Transcript TRAITS

Chapter 11
Genetics
11.4 Vocabulary
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Homologous - glossary
Diploid - glossary
Haploid - glossary
Meiosis
Tetrad - glossary
Crossing Over - glossary
Zygote - glossary
Section 4
Meiosis
Standards: 4C.1, 4C.3
Objectives:
• Summarize the events of meiosis.
• Explain the reduction in chromosome number
that occurs during meiosis.
• Analyze the importance of meiosis in providing
genetic variation.
• Compare/contrast mitosis and meiosis.
REVIEW
Asexual Reproduction
• Cell copies itself through MITOSIS
• Cells divide producing more cells
• Chromosomes inherited from a single parent 
genetically identical to offspring  same DNA
• Occurs in all organisms
Budding in Yeast
Sexual Reproduction
• DNA is combined from two different sources
through MEIOSIS
• ½ DNA from each parent
• Produces genetically different cells
• Increases beneficial mutations faster than
asexual reproduction
• Occurs in many organisms
DNA, Genes, & Chromosomes
• Trait – characteristics (hair color, height, eye color)
• Chromosomes contain instructions for traits
– DNA on chromosomes is arranged in segments (genes)
which control the production of proteins.
– Each chromosome contains thousands of genes 
determines characteristics and functions of cells.
Human Body Cells
• 46 chromosomes arranged in 23 pairs
– 23 chromosomes from each parent
– Every body cell contains a complete set of chromosomes
– Homologous Chromosomes – pair of chromosomes; one
chromosome from each parent
• Same length
• Same centromere position
• same genes (different traits)
46 Human Homologous
Chromosomes
23 Human Nonhomologous
Chromosomes
Maintaining Chromosome Number (n)
• Autosomes – non-sex chromosomes (44 total)
– Diploid – 2 sets of each chromosome (2n)
• Gametes – sex cells  sperm and egg
– involved in reproduction
– ½ the number of chromosomes (23 total)
– Not in pairs; each carries different genetic info.
– Haploid – 1 set of each chromosome (n)
Fertilization
• Fertilization – process of sperm and egg joining
– Fertilized egg  zygote
– Haploid + Haploid = Diploid
n + n = 2n
– Each gamete gives 23 chromosomes to offspring
23 + 23 = 46
– 23 pairs of chromosomes, 46 total chromosomes
How Are Gametes Formed?
• NOT through mitosis
• Gametes are formed from diploid cells that start
with all 46 chromosomes called germ cells.
Germ cells go through meiosis.
– Males  spermatogenesis produces 4 sperms cells
– Females  oogenesis produces 1 egg cell
Review: Comparing Haploid and Diploid
How many
chromosomes in ……..
1) n cells?
2) Diploid cells?
3) Gamete cells?
4) Cells that asexually
reproduce?
5) Somatic cells?
6) Sex cells?
7) Haploid cells?
8) 2n cells?
9) Sperm cells?
10) Cells that sexually
reproduce?
“Normal”
Human
Bald Eagles 66 chromosomes
in their body cells.
Meiosis
• Process of cell division that reduces the number
of chromosomes by half  “reduction division”
• Occurs in reproductive structures to produce
gametes  sperm & eggs
• Sexual reproduction
• Produces haploid cells
• Two Divisions: Meiosis I and Meiosis II
Interphase I
• Normal metabolic processes: increase size, produce
RNA, synthesize proteins, & replicate DNA.
Prophase I
• Nucleus disappears
• Centrioles move to opposite poles & spindle
apparatus forms.
• Replicated chromosomes condense and become
visible  each with two sister chromatids.
• Synapsis  homologous chromosomes pair up (tetrad)
Prophase I
• Crossing Over – homologous chromosomes
exchange DNA  increases genetic variation.
Prophase I
Metaphase I
• Spindle fibers attach to centromeres of each
homologous chromosome.
• Pairs of homologous chromosomes line up at the
middle (equator) of the cell.
• Independent Assortment – pairs of homologous
chromosomes randomly line up  increases
genetic variation.
