Unit 7 Genetics

Mendelian Genetics

Heredity Terminology Self-fertilization – sexually reproducing organism reproducing with itself Common in hermaphroditic flowering plants Or, plant breeders (gardeners) will do this to the plant True-breeding (purebred) – refers a population that always produces the same trait(s) Results from many self-fertilized generations Populations are genetically very similar

X Heredity Terminology Cross-fertilization – reproduction between two different organisms Usually refers to two different true-breeding plants Example: true-breeding purple flower peas mated with true- breeding white purple flower peas Hybrid – offspring of purebreds X

Heredity Terminology Generations P generation – true- breeding F1 generation – P generation offspring F2 generation – offspring when F1 generation self- fertilizes (or fertilize each other)

Homologous chromosomes and Alleles Homologous chromosomes, genes, alleles Allele – different variations of the same genes Example: Gene: flower color Alleles: purple gene or white gene

Gregor Mendel Austrian monk Lived during the 1800s “Father of Genetics” Use garden pea plants to do his research Recorded accurate data (kinda) Observed large populations Why pea plants?

7 Traits studied by Mendel Obj 3 7 Traits studied by Mendel Seed shape (round vs wrinkled) Seed color (yellow vs green) Seed coat color (brown vs white) Pod color (green vs yellow) Pod shape (inflated vs wrinkled) Stem Length (long vs short) Flower Position (axial vs terminal)

Major Observations by Mendel Traits are not simply blended Many pea plant traits came in pairs When starting with true- breeding P generation plants traits will skip the F1 generation and reappear in the F2 generation. Occurs across all 7 traits and in the same ratio!!!!!

Mendel’s four hypotheses There are different versions of genes (alleles) Mendel’s 7 pea plant traits only have 2 alleles. But, there can be more than 2 alleles for genes (less than simple heredity) Each organism inherits 2 alleles for each character. One from each genetic donor Homozygous – 2 identical alleles (called a homozygote) Heterozygous – 2 different alleles (called a heterozygote)

3. Law of Dominance Explains why all the F1 generation plants only show one trait. Explains why the second trait reappears in the F2 generation. When both alleles are inherited (heterozygous) the dominant allele controls the physical characteristic that is “seen”. Recessive allele has no physical effect Example: Gene – Seed coat Dominant Allele – Round (R) Recessive Allele – wrinkled (r) RR rr Rr

4. Law of Segregation 2 alleles for a given trait separate during formation of the gametes (meiosis) Each somatic cell (diploid) has 2 copies of each gene… Each sex cell (haploid) has only one copy Each parent passes on at RANDOM only 1 allele for each trait Genes on separate chromosomes will sort independently

Punnett Square Diagram used to determine the possible combination of alleles. Use to predict the genotypic and phenotypic ratio of a cross. Example: Shows the expected out come of cross between two heterozygous purple flowers P p Gametes

Genotype and Phenotype Ratios OBJ 5 Genotype and Phenotype Ratios Genotype = Alleles Phenotype = physical outcome of the combination of alleles Genotypic ratio 1:2:1 Phenotypic ratio 3:1

Independent Assortment – Dihybrid Cross Parents = RRYY x rryy Gametes = RY x ry F1 generation = RrYy If the genes were independent, the F1 could make: RY and ry gametes Ry and rY gametes Then we could do a dihybrid cross (or 2-factor cross) to find out possible offspring Y Y y y y y Y Y OR R R r r R R r r

4 possible Female Gametes RY Ry rY ry RRYY RRYy RrYY RrYy RRyy Rryy rrYY rrYy rryy 4 possible Male Gametes Dihybrid Cross 4 possible Female Gametes Possible Zygotes

RY Ry rY ry RRYY RRYy RrYY RrYy RRyy Rryy rrYY rrYy rryy Dihybrid Cross: Genotypic ratio: 1:1:2:2:4:2:2:1:1 RY Ry rY ry RRYY RRYy RrYY RrYy RRyy Rryy rrYY rrYy rryy 9 Different Genotypes

RY Ry rY ry RRYY RRYy RrYY RrYy RRyy Rryy rrYY rrYy rryy Dihybrid Cross: Phenotypic ratio: 9:3:3:1 RY Ry rY ry RRYY RRYy RrYY RrYy RRyy Rryy rrYY rrYy rryy 4 Different Phenotypes

Rules of Probability Rule of multiplication – two (or more) events both happen Rule of addition – either of two events occur (or when an event can happen in 2 or more ways) Examples: When rolling a die twice, what is the chance of rolling a 4 both times? You roll a die, what is probability of getting a 2 or a 4?

Rules of Probability – Genetics Applications OBJ 10 Rules of Probability – Genetics Applications What are the odds of two Cc parents have a child that is also Cc? (don’t use a Punnett square…try this with probability) For two people with the genotypes AaBbCcDd, what are the odds they will have a child with all dominant alleles?

Alternative Inheritance Non-Mendelian Patterns

Incomplete Dominance Heterozygous individuals have an appearance that is intermediate between the phenotypes of a homozygous dominant organism and a homozygous recessive organism

3 phenotypes and 3 genotypes OBJ 11a Homozygous Red Heterozygous Pink Homozygous White 3 phenotypes and 3 genotypes

Incomplete Dominance in Humans LDL – Low density lipoproteins LDL receptors remove LDLs from the blood stream. Low expression of LDL receptors is one variable in the development of artherosclerosis

Codominance Both alleles contribute to the phenotype of a heterozygous individual Similar to incomplete dominance, but there is no mixing, both alleles are separately expressed in the phenotype

Multiple Alleles Traits that are determined by more than 2 alleles Example: fur coloring in rabbits 4 primary alleles Agouti (C) > chinchilla (silver) (cch) > Himalayan (ch) > albino (ca) > Homozygous for each allele pictured

Human Blood Types – An example of Multiple Alleles, Codominance and Dominance Multilpe Alleles – 3 alleles that express cell surface proteins A – A protein B – B protein O – no protein Codominance AB blood – both proteins are expressed Dominance A over O B over O

Matching Blood types – Why? Red Blood Cell surface proteins interact with anti-bodies in the blood serum Example – Antibody-B will bind to surface protein B and trigger the cells to clot, thus limiting/stopping blood flow.

Polygenic inheritance Two or more genes contribute to a physical characteristic. Example: Human Skin color (polygenic and incomplete dominance)

Sex-linked genes Genes located on X chromosomes. XX female XY male

Hemophilia – Royal Families of Europe