Using Biotechnology Unit 3 Chapter 16 Lesson 2

Genetic Terminology Variability –Differences in animals or plants of the same species –Example: hair color, skin color, height, weight Genome –Total genetic make-up of an organism Chromosomes –Threadlike structures that hold DNA within a cell

Genetic Terminology Loci –Numbered “locations” of chromosomes in a species at which there is a pair of chromosomes –Humans = 23 –Sheep = 27 –Horses = 30 Homologous chromosomes –Pair of chromosomes found at a loci

Genetic Terminology Diploid cell (body cells) –Cell having all chromosomes required for the species (2 at each loci) –Humans = 46 –Sheep = 54 –Horses = 60 Haploid Cells (reproductive cells) –Cells with only one chromosome for each loci –Half the number required for a species

GENETICS Gregor Mendel ( ) –Austrian monk –“Father of Genetics” –Experimented with pea plants –Used quantitative data analysis –Traced the inheritance patterns of certain traits in pea plants –Known as Mendelian genetics

Allele –Different forms of a gene –2 alleles combine to form 1 gene –One allele is inherited from each parent Pea Plant Genetics –Tt = a pair of alleles for 1 characteristic – plant height –Rr = a pair of alleles for 1 characteristic – seed shape –Gg = a pair of alleles for 1 characteristic – seed color –Bb = a pair of alleles for 1 characteristic – flower color Genetics Video Clip

Pea Plant Characteristics: Round – Wrinkled Seed Short – Tall Green – Yellow Seed Purple – White Flower Mendel’s GENETIC Studies

Genetics Some trait are dominant –Dominant = An allele is said to be dominant if it expresses its phenotype even in the presence of a recessive allele. –Always represented with a capital letter: T = Tall Some traits are recessive –Recessive = A part of the gene that is only expressed if a dominant allele is not present –Always represented with a lower case letter: t = short If more than 2 alleles exist for a gene, then some of the recessives will be written with a superscript –Example: E (dominant), e (most recessive), e ch (recessive to E, but dominant to e) T t

Genetics Terms Homozygous –Gene with 2 alleles that are the same –homo = same –AA, BB, DD, ee, ff Heterozygous –Gene with 2 alleles that are different –hetero = different –Aa, Bb, Dd, e ch e, Ff

Genetic Terms Genotype –The genetic make-up of an animal –Angus Cattle Color Genotypes = BB, Bb, or bb Phenotype –Physical appearance of an organism –Phenotypes of Cattle colors = Black or red

Genetic Predictions To figure out which traits will be present you need to set up a Punnett Square, invented by RC Punnett. Can show 2 types of crosses – monohybrid or dihybrid crosses. –Monohybrid cross = organisms differing in only one trait are crossed. (Tt x Tt) or (AA x aa) or (Ss x Ss) –Dihybrid cross = organisms differing in two traits. –Mendel invented the dihybrid cross to determine if different traits of pea plants, such as flower color and seed shape, were inherited independently.

Making a Punnett Square Step 1 Make a chart with 2 vertical and 2 horizontal lines (like tic-tac-toe)

Making a Punnett Square Step 2 List the alleles of parent 1 along the top and parent 2 along the left side. (Parent 1 = AA, Parent 2 = aa) AA a a

Making a Punnett Square Step 3 Determine offspring possibilities by “adding” the table (top + left) AA a a Aa

Making a Punnett Square Step 4 Determine the ratio for phenotype and genotype In our example, all of the offspring would look like the capital A gene and have a ratio of 1:0 for phenotype and genotype

A Mendel Example Flower color BB or Bb = Purple bb = white Genotype: 1BB: 2Bb:1bb Phenotype: 3 Purple: 1 White 75% Purple: 25% White

Mendel Experiment P1 Generation –the first parents crossed F1 Generation –the first offspring F2 Generation –Offspring of second cross –Cross between 2 F1 parents

Punnett Square Practice Breeding cattle: –P1 = Purebred black (BB) x purebred red (bb) Produce F 1 Offspring B b Bb Bb Phenotype: 100% black Genotype: 100% Bb

Produce the F 2 Offspring by breeding 2 F 1 offspring together Bb B BB Bb b Bb bb Phenotype: 3:1 75% black 25% red Genotype: 1:2:1 25% BB 50% Bb 25% bb Punnett Square Practice

Dihybrid Cross Example Alleles –Horned (H) or polled (h) –Black (B) or red (b) P1 –BBHH X bbhh BH bhBb Hh bhBb Hh bhBb Hh bhBb Hh F1 : BbHh 100% Black Horned

Dihybrid Cross Example F2 Generation BbHh X BbHh BHBhbHbh BHBB HH BB Hh Bb HH Bb Hh BhBB Hh BB hh Bb Hh Bb hh bHBb HH Bb Hh bb HH bb Hh bhBb Hh Bb hh bb Hh bb hh F2 generation (9:3:3:1) 9 Black horned 3 Black polled 3 Red horned 1 Red polled

The Law of Segregation states: 1. The concept of alleles. Alleles are different versions of genes that impart the same characteristic. For example, each human has a gene that controls eye color, but there are variations among these genes in accordance with the specific color the gene "codes" for. 2. For each characteristic, an organism inherits two alleles, one from each parent. 3. Only the dominant trait is seen in the phenotype of the organism. This allows recessive traits to be passed on to offspring even if they are not expressed. 4. The two alleles for each characteristic segregate (separate) during gamete production. This means that each gamete will contain only one allele for each gene. This allows the maternal and paternal alleles to be combined in the offspring, ensuring variation. Mendel’s Laws

Law of Independent Assortment –during gamete formation the allele pairs sort separately –states that the emergence of one trait will not affect the emergence of another –Example: there is no relation between a cat's color and tail length. Mendel’s Laws

Draw and label a homologous chromosome pair with heterozygous alleles highlighting a particular gene location.

Incomplete Dominance Neither allele is dominant. Both phenotypes blend to form a difference phenotype.

Codominance Alleles share expression. Both phenotypes are shown.