellow pea plant

Test cross-a test to find out if an organism is heterozygous for a trait. This is needed when an organism displays a dominant phenotype.

-Unless both of it’s parents were homozygous dominant as well, there is a chance that the organism has the alleles (Gg).

-This would mean that it displays the dominant phenotype, but there is a chance its offspring would not.

Dihybrid crosses

• Dihybrid cross-a cross between two individuals that are both heterozygous for different traits.

Ex.-Both parents with the genotype (Ee, Tt) Since both parents have two hybrid traits, they are known as dihybrids. When dihybrids are crossed, they make four possible gamete types, displayed on the box all the way to the right. Key: E=two eyes, ee=one eye

T=triangular head, tt=pentagonal head

Genotype and Phenotype

• Genotype-the genetic coding of an organism, the genotype is what is passed copied every time a cell divides. It is something you cannot see with your eyes.

Ex.-heterozygous, homozygous, dominant, or recessive alleles

• Phenotype-the observable, physical aspects of an organism. It entails the physical characteristics

Ex.-colors, growth, etc.

Phenotypes

The phenotype is the physical characteristic or

trait represented.

A-Browna-Blue

Current EventsJanuary 5, 2010ObservatoryWhite Lizards Evolve in New Mexico Dunes By HENRY FOUNTAINThe White Sands of New Mexico are a good place to study evolution in progress. One reason is that the terrain, gypsum dunes white as a sheet of paper, is so different from the surrounding area. Another is that the dunes formed only about 6,000 years ago.“From an evolutionary perspective, that’s really the blink of an eye,” said Erica Bree Rosenblum, a professor at the University of Idaho who has been studying evolution at White Sands for much of the past decade. Her focus has been on three lizard species that elsewhere are dark skinned but in White Sands have each evolved a white-skinned variety that makes them hard to find. “It’s really obvious what’s happened,” Dr. Rosenblum said. “Everybody got white so that they could better escape from their predators.” It’s a great example of convergent evolution, of species independently acquiring the same traits.One question about convergent evolution is the mechanism by which it happens. Sure, these three lizards all developed white skin, but did they do it in the same way? Dr. Rosenblum and her colleagues have provided answers to this question in a paper in The Proceedings of the National Academy of Sciences.“At first blush it seems like the answer is yes,” she said. In at least two of the lizard species, the researchers found that mutations on the same gene, linked to the production of the skin pigment melanin, were responsible. The second part of the story is more interesting, Dr. Rosenblum said. In the two species, the mutations are different, and the molecular mechanism by which less melanin is produced is different, too. And, she said, the different mechanisms have had an effect on how the white-skinned trait has spread through the populations. In one, the mutation has made the white-skinned trait dominant; in the other, the mutation has made it recessive. So, according to basic Mendelian genetics, the trait spreads more quickly in the first lizard species than the second.

Genotypes

Genotype is the genetic

constitution of an individual

or cell

AA Aa aa

Incomplete Dominance