Living Environment Mrs. Lawlor Mendelian Genetics:

Where we’ve been, where we are going…. We know: In sexual reproduction, the new offspring formed is a UNIQUE individual that has been formed from the FUSION of two GAMETES that came from a MOM and a DAD. Unless they have an identical sibling (relatively rare) no other individual has that combination of chromosomes or genes. Where we are headed: ___________________ is the branch of biology that studies the ways that hereditary information is transmitted from parents to their offspring. The field of genetics all started with the work of a Austrian monk by the name of _______________________________. Genetics Gregor Mendel

Who is Mendel? Gregor Johann Mendel ( ) was an Augustinian priest and scientist, who gained fame as the “Father of Genetics “for his study of the inheritance of certain traits in pea plants. Mendel showed that the inheritance of these traits follows predictable patterns. The significance of Mendel's work and ‘laws’ were not recognized until the turn of the 20th century long after his death. The independent rediscovery of these laws formed the foundation of the modern science of genetics.

Why peas? Pisum sativum Easy to grow and care for Easy to control the pollination Very observable traits

Terms I have to elaborate on: We have talked about the 23 pairs of chromosomes for weeks now. For simplicity’s sake, we always referred to a chromosome as controlling a single trait. For example, you have heard me say “This is the chromosome that controls for eye color.” The reality is a chromosome controls dozens of traits, hundreds even. Chromosome: a length of DNA containing many dozens of genes. Gene: a portion of a chromosome/DNA that codes for ONE trait (protein) Allele: the ‘version’ of the gene. (whole strand) (eye color) Allele (green vs. blue)

More critical vocab: Genotype :Phenotype : is the _______________ of an organism. Is usually represented using two letters (capital or lower cases depending on if it is dominant or recessive-more on that later.) ____________________ of the trait in an organism. Expressed with a descriptive words about observable characteristics Ex: genotype: TT Ex: genotype: tt Ex: genotype: Tt genetic makeupphysical appearance Let T = can roll tongue Let t =can’t roll tongue Ex: phenotype: can roll tongue Ex: phenotype: can’t roll tongue Ex: phenotype: can roll tongue from MOM from Dad

More critical vocab: Dominant :Recessive : An allele or a gene that is expressed in an organism’s phenotype, masking the effect of the recessive allele or gene when present use a capital letter a gene (or allele) whose phenotypic expression is masked by a dominant gene (or allele). Use a lower case letter dominant recessive

More critical vocab: Homozygous :Heterozygous : containing two copies of the same allele for a particular trait (A genotype that has the same letters with the same case.) “pure” containing two different alleles for a particular trait. (A genotype that has different letters or different cases.) “hybrid” Ex: genotype: NN Ex: genotype: nn Ex: genotype: Nn samedifferent homozygous dominant homozygous recessive

Mendel's Laws of Inheritance 1. The Law of Dominance 2. The Law of Segregation and Recombination 3. The Law of Independent Assortment the principle of segregation (First Law): The two members of a gene pair (alleles) segregate (separate) from each other in the formation of gametes. Half the gametes carry one allele, and the other half carry the other allele. the principle of independent assortment (Second Law): Genes for different traits assort independently of one another in the formation of gametes. the simple assumption that one allele is dominant to the other allele. After testing these laws for several years, Mendel noticed a pattern or a “mathematical” way to predict the offspring's phenotypes or “looks.” Through his studies, he developed 3 crucial rules:

These laws are the foundation for the tool you learned to use back in Middle School Science…. …..the PUNNETT SQUARE ! BB B B BB bb b b bb Bb B b BBBb bb If you know the genotypes of the parents, a Punnett Square can be used in to calculate the frequencies of the different genotypes and phenotypes among the offspring of that cross. parent’s genotypes offspring’s genotypes

Betcha you didn’t realize back then…. You were keeping track of genes in GAMETES! You were keeping track of genes in GAMETES! These demonstrate the Law of Segregation! These are embryos (the next generation!) These demonstrate the Law of Recombination!

offspring genotype ratios or % offspring phenotype ratios or % TT = 1 Tt = 2 tt = 1 (25%) (50%) (25%) Can roll = 3 Can’t roll = 1 (25%) (75%) Practice cross: ______________ T t x T t

offspring genotype ratios or % offspring phenotype ratios or % TT = 2 Tt = 2 (50%) Can roll = 4 (100%) TRY THIS- cross: ______________ T T x T t

There are many times when a simple Punnett Square doesn’t completely explain the pattern of inheritance. The next examples use the fundamentals of Mendel’s Laws, with a twist! Co-dominance: Incomplete Dominance: blending both show Ex: four O’Clock flowers Ex: Roan cattle

YR yr YR yr YyRrYyRr YyRrYyRr YyRrYyRr YyRrYyRr YyRrYyRr YyRrYyRr YyRrYyRr YyRrYyRr YyRrYyRr YyRrYyRr YyRrYyRr YyRrYyRr YyRrYyRr YyRrYyRr YyRrYyRr YyRrYyRr Genotype: 100% YyRr Phenotype: 100% Yellow and Round A simple Punnett Square keeps track of on trait or gene at a time. A _______________________ is used to keep track of two traits in each parent and therefore in the offspring! Let Y = Yellow pea Let y = Green pea Let R = Round pea Let r = Wrinkled pea DiHybrid Square Parent cross: YYRR x yyrr YyRr = 100% yellow round peas =100% yr

YRYr YR Yr yRyr yR yr YYRR YYRr YyRR YyRr YYRr YYrr YyRr Yyrr YyRR YyRr yyRR yyRr YyRr Yyrr yyRr yyrr What if the parents are two DIHYBRIDS: YyRr x YyRr ____________ Yellow and Round ____________ Yellow and wrinkled _______________ green and Round _______________ green and wrinkled Phenotype ratios

human blood type (the ABO blood system). There are 3 alleles that we will study that control for blood type: I A = type A I B = type B i = type O Type O blood is recessive Types A and B are domin- ant over type O, but neither is dominant over the other Some phenotypes are controlled by MULTIPLE ALLELES, or more than just two versions (one dominant, one recessive.) Human blood type is an example of both co-dominance as well as multiple alleles. Anti-B antibodies Anti-B antibodies Anti-A antibodies Anti-A antibodies NO antibodies NO antibodies Anti-A/Anti-B antibodies Anti-A/Anti-B antibodies IAIA IAIBIAIB IAIBIAIB IAIBIAIB IAIA i IAIA IAIAIAIA IAiIAi IAiIAi i i IAIA i IBIB i IAIBIAIB IBiIBi IAiIAi IAIA IBIB IBIB IAIBIAIB i = type A B =A =B =all AB AA AO ABB O A v

Sex Determination and Sex-linked traits (gene located on X chromosome.) ♀ ♂ ♀ ♂ Mom’s eggs Dad’s sperm It’s the male gamete that determines gender of the offspring! XCXC X¢X¢ XCXC Y XCXCXCXC X C X ¢ XCYXCY X¢YX¢Y Mother is a carrier Father has normal vision Female offspring with normal vision Male offspring are Color blind !! 100% 50% Ex: colorblindness

Consider a Career in genetics!! Do you like this stuff? Family PEDIGREE