Download Ch 8: Mendel and Heredity

Document related concepts

Transgenerational epigenetic inheritance wikipedia , lookup

Genome evolution wikipedia , lookup

Genetic testing wikipedia , lookup

Gene expression profiling wikipedia , lookup

Polyploid wikipedia , lookup

Site-specific recombinase technology wikipedia , lookup

Epigenetics of human development wikipedia , lookup

Nutriepigenomics wikipedia , lookup

Artificial gene synthesis wikipedia , lookup

Polymorphism (biology) wikipedia , lookup

X-inactivation wikipedia , lookup

Gene expression programming wikipedia , lookup

Heritability of IQ wikipedia , lookup

Biology and consumer behaviour wikipedia , lookup

Epistasis wikipedia , lookup

Pharmacogenomics wikipedia , lookup

Human genetic variation wikipedia , lookup

Twin study wikipedia , lookup

Genomic imprinting wikipedia , lookup

Public health genomics wikipedia , lookup

Genetic engineering wikipedia , lookup

Behavioural genetics wikipedia , lookup

Gene wikipedia , lookup

History of genetic engineering wikipedia , lookup

Medical genetics wikipedia , lookup

Population genetics wikipedia , lookup

Inbreeding wikipedia , lookup

Genome (book) wikipedia , lookup

Genetic drift wikipedia , lookup

Hardy–Weinberg principle wikipedia , lookup

Quantitative trait locus wikipedia , lookup

Designer baby wikipedia , lookup

Microevolution wikipedia , lookup

Dominance (genetics) wikipedia , lookup

Transcript
Ch 8:
Mendel and Heredity
8.1 The origins of genetics
8.2 Mendel’s theory
8.3 Studying heredity
8.4 Complex patterns of heredity
Enduring Understanding
Living systems store, retrieve, transmit & respond
to information essential to life’s processes.
Essential Questions:

Why are the sciences of genetics and evolution
foundational to modern biology?

How is heredity understood by modern scientists?

Why might a knowledge of genetics be useful to modern
scientists?
8.1 Origins of Genetics

From very early times, people have been curious
about how traits are passed down through the
generations.

Within the last one hundred years, since the
rediscovery of Mendel's work, we have been able to
start to understand the processes of heredity.

Mendel's revolutionary work was almost completely
ignored when first published.

Only after 35 years was it rediscovered and the
modern study of genetics began.
Heredity

Passing of characters ; parents to offspring
Ex. Shape of your eyes
 Ex. Texture of your hair


Before DNA and chromosomes were
discovered, heredity was once of the biggest
mysteries of science.
To do!

Name 5 characteristics that are passed on
in families.
Eye, hair and skin color, height etc.

Name one characteristic that may be
inherited but is also influenced by behavior
or environment.
Muscle size, body weight, sun tan.
Gregor Mendel

Gregor Johann Mendel was an Austrian monk.

Carried out experiments in which he bred
different varieties of the garden pea.

First to develop rules that accurately predicted
patterns of heredity.

The patterns that Mendel discovered formed the
basis of genetics - the branch of biology that
focuses on heredity.
Gregor Mendel

Mendel knew much about agriculture.

He studied science and math at the University of
Vienna.

He repeated the experiments of the British
farmer T. A. Knight, but Mendel counted the
number of each kind of offspring and analyzed
the data.
Gregor’s Breeding Experiments

Used PEAS

WHY??
1.
Flower color – purple or white
2.
Male and female reproductive parts are
enclosed in the same flower – can control
mating or can cross pollinate
3.
Garden pea is small, grows easily, matures
quickly, and produces many offspring.
Gregor’s Breeding Experiments

See table 1 p. 163
The seven
characters
that
Mendel
studied and
their
contrasting
traits.
Plant height
Mendel’s
Monohybrid Cross
Phenotype
 "the form that is shown";
 outward, physical appearance of a trait

Mendel looked at phenotypes & kept records!

Monohybrid cross – cross that involves
only one pair of contrasting traits
Purple vs white
 Round vs wrinkled


True breeding – offspring would display
only one form of the character

HOMOZYGOUS

P generation – parent generation – first
two individuals that are crossed

F1 generation – first filial generation –
offspring of parent generation

F2 generation – second filial generation –
offspring of the F1 generation
Parental
Generation
DD
Parental Gametes
D
F1 Genotype
x
dd
d
Dd
P1
F1
F2
Mendel’s Results

For each of the seven traits that Mendel
studied, he found the same 3:1 ratio of
plants expressing the contrasting traits in
the F2 generation.
F1 generation all showed the same trait.
 In the F2 generation the recessive allele
reappeared.

Mini quiz

Describe the contribution of Mendel to the
foundation of modern genetics.
Mendel was the first to develop rules
that accurately predict patterns of
heredity.
The offspring of true breeding parents are
called
A.
B.
C.
D.
F1 generation
F 2 generation
Dominant offspring
Recessive offspring
Which of the following is NOT a good reason
why Pisum sativum makes an excellent
subject for genetic research?
A.
B.
C.
D.
Many varieties exist.
They require cross-pollination.
They grow quickly.
The demonstrate complete dominance.

