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Patterns of Heredity
- Genetics -
Sections: 10.2, 11.1, 11.2, & 11.3
Genetics = the study of heredity by which traits are
passed from parents to offspring
Page. 227
Heredity = 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, weight,
resemble those of
your parents!
How are traits passed on?
….. CHROMOSOMES!
Let’s review the structure of a
chromosome...
● A pair of chromosomes are
considered homologous
(homo meaning same)
● Homologous chromosomes
have the same size,
structure, and genetic
information (genes).
What is a gene?
A unit of heredity that
occupies a specific location on
a chromosome and codes for
a particular protein.
It consists of a specific
nucleotide sequence
Alleles
Alternative forms of a
gene that occupy
corresponding
positions on
homologous
chromosomes.
Autosomes and Sex Chromosomes
● We have 23 pairs of chromosomes
● 1 pair are known as the sex chromosomes, which
determines the sex of the offspring (and has other
important genetic information too!)
● Males = XY
● Females = XX
Think - Pair - Share
1. Does the mother or the father determine the
gender of the child?
2. What do you
call this set up
to the right? →
The History of Gregor Mendel
● Austrian Monk – Czech
● Bred different varieties of
garden pea.
● First to develop rules that
accurately predict patterns
of heredity.
● Determined specific units
of inheritance = genes and
alleles
Page. 277
https://www.youtube.com/watch?v=Mehz7tCxjSE
Pollination - transfer of pollen from anthers
to stigma in flowers
Two types:
1. Self pollination occurs within the
same flower or
same plant
2. Cross pollination occurs between
two different
Why are pea plants a great subject to use
when studying heredity?
1.
Several traits exist in two clear different forms.
Ex: Flower color was either purple OR white
2.
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).
3.
The garden pea is small, grows easily, matures
quickly, and produces many offspring. Results can
be obtained quickly with many offspring.
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
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)
3.
Allowed the F1 generation to self-pollinate and those
offspring are called the F2 generation.
F2 Generation = Filial generation 2
Mendel’s Crosses with Pea Plants
P1
parental
generation
Pure tall
plants
X
Cross
F
first filial
generation
Pure short
plants
Pollination
All Tall
plants
Self
Pollination
1
F
2
second filial
generation
787 tall plants, 277 short plants
3 to 1 ratio
Ratio of Mendel’s Research
● P Generation had a true-breeding purple and white flower
● The F1 generation consisted of ALL purple flowers
● The F2 generation had 705 purple flowers and 224 white
flowers.
● That is a ratio of about 3:1 or 3/1
● He found that ratio for all of the traits
Color and texture
Mendel’s 3 Principles of Inheritance
1) The Law of Segregation: Parental genes are randomly separated
to the sex cells so that sex cells contain only one gene of the pair.
Offspring therefore inherit one genetic allele from each parent.
2) The Law of Independent Assortment: Genes for different
traits are sorted separately from one another so that the inheritance of
one trait is not dependent on the inheritance of another.
3) The Law of Dominance: An organism with alternate forms of a
gene will express the form that is dominant.
Mendel’s 3 Principles of Inheritance
(Laws)
1. The Law of Dominance: An organism with alternate
forms of a gene will express the form that is dominant.
● If an organism has at least 1 dominant allele, that trait
will be expressed!
Dd
2. The Law of Segregation: The two alleles for a trait
segregate into gametes during meiosis
3. Law of independent assortment – alleles of different genes
separate independently of one another during gamete formation.
Phenotype vs. Genotype
Genotype: The set of alleles that an individual has
(not always obvious)
phenotype: the physical appearance of a trait
Heterozygous vs. Homozygous
● Different alleles present ● Two of the same alleles
● Ex: BB or bb
● Ex: Bb
● Homozygous recessive or
homozygous dominant
Recessive vs. 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)
Example: In dogs, black fur is dominant
over white fur color. B = black b = white
BB or Bb
bb
DO NOW
If Chris Hemsworth’s phenotype is blonde hair…
(H=Black, h=blonde)
● 1. What his genotype?
●
2. Would his alleles be homozygous dominant,
homozygous recessive, or heterozygous?
Beyonce’s phenotype is brown hair.
● 1. What is her genotype?
●
2. Would her alleles be homozygous dominant,
homozygous recessive, or heterozygous
What are the chances their offspring would have
brown hair? Create a punnett square?
Punnett Square
● 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. Phenotypic Ratio and %:
2. Genotypic Ratio :
1. Phenotypic Ratio and %:
2. Genotypic Ratio :
1.
Phenotypic Ratio and %:
2.
Genotypic Ratio :
Probability
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.
How do you write a ratio?
