G ENETICS

Genetics is the study of heredity

G REGOR M ENDEL (1822 – 1884) Recognized as the “Father of Genetics” An Austrian monk Tended to the gardens at the monastery Observed plant growth and researched hereditary characteristics

Mendel experimented on pea plants. Why? They were easy to grow Could produce a large number of offspring in a short amount of time.

M ENDEL ’ S O BSERVATIONS Noticed that some traits are passed on from one generation to the next. Noticed that traits exist in two possible forms. Noticed that for each trait, one form dominates the other.

G ENES Paired units which transmit hereditary traits.

G ENES Occur in pairs in the nucleus.

G ENES Separation of homologous chromosomes during meiosis determines which genes the offspring will get.

L AWS OF H EREDITY Law of Dominance The dominant form of the trait prevents the expression of the recessive form.

L AWS OF H EREDITY Law of Segregation The pair of genes responsible for each trait separate so that each gamete contains only one gene for each trait.

L AWS OF H EREDITY Law of Independent Assortment Genes for different traits are inherited independently of each other.

G ENETIC T ERMINOLOGY Allele The possible form a gene may take

G ENETIC T ERMINOLOGY Dominant trait Prevents the expression of a recessive trait Represented by a capital letter (T)

G ENETIC T ERMINOLOGY Recessive Trait Form of a trait that can be hidden. Represented by a lower case letter (t).

G ENETIC T ERMINOLOGY Homozygous Having two identical alleles

G ENETIC T ERMINOLOGY Heterozygous Contains one of each allele

G ENETIC T ERMINOLOGY Genotype The combination of alleles (type of genes) Homozygous Dominant = Heterozygous Dominant = Homozygous Recessive =

G ENETIC T ERMINOLOGY Phenotype The physical expression of the trait (how it looks). Example: Blue eyed, right handed, tall, curly, etc.

G ENETIC T ERMINOLOGY Punnett Square Shows the possible outcomes from the cross of a trait.

G ENETIC C ROSSES

M ONOHYBRID C ROSSES Dominant/Recessive Cross Offspring show either the dominant or the recessive phenotype Example 1: Cross a homozygous right handed mom with a left handed dad. Parents Genotype: _____________ X ______________

Genotypic Ratio: Phenotypic Ratio:

Example 2: Cross a heterozygous right handed mom with a left handed dad. Parents Genotypes: ___________ X ____________ Genotypic Ratio: Phenotypic Ratio:

Example 3: Cross two heterozygous right handed parents. Parents Genotypes: ___________ X ____________ Genotypic Ratio: Phenotypic Ratio:

M ONOHYBRID C ROSSES Incomplete Dominance The heterozygous genotype creates a new, blended phenotype. Example: Cross a red flower with a white flower. Parents Genotype: _____________ X ______________

Genotypic Ratio: Phenotypic Ratio:

M ONOHYBRID C ROSSES Co-Dominance Both traits are expressed equally Example: Cross a black chicken with a white chicken. Parents Genotype: _____________ X ______________

Genotypic Ratio: Phenotypic Ratio:

M ONOHYBRID C ROSSES Sex-Linked Traits Sex chromosomes: X and Y chromosomes (all other chromosomes are called autosomes) Females: have 2 X chromosomes (XX) (only one type of allele) Males: have 1 X and 1 Y chromosome (one of each allele)

Sex-Linked Traits: traits inherited on sex chromosomes Genes for some traits are on sex chromosomes Some traits are determined by only one gene (the X or the Y, not both) Some genes are only found on the Y chromosome (adam’s apple, hairy ears)

Example : In a certain animal, the gene for black color coat (B) is dominant to the gene for orange coat color (b). The characteristic is sex-linked. Parents: Female Genotype ____________Gametes _______ & _______ Male Genotype_______________Gametes _______ & _______

Genotypic Ratio: Phenotypic Ratio:

M ONOHYBRID C ROSSES Multiple Alleles One trait is controlled by more than one allele Genetic Example: Blood type Alleles I A I B I O or i

I A and I B are dominant to i Neither I A or I B is dominant over the other; they are co-dominant This results in the 4 possible blood types A B AB O

Example: Cross a heterozygous type A parent with a heterozygous type B parent. Parents ______________ X ______________ Genotypic Ratio: Phenotypic Ratio:

D IHYBRID C ROSSES A cross involving two traits When setting up your Punnett square use the foil method to determine your gametes.

Example: Cross a heterozygous tall, heterozygous round pea plant with a short, wrinkled pea plant. Parents: ___________________ X _____________________ Genotypic Ratio: Phenotypic Ratio: