Genetics Explaining Inheritance

Early Ideas- Unilateral Inheritance SpermistsOvists

Early Ideas- Blending Blue + Yellow Green

Traits Skipping Generations Generation 1Generation 2Generation 3

Gregor Mendel  Austrian Monk  Research in monastery garden  Garden pea

Characters & Traits Flower Position Stem Length Seed Shape Seed Color Flower Color Pod Color

Pea Anatomy  Naturally self- fertilizing  Experimental cross: Remove anthers Dust stigma with pollen

Inheritance of seed color P F1F1 F2F2 Pollen from stock pure- breeding for yellow seed cross Dust on stigma of plant from stock pure-breeding for green seed Hybrid seed Plants grown from hybrid seed produce green and yellow seed

Quantitative Analysis Hybrid PlantYellowGreen TOTAL :1

F 2 Ratios Stem Length 2.84 : 1 Seed Shape 2.96 : 1 Seed Color 3.01 : 1 Flower Color 3.15 : 1 Pod Color 2.82 : 1 Flower Position 3.14 : 1

Mendel’s Explanation  Characters controlled by two “factors”  These segregate during reproduction  One factor is dominant, the other is recessive Y = factor for yellow seed color y = factor for green seed color

Inheritance of seed color P F1F1 F2F2 Hybrid seed Plants grown from hybrid seed produce green and yellow seed Y Pollen from stock pure- breeding for yellow seed cross Dust on stigma of plant from stock pure-breeding for green seed y Yy yy ????? Yellow Dominant Green Recessive

Test Cross Phenotype =Genotype = ??? Y_ X yy Unknown is YY Y_ X yy Unknown is Yy

Punnett Square Y y yY ½ ½ ½½ Pollen from hybrid plant Ova from hybrid plant YY ¼ Yy ¼ Yy ¼ yy ¼ 3.. 1

Useful Terms:  Phenotype- Outward appearance e.g. yellow, green  Genotype- Genetic makeup e.g. YY, Yy, yy  Homozygous- YY or yy  Heterozygous-Yy

Monohybrid CrossDihybrid Cross Follow inheritance of one character Follow inheritance of two characters Seed Color Seed Shape RR, Rr rr

Dihybrid Cross P Plants grown from hybrid seed produce: rY Ry F1F1 Hybrid seed RrYy Pollen from stock pure- breeding for wrinkled, yellow seed cross Dust on stigma of plant from stock pure-breeding for round, green seed F2F2 Four types of seed!Genetic Recombination

9:3:3:1 ratio of phenotypes in F 2 Seed Color ¾ ¼ Seed Shape ¾ ¼ ¾ ¼ ¾ X ¾ = 9/16 ¾ X ¼ = 3/16 ¼ X ¾ = 3/16 ¼ X ¼ = 1/16

Independent Assortment Seed Color ¾ ¼ Seed Shape ¾ ¼ ¾ ¼ ¾ X ¾ = 9/16 ¾ X ¼ = 3/16 ¼ X ¾ = 3/16 ¼ X ¼ = 1/16 ¾ Yellow¼ Green

Independent Assortment Seed Color ¾ ¼ Seed Shape ¾ ¼ ¾ ¼ ¾ X ¾ = 9/16 ¾ X ¼ = 3/16 ¼ X ¾ = 3/16 ¼ X ¼ = 1/16 ¾ Round ¼ Wrinkled

Simple Dominance

(W)Widows Peak vs. Straight (w)

(F)Free Earlobe vs. Attached (f)

(E)Wet ear wax vs. Dry ear wax (e)

Six-digits (F)

Cleft chin (C)

Tongue Roll (T), non-rolling (t)

Hitchhiker’s Thumb (H)

Incomplete Dominance Four-o’clocks

An intermediate phenotype is shown

Incomplete Dominance  Three Shades:  Dark = DD  Medium = DL  Light =LL

Co-dominance - Both alleles can be expressed  For example, red cows crossed with white will generate roan cows. Roan refers to cows that have red coats with white blotches.  One allele of the gene codes for an enzyme that functions in the production of the red color. The other allele codes for the gene to make white color. If both alleles are present, both are expressed, resulting in a cow that has some red and some white.

Co-dominance AAndalusian Fowl also show this pattern of inheritance. IIf you cross a black (BB) rooster WWith a white (WW) chicken YYou get black+white speckled (BW) offspring

Incomplete Dominance vs. Co-Dominance  Red and White Camellia  Red and White Snapdragons

X-Linked Traits  A carrier female  A normal male

X-Linked Traits  Some genes are located on the X chromosome. Females receive two alleles for these genes, but males only receive one.  In humans, hemophilia and color blindness are sex-linked traits.  When doing a Punnet square, use large X's and Y's to denote male and female, use superscript letters to designate the alleles.  If the parent is a male, the genotype is automatically known. A colorblind male has to be b, since he only has one allele and colorblindness is recessive. A normal male must then be B  Females can be heterozygous for the colorblindness trait - they are called carriers. A female can be BB - normal, Bb - carrier, or bb - colorblind

Multiple Alleles

b C b C b C lethalb C _ black b ST b ST b ST blackb ST _ black bbb blackbb + red b t b t b t brownb t b + red b + b + b + red  The black locus of Tribolium

Gene: Locus & Allele  Locus- place on a chromosome, responsible for a character, e.g. seed color  Allele- version of a locus, responsible for a trait, e.g. yellow or green

Pleiotropy Locus affects more than one character  b ST color and lethality  Antenna bifurcata (ab) antenna shape & male sterility

Epistasis

 Interaction of alleles at two loci: Locus 1 R = Red pigment r = yellow pigment Locus 2 Y = no chlorophyll y = chlorophyll Four Phenotypes R_Y_ = Red R_yy = Brown rrY_ = Yellow rryy = Green

Epistasis RRyyrrYY RrYy R_Y_rrY_R_yyrryy

Explain the function of each allele: B b C c

Polygenic Inheritance Quantitative Characters

We are the product of 30,000 genes Five generations