Download Mendel`s Laws of Heredity

Mendel’s Laws of
Heredity – Chp 10.1
Why we look the way
we look...
What is heredity?
The
passing on of
characteristics (traits)
from parents to offspring
Genetics is the study of
heredity
Who was Gregor Mendel?
(1822-1884)
Considered the Father of
Heredity
 Monk who first discovered
that there are RULES or
LAWS governing how traits
are passed from parents to
offspring
 He crossed 1000’s of pea
plants over many years to
make his discovery

Traits Mendel Studied:
Crossing Pea Plants:
Fertilization
- the uniting of
male and female gametes
Cross - combining gametes
from parents with different
traits (TT x tt)
• P1 = parent generation
• F1 = 1st offspring generation
• F2 = 2nd offspring generation
Draw in notes from board!
Part 2: Mendel’s Rules & Laws
1) Rule of Unit Factors
Each
organism has two
alleles for each trait
–Alleles - different forms of
the same gene
–Genes - located on
chromosomes, they control
how an organism develops
2) Rule of Dominance
The
trait that is observed
in the offspring is the
dominant trait (uppercase)
The trait that disappears
in the offspring is the
recessive trait (lowercase)
Dominant and Recessive
 Observed
= dominant
• B = brown hair
• R = can roll tongue
• T = tall
 Hidden
trait = recessive
• b = red hair
• r = can’t roll tongue
• t = short
Phenotype & Genotype
Phenotype
- the way an
organism looks
– red hair or brown hair
genotype
- the allele
combination of an organism
– AA or Aa or aa
Heterozygous &
Homozygous
 Heterozygous
- if the two alleles
for a trait are different (Aa)
 Homozygous
- if the two alleles
for a trait are the same (AA or
aa)
• Homozygous dominant = AA
• Homozygous recessive = aa
3) Law of Segregation
The
two alleles for a trait
must separate when
gametes are formed
A parent randomly passes
only one allele for each
trait to each offspring
Law of Segregation explained

During Meiosis – homologous chromosomes
and their alleles separate.
N = normal skin
Nn
Parent cell diploid
Bb
n = albino
B = brown eyes
N
B
N
b
n
B
n
b = blue eyes
b
Gamete possibilities - haploid
4) Law of Independent
Assortment
The
genes for different
traits are inherited
independently of each other.
Just because you get Dad’s
blue eyes doesn’t mean you
will get his blonde hair also!
Monohybrid Cross
Monohybrid Cross - crossing
parents who differ in only
one trait (TT, Tt, tt)
- Use a special method called
punnet squares.
Questions...
1) How many does alleles
does an individual receive
for each trait?
2)What is an allele?
3)How many alleles does a
parent pass on to each
offspring for each trait?
4) What are the gametes of
the following parents?
a) Aa
b) gg
c) RR
5) What do we call the trait
that is observed? What case
(upper or lower) is it written
in?
6) What about the one that
disappears? What case is it
written in?
7) What is the difference
between phenotype and
genotype?
8) If green peas (G) are dominant
over yellow peas (g), give the
phenotypes for the following
genotypes:
a) GG
b) Gg
c) gg
9) What is the difference
between homozygous and
heterozygous?
10) Round peas (R) are
dominant over wrinkled peas
(r). Give the genotypes for
the following phenotypes:
a) Round
b) Wrinkled