Heredity Obj. 3d

Heredity The passing of traits from parent to offspring Traits: physical characteristics of an organism –Example: eye color, hair color, & height

Passing Traits to Offspring Sex cells have 23 chromosomes and the two sex cells combine to form body cells with 46 chromosomes. In fertilization, one sperm joins with one egg. The offspring receives half of its genetic information from its mother and the other half from its father.

Genetics The study of how traits are passed from parent to offspring by looking at genes Genes are small sections of DNA on a chromosomes that has information about a trait Each chromosome has a gene for the same trait (eye color from mom & eye color from dad) Traits are determined by alleles on the chromosomes Each gene of a gene pair is called an allele Inherited traits are determined by the alleles on the chromosome

DOMINANT AND RECESSIVE Dominant Alleles describe a genetic factor that is always expressed. –It prevents a recessive trait from showing up in offspring. –Represented by capital letters (B) Recessive Alleles describe a genetic factor that is not always expressed. –It only expresses itself when both of the recessive traits are inherited –Represented by lowercase letters (b)

Examining & Studying Traits Two ways scientist study traits –Phenotype: Physical appearance or outside expression of a gene Blue Eyes –Genotype: the two alleles a person has inherited that can only be seen on the DNA BB, Bb, or bb Two categories of genotypes –Homozygous: inherited two identical alleles BB (pure dominant) or bb (pure recessive) –Heterozygous: inherited two different alleles Bb (hybrid)

INHERITANCE & PASSING TRAITS

Punnett Squares Shows all possible combinations of alleles that children can inherit from parents Mom’s genotype for brown eyes (Bb) Dad’s genotype for brown eyes (Bb) Offspring’s Phenotype –75% brown, 25% blue Offspring’s Genotype –25% BB, 50% Bb, 25% bb Bb B BBBb b bb

Punnett Square A Punnett square is actually a way to show the events that occur at meiosis.

A Punnett Square The diagrams show how to make a Punnett square. In this cross, both parents are heterozygous for the trait of seed shape. R represents the dominant round allele, and r represents the recessive wrinkled allele.

DOMINANT & RECESSIVE

VARIATIONS Variations are the different ways that a certain trait appears. These variations would allow one offspring to have light brown hair & another to have darker brown hair

Genetic Advantages & Disadvantages Selective Breeding organisms for a certain trait –Pure breeding Advantages: allows breeder to have desirable traits expressed in offspring Disadvantages: unfavorable traits can be passed & lack variety to survive diseases or climate changes –Hybrid Advantages: has genetic variety to increase variations that allows species to adapt to climate changes or recover from diseases Disadvantages: traits are uncertain in predicting

Gregor Mendel Known as the father of genetics Studied several traits in pea plants and discovered patterns in the way traits are passed from one generation to another Discovered dominate & recessive traits

Mendel’s Work with Crossing Pea Plants

Mendel’s Experiments In all of Mendel’s crosses, only one form of the trait appeared in the F 1 generation. However, in the F 2 generation, the “lost” form of the trait always reappeared in about one fourth of the plants.

Thomas Hunt Morgan First person to definitively link trait inheritance to a specific chromosome Studies fruit flies eye color