Why did Mendel allow the pea plants to
self pollinate for several generations
before beginning his crosses?

To ensure that each variety was true
breeding.

Define heredity.

Heredity is the passing of traits from
parents to offspring.
8.2 Mendels’ Theory
Mendel’s Hypothesis
1.
For each inherited character, an
individual has two copies of the same
gene – one from each parent.
2.
There are alternative versions of genes.

Alleles
3. When two different alleles occur together, one of them
may be completely expressed, while the other may
have no observable effect on the organism’s
appearance.

Dominant – expressed form of the character
present

Recessive – trait that is not expressed when
dominant form is present.
4.
When gametes are formed, the alleles for each gene in
an individual separate independently of one another.

Gametes only carry one allele

When gametes unite during fertilization – each
gamete contributes one allele.
Mendel’s findings in modern terms
Genes and homologous chromosomes
1.
Diploid organisms (like peas) have two sets of chromosomes (one from the
male, one from the female) and these are called homologous
chromosomes.
2.
At equivalent positions on these chromosomes exist genes. The location of
these "gene pairs" is called the locus.
3.
Alternate forms of the gene (ones that differ by mutations in the DNA) are
called alleles.
4.
Dominant traits we now know are the same as dominant alleles, recessive
traits are the same as recessive alleles.
1.
Dominant usually capital letter (here G, R, S, Z) and recessive lower case letters
(here g, r, s, z).

True-breeding traits exist when the organism
has two dominant alleles (e.g. TT) or two
recessive alleles (tt).


homozygous for that gene or those alleles.
The F1 individuals above that resulted from a
cross between tall and short pea plants have
both a dominant (T) allele and a recessive (t)
allele.

heterozygous for that gene or those alleles.

Phenotype = appearance of organism

Genotype = genetic makeup of organism


the set of alleles that an individual has for a character
often represented by letters,
genotype
Genetic makeup of organism = _________
phenotype
Appearance of organism = ____________
The Laws of Heredity
The Law of SegregationThe two alleles for a character separate
when gametes are formed.
The Law of Independent AssortmentThe alleles of different genes separate
independently of one another during
gamete formation.
Mini quiz
The color of a dog’s coat is the dog’s
A.
B.
C.
D.
Dominance
Pedigree
Phenotype
Genotype

How are the genotype of a dominant allele
and a recessive allele written?

Dominant – CAPITAL LETTER
Recessive – lowercare letter

What is the genotype of
a purple-flowered pea plant?


PP or Pp

What is a dihybrid cross?
A
cross that considers two pairs of
contrasting traits.
The scientist whose studies formed the
basis of modern genetics?
A.
B.
C.
D.
T.A. Knight
Gregor Mendel
Louis Pasteur
Robert Hooke
8.3 Studying Heredity
Punnett Square

A diagram that predicts the outcome of a
genetic cross by considering all possible
combinations of gametes in a cross.

Named for its inventor – Robert Punnett
Types of crosses using Punnett Square

Monohybrid cross cross involving a single
trait



COLOR
PLANT HEIGHT
Dihybrid cross - cross
involving 2 traits

COLOR and PLANT
HEIGHT
Monohybrid cross –
homozygous
-Produce only red
heterozygous offspring
- 4/4 =All are
heterozygous offspring
Monohybrid cross heterozygous

Produce

¼ BB (homozygous dominant)
2/4 Bb (heterozygous)
¼ bb (homozygous recessive)


Make your own punnett square

Exploring further p. 171 – Dihybrid Cross
( 2 characters)
Color
Shape
Determining Unknown Genotypes

Test cross- an individual whose phenotype is
dominant, but whose genotype is not known, is
crossed with a homozygous recessive individual.
Test
cross
Analyzing a Test Cross

P. 172 Data Lab
Outcomes of Crosses

Like Punnett squares, probability
calculations can be used to predict the
results of genetic crosses.

Probability is the likelihood that a specific
event will occur.

Probabilities can be expressed in words,
decimals, percentages, or fractions.
Probability
Probability = number of one kind of outcome
total number of all possible outcomes
-
Can be used to predict the probability of an
allele being present in a gamete.
-
To find the probability that a combination of two
independent events will occur , multiply the
separate probabilities of the two events.
- ½ x ½ = 1/4
Math Lab p. 174

Predicting the results of crosses using
probabilities.
Inheritance of traits

Pedigree – family history that shows how
a trait is inherited over several
generations.

Helpful in to follow genetic disorders.

Carriers do not express the disorder, but can
pass the allele for the disorder to their
offspring.
Sex-linked genes

If a gene is autosomal, it will appear in
both sexes equally.

