Download Notes-Mendel and nonMendel genetics

Introduction to
Genetics and
Human Genetics
Chapters
11.1-11.3
&
14.1-14.2
Standard #1
Determine how an organism passes its
characteristics on to its offspring. (11.1)
A. Describe Mendel’s studies and conclusions
about inheritance.
B. How does an organism get its unique
characteristics?
C. Explain how different forms of a gene are
distributed to offspring.
1.A. Describe Mendel’s studies and conclusions
about inheritance.
Heredity
• the transmission of characteristics from
parents to offspring
Genetics
• the study of how characteristics are
transmitted from parents to offspring and
how the traits are expressed
1.A. Describe Mendel’s studies and conclusions
about inheritance.
Gregor Mendel (father of genetics)
• observed 7 characteristics of pea plants
• each had 2 contrasting traits
• seeds from purple flowered plants produced
purple flowered plants but some white flowered
plants also were produced (why?)
• to document traits of each generation, he
controlled the pollination
1.A. Describe Mendel’s studies and conclusions
about inheritance.
Pollination
• pollen grains from anthers
transferred to stigma
Types of pollination:
• self-pollination
• pollen from anther to stigma of same flower or from
the another flower on the same plant (normal method)
• cross-pollination
• involves flowers of two separate plants
1.A. Describe Mendel’s studies and conclusions
about inheritance.
Why Did Mendel use pea plants?
• Easy to care for
• Short generation time
• Many offspring each generation
• Can control mating between plants
• Require little space to grow
• Several contrasting traits
1.A. Describe Mendel’s studies and conclusions
about inheritance.
Mendel's Experiments:
• plants pure for each trait - always produce offspring
with that trait called pure strain
Terms:
• P1 generation (parental) - a pure strain plant for some
trait
• cross-pollinated these
• F1 generation (first filial) - offspring of the P1 generation
• allowed these to self pollinate
• F2 generation (second filial) - offspring of F1 generation
1.A. Describe Mendel’s studies and conclusions
about inheritance.
Mendel Results:
1.A. Describe Mendel’s studies and conclusions
about inheritance.
Mendel's Conclusions:
• green pods X yellow pods
• F1 all green pods
• F1 green pod X green pod
• F2: ¾ green pod : ¼ yellow pod
• Factors (alleles)
•something in pea plants controlling traits
•hypothesized each characteristic controlled by separate factor
•since each characteristic had 2 alternative forms, must be pair of factors
for each trait
1.B. How does an organism get its unique
characteristics?
Gene
• Factors that are passed from parent to offspring
• segment of DNA on chromosome controlling a
trait
• chromosomes in pairs, so genes are in pairs
Allele
• the alternative forms of a gene
1.C. Explain how different forms of a gene are
distributed to offspring.
Law of dominance
• trait appearing in F1 must be controlled by
dominant factor
• prevents other factor from having an effect
• trait not appearing in F1 but reappearing in F2 must be
controlled by recessive factor
• factor hidden by dominant
Law of Segregation
• a pair of factors is segregated, or separated, during
the formation of gametes
• describes what happens in meiosis
Standard 2:
Predict the outcome of genetic crosses.
(11.2)
A. How do geneticists use the principles of
probability to make predictions about
inheritance?
B. Explain the principle of independent
assortment.
2.A. How do geneticists use the principles of
probability to make predictions about inheritance?
Probability
• the fraction or percentage that describes the chance of
an event taking place
• probability = # of times an event is expected to happen
# of opportunities for an event to happen
• predicts what should happen mathematically, not what
will happen (chance)
• the larger the sample size (# of trials) the close
expected and observed results should be
2.A. How do geneticists use the principles of
probability to make predictions about inheritance?
• flipping a coin, throwing a die, spinner activity
• flipping 2 coins ½ x ½ = ¼
• throwing 2 dice: 1/6 X 1/6 = 1/36
• Occurring together = ¼ x 1/36 = 1/144
• product rule
• probability of 2 or more independent events occurring
together, is the product of their individual probabilities
Terms:
• dominant allele represented by capital letter (G)
• recessive allele represented by lower case same letter (g)
• homozygous (pure strain) - both alleles of pair are alike
• GG - homozygous dominant
• gg - homozygous recessive
• heterozygous (hybrid) - two alleles of pair are different- Gg
• genotype - genetic makeup of organism (alleles it possesses
for a trait) Examples: GG, Gg, gg
• phenotype - the physical appearance of an organism as a
result of its genotype
• genotypic ratio - ratio of genotypes appearing in offspring
• phenotypic ratio - ratio of offspring's phenotypes
2.A. How do geneticists use the principles of
probability to make predictions about inheritance?
