Download Mendel**.. The Father of Genetics

Mendel……..
The Father of Genetics
Mendel (1866)
Austrian Monk
Gardener & Mathematician / Statistician
Bred pea plants for different traits
Pea plants self-pollinate so all the pea plants
in a patch would all have the same genes =
true breeding
Mendel discovers each parent has 2
copies of gene
Different versions of gene
Mendel discovers dominant & recessive
Law of segregation
Law of independent Assortment
Sources of variation
Gene = DNA code for one protein
Protein causes trait
Trait = characteristic = phenotype
Alleles = versions of a gene
For example if the gene is height the alleles are

tall and short
If the gene is seed color the alleles are

green and yellow
If alleles are blue and brown the gene could be

eye color
Dominant vs. Recessive Alleles
Dominant alleles over shadow recessive alleles
if an individual gets one of each
Dominant alleles … use a Capital letter
Recessive alleles …use a lower case letter
For height Tall is dominant & short is recessive
Tall = H
short = h the gene is height
Same gene must use the same letter of the
alphabet
Genotype vs. Phenotype
Genotype = what type of alleles you have
ex. HH, Hh, or hh



Homozygous dominant = HH
Homozygous recessive = hh
Heterozygous = Hh
Phenotype = what type of physical
appearance you have

short (recessive) or tall(dominant)
Determining phenotype
All individuals with even one dominant allele

look like the dominant trait
The only way to look recessive is to have

two copies of the recessive allele
hh = looks short
Hh = looks tall
HH = looks tall
Determining Genotype
Any individual that looks recessive has….

2 recessive alleles (hh)
Any individual that looks like dominant trait has:
………at least one dominant allele (H ?)
The second allele can only be determined if…
...the individual’s parent or child looks recessive
 if a parent or child look recessive the individual
……… is heterozygous (Hh)
Generations in genetics experiments
P generation = parents
(first 2 individuals crossed)
F1 generation = offspring
of the original parents
F2 generation = offspring
resulting from a cross of
two F1 individuals
Punnett Squares – used to predict
the phenotypes / genotypes of
offspring
Punnett Square Layout
Top & side of box = possible egg/sperm
 each parent can only give one copy of a gene
 so egg/sperm can only have one of each letter
Squares inside box = possible children
 (offspring genotypes) so must have 2 of each
 gene so 2 of each letter
Only reflect probability or odds!!!
Probablilty
Dad has an X chromosome & a y chromosome
What one ( X or y) each child gets is random
Do all family's have equal numbers of
boys/girls?
Independent assortment = pairs of
chromosomes sorted independently. Each pair
gets a 50/50 chance of Dads C going to the
child.
Types of Crosses
Monohybrid

looks at one gene
Dihybrid looks

2 different genes
Each different gene MUST have a different letter
of alphabet
gene= height
T= tall
t = short
gene = color
G = green g= yellow
individuals needs 2 of each letter so…
TTGG or TtGG or ttGg and so on
Dihybrid Punnett squares
All possible gametes on top
Heterozygous for both traits makes ..
4 different gametes
RrYy parent makes:
RY or Ry….rY or ry
Each box is a zygote so
2 letter r’s & 2 letter y’s
(2 copies of each gene)
Any other parent will not make all 4
gametes so Punnett squares can be
smaller
Pedigree = a diagram of a families'
genetic history
Black circles
/squares show
individuals with the
phenotype being
studied
If a circle or square
is half shaded in …
the individual is
heterozygous for the
trait being studied