Patterns of Heredity
Ch. 4 Genetics!!
Do Now!! 
True or False??
• Color blindness is more common in males
than in females.
• A person may transmit characteristics to
offspring which he/she does not show.
• Certain inherited traits may be altered by the
stars, planets or moon early in development
• There is such a thing as “werewolf
syndrome” that could be linked to genes.
Hypertrichosis
(“werewolf syndrome”)
Stephen Bibrowski as
“Lionel the Lion-faced
Man”
Objectives
• To define heredity and inheritance
• To determine how we inherit traits from our
parents
• To take an inventory of our class’s traits!
Genetics = the study of heredity by which traits are
passed from parents to offspring
 The passing of genes/traits from parents to
offspring.
•
Many of your traits,
including eye color,
shape of your eyes,
texture of your hair,
height, and weight
resemble those of your
parents!
• A unit of heredity that
occupies a specific location
on a chromosome and
codes for a particular
product.
• A specific segment of DNA
found on the chromosome
Thanks Mom and Dad!
• We inherit genes from
our parents
• Those genes code for
the traits we express
• Most traits are coded by
more than 1 gene:
• Ex: Height
Homologous Chromosomes
• A pair of
chromosomes are
called homologs
(homo meaning
same)
• Homologous
chromosomes have
the same size,
structure, and genetic
information.
• Versions of a gene
that occupy
corresponding
positions on
homologous
chromosomes
• We inherit 2 alleles
for each gene:
•
1 from mom and 1
from dad!!
Sex Chromosomes
• We have 23 pairs of chromosomes
• 1 pair are known as the sex chromosomes,
which determines the sex of the offspring
• Males = XY
• Females = XX
Do Now!! 
• What is an allele?
• What are homologous chromosomes?
• Give an example of a trait that is coded by
more than one gene!
Objectives
• To discuss the importance of Gregor Mendel
• To identify the parts of Mendel’s pea plant
experiments
• To differentiate between dominant and
recessive alleles
The history of Gregor Mendel
• Father of genetics!
• Bred different varieties of
garden pea.
• First to develop rules that
accurately predict
patterns of heredity.
• Discovered how traits
were inherited
– transfer of pollen from
anthers to stigma in flowers
1) self pollination
occurs within the
same flower or same
plant
2) cross pollination
occurs between
different plants
• Several traits exist in two clear different
forms.
Ex: Flower color was either purple OR white
• The male and female reproductive parts are enclosed within
the same flower.
• It is easy to control mating by allowing a flower to fertilize
itself (self fertilization), or you can transfer pollen to another
flower (cross pollination).
• The garden pea is small,
grows easily, matures
quickly, and produces many
offspring.
• Results can be obtained
quickly.
Steps in Mendel’s research…
1. Allowed each garden pea to self-pollinate for
several generations to ensure “true-breeding” for
that particular trait.
*P Generation = parental generation
Steps in Mendel’s research (cont.)
2. Mendel then cross-pollinated two P generation
plants that had different forms of the trait (purple
and white flower). The offspring from that were
called the F1 generation.
*F 1 generation = Filial generation (of son or daughter)
Steps in Mendel’s Research (cont.)
3. Allowed the F1 generation to self-pollinate and those
offspring are called the F2 generation.
* F2 Generation = Filial generation 2
Ratio of Mendel’s Research
• P Generation had a true-breeding purple and white
flower
• F1 generation: ALL purple flowers
• F2 generation: 705 purple flowers and 224 white
flowers.
• That is a ratio of about 3:1
Mendel’s Crosses with Pea Plants
P
parental
1 generation
Pure tall
plants
X
Cross
F1
F2
first filial
generation
Pollination
All Tall plants
Self
second filial
generation
Pure short
plants
Pollination
787 tall plants, 277 short plants
3 to 1 ratio
Mendel’s 3 Laws of Inheritance
1. Law of Dominance- Each trait is controlled
by 2 factors:
•
•
Dominant- what is expressed
Recessive- masked in presence of dominant
*Reminder!!
• Alleles are alternative forms of a
gene.
• Can be dominant or recessive!
Dominant
capital letter (shields
recessive trait)
Recessive
Lowercase letter
(usually hidden)
T = tall
t = short
Mendel’s 3 Laws of Inheritance
2. Law of Segregation-Each allele separates into
different gametes
Ex. Ww – one W goes in one sperm and the other w goes
into another sperm
Ww
w
W
Mendel’s 3 Laws of Inheritance (cont.)
3. Law of Independent Assortment- Gene pairs
(homologous) will separate randomly into
gametes during meiosis
(Why? Random orientation of homologous pairs at the metaphase
plate)
Do Now!! 
• What are Mendel’s 3 laws of inheritance?
• What is the difference between dominant and
recessive traits?
• Below is a chart of Mendel’s experiment. Fill it in!:
1
4
6
2
3
5
7
Objectives
• To differentiate between phenotype and
genotype
• To define homozygous and heterozygous
• To practice monohybrid punnett squares
Genotype: The set of alleles that an individual has (not
always obvious)
Phenotype: the physical appearance of a trait
Homozygous – when both alleles
of a pair are the same
homozygous
dominant
homozygous
recessive
TT
tt
Heterozygous – when both alleles
of a pair are not the same
heterozygous
(tall)
Tt
• Different alleles
present
– Ex: Bb
• Two of the same alleles
– Ex: BB or bb
• Can be homozygous
recessive or
homozygous dominant
Recessive: The trait not
expressed when the
dominant form of the trait
is present
Dominant: The expressed
form of the trait when
present (even if it is just 1
allele)
B = black fur
b = white fur
BB or Bb
bb
• If Jon Snow is heterozygous
for black hair… (H=Black, h=blonde)
– 1. What is Jon Snow’s genotype?
– 2. What is Jon Snow’s phenotype?
• Beyonce is BB. (B= brown eyes, b=blue eyes)
– 1. What is her genotype?
– 2. What is her phenotype?
– 3. Is she heterozygous or homozygous? Explain.
• Probability calculations can predict the results of
genetic crosses. It is the likelihood that a specific event
will occur.
= number of one kind of possible outcome
Total number of all possible outcomes
Example: If you flip a coin, you will
have 1 outcome, but two possible
outcomes. Your answer would be ½.
• When flipping a coin and it lands on tails  ½ or
1:2
• Genotypic ratio: What is genetically written
• Phenotypic ratio: what physical traits you would see
3:1
3 Black : 1 White
• A diagram that predicts the outcome of a
genetic cross by considering all possible
combinations of gametes in the cross
Crossing only 1 trait is called a
monohybrid cross.
Crossing 2 traits is called a
dihybrid cross.
1.
2.
3.
4.
5.
6.
Assign symbols
Determine parents genotype
Draw punnett square
Place gametes on left + top of square
Fill in punnett square
Analyze + answer questions
T: Tall plants
t: Short plants
1. Phenotypic Ratio and %:
2. Genotypic Ratio :
R: round seeds
r: wrinkly seeds
1. Phenotypic Ratio and %:
2. Genotypic Ratio :
Crosses that involve 2 traits
1. Phenotypic Ratio:
2. Genotypic Ratio :
Gene Linkage and Polyploidy
• There are several genes on a chromosome
• Gene Linkage:
– When two genes are close to each other on the
same chromosome
Gene Linkage
 Linked genes on a chromosome results in an
exception to Mendel’s law of independent
assortment
 Linked genes usually do not segregate
independently
Drosophila melanogaster (Fruit Flies)
First organism
with linked genes
Linked genes
typically travel
together during
crossing over
Chromosome Map
• A map of genes on a chromosomes
• Crossing over occurs more frequently between genes
that are far apart
Polyploidy
Cells that contain more than 2 homologous
sets of chromosomes
Ex. A triploid organism (3n) - means that it
has three complete sets of chromosomes.
Strawberries are octoploid!!
Matching
Pedigree
• Shows history of a trait in a family
• Allows researchers to analyze traits within
a family
In a pedigree…
• You can see how a genetic disorder runs in a
family.
• Carriers are individuals who are
heterozygous for an inherited disorder but
do not show symptoms.
• Carriers can pass the allele for the disorder
to their offspring
DO NOW!! 
• Fill in genotypes!
• B: Brown eyes
• b: blue eyes
Multiple alleles – 3 or more alleles that
control a trait
• Example: blood type!
– Possible alleles: IA, IB, i
– Which genotypes are heterozygous? Homozygous?
GENOTYPES
RESULTING PHENOTYPES
IAIA
IAi
IBIB
IBi
IAIB
Type A
Type AB
ii
Type O
Type B
Antigens vs. Antibodies
• Antigen: substance foreign to the body that causes
an immune response:
– Can act as surface markers
– EX: type A antigens on surface of type A blood
cells
• Antibody: protein that reacts with specific antigen:
– EX: Type B blood contains anti-A antibodies
Which is the universal donor?
Universal acceptor?
Determine Blood Type
• Determine the possible offspring of the
following crosses
• 1. AB and O
• 2. Homozygous A and heterozygous B
• 3. AB and AB
Do Now!! 
• Determine the possible blood types:
• Cross homozygous A and heterozygous B
• AB x AB
Polygenic Traits
 Polygenic traits arise from the interaction
of multiple pairs of genes.
Incomplete dominance
o Heterozygous phenotype is intermediate
between two homozygous phenotypes:
o In between two extremes
o Heterozygous phenotype appears blended.
o Ex: Four O’clock flowers
+
Examples!
• Both traits are expressed (no blending)
• Ex: Roan Cows
– white hair (HW) is codominant with red hair (HR)
– cows with genotype (HRHW) have coats with a
mixture of red and white hairs (roan)
• Red + White = RED AND WHITE
Examples!
Sex Linked Traits
• Traits located on the sex chromosomes (X or Y)
• X linked: gene is located on the X chromosomes
• Y linked: gene is located on the Y chromosome
• Ex: color-blindness is X-linked!
Sex-Linked Traits
• A man who is color blind marries a woman
that is heterozygous for color blindness.
What is the chance of having a color blind
boy?