Predicting Results of Monohybrid Crosses
• cross involving one pair of contrasting traits
• Punnett square - diagram to predict probability
that certain traits will be inherited by offspring
P
P
Key: P = purple flower
p = white flower
p
genotypic ratio
phenotypic ratio
p
Monohybrid Problem #2
Key:
B= black coat
b = brown coat
genotypic ratio
phenotypic ratio
Cross
Bb x Bb
Monohybrid Problem #3
Key:
B= black coat
b = brown coat
genotypic ratio
phenotypic ratio
Cross
Bb x bb
Problem #4
How do you know if a black guinea pig is
homozygous or heterozygous?
• test cross
• organism of unknown genotype is mated with a
homozygous recessive organism
2.B. Explain the principle of independent assortment.
Law of Independent Assortment
• P1 yellow seed, round seed X green seed, wrinkled seed
• F1 all yellow, round
• F1 yellow, round X yellow, round (offspring F1)
• F2: yellow, round
green, wrinkled
green, round
yellow, wrinkled
• factors for different characteristics are distributed to gametes
independent of each other
• dominant factors don't have to appear together nor do
recessive
• described by tetrads lining up randomly in metaphase I
Dihybrid problems
Predicting Results of Dihybrid Crosses
• cross involving 2 pairs of contrasting traits
Key:
Parental Cross
R= round seeds
RRYY x rryy
r = wrinkled seeds
F1
Y = yellow seeds
RrYy
y = green seeds
all round and yellow
Dihybrid Problem
RrYy x RrYy
Possible gametes:
Dihybrid Results
Genotypic ratio:
RRYY : RRYy : RRyy : RrYY : RrYy : Rryy : rrYY : rrYy: rryy
Phenotypic ratio:
Round Yellow :Round Green :Wrinkled Yellow :Wrinkled Green
Standard #3
Determine how different factors can affect an
organism’s traits. (11.3 & 14.1)
A. Describe the patterns of inheritance of human traits.
Give an example using a punnett square for each
pattern:
•
Dominant vs. recessive, Incomplete dominance,
Codominant, Multiple alleles, Polygenes, Sex linked, &
X-chromosome in activated
B. Explain how the environment plays a role in how genes
determine traits.
C. Explain how to use chi-square and how it relates to
genetics?
3.A.Describe the patterns of inheritance of human traits.
Human Single allele traits (more than 250)
• can be due to autosomal recessive or dominant alleles
• Dominant alleles
• cleft chin, freckles, free earlobes, webbed fingers, Rh factor
• Recessive alleles
• PKU, sickle cell anemia, MC1R gene (Red hair)
• PKU can’t make enzyme to break down amino acid, phenylalanine - it
accumulates, destroys brain cells - severe mental retardation
• genetic marker - short section of DNA that is
known to have close association with particular gene
nearby
3.A.Describe the patterns of inheritance of human traits.
Incomplete dominance
• two or more alleles influence phenotype, resulting
in intermediate phenotype between dominant and
recessive
RW x RW
Key:
RR= red flowers
WW = white flowers
RW = pink flowers
3.A.Describe the patterns of inheritance of human traits.
Codominance
• neither allele dominant or recessive, nor do allele blend
• both alleles expressed in heterozygous individual
RR’ x RR’
KEY:
RR = red coat
R'R’ = white coat
RR' = roan coat
3.A.Describe the patterns of inheritance of human traits.
Multiple Alleles:
• controlled by 3 or more alleles of same gene
• blood type alleles - IA, IB, Ii
• IA and IB are codominant when both expressed together
and both are dominant to i
genotype
• phenotype
type A
type B
type AB
type O
IAIA : I Ai
IBIB: IBi
I AIB
ii
Blood Type Problem
I A IB x IBi
genotypic ratio
phenotypic ratio
Blood Transfusions and Rh Factor
Antibody: a protein produced to bind to an antigen,
protects body from foreign substances (in plasma)
Antigen: a protein that stimulates a response from
the immune system (on the RBC’s)
• Transfusions
• concerned with antibodies of recipient
• antibodies agglutinate (clump) antigens
Type
Antigens
Antibodies Can receive from Can donate to
A
A
b
A,O
A,AB
B
B
a
B,O
B,AB
AB
A&B
none
A,B,AB,O
AB
O
none
a&b
O
A,B,AB,O
Rh Factor
• another antigen on RBC’s
• 85% Rh + (have antigen)
• 15% Rh - (no antigen)
• Rh + blood given to Rh - person
• Rh - person develops antibodies against Rh
antigen
• little problem on 1st transfusion but subsequent
one could be fatal
Erythroblastosis fetalis: (RBC) (destruction) (fetus)
• mother Rh -, father Rh +, baby Rh +
• 1st child (Rh +)
• if any leakage across placenta to uterine blood vessels, mother will
make antibodies against Rh antigen
• antibodies not made fast enough to affect baby
• subsequent child (Rh +)
• antibodies already present will destroy baby’s RBC’s
• can transfuse baby with Rh - blood in utero (dangerous)
• Rhogam shot
• given to mother within 72 hours of birth of child
• destroys any Rh + blood antigens mother may have
gotten from child (contains anti Rh antibodies)
3.A.Describe the patterns of inheritance of human traits.
