Genetics

Genetics What is genetics? study of inherited traits What is heredity? passing of traits from parents to offspring What is a trait? feature an organism can pass on to offspring ex) hair color, eye color, etc What are Your Traits?

What Determines Traits? Genes! Genes-segments of DNA on chromosomes that code for a protein which produces a trait. There are 1000’s of genes on each chromosome. Chromosomegeneproteintrait

Genes Some traits are coded for by one gene which codes for one protein. i.e. freckles, earlobe attachment, etc

Other traits are coded for by two or more genes together- polygenic Polygenic Inheritance – When a Single Trait is Influenced by Many Genes Other traits are coded for by two or more genes together- polygenic More than one gene=more than one protein that causes the trait so more complex traits are shown Hand span, height, eye color, etc. Height is a polygenic trait

Genes Homologous chromosomes–two chromosomes that have the same number and types of genes. Each HUMAN somatic cell has 23prs of homologous chromosomes Other species have different numbers.

Homologous Chromosomes Mom contributes one and Dad contributes other of each pair This means each somatic cell has two copies of each chromosome, and therefore, each gene.

Alleles Alleles - forms of genes Allele for round peas--R Position on chromosomes where pea shape gene is located Allele for wrinked peas--r

Genotype vs. Phenotype Genotype: the genetic makeup of an organism RR, Rr, or rr 2 letters-one copy from each parent Phenotype: the physical traits the organism shows round or wrinkled peas ***Phenotype = Genotype + Environment

Genotypes The 2 alleles on homologous chromosomes can be the same or different Homozygous (purebred)- having two identical alleles for a particular trait. i.e. pea shape gene: Alleles: R=round and r=wrinkled RR or rr Heterozygous (hybrid) – having different alleles for a particular trait on homologous chromosomes ????

Genotype Example Phenotype Homozygous Dominant RR Round Homozygous Recessive rr Wrinkled Heterozygous Rr

Early Ideas - Heredity Gregor Mendel decided to test this idea Father of genetics It was originally believed a child’s traits were result of “blending” between parent’s traits He knew nothing about DNA!

Mendel’s Pea Plants Why did Mendel use pea plants? 1. Peas had several Characters investigated by Mendel Why did Mendel use pea plants? 1. Peas had several contrasting traits he could observe easily 2. He understood their method of reproduction 3. They reproduced quickly

Reproduction in Plants Plant cells undergo meiosis, just like animals, to create gametes: pollen and ovules! Pollination Anther releases pollen (“plant sperm”) Stigma receives the pollen which the fertilizes the ovules (“plant eggs”) Similar to fertilization in animals. Mendel could control how plants were fertilized because he understood this process

Mendel’s Experiments con’t Parental generation (P) “original group” First filial generation(F1) offspring of the parental cross Second filial generation (F2) offspring of crossing two F1 plants

Mendel’s First Experiment Wanted to know what would happen if cross 2 plants with different forms of a trait. The 1st thing Mendel did was cross 2 purebred (homozygous) plants. ?

Results? In F1 generation NO blending resulted. Round allele (R) dominated over wrinkled form of the gene (r) Dominant allele - hides other allele; R Recessive allele- form NOT expressed in presence of dominant form, “hidden”; r Genetics Rule #1: Principle of Dominance- one allele dominates so trait coded by other allele hidden. R dominates over r when both present ALL ROUND F1

Mendel’s 2nd Experiment The next question: If all the seeds were round in the F1 generation, had the wrinkled allele disappeared? Mendel extended his experiment and cross two of his F1 plants… ?

Results? F2 (Second filial generation)- offspring of F1 cross Some offspring showed recessive trait, some the dominant trait 3:1 ratio (round: wrinkled) Do a Punnett square to show his results for the F2.

Mendel’s Conclusion The dominant allele hides the recessive allele in the F1 Since the recessive allele (wrinkled) reappeared in the F2, it must have “separated” from the dominant allele Law of Segregation- during meiosis when gametes form, alleles for a trait are separated (each parent gives only one allele in egg or sperm to offspring)

Passing of One Gene Figure out the possible gamete genotypes these parents could make: Parent 1: Parent 2: RR Rr ? Gametes ? ? Gametes ?

Passing of One Gene Parent 1: Parent 2: RR Rr R or R R or r Remember that when considering only ONE gene, the gametes that form only have ONE copy of every gene because the gametes only get ONE copy of every chromosome. Parent 1: Parent 2: RR Rr R or R R or r

DIPLOID BODY CELL FROM WHICH EGG AND SPERM COME FROM— 2 COPIES OF EVERY CHROMOSOME AND THEREFORE, EVERY GENE R r MEIOSIS-FORMATION OF GAMETES IN WHICH GENETIC MATERIAL IS CUT IN HALF HAPLOID GAMETES ARE FORMED--1 COPY OF EVERY CHROMOSOME AND, THEREFORE, EVERY GENE. r R

Consider TWO Genes! Try to figure out the possible gamete genotypes a parent could make: **Remember there must be ONE copy of every gene in each gamete! Parent 1: Parent 2: RrYy RrYy ? Gametes ? ? Gametes ?

R r Y y X R r Y y FOIL – FIRST, OUTER, INNER, LAST 1. RY BOTH PARENTS ARE THE SAME, SO THEIR GAMETE GENOTYPE POSSIBILITIES FOR BOTH PARENTS ARE, TOO! 2. Ry 3. rY 4. ry

y Y BODY CELL FROM WHICH EGG AND SPERM COME FROM—DIPLOID 2 COPIES OF EVERY CHROMOSOME AND THEREFORE, EVERY GENE R r MEIOSIS RY Ry r Y ry 4 gametes each with ONE copy of each gene!!!

Show the Punnett Square! Round, yellow: 9 Round, green: 3 Wrinkled, yellow: 3 Wrinkled, green: 1 R r Y y X R r Y y RY Ry rY ry RY RRYY RRYy RrYY RrYy Ry RRYy RRyy RrYy Rryy rY RrYY RrYy rrYY rrYy ry RrYy Rryy rrYy rryy Each gamete MUST have one copy of EVERY gene so the children will have complete pairs!

Law of Independent Assortment Does everyone with brown hair have blue eyes? Does everyone with a big nose have freckles? NO! Mendel’s Law of Independent Assortment- inheritance of one trait will not affect inheritance of another. They are not “tied” together! Peas could be green and wrinkled or green and round. The pea shape gene and the pea color gene assort independently into the gametes.