● 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
Relate probability to a
Punnett Square
1. What is the phenotypic ratio?
2. What is phenotypic %?
Test Cross
● In a test cross, an individual whose phenotype is
dominant, but whose genotype is not known, is
crossed with a homozygous individual.
● Ex: Brown eyes are brown, but can be BB or Bb.
● To find out if the person with brown eyes is
homozygous or heterozygous, you cross it with a
recessive person's genotype and the outcome will tell
you depending on the ratio
Spongebob squarepants doesn’t know
whether or not he is Homozygous Dominant
or Heterozygous for his yellow color. The
recessive trait is a white sponge. Let’s say that
we perform a “test cross” on spongebob
(spongebob + a white female sponge) and all
of the baby sponges are yellow. What would
spongebob’s genotype be?
Pedigree -
a family history that shows how a trait
is inherited over several generations.
● 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 possible genotypes!
Types of Inheritance
Incomplete dominance – a trait that
is intermediate between two parents
Codominance
● Neither trait is dominant instead, both traits are
shown (No Blending)
● Ex) Roan Cows
● Red + White = RED AND WHITE
Codominance – two dominant alleles are
expressed at the same time.
Determine Blood Type
● Determine the possible offspring of the following
crosses below →
● 1. AB and O
● 2. AA and BO
● 3. AB and AB
Multiple alleles – genes with
3 or more alleles
Polygenic Traits – several
genes influence a trait
A wide range of variability! Genes can be located on different chromosomes
Sex-Linked Traits
● Red-green colorblindness
● Male Pattern Baldness
● Hemophilia
Compare:
Male : XhY
X HY
Female: XHXH
X HX h
X hX h
Autosomal vs. Sex-Linked
What do you see?
Pleiotropy
The single gene controlling or
influencing multiple, possibly
unrelated, phenotypic traits.
Ex: albinism
Polyploidy
● Occurrence of one or more extra sets of all
chromosomes in an organism.
● Ex. A triploid organism (3n) - means that it has three
complete sets of chromosomes.
Gene Linkage
● When two genes are close to each other on the same
chromosome and tend to be passed on together
● There are several genes on a chromosome
Gene Linkage cont...
▪ Linked genes usually do not segregate independently
because they are so close together on a chromosome.
Traits can be influenced by
the environment!
Hydrangea Flowers:
When in acidic soil, they bloom blue flowers
When in basic soil, they will bloom pink flowers
Arctic Fox – Enzymes will make pigments during a certain
time of the year.
Genetic Disorders
● Sickle Cell Anemia
● Cystic Fibrosis (CF)
● Hemophilia
● Tay- Sachs Disease
● Huntington’s Disease (HD)
● Hypercholesterolemia
● In Groups, you will research a specific disease and
present it to the class.
● Sickle Cell Anemia - Red blood cells are c-shaped
or sickled. This disease lacks the correct amount of
hemoglobin.
● Cystic Fibrosis (CF) - A thick mucus is constantly
created in the lungs and intestinal tract. It is a
recessive disorder.
● Hemophilia - Specific protein for blood clotting is
not created, thus making it very hard to stop cuts.
Bruising and internal bleeding occur. SEX LINKED!
● Tay- Sachs Disease - Breaks down nerve cells,
brain cells, and deteriorate the spinal cord. A
recessive disorder.
● Huntington’s Disease (HD) - Symptoms appear
later in life and is a dominant disorder. Movement
and cognitive ability is impaired.
Treating Genetic Disorders
● Most genetic disorders cannot be cured, although
progress is being made.
● Families who have a history of genetic disorders are
recommended to undergo counseling before having
a child. They can find out how it could affect their
offspring.
● Some genetic disorders can be treated if diagnosed
early enough, such as PKU (lacking a certain
enzyme).
● If known, that child can be put on a certain diet and
medicine routine.
Gene Therapy
●
May soon allow scientists to correct certain recessive genetic disorders by
replacing defective genes with copies of a healthy one.
●
First step of gene therapy is to isolate a copy of the gene.
●
Scientists are trying to input that gene into the cell by attaching it to a cold
virus. Attempts in humans have not been successful.
●
However, the outlook is promising.
What is genetic mapping?
● Genetic mapping - also called linkage mapping - can
offer firm evidence that a disease transmitted from
parent to child is linked to one or more genes. It also
provides clues about which chromosome contains the
gene and precisely where it lies on that chromosome.
● Genetic maps have been used successfully to find the
single gene responsible for relatively rare inherited
disorders, like cystic fibrosis and muscular dystrophy.
Maps have also become useful in guiding scientists to
the many genes that are believed to interact to bring
about more common disorders, such as asthma, heart
disease, diabetes, cancer and psychiatric conditions.