GeneticsExplaining Inheritance

Early Ideas- Unilateral Inheritance

Spermists Ovists

Early Ideas- Blending

Blue + Yellow Green

Traits Skipping Generations

Generation 1 Generation 2 Generation 3

Gregor Mendel 1822-1884 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

F1

F2

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 AnalysisHybrid Plant Yellow Green

1 25 11

2 32 7

3 14 5

4 70 27

5 24 13

6 20 6

7 32 13

8 44 9

9 50 14

10 44 18

TOTAL 6022 2001

3.01:1

F2 Ratios

Stem Length2.84 : 1

Seed Shape2.96 : 1

Seed Color3.01 : 1

Flower Color3.15 : 1

Pod Color2.82 : 1

Flower Position3.14 : 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 colory = factor for green seed color

Inheritance of seed color

P

F1

F2

Hybrid seed

Plants grown from hybrid seed produce green and yellow seed

YPollen from stock pure-breeding for yellow seed cross

Dust on stigma of plant from stock pure-breeding for green seed

y

YyYyYyYyYy

yyyy? ? ? ? ?

Yellow Dominant

Green Recessive

Test Cross

Phenotype = Genotype = ???

Y_

X

yy

Unknown is YY

Y_

X

yyUnknown is Yy

Punnett Square

Y

y

yY

½

½

½ ½

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 Cross Dihybrid Cross

Follow inheritance of one character

Follow inheritance of two characters

Seed Color

Seed ShapeRR, Rrrr

Dihybrid Cross

P

Plants grown from hybrid seed produce:

rY Ry

F1Hybrid 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

F2Four types of seed! Genetic

Recombination

9:3:3:1 ratio of phenotypes in F2

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 Yellow

¼ 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 Andalusian Fowl also show this

pattern of inheritance. If you cross a black (BB) rooster With a white (WW) chicken 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

Multiple Alleles

bC bC bC lethal bC_ black

bST bST bST black bST_ black

b bb black bb+ red

bt bt bt brown bt 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

PleiotropyLocus affects more than one character bST color and lethality Antenna bifurcata (ab)

antenna shape & male sterility

Epistasis

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_yy rryy

Explain the function of each allele:B b C c

Polygenic Inheritance

Quantitative Characters

We are the product of 30,000 genes

Five generations