Polygenic traits
• controlled by 2 or more genes
• each gene has a small additive effect
• continuous variation shown in the trait
•
•
•
•
•
•
skin color
eye color
foot size
Height
Weight
intelligence
3.A.Describe the patterns of inheritance of human traits.
Sex linked: X-linked
• A gene located on the sex
chromosome
• Sex linked genetic disorders
• occur more in males
• only one X chromosome
• color-blindness, hemophilia,
Duchenne muscular dystrophy
• many other genes code for
proteins needed for normal
functions
3.B. Explain how the environment plays a role in how
genes determine traits.
• Environment can influence gene expression and
influence genetically determined traits
• An individuals phenotype is determined by
• Genes
• environment
• Example: Western White Butterfly
• Hatch in spring months- need more pigmentation
to reach body temp needed for flight
• Hatch in summer- need less pigmentation to avoid
overheating
3.B. Explain how the environment plays a role
in how genes determine traits.
How the environment plays a role with human genes?
• characters that are influenced strongly by environment
and by genes
• most complex traits are also polygenetic traits
• skin color- expose to the sun causes the skin to
become darker, no matter what the genotype is
• Height- influenced by an unknown # of genes, but
also a person’s nutrition and diseases
• breast cancer, diabetes, heart disease, stroke, and
schizophrenia
Standard #4
Analyze how studying the human genome
explains how traits are inherited (14.1).
A. What is a karyotype?
B. Identify the types of chromosomes in a
karyotype.
C. Analyze pedigree to determine traits.
4.A.What is a karyotype?
Karyotype:
• Shows a complete set
of diploid
chromosomes
• Grouped in pairs
• Arranged in order of
decreasing size
4.B. Identify the types of chromosomes in a
karyotype.
• Autosome
• any chromosome but the sex chromosomes
• Sex Chromosomes
• determine the sex of the organismin humans X
and Y determine the sex in the offspring
• XX= female
• XY= male
4.C. Analyze pedigree to determine traits.
Human Pedigrees
• pedigree –
• family record showing how trait is inherited over
several generations (to find how traits are inherited)
• show patterns of inheritance
• carriers - have one recessive allele but don’t express it
(can pass it on to offspring)
http://www.youtube.com/watch?v=eYlJH81dSiw
Standard #5
Explain causes of genetic disorders (14.2).
A. Explain how small changes in DNA cause genetic
disorders. Do genetic disorders have advantages?
B. Summarize the problems caused by
nondisjunction.
C. Explain the how genetic disorders can be
detected.
4.A. Explain how small changes in DNA cause
genetic disorders.
Small Changes: (review)
• Sickle cell anemia• point mutation
• substitution
• Cystic fibrosis• frameshift mutation
• deletion of 3 bases
• Huntington’s disease
• Dominant allele
4.A. Explain how small changes in DNA cause genetic
disorders.
Do genetic disorders have advantages?
Sickle cell anemia:
• People who are heterozygous
• Are generally heathly
• Highly resistant to malaria (claims 1 million lives a year)
Cystic Fibrosis (CF)
• People who are heterozygous
• Protein produced by CF allele blocks the entry of
typhoid bacterium (enter though digestive system)
• People who live in city with poor sanitation and
polluted water
4.B.Summarize the problems caused by nondisjunction.
Nondisjunction disorders
• monosomy - 45
chromosomes in zygote
(one copy of a particular
chromosome)
• trisomy - 47
chromosomes in zygote
(three copies of a
particular chromosome)
4.B.Summarize the problems caused by nondisjunction.
• Down syndrome
• 47 chromosomes
• trisomy #21
• both sexes
• Turner syndrome –
• 45 chromosomes (XO)
• Only females
• Klinefelter syndrome
• 47 chromosomes (XXY)
• Only males
• Super female –
• 47 chromosomes
• trisomy of X
• XXX
• XYY (males)
4.C.Explain the how genetic disorders can be detected.
Detecting Genetic Disorders
• genetic screening for those with history of genetic
disorders
• karyotype, examine blood for presence or absence of
certain proteins
• genetic counseling
• medical guidance informing them of potential problems
for offspring
• amniocentesis
• some amniotic fluid removed at 14-16 weeks
• analyze fetal cells and proteins, make karyotype
4.C.Explain the how genetic disorders can be detected.
4.C.Explain the how genetic disorders can be detected.
• chorionic villi sampling –
• sample of tissue between uterus
and placenta at 8-10 weeks
• villi same genetic makeup as
embryo
• make karyotype
• genetic screening after birth for
PKU
• ultrasound –
• sonogram (use sound waves)
• fetoscopy –
• view fetus, take picture