Textbook Chapters 10-13 Review Book Topic 3 Genetics Textbook Chapters 10-13 Review Book Topic 3

Mendelian Genetics 1866 – Gregor Mendel (Austrian monk) Studied inheritance of traits in pea plants Easy to grow, breed, control “True breeding” – meaning they always produce offspring with only one form of a trait Inheritance (heredity) – passing of traits onto the next generation Known as the “father of genetics”

Noticed that certain characteristics are passed onto offspring from generation to generation (traits) Mendel controlled cross- pollination (breeding) between plants by removing the male organs from the flower He then chose which plants reproduced

Mendel called the parent plants the “P” generation When crossing two “P” generation, the offspring produced were called the “F1” generation (hybrids) By crossing two “F1” generation, Mendel could study if characteristics could skip generations Creates the “F2” generation

Mendel studied seven different traits Seed color Flower color Seed pod color Seed shape or texture Seed pod shape Stem length Flower position

After his experiments Mendel concluded: There must be two forms of a trait Each form is controlled by an allele Allele – alternate form of a single gene passed on from generation to generation

Doesn’t mean it is stronger or more present in the population Dominant allele (A) – form of the trait that appears in the F1 generation (shown) Doesn’t mean it is stronger or more present in the population Ex. Polydactyly Recessive allele (a) – form of the trait that is masked in the F1 generation (not shown)

Traits are different forms of a single gene Genes contain a segments of DNA which codes for a specific protein

Law of Segregation Homologous traits occur in pairs on homologous chromosomes Separated from each other during gamete formation (Law of Independent Assortment) Recombine at fertilization One form of a trait is inherited from each parent

Law of Dominance Homozygous – an organism with two of the same alleles for a given trait (AA, aa) Heterozygous – an organism with two different alleles for a given trait (Aa) When heterozygous, the dominant trait will be observed

Three forms of dominance: Homozygous dominant – AA Heterozygous – Aa Homozygous recessive – aa

Characteristics The outward appearance does not always indicate which pair of alleles is present Genotype – organism’s allele pairs (AA, Aa, aa) Phenotype – observable characteristic of an allele pair (tall, short, green, yellow)

It is possible for two organisms to have the same phenotype but different genotypes The genotype and phenotype of an organism is called a genome

Activity #1 Genotype versus phenotype smiley face activity

Punnett Squares (1900s) Used to predict the possible offspring of a cross between two known genotypes Each parent contributes one allele per square in the box

Homozygous-homozygous AA x AA AA x aa aa x aa Homozygous-heterozygous Monohybrid cross – only the inheritance of one trait is being studied Homozygous-homozygous AA x AA AA x aa aa x aa Homozygous-heterozygous AA x Aa aa x Aa Heterozygous-heterozygous Aa x Aa

Dihybrid cross – inheritance of two or more different traits are being studied

Test Cross An individual of unknown genotype is mated with an individual showing the homozygous recessive trait Unknown could be homozygous or heterozygous Look at offspring produced to determine unknown genotype

Law of Independent Assortment Allele pairs are randomly separated independently during gamete formation (meiosis) Different traits are inherited separately Exception is gene linkage Linked genes are inherited together

Activity #2 Punnett square practice worksheet

Law of Probability “Law of chance” Inheritance of genes can be compared to flipping a coin Probability = # of ways a specific event can occur # of total possible outcomes

Activity #3 Probability and Inheritance Lab

Heredity BrainPop

Exceptions to Mendel’s Laws Incomplete dominance Both alleles contribute to the phenotype Heterozygote is an intermediate of two parent’s traits

Codominance No single allele is dominant Both alleles expressed at same time

Polygenic Inheritance More than one gene can affect a single trait Ex. Four genes are involved in eye color Ex. Human height Ex. Skin color

Pleiotrophy A single gene can affect more than one trait Ex. Cystic fibrosis, sickle cell anemia

Gene Interactions (epistasis) Products of genes (proteins) can interact to alter genetic ratios Ex. Coat color in mammals Ex. Purple pigment in corn

Environmental Effects Genes may be affected by the environment Ex. coat color in arctic fox or hares (rabbits) Ex. Siamese cats

Multiple alleles for one gene Genes may have more than two alleles Ex. blood type A, B, O alleles Types: A, B, AB, O IAIA / IAi (A); IBIB / IBi (B); IAIB (AB); ii (O)

Pedigrees Diagram that shows the phenotypes of several generations in a family tree for a specific trait Symbols used: Female -  Male –  Shading indicates individual shows the trait Marriage represented by horizontal line between Offspring represented by vertical lines

Applied Genetics Selective Breeding Humans breed animals/plants with certain traits to obtain offspring that have desired traits Results in traits becoming more common in a breed                                                          

Hybridization Animals/plants are bred to form heterozygotes Heterozygous advantage Ex. Disease resistance, increased offspring variation, faster growth, higher fruit yield Disadvantages: Time consuming Expensive Careful selection of parents to produce correct combinations of traits in offspring

Inbreeding Two closely related organisms are bred to have the desired traits Also to eliminate the undesired traits in future generation Disadvantage – harmful recessive traits also can be passed on to future generations in homozygous recessive individuals

Examples of Human Inbreeding Ancient Egypt Pharaohs married their sisters Royal Europe Royalty married within their family