Metaphase I
Anaphase I
• Homologous chromosomes separate and
move to opposite poles.
– Reduces chromosome number  each side will
receive 23 chromosomes.
Anaphase I
Anaphase I
Telophase I
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Homologous chromosomes reach opposite poles.
Chromosomes relax  chromatin
Spindle apparatus disappears
Nucleus reappears
Cleavage Furrow  animal cells
Telophase I
Telophase I
Cytokinesis
• Cytoplasm divides forming two haploid cells.
• Plants  cell plate forms
Cytokinesis (after Meiosis I)
At the End of Meiosis I
• Only halfway through meiosis.
• Cell may undergo interphase but DNA is NOT
replicated this time.
Prophase II
• Nucleus disappears
• Spindle apparatus reappears
• Chromosomes condense  visible  each still
containing two sister chromatids.
Prophase II
Prophase II
Metaphase II
• Spindle fibers attach to centromere and
chromosomes RANDOMLY line up at the center.
Metaphase II
Metaphase II
Anaphase II
• Sister chromatids separate by the spindle fibers
pulling opposite directions.
• Single chromosomes move to oppose poles.
– Reduce chromosome number  each side will receive
23 chromosomes.
Anaphase II
Telophase II
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Chromosomes reach opposite poles.
Chromosomes relax  chromatin
Spindle apparatus disappears
Nucleus reappears
Telophase II
Cytokinesis
• Cytoplasm divides forming 4 different haploid
cells.
Cytokinesis (after Meiosis II)
At the End of Meiosis II
• In humans  each cell contains 23 chromosomes.
• Daughter cells produced during meiosis are
genetically different because of:
1. DNA from two parents
2. Crossing over
3. Independent assortment
Review: Sequence Meiosis I and II
1) ___
2) ___
3) ___
4) ___
5) ___
6) ___
7) ___
8) ___
Review: Comparing Mitosis & Meiosis
Mitosis
Produces more cells
Body cells
Produces haploid cells
Sexual Reproduction
Sperm & Egg
Gametes
Genetically identical cells
Produces diploid cells
Increases genetic variation
Sex cells
Somatic cells
Genetically different cells
Asexual Reproduction
Meiosis
Review: Comparing Mitosis & Meiosis
Mitosis
TWO divisions
DNA from one parent
Occurs in ALL organisms
“Crossing Over”
Occurs in many organisms
DNA from two parents
Reduces chromosome number
Maintains chromosome number
ONE division
Produces cells with 23 chromosomes
TETRAD
Skin cells, liver cells, hair cells
Produces cells with 46 chromosomes
Meiosis
Review: Comparing Mitosis & Meiosis
Review: Comparing Mitosis & Meiosis
prophase (I)
metaphase (I)
anaphase (I)
telophase (I)
11.1 & 11.2 Vocabulary
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Genetics
Fertilization
Trait
Hybrid
Gene - glossary
Allele
Principle of Dominance
Segregation - glossary
Gamete
Probability
Homozygous
Heterozygous - glossary
Phenotype
Genotype
Punnett Square - glossary
Independent Assortment
Sections 1 & 2
Mendelian Genetics
Standards: 4C.2
Objectives:
• Explain the significance of Mendel’s experiments
to the study of genetics.
• Summarize the law of segregation and law of
independent assortment.
• Predict genetics of offspring using a Punnett
Square.
Review
• Most organisms have diploid cells
• Polyploidy – one or more extra sets of all
chromosomes in an organism.
– Triploid  3 complete sets of chromosomes  3n
– Rarely occurs in animals; humans = lethal
– Occurs in flowering plants  increased size
Strawberries are 8n.
46 Human Homologous
Chromosomes
Review
• Sexual Reproduction: DNA for offspring comes
from different individuals
– Parents: father & mother
• Fertilization: 1 gamete from each parent fuse to
form offspring
– Each gamete donates ½ amount of DNA needed
• Male gamete = sperm/pollen
• Female gamete = egg
Review
• DNA is divided into units called genes
• Genes code for proteins
• Proteins control how you look
• The passing of this genetic information from
parents to offspring is called heredity
• Genetic Recombination – new combination of genes
produced by crossing over and independent assortment.
