MENDELIAN GENETICS– CHAPTER 6.3 – 7.4 Mrs. Williams Freshman Biology Honors; Semester Two

Pre-Test  Get out your cell phones! Get out your cell phones!

Genetics  Genetics is the study of traits and how they are passed from one generation to the next.  BrainPop BrainPop  Greatest Discoveries Greatest Discoveries

Gregor Mendel  Austrian monk  Performed genetic experiments in the 1850’s and 1860’s  Considered the “Father of Genetics”  His work was performed with no knowledge of DNA, cells, or meiosis!

Mendel’s Experiments  Worked with pea plants in the monastery gardens  Followed the inheritance patterns of seven different traits (characteristics) in the plants

Creating the F 1 Generation  For each trait:  Mendel used a true-breeding plant for each form of the trait for the parent (P) generation Ex- True-breeding purple flower x true-breeding white flower  Cross-pollinated the plants to produce offspring  Created F 1 generation which only displayed one form of the trait (hybrids) Ex- all F 1 plants were purple flowered

Conclusions  Pea plants were passing a chemical message from one generation to the next that was controlling the trait (Ex- flower color)  This is a gene (Ex- gene for flower color) Genes are sections of DNA on chromosomes that code for a trait  Different forms of a trait are called alleles There is a purple and a white allele for flower color

More Conclusions  Principle of Dominance  One allele is dominant over the other  Dominant will always be displayed when present  Recessive is only seen when it is the only allele present

Review – Grab a set of flip cards!  1. Meiosis occurs in what type of cells?  A. Somatic Cells  B. Gametes  2. How many times does DNA replicate during meiosis?  A. Once  B. Twice  C. Three Times  D. Four Times

Review Continued  3. What are the steps, in order, of meiosis I?  A. Metaphase I, Telophase I, Interphase I, Anaphase I  B. Interphase, Metaphase I, Prophase I, Telophase I, Anaphase I  C. Interphase, Prophase I, Metaphase I, Anaphase I, Telophase I  D. Telophase I, Metaphase I, Anaphase I, Prophase I  4. How many functional egg cells are made during each cycle of meiosis?  A. Four  B. Three  C. Two  D. One

Review Continued  5. Who is considered the “Father of Genetics”?  A. Gregorovich Butinsky  B. Gregor Mendel  C. Viktor Krum  D. Anton von Leuweenhoek  6. What plants were used to do genetics experiments?  A. Pea plants  B. Petunias  C. Pansies  D. Tomato plants

Review Continued  7. What states that if a dominant allele is present, it will always be expressed?  A. The Law of Independent Assortment  B. The Principle of Dominance  C. The Law of Segregation  D. The Order of the Phoenix  8. In order for a recessive trait to be expressed, both parents must donate a  A. Dominant allele  B. Recessive allele  C. One parent gives a dominant, and one parent gives a recessive

Creating the F 2 Generation  For each trait  Mendel self-pollinated plants from the F 1 generation Ex- F 1 purple flower is crossed with itself  Created the F 2 generation which displayed both traits in a 3:1 ratio For every 4 flowers, 3 were purple flowered and one was white flowered

Conclusions  Each pea plant has two copies of every gene  Each copy is found on one of the homologous chromosomes  Each individual has three possible types of combinations Two dominant alleles- homozygous dominant Two recessive alleles- homozygous recessive One of each- heterozygous

More Conclusions  Principle of Segregation  The two copies of a gene that an individual has separate (segregate) from each other during gamete formation  The copy to be put in the gamete is chosen at random  This happens during Anaphase I when the tetrads separate

Tetrad Separation

Predicting Inheritance Outcomes  Probability- rules that predict the likelihood of an event occurring  Punnett squares- tool used in genetics to figure out the probability of a genetic cross  Monohybrid cross- Punnett square showing the outcome of the inheritance of one trait  Dihybrid cross- Punnett square showing the outcome of the inheritance of two traits

Information About Traits  Physical form of the trait seen is the phenotype (show either dominant or recessive)  Genotype is the alleles that an individual has for a trait (2 alleles/trait)  Represented by letters (capital for dominant, lower-case for recessive)  Letter is chosen based on dominant allele  Possibilities (using flower color as example) Homozygous dominant PP Heterozygous Pp Homozygous recessive pp  Heredity Heredity

Setting Up a Punnett Square  One parent’s possible gametes go on the top  Other parent’s possible gametes go on the side  Squares are filled in with the column and row header  Dominant letter is written first

Mendel’s Dihybrid Experiment  Mendel crossed two plants that were true-breeding for two traits  Ex- True-breeding round and yellow peas (RRYY) x True- breeding wrinkled and green peas (rryy)  F 1 generation was all round and yellow  F 1 generation was self-pollinated to create F 2  F 2 generation showed all 4 possible phenotype combinations in a 9:3:3:1 ratio

Conclusions  Law of Independent Assortment  Each gene segregates on its own  The inheritance of one trait does not influence the inheritance of another; each trait is chosen randomly and independent from each other For example, a pea plant that inherited the dominant yellow pea color did not automatically inherit the round (dominant) pea shape.

Setting Up a Dihybrid Punnett Square  All possible allele combinations from one parent are placed along the top (4 total)  For example- an F 1 round and yellow pea plant (RrYy) could produce RY, Ry, rY, and ry gametes  All possible allele combinations from the other parent are placed along the side (4 total)  Square are filled with the column and row headers (16 squares)  Letters from one trait go first, then the other  Capital letter for that trait are put in front

Dihybrid Punnett Square

Uses for Punnett Squares  Give all possible outcomes for a cross between two different parents  Predicts expected (not actual) ratios among the offspring

Beyond Mendelian Genetics  Incomplete dominance  Codominance  Multiple alleles  Polygenic traits  Multifactorial traits

Incomplete Dominance  One allele is not completely dominant over the other; heterozygotes show a blending of the trait

Codominance  Neither allele is dominant over the other; heterozygotes express both alleles at the same time (not a blending)  Ex: Both black and white feathers in chickens  Ex: Both white and red hairs in roan cattle

Multiple Alleles  Gene has more than just two alleles possible  Remember- each individual still just has 2  Ex- rabbit fur color (4 alleles)

Human Blood Types  Human Blood Types have a gene that displays multiple alleles and codominance  ABO gene has three alleles  I A codes for a A-type ID tag on red blood cells  I B codes for a B-type ID tag on red blood cells  i codes for no ID tag on red blood cells  I A and I B alleles are codominant

Human Blood Types Continued  Possible Phenotypes and Genotypes  A blood type (I A I A or I A i)  B blood type (I B I B or I B i)  AB blood type (I A I B )  O blood type (ii)

Polygenic Traits  More than one gene codes for a trait  Wide range of phenotypes and genotypes possible  Ex- eye color

Multifactorial Traits  Phenotype is a blend between genetic inheritance and environment

Revisiting Independent Assortment  Not all genes independently assort  Only happens with genes on different chromosomes  Genes on the same chromosome are linked (where one goes the others go too)  For example, if One homologous chromosome has alleles A, B, and c for three genes The other homologous chromosome has alleles A, b, and C Then the offspring cannot get A, B, and C or a, b, and c or any other combinations

Crossing-Over Revisited  Crossing-over can change the combinations of linked genes  The further apart that two genes are on a chromosome, the more likely that they are to cross-over  Gene maps are maps of chromosomes that show the locations of genes and the distances between them