Transcript chapter twelve INHERITANCE PATTERNS AND HUMAN GENETICS

INHERITANCE PATTERNS
AND HUMAN GENETICS
Chapter 12
Quick review…
Genetics is the field of biology devoted to
understanding how characteristics are
transmitted form parents to offspring.
Generations:
P Tall x Short
F1 Tall (tall is dominant)
F2 3 Tall : 1 short
• The DOMINANT factor/gene
masks the effect of the other
factor in the F1 generation.
– Use CAPS ex. T for tall
• The RECESSIVE
factor/gene’s effect can only
be seen in the P generation or
F2 generation when the
DOMINANT gene is absent.
– Use lower case ex. t for short
MENDEL’S 2 LAWS:
#1 LAW OF
SEGREGATION:
• A pair of factors is
segregated, or separated,
during the formation of
gametes.
#2 LAW OF INDEPENDENT
ASSORTMENT:
• Factors for different
characteristics are
distributed to gametes
independently.
GENOTYPE is the genetic
makeup of the organism.
TT = homozygous
dominant
Tt = heterozygous
tt = homozygous
recessive
PHENOTYPE is the physical
appearance of that
organism.
Ex. Tall or short
MENDELIAN INHERITANCE- DOMINANCE…. 2 phenotypes only.
If someone has the dominant phenotype but you aren’t sure of
Their genotype… use a pedigree (humans) or do a test cross.
Other Patterns of Inheritance:
1. Incomplete Dominance- blending seen in
heterozygote (ex. pink flowers, brown hair)
2. Codominance- both dominant and recessive
phenotypes seen in heterozygote. (ex. type AB
blood, roan horse fur color)
3. Polygenic- more than 1 gene determines the
phenotype. (Ex. Eye color, Hair color aabbcc)
4. Multiple alleles- more than just 2 alleles
(Ex. Blood type = A allele, B allele, O allele is
recessive.)
EX. Polygenic Inheritance- when
the trait is controlled by multiple genes so
many phenotypes are possible.
AaBbCc x AaBbCc
Huge variety in possible
Phenotypes of the offspring
- skin, hair, eye color
- foot size
- nose length
- height
Multiple alleles- trait controlled by
three or more alleles.
-Ex.
ABO blood groups:
- TYPE A
- TYPE B
- TYPE AB Shows
Codominance!
- TYPE O
The process of using
phenotypes to deduce
genotypes
When someone has
the DOMINANT
phenotype you are
uncertain of their
genotype.
TT
or
Tt
When someone has
the recessive
phenotype you can
be sure of their
genotype.
tt
DIRECTIONS:
• For each of the following single gene/ Mendelian
traits, write your phenotype on the line.
• Write as much of your genotype as you can be
certain.
- both alleles if RECESSIVE (rr)
- one allele if DOMINANT (R __)
• Repeat the process by studying two blood
relatives (parents work the best)
• Use a pedigree.
1. HAIR TYPE
very curly
or
TT, Tt
straight
tt
2. Hair Color
Dark
or
DD, Dd
Light
dd
3. Hair Line
Continuous or Widow’s Peak
WW, Ww
ww
4. Iris Color
Pigmented
EE, Ee
or
Blue
ee
5. Lens of Eye
Astigmatism or
AA, Aa
Normal
aa
6. Nose Shape
Roman (convex) or Concave
NN, Nn
nn
7. Ear Lobe
Free/Long or Attached
LL, Ll
ll
8. P.T.C. Taster
Taster
or
Nontaster
RR, Rr
rr
9. Tongue Curling
Can curl or
Can not curl
CC, Cc
cc
10. Point of chin
Dimpled
or
NO dimple
II, Ii
ii
11. Number of Fingers
Polydactylism or Normal #
PP, Pp
pp
12. Little Finger
Bent or Straight
FF, Ff
ff
13. Hypermobility of Thumb
Loose Jointed
or
Not so
HH, Hh
hh
14. Thumb Extension
Hitchhiker’s Thumb or Not
H’H’, H’h’
h’h’
15. Middigital Hair
Present
or
Absent
MM, Mm
mm
16. Palmar Muscle
Normal (2) or Long (3)
UU, Uu
uu
17. Allergies
Tendency Or No tendency
A’A’, A’a’
a’a’
18. Veins
Varicose
VV, Vv
or
Normal
vv
19. White Skin Spotting
Freckles
or
No freckles
SS, Ss
ss
20. White Forelock
LIST OF STRANGE MENDELIAN TRAITS
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Ear wiggling
Misshapen toes or teeth
Inability to smell musk or skunk
Lack or teeth, eyebrows, nasal bones or
thumbnails
Whorl in the eyebrow
Tone Deafness
Hairs that are triangular in cross-section or
that have multiple hues (colors)
Hairy knuckles, palms, soles, or elbows
Egg-shaped pupils
Magenta urine after eating beets
Sneezing fits in bright sunlight.
