Download Mendel`s Laws of Heredity Why we look the way we look

Mendel’s Laws of
Heredity
Why we look the way we
look...
Mendel used peas...
 They reproduce sexually
 They have two distinct, male
and female, sex cells called
gametes
 Their traits are easy to
isolate
Mendel crossed them
 Fertilization - the uniting of
male and female gametes
 Cross - combining gametes
from parents with different
traits
What Did Mendel
Find?
 He discovered different laws
and rules that explain
factors affecting heredity.
1. Rule of Dominance
 The trait that is observed in
the offspring is the
dominant trait (uppercase)
 The trait that is masked in
the offspring is the recessive
trait (lowercase)
2. Law of Segregation
 Genes appear in pairs on
homologous chromosomes
 SEPARATED when gametes are
formed
 Recombine during fertilization
3. Law of Independent
Assortment
The genes for different traits are
inherited independently of each
other.
 Homologous chromosomes move
randomly to gametes
 Explains why siblings look different

Genetics Continued
Dihybrid crosses
 Exceptions to Mendelian Genetics

◦
◦
◦
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Incomplete vs. Complete Dominance
Codominance
Sex-Linked Genetics
Blood Types (Multiple Alleles)
Monohybrid Vs Dihybrid
 Monohybrid
Cross - crossing
parents who differ in only
one trait (AA with aa)
 Dihybrid
Cross - crossing
parents who differ in two
traits (AAEE with aaee)
S= yellow
 s= green
 Y= round
 y= wrinkled

How many round yellow?
How many round green?
How many wrinkled yellow?
How many wrinkled green?
Dihybrid Cross - 2 traits
Bozeman Tutorial
http://www.youtube.com/watch?v=Y1P
CwxUDTl8
Incomplete Dominance - Blend
Heterozygous genotype=
blend of two phenotypes
RR= Red
RW= pink
WW= white
Codominance – Both show
Both alleles of the trait show in the
heterozygote
Codominance: Both traits show
in heterozygotes
Try these: what are the phenotype ratios?
Cows
R= Brown
W= white
Calico Cat Coats
B: Black
Y: Yellow
Sex-Linked
Sex-Linked
Sex-linked Punnett
C= color-blindness
XX= Female
XY= Male
Is mom colorblind?
Is dad colorblind?
What is the chance that they have:
1)
2)
3)
4)
a colorblind girl?
a female carrier?
an unaffected male?
an affected male?
Polygenic: controlled by many genes
Polygenic inheritance
is a fancy term for
those genetic traits that
are controlled by more
than 1 gene
-
Height, Skin Color
Because there are
MANY genes that
influence polygenic
inheritance, you
see a spectrum of
phenotypes
Blood Types: Multiple Alleles
- What is multiple allele inheritance?
- Non-Mendelian Inheritance Pattern
- involves more than just 2 alleles
- that means there is more than two
phenotypes
Blood Types:
Multiple Alleles
- Example: Blood Type (Red Blood Cells)
- There are markers on the surface of RBCs
- Our immune system has antibodies:
ATTACK foreign invaders (germs, viruses)
- YOU DO NOT WANT ANTIBODY for your
BLOOD TYPE
- What would be the result? Your immune
system attacks your body!!
Multiple Alleles - Blood Type
Universal Donor (can give to everyone): 0 Blood…. why?
Universal Recipient (can accept from anyone): AB Blood…..why?