– Increases genetic diversity!
Gregor Mendel
• “Father of Genetics”
– Genetics – study of heredity
• 1866  published finding of Inheritance
(traits passed from generation to the next).
• Studied pea plants
Mendel’s Experiments
• Mendel studied 7 different pea characteristics.
– Characteristic = GENE
• Each characteristic had 2 different variations.
– Variation = ALLELE (different form of a single gene)
TRAITS
Mendel’s Experiments
• Mendel controlled which plants bred with each
other through a process called cross-pollination.
Self-Pollination
Cross-Pollination
Mendel’s Experiments
• Mendel bred plants with different traits to see
what kind of traits the offspring would have.
Parent Generation
(P)
Offspring Generation
(F1)
X
Purple
Flowers
X
White
Flowers
Purple
Flowers
Mendel’s Experiments
• Mendel started each experiment with purebred
plants expressing a specific trait.
– Purebred – organism that expresses and passes on
unchanging traits from generation to generation.
X
X
P Generation
Purebreds
Mendel’s Findings
1. Some traits always appeared
2. Some traits always disappeared
3. Traits that disappeared would reappear in the
next generation IF he let the plants self-pollinate.
Mendel’s Findings
X
Purebred
1st Generation (F1)
2nd Generation (F2)
X
Cross-pollinate
X
Self-pollinate
Purebred
Mendel’s Law of Dominance
• Forms of a trait that “disappear” are really hidden
by the other form of the trait.
– Hidden (or masked) traits  Recessive  lowercase
letter
– Traits that appear & do the hiding  Dominant 
capital letter
Genes – factors passed from parent to offspring
Genotype/Phenotype
• Genotype – genetic makeup
– Represented by letters
• Phenotype – physical traits
Homozygous/Heterozygous
• Homozygous  identical alleles for a specific gene
– Homozygous Dominant  2 capital letters (AA)
– Homozygous Recessive  2 lowercase letters (aa)
• Heterozygous  different alleles for a specific gene
– Heterozygous  1 capital & 1 lowercase (Aa)
– Also called Hybrids (different)
Pp
= Heterozygous
Homozygous/Heterozygous
X
X
AA
aa
aa
AA
X
_____
_____
_____
_____
_____
_____
_____
Probability
• Probability – likelihood that an event will occur
Chance of T?
Chance of t?
Chance of TALL?
Chance of short?
Chance of Heads?
Mendel’s Law of Segregation
• Chromosomes separate during
meiosis II.
• Each gamete receives 1 of the 2
alleles (= chance).
• During fertilization (sperm &
egg unite)  two alleles unite.
• Each parent passes one copy of
its traits  offspring look
similar but not exact.
Mendel’s Law of Segregation
Mendel’s Law of Independent
Assortment
• Each trait has same chance of being inherited  no
1 trait prevents the inheritance of another (unless
genes are linked).
• Genes on separate chromosomes separate
independently during meiosis.
• Creates many possible combinations of traits.
Mendel’s Law of Independent
Assortment
Mendel’s Law of Independent
Assortment
Punnett Square
• Diagram used to predict probabilities of allele
combinations.
– Must know parent genotypes
Monohybrid Cross
• Inheritance of a
single trait.
– 1 gene, 2 alleles
– 4 boxes
Dihybrid Cross
• Inheritance of two
traits.
– 2 genes, 4 alleles
– 16 boxes
How to Use a Punnett Square
• Step 1: List dominant and recessive phenotypes
 assign letters.
– Always use the same letter for the same
gene/characteristic!
– Dominant  UPPERCASE Recessive  lowercase
How to Use a Punnett Square
• Step 2: What are the parent genotypes?
– Think of the possible parent genotypes based on
offspring.
– Homozygous (same)  if parent only produces
one type of a trait
– Heterozygous (different)  if parent produces
both types of a trait
How to Use a Punnett Square
• Step 3: Determine what information you are
trying to find out.
– Offspring genotypes
– Offspring phenotypes
– Ratios for both
• Step 4: Draw Punnett Square
– Monohybrid (4 boxes) or Dihybrid (16 boxes)
How to Use a Punnett Square
• Step 5: Write alleles or both parents on
Punnett square (one on top and one down
the side)
How to Use a Punnett Square
• Step 6: Cross Parents
• Step 7: Analyze Results
Genotypes
y
y
Y
Yy
Yy
y
yy
yy
Phenotypes
Practice: Setting Up Punnett Square
In mice, brown fur is dominant to white fur. If a
pure-bred brown mouse is crossed with a white
mouse, what is the probability that they have
brown offspring?
– What is the gene?
– What are the alleles?
• Dominant allele =
• Recessive allele =
– What are the parent genotypes?
• Pure-bred brown =
• White =
1) Monohybrid Practice
In dogs, black fur is dominant to white fur. If you cross a
homozygous male black dog to a heterozygous female black
dog, what are the possible genotypes and phenotypes of the
offspring?
Genotypes
Phenotypes
2) Monohybrid Practice
In cabbage butterflies, white wings are dominant to yellow
wings. A heterozygous butterfly is crossed with a
homozygous yellow butterfly.
Genotypes
Phenotypes
3) Monohybrid Practice
In dogs, there is a hereditary type of deafness caused by a
recessive gene. Two dogs who carry the gene for deafness
but have normal hearing are mated.
Genotypes
Phenotypes
4) Monohybrid Practice
In guinea pigs, short hair is dominant over long hair. A
homozygous short haired one is crossed with a homozygous
long haired guinea pig.
Genotypes
Phenotypes
5) Dihybrid Practice
Black hair is dominant over blonde hair and brown eyes are
dominant over blue eyes. Father is heterozygous for black
hair and brown eyes and mother has blonde hair and blue
eyes.
6) Dihybrid Practice
Black hair is dominant over blonde hair and brown eyes
are dominant over blue eyes. Both parents are
heterozygous for both traits.
11.3 Vocabulary
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Incomplete Dominance
Codominance
Multiple Allele
Polygenic Trait
Section 3
Other Patterns of Inheritance
Standards: 4C.2
Objectives:
• Distinguish between various complex
inheritance patterns.
• Analyze sex-linked and sex-limited inheritance
patterns.
Complex Inheritance
• Not all genetics shows simple patterns of
inheritance  exceptions to Mendel’s principles.
– Genes may have more than 2 alleles
– Many traits controlled by more than one gene
• Complex Inheritance:
–Incomplete Dominance
–Codominance
–Multiple Alleles
–Polygenic Traits
–Sex-Linked Traits
Gene Linkage
• Genes close on the same chromosome are
“linked” and travel together during meiosis 
inherited together.
– Linked genes do not segregate independently
exception to independent assortment
Incomplete Dominance
• Neither allele is completely dominant
• Blend of both the dominant & recessive alleles
Practice Incomplete Dominance
• Straight hair is dominant to curly hair and the
blend of both is wavy hair. Use “S” and “C”.
Cross two wavy haired people.
• Use “S”. Cross two wavy haired people.
Codominance
• Heterozygous  both alleles act dominantly
and are expressed in phenotype
Sickle-Cell Disease
Roan Cows
Multiple Alleles
• More than two alleles for a specific trait (or gene)
• Example  Blood Type
• Red blood cells (RBC) are covered in proteins
called antigens that help cells identify each other.
– 3 Types of alleles (A, B, O) exist for blood
– 4 Blood Types:
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Type A
Type B
Type AB
Type O
Type O
Universal Donor
Type AB
Universal Receiver
Blood Type
Possible Allele Combinations
Blood Types
A
B
iA iA
(homozygous)
iB iB
(homozygous)
AB iA iB
(heterozygous)
O
ii
(homozygous)
iA i
(heterozygous)
iB i
(heterozygous)
Blood Typing Practice
• What are the possible offspring blood types if
mom is homozygous Type A and dad is
homozygous Type B?
