Download Mendelian Genetics Presentation

I. Introductory Definitions
A. Heredity: passing traits from
parents to offspring
B. Genetics: study of heredity
C. Chromosomes:rod-shaped, coiled DNA;
transmits hereditary info
D.Genes: units of heredity located
on chromosomes
E.Allele: one form of a gene
II. Mendel’s Pea Plants
A. 1850s
B. Why pea plants?
1. Lots of offspring
2. Grow quickly
3. Self-pollinate (offspring identical
to themselves)
4. Cross-pollinate (2 parents)
C. Studied 7 traits (e.g. tall/short) by
controlling pollination
D.Mendel’s experiments
1.P (parental) generation
a)14 pure strains (ex: pure tall)
2.F1 generation
a)Hybrids: offspring from crossing
opposite pure strains
b)Ex: breed tall with short
3.F2 generation
1.Offspring from self-pollinating F1
generation
E.Mendel’s results
1.F1 generation
a)One trait always disappeared
b)Ex: tall X short --> all tall
2.F2 generation
a)“invisible” trait reappeared
b)Ex: F1 tall X F1 tall -->
3/ tall & 1/ short
4
4
P Generation
Tall
Short
F1 Generation
Tall
Tall
F2 Generation
Tall
Tall
Tall
Short
F.Mendel’s conclusions
1.Traits controlled by
pairs of genes (FACTORS)
2.Principle of Dominance: one gene
in a pair may mask the other (tall
masks short gene)
a)Dominant allele = capital letter (T
= tall)
b)Recessive allele = small letter (t
= short)
c)Possible pair combinations:
• Homozygous (purebred): both
genes in pair identical
 Homozygous dominant: TT
 Homozygous recessive: tt
• Heterozygous (hybrid): one
dominant & one recessive: Tt
3.Principle of segregation: each pair
of genes (alleles) separates when
sex cells are formed (MEIOSIS)
• each F1 plant produces two
different gametes (Tt --> T gamete
& t gamete)
4.Principle of Independent
Assortment: gene pairs separate
independent of other gene pairs
III.Punnett Square
A. Diagram that shows the gene
combinations that might result
from a cross
B. Genotype: the gene combination
of an individual
• Ex: TT, Tt, tt
C. Phenotype: physical traits as
determined by the genotype
• Ex: TT & Tt= tall, tt = short
Genotype: 100% Ee
Phenotype: 100% long ears
D.Monohybrid cross
1.single genetic trait
2.Each parent will pass on one
allele to the offspring
3.Each offspring will have 2
alleles (one from each parent)
Monohybrid Cross
1/
2/ Tt: 1/ tt
TT:
4
4
4
3/
1/ Short
Tall
:
4
4
E.Dihybrid cross
1.Two genetic traits
2.Each parent will pass on one
allele from each gene
3.Each offspring will have 2 pairs
of alleles (2 alleles from each
parent)
4.Since the parents in a dihybrid
cross are heterozygous, there are
4 different combinations of alleles
(gametes) they can pass on to
their offspring:
RY
RrYy
Ry
rY
ry
Dihybrid Cross
9/16 Round yellow
3/16 Round green
3/16 Wrinkled yellow
1/16 Wrinkled green
9:3:3:1
IV.Beyond Dominant & Recessive
A. Incomplete dominance
-One allele is not completely
dominant
1. Heterozygous phenotype is
between the two parent
phenotypes
2. Ex: red X white --> pink
Red X white
4/
4
pink
B.Codominance
1.both alleles are expressed in
the phenotype
2.Ex: red X white --> roan (red &
white both present)
P generation
F1 generation
F1 generation
F2 generation
C.Multiple alleles: gene with more
than 2 possible alleles
1.Each individual inherits only 2
2.Examples: Blood types (A B o)
+ Rabbit Coats
(C
ch
h
c
)
D.Polygenetic traits: some
characteristics are controlled by
two or more gene pairs
1.Wide range of phenotypes
2.Ex: skin color, eye color,
Human Height
“Labrador Coat Colors –Epistasis”