Gregor Mendel – Father of Genetics 3 minute intro to Mendel/Genetics gZUnJdAY .
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Transcript of Gregor Mendel – Father of Genetics 3 minute intro to Mendel/Genetics gZUnJdAY .
Mendelian genetics
Trait• color, height,
•ex: purple True-bred / Homozygous
• HH or hh Hybrid
• Heterozygous / Hh• Cross of two pure breeding
P generation = parents F1 generation = first filial
generation
Alleles = Different form of genes •one from each
parent If the two alleles
are different •the dominant
allele is expressed
• the recessive allele is “hidden”
Genetic vocabulary……. Punnett square:
• Cross for working out problems
Homozygous: BB / bb• alleles are the same
Heterozygous: Bb• two alleles are different
Phenotype: • an organism’s traits • (what you SEE)
Genotype: • an organism’s genetic
makeup: TT, Tt, tt Testcross:
• cross with a homozygous recessive = tt
• With dominant phenotype • (but unknown genotype)
LE 14-14a
Ww ww ww Ww
Ww wwWwwwwwWw
WW wwor
Ww
No widow’s peak
Thirdgeneration
(two sisters)
Widow’s peak
Second generation(parents plus aunts
and uncles)
First generation(grandparents)
Dominant trait (widow’s peak)
LE 14-14b
First generation(grandparents) Ff Ff
FF or Ff ff ff Ff Ff
ff
ff
Ff
Second generation(parents plus aunts
and uncles)
Thirdgeneration
(two sisters)
Attached earlobe Free earlobe
ff FForFf
Recessive trait (attached earlobe)
Genes working together
Incomplete dominance: blending of the phenotypes of the 2 parents. • Ex: snapdragons
Codominance: two alleles affect the phenotype in separate ways • Ex: human blood types A & B
Multiple alleles: more than 2 possible alleles for a gene. • Ex: human blood types
LE 14-10
RedCRCR
Gametes
P Generation
CR CW
WhiteCWCW
PinkCRCW
CRGametes CW
F1 Generation
F2 Generation Eggs
CR CW
CR
CRCR CRCW
CRCW CWCW
CW
Sperm
12
12
12
12
12
12
Blood Typing
A & B are Co-Dominant O is recessive
•AA or AO = type A ( IA IA or IA i )
•BB or BO = type B ( IB IB or IB i )
•AB = type AB ( IA IB )
•OO = type O ( ii )
Blood Types - USA
•O+ = 37.4%
•O- = 6.6%
•A+ = 35.7%
•A- = 6.3%
•B+ = 8.5%
•B- = 1.5%
•AB + = 3.4%
•AB- = .6%
Gene Interaction
Pleiotropy: genes with multiple phenotypic effect.
• Ex: sickle-cell anemia
Epistasis: a gene can interfere with another gene showing up; even if it is dominant
• Ex: mice coat color
Polygenic Inheritance: an additive effect of two or more genes on a single phenotypic character Ex: human skin pigmentation and height
LE 14-11
Sperm
BC bC Bc bc
BbCcBBCcBbCCBBCC
BbCC bbCC BbCc bbCc
BbccBBccBbCcBBCc
BbCc bbCc Bbcc bbcc
BC
bC
Bc
bc
BbCc BbCc
14
14
14
14
14
14
14
14
916
316
416
Epistasis
•Polygenic inheritance
•Quantitative variation usually is additive effect of two or more genes on a phenotype
•Skin color in humans is an example
Human disordersThe family pedigree Recessive disorders:
••Cystic fibrosis
••Tay-Sachs
••Sickle-cell Dominant disorders:
•Huntington’s Can be determined by a
Karyotype
LE 14-8
P Generation
F1 Generation
YYRR
Gametes YR yr
yyrr
YyRr
Hypothesis ofdependentassortment
Hypothesis of independent assortment
SpermEggs
YR
Yr
yrYR
YR
yr
Eggs
YYRR YyRr
YyRr yyrr yR
yrPhenotypic ratio 3:1
F2 Generation(predictedoffspring)
YYRR YYRr YyRR YyRr
YYRr YYrr YyRr Yyrr
YyRR YyRr yyRR yyRr
YyRr Yyrr yyRr yyrr
Phenotypic ratio 9:3:3:1
YR Yr yR yr
Sperm
12
14
14
14
14
1 43
4
12
12
12
14
916
316
316
316
14
14
14