Genetics The study of heredity

Heredity and environment are two factors that influence the development of living things Heredity is the passing on of traits from parents to offspring Genetics is the study of heredity and how genes work in this process.

Gregor Mendal's conclusions. 1.Genes occur in pairs. (Remember: genes are just regions on a chromosome that code for a trait. Chromosomes are made of DNA.) 2. Genes display dominance and recessiveness. - Since genes occur in pairs, usually only one gene will show its trait.

Dominant gene = the gene whose trait will be expressed in an individual. Dominant genes are noted by capital letters. example: If tall is dominant over short in pea plants, then the plant with either of these two gene pairs (TT or Tt) will be tall.

Recessive gene = - Does not show its trait if the other gene in the pair is dominant. - This gene is overpowered by the dominant gene. - Noted by using small letters (t). - Only if both genes in a gene pair are recessive will the recessive trait be expressed. example: Tt = tall plant TT = tall plant tt = short plant (because of two recessive genes that code for short plants)

3. The law of segregation: When gametes are formed only one gene of a pair will be found in that gamete. (a result of meiosis). 4. The law of independent assortment: When genes pairs separate they go to gametes independently of other gene pairs. example: The genes for eye color are not related to genes for hair color, or height, etc.

Combinations of genes could be: Homozygous - Both genes the same - either dominant or recessive (TT or tt) - true-breeding, purebred Heterozygous - Genes are different (Tt) - hybrid

t T Phenotype - What an individual looks like Genotype - Genes that an organism possesses Genes occur in pairs... On homologous chromosomes Could be: Dominant t T Recessive - Represented by capital and lower case letters

Gametes - with only one copy of the gene DNA replication T T t t Then... Meiosis Gametes - with only one copy of the gene

T t TT Tt T t Tt tt Punnett square shows: - Results of meiosis (gametes) & -POSSIBLE results of fertilization Parent 1 T t TT Tt T t Parent 2 Tt tt

How to Solve a Genetics Problem Read the problem and determine the dominant trait(s) Make a key to describe what genes your letters represent. Ex. T = tall t = short Determine genotype of parents Determine possible gametes formed by parents

Draw a punnett square Place gametes of each parent on top and along left side Show results of fertilization by filling in boxes List results = Genotype & Phenotype

Monohybrid Cross In pea plants tall is dominant over short. Cross a homozygous tall plant with a heterozygous tall plant. What are the possible outcomes?

Freckles are dominant in humans Freckles are dominant in humans. Cross a purebred freckled man with a woman who does not have freckles.

In chinchillas black is dominant over grey In chinchillas black is dominant over grey. Cross two heterozygous individuals.

Dihybrid Cross In pea plants tall plants and yellow seeds are dominant over short plants and green seeds. Cross a heterozygous tall yellow plant with a homozygous tall green plant. What are the possible outcomes? Punnett square: Key: Parents Genotypes: Results: _______ X ________ Determining Gametes

Cross a homozygous tall, yellow plant with a short, green plant Cross a homozygous tall, yellow plant with a short, green plant. What could the F2 generation of this cross look like?

Intermediate Inheritance In some cases there are no dominant genes. Or equally dominant genes. As a result, a cross may result in: - a true blending of the characteristics - both characteristics being present

Many traits are incompletely dominant over others, which result in intermediate forms.

In guinea pigs the straight hair shape is dominant and curly hair is recessive. Wavy hair is also a phenotype. Cross a guinea pig with straight hair to a curly haired guinea pig, and list the results.

In snap dragons, red in incompletely dominant over white In snap dragons, red in incompletely dominant over white. Pink is also a phenotype. Cross a white flower with a pink flower and list the results.

In horses, roan color is the result of codominant genes both showing up. Individual hairs are either one color or the other.

Sex-linked traits traits whose genes are located on the X chromosome alleles are shown by XN = normal and Xn = affected show up more often in males There is no second X chromosome to contain a dominant gene.

Red green Colorblindness is a sex-linked trait Red green Colorblindness is a sex-linked trait. Cross a carrier female with a normal male. What are the possible results?

Genes with more than 2 alleles Multiple alleles Genes with more than 2 alleles Most commonly used example is blood types IA, IB, i A person with blood type AB marries a person with blood type O. What are the possible blood types of their children?

2. Cross a person with an AB blood type with an AO blood type and list the results. 3. A woman with type B blood is accusing a man with type A blood of being the father of a child with type O blood. Will the courts be able to prove that the man is not the father of the child? Is it possible that the man is the father of the child? Do a cross and list the results to justify your answer.