Post on 04-Jan-2016
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Chapter 14~Mendel & The Gene Idea
Mendelian genetics
Trait– variant for a character ex:
purple
True-breeding – all offspring same variety
Hybridization – Cross of two pure breeding
P generation = parents F1 generation = first
filial generation
Leading to the Law of Segregation Alleles = Different
versions of genes – one from each parent
If the two alleles are different – the dominant allele is
expressed– the recessive allele is
“hidden” Mendel’s Law of
Segregation– The alleles for each
character segregate during gamete production
Genetic vocabulary……. Punnett square: predicts
the results of a genetic cross between individuals of known genotype
Homozygous: alleles are the same
Heterozygous: 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 x dominant phenotype (but unknown genotype)
The Law of Independent Assortment
Monohybrid cross vs. dihybrid cross
The two pairs of alleles segregate independently of each other.
Mendel’s Law of Independent Assortment
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
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
Gene Interaction
Pleiotropy: genes with multiple phenotypic effect. – Ex: sickle-cell anemia
Epistasis: a gene at one locus (chromosomal location) affects the phenotypic expression of a gene at a second locus. – 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
Pleiotropy
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 disorders
The family pedigree: – Diagram showing family relationships:
• Circle - female• Square - Male
Recessive disorders:– •Cystic fibrosis– •Tay-Sachs– •Sickle-cell
Dominant disorders:•Huntington’s
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)
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)
TESTING
•Amniocentesis: (between week: 15-18) Prenatal diagnosis of chromosomal abnormalities
•CVS = Chorionic villi (villus) sampling (10-12 weeks)
Bozeman: Mr. Anderson
https://www.youtube.com/watch?v=rIe7mPXkYhs