Blood Typing Practice
• What are the possible offspring blood types if
mom is heterozygous Type A and Dad is
heterozygous Type B?
Blood Typing Practice
• What are the possible offspring blood types if
mom is Type AB and dad is Type O?
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Polygenic Traits
Traits controlled by interaction of multiple genes
Polygenic = many genes
Results in high level of variation
Shows bell shaped curve when graphed
Examples: skin color, height, eye color, fingerprint
Environmental Influences
• Genes provide plan for development but how
the plan unfolds also depends on environment.
• Environment can affect how a gene functions.
• Phenotype partially determined by genotype.
• Environment has an effect on phenotype:
– Sunlight & Water
– Temperature
– Diet & Nutrition
– Ecological Factors (weather, soil nutrients, toxins)
Environmental Influences
Western White Butterfly
Summer
Autumn
Heredity or Environmental Influences?
• How do you determine if the expression of a
certain trait is a result of heredity or
environmental influences?
– Scientists study identical twins  same genetics
 inherited traits will be expressed in both
individuals.
• Traits that appear frequently  Heredity
• Traits expressed differently  Environment
Chapter 14
Human Heredity
14.1 & 14.2 Vocabulary
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Genome
Karyotype – picture of a complete set of chromosomes
arranged in order of decreasing size
Sex Chromosome - glossary
Autosome - glossary
Sex-Linked Gene
Pedigree – glossary
Nondisjunction – glossary
Gel Electrophoresis - glossary
Sections 1 & 2
Human Chromosomes & Genetic Disorders
Standards: 4C.2, 4D.1
Objectives:
• Analyze genetic patterns to determine dominant
or recessive inheritance patterns.
• Summarize examples of dominant and recessive
disorders in humans.
• Construct human pedigrees from genetic
information.
Human Chromosomes
• Genome – an organism’s full set of genetic info.
• Karyotype – picture of a complete set of
chromosomes arranged in order of decreasing size
– Homologous chromosomes arranged in pairs
– Shows type and number of chromosomes
Individual 1
Individual 2
Karyotype
Male or Female?
Review: Karyotype
Match each organism with its karyotype:
Mouse
40 chromosomes
Dog
78 chromosomes
Normal
Human Male
Normal
Human Female
Sex Determination
• Sex Chromosomes – determines gender; X and Y
• Autosomes – any chromosome that is NOT a sex
chromosome
• Normal Humans have 46 chromosomes:
– 44 autosomes and 2 sex chromosomes
– Female has XX and Male has XY
X and Y Chromosome
X chromosome
1200 genes
Y chromosome
140 genes
Sex Determination Problem
• What is the probability of a man and woman
having a baby girl?
Sex-Linked Inheritance
• Sex-Linked Gene – gene located on sex
chromosome
• Sex-Linked Traits – characteristic controlled by
genes on the X or Y chromosome
– X Linked  traits found on the X chromosome;
expressed in males & females
– Y-Linked  traits found on the Y chromosome;
expressed only in males
passed from father to son
Dominant X-Linked Traits
• Trait is expressed in females and males, if they
have 1 copy of the dominant allele.
– Male  XAY
– Female  XAXA or XAXa
• Trait is NOT expressed if male has 1 copy of
the recessive allele and female has 2 copies of
the recessive allele.
– Male  XaY
– Female  XaXa
Recessive X-Linked Traits
• Trait is expressed only in females that have 2
copies of the recessive allele.
– Female  XaXa
• Trait is expressed only if males have 1 copy of
the recessive allele
– Male  XaY
Sex-Linked Trait Practice
Circle those affected by a dominant X-linked trait.
XBXb XcY XdXd
XRXR XNY
Circle those affected by a recessive X-linked trait.
XaXa XLY
XTXt
XZXZ
XpY
Sex-Linked Trait Practice
• The trait for red-green colorblindness is a recessive Xlinked trait. The mother is a carrier for colorblindness
and the father is not color blind, what is the probability
that they will have a child that will be color blind?