A sex-linked gene’s allele is located
only on the X or Y chromosomes.

Most sex-linked genes are carried on the X
chromosome and are recessive.
See albinism
pedigree on
p. 175
Mini quiz
If smooth peas are dominant over wrinkled
peas, the allele for smooth peas should
be represented as
A.
B.
C.
D.
W
S
w
s

What is the probability of two parents each
carrying a recessive gene for an inherited
disease to produce a child that will have
that disease?

¼ Simple cross Dd X Dd
¼ chance dd having disease

Explain how the parents of an individual
who expresses a recessive gene can both
not express the gene.

Parents must both be heterozygous
dominant.
8.4 Complex Patterns of Heredity
8.4 Complex Patterns of Heredity

Polygenic inheritance: when several
genes influence a character

Can be scattered among the same
chromosome or located on different
chromosomes.

Eye color, height, weight, hair color, skin color
Incomplete dominance:
Snapdragon
Incomplete dominance:
individual displays a
phenotype that is an
intermediate between
the two parents.

Snapdragon- red x white =
pink flowers

Wavy hair
Multiple Alleles

Genes with 3 or
multiple alleles.

Ex: blood types in humans

more alleles are said to have
ABO blood groups
 I A, I B,


A and B refer to two carbohydrates on surface of red
blood cells
In i allele, neither carbohydrate is present
 IA


i
and IB are both dominant over i, but are not dominant
over each other
When IA and IB are both present, they are co-dominant
The 3 different alleles can code for 4 types of blood
Blood
Groups
Figure 14 p. 178
- The 3 different
alleles can code
for 4 types of
blood
When IA and IB are both
present, they are codominant
There are two special genotypes when it comes to
blood transfusions:
What are they?
OO = universal donors
- can donate blood to
everybody.
- can only receive blood from
other type O donors.
Frequency in
US
46%
4%
40%
AB blood =universal
recipients
- can receive blood from
people with all four blood
types.
10%
Codominance

2 dominant alleles are expressed at the
same time.

Different than incomplete dominance b/c
both traits are displayed.

Ex: IA and IB blood alleles
Characters influenced by environment

An individual’s phenotype often depends on
conditions in the environment.

Ex: Hydrangea –acidic soil – bloom blue
basic soil – bloom pink

Ex: Artic fox- temperature affected



Summer – enzymes produced = red/brown color
Winter – cold temperatures = white color
Ex: height in humans = nutrition
pH 4.5
pH 7.0
Genetic disorders

Genes can be copied wrong or have a mutation.

Genetic disorder – inherited genetic mutations

Often carried by recessive alleles

See Table 2 p. 181 for a list
of genetic disorders.
Sickle Cell Anemia

Recessive genetic disorder.

Mutated allele that produces a defective form of
hemoglobin – red blood cells bend shape.

Sickle-shaped cells rupture easily, resulting in
less oxygen being carried by the blood.

Poor blood circulation.

Recessive allele that causes sickle-cell anemia
also helps protect the cell against malaria.

1 in 500 African Americans
Sickle Cell- Video
Cystic Fibrosis (CF)

Most common, fatal,
hereditary, recessive disorder
among Caucasians.

The airway of the lungs
becomes clogged with a thick
mucus, and the ducts of the
liver and pancreas become
blocked.

Treatments can relieve
symptoms, but no known
cure.

Individuals do not usually live
to an old age.
1 in 2,500 Caucasians

Hemophilia

Recessive genetic disorder, that impairs that
blood’s ability to clot.

Is a sex-linked trait.

Carried on X from female in Hemophilia A and
most affects males with only one X.

1 in 10,000 males
• In hemophilia,
one clotting
factor is missing,
or the level of
that factor is low.
• This makes it
difficult for the
blood to form a
clot, so bleeding
continues longer
than usual, not
faster.
• Nearly all affected people are
male.
• An affected male never
transmits the trait to his sons.
• All daughters of an affected
male will be carriers (if the
mom is not a carrier).
• A carrier female transmits the
trait to her sons 50 percent of
the time.
• No daughters of a carrier
female will show the trait, but a
daughter in this case (if the
dad is not affected) will be a
carrier 50 percent of the time.
Huntington’s Disease (HD)

Dominant allele on an autosome.

Gradual deterioration of the brain tissue in
middle age – shortened life expectancy

Symptoms appear in a person’s 30-40’s so may
have already reproduced and passed on the
allele.

1 in 10,000 (frequency among human births)

The part of the brain most affected by HD is a group of
nerve cells at the base of the brain known collectively as
the basal ganglia. The basal ganglia organize muscledriven movements of the body, or “motor movement.”
Treating Genetic Disorders
1.
2.
Most can not be cured, although still searching
for cures.
Genetic counseling – form of medical
guidance before reproducing that informs
parents of possible genetic problems.
3.
Some can be treated.
4.
Gene therapy – isolate defective gene and
replace it
Human Chromosome Viewer
The End