genetics explaining inheritance. early ideas- unilateral inheritance spermistsovists
TRANSCRIPT
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