Sex-Linked Trait Practice
• Hemophilia is a recessive X-linked disorder of the
blood. Two normal parents have a son that has
hemophilia, what is the probability that they will
have a daughter that has hemophilia?
Sex-Linked Trait Practice
• Hairy ears is inherited as a Y-linked trait. A man
with hairy ears marries a woman with normal ears.
What is the probability that they will have a female
child with hairy ears? Male child with hairy ears?
Sex-Linked Trait Practice
• This disease is inherited as an X sex-linked dominant
disease? An affected male marries a homozygous
recessive female. What is the probability that they
will have an affected daughter? Affected son?
Changes in DNA = Changes in Phenotype
• Changes in a gene’s DNA sequence can change
proteins by altering their amino acid sequences,
which may directly affect one’s phenotype.
• Genetic disorders caused by changes in genes 
changes proteins.
Recessive Genetic Disorders
• A recessive allele codes for a faulty protein.
• Carrier – an individual that is heterozygous for
a recessive disorder.
– 50% chance of passing recessive allele to child
–AA  no disorder
–Aa  no disorder but a carrier for it
–aa  disorder
What is the % a child could have a
recessive genetic disorder?
Recessive Genetic Disorders
Cystic Fibrosis (CF)
Dominant Genetic Disorders
• A dominant allele codes for a faulty protein.
– Only one parent needs to have one copy of the
defective allele in their gametes to pass the disorder
to their children.
–AA and Aa  disorder
–aa  no disorder
Pedigree
• Pedigree – chart that shows traits, diseases, or
disorders within a family across several
generations.
– Used to infer genotypes by observing phenotypes.
– Tracks dominant, recessive, and sex-linked traits.
– Dominant traits easier to recognize.
– Accurate records of family history  predict
effects in future offspring.
Males
Squares
Females
circles
Expresses Trait
filled
No Trait
unfilled
Carrier for Trait
partially filled
Roman Numerals
generations
(P1, F1, F2)
I, II, III
Numbers
birth order of
offspring
1, 2, 3
Pedigree
Pedigree
white lock of hair - dominant
Recessive or Dominant?
Recessive or Dominant?
Sex-Linked Trait?
Recessive or Dominant?
Sex-Linked Trait?
Recessive or Dominant?
Sex-Linked Trait?
Albinism – Recessive Trait
1. Phenotypes?
– AA = ___________________________
– Aa = ___________________________
– aa = ___________________________
2. Draw a punnett square & record the genotypes:
Albinism – Recessive Trait
3.
4.
5.
6.
7.
Children?
Gender of children?
Generations?
Carriers?
Assume the 3rd child mated with an albino male,
how likely is it that their child will be albino?
Albinism – Recessive Trait
1.
2.
3.
4.
5.
Record genotypes.
Children from original couple?
Grandchildren?
Grandchild gender?
Carriers?
Dwarfism
DD
dd
1.
2.
3.
4.
Affected individuals?
Dominant or Recessive Trait?
Genotype of A, B, C, D?
Generations?
Nondisjunction
• Nondisjunction – homologous chromosomes fail
to separate properly during meiosis cells having
abnormal number of chromosomes 
chromosomal disorders.
– Normal = 46
– Any number other than 46 = Abnormal
• Only 1 chromosome copy = monosomy
• 3 chromosomes of one type = trisomy
– Nondisjunction = serious disorders  often fatal
Nondisjunction
Down Syndrome
• Also called Trisomy 21
• Nondisjunction of
chromosome #21
• Symptoms: distinct facial
features, mental retardation,
short stature, heart defects.
• Affects 1/800
• Frequency increases with
mother’s age.
Nondisjunction
• Can occur with autosomes and sex chromosomes.
– Turner’s Syndrome – female is missing X chromosome
– Triple X Syndrome – female with 3 X chromosomes
– Klinefelter’s Syndrome – male with XXY
– Death – male just receives Y chromosome & no X
Fetal Testing
• Tests that provide genetic information on
developing fetus.
• Benefits  diagnosing chromosomal abnormalities
early
• Risks  miscarriage & infection