DNA in chromosomes contain
information to make proteins.
Geneticists use their
knowledge of DNA
and the way
chromosomes
behave to study how
traits are inherited
and expressed.
The parent’s genotype can be a
gene pair of either:
- TT homozygous dominant
- tt homozygous recessive
- Tt heterozygous
The parent can make gametes
(sperm or eggs), through the
process of MEIOSIS, that have
either one or the other of the
gene pair in it.
SEX DETERMINATION
MORGAN’s Fruit fly (Drosophila)
breeding experiments of
the 1900’s revealed the
identity of sex chromosomes.
In males they were different
XY; in females they were the
same XX.
The other chromosomes
(22 in humans) are
AUTOSOMES.
The male determines the sex
of the offspring…
<--The FEMALE XX can
only make X gametes.
<--The MALE XY can make
either X gametes or Y
gametes.
SEX LINKAGE
traits caused by genes found on a
sex chromosome
X-LINKED GENES:
Genes located on the X chromosome.
• Women can be carriers.
• Ex. gene for ALD (Lorenzo’s Oil)
Y-LINKED GENES:
Genes located on the Y chromosome.
Only males show these traits.
Ex. SRY- triggers male development
of testis.
Males exhibit X-linked traits more
often than women because they
only have ONE X chromosome.
• Females have two XBXb or sex linked
genes.
• Females can be “carriers” of the bad
gene yet not show the disease..
• Males only have one X or sex linked
gene since they are XbY.
• Males have a higher chance of
having the condition than if it were on
an autosome.
• THERE IS NO HETEROZYGOUS for
men.
X-linked Examples:
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Eye color in Drosophila
Red-green colorblindness
Male Pattern Baldness
Hemophilia
Duchenne Muscular Dystrophy
ALD (adreno leuko dystrophy)
What do you see in
the circle?
Do your bruises
look like this?
If a carrier (woman) for hemophilia marries a normal man, what are the
chances of having kids who are hemophiliacs? Who are not?
What if the man is a hemophiliac???????
LINKAGE
GROUPS
Genes located on
the same
chromosome are
said to be linked.
Linked genes tend
to be inherited
together.
Examples: Hair color and intelligence are linked in humans.
fur color and deafness in cats are linked.
I’m kidding about intelligence
and hair color being linked.
• But if they were
linked…
• What would the
phenotype(s) be
of children of a
dumb,blonde &
smart,brunette
smart,brunette
• If that smart,brunette had kids w/ a
dumb,blonde
What kinds of kids could they have?
What is the probability of each?
Parental
Phenotypes:
• Smart, brunette
• Dumb, blonde
Recombinant
Phenotypes:
• Smart, blonde
• Dumb, brunette
Linked genes result in traits that tend
to be inherited together…
If you do a test cross of your
Heterozygote you can see if the genes
Are linked (5:5:1:1) or not (1:1:1:1).
If the intelligence and hair color genes were linked, we’d only
see smart-brunettes and dumb-blondes. (HA HA)
So, since there are smart blondes- are these genes on
separate chromosomes or on the same chromosome yet
separated by crossing over?????
Chromosome maps can be
created by conducting
breeding experiments.
Linked genes that separate by
crossing over X% of the time
are X map units apart.
Compare 4 phenotype
inheritance to 2 phenotype
inheritance.
Genes can now be placed on
a chromosome in some order.
• Genes W and Z separate by crossing
over 20% of the time.
• Genes W and X separate by crossing
over 5% of the time, and
• genes Z and X are separated by
crossing over 25% of the time.
• CONSTRUCT A CHROMOSOME MAP.
• Z
W
X
• I----20-------I--5--I
Mutations, Disease, & Human
Mendelian Traits
1.
2.
3.
4.
Where they occur/ significance.
Types: Chromosome or Gene
Diseases & Inheritance Patterns.
Using Phenotypes to deduce
Genotypes
1.
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Germ cell mutation
occurs in the gametes
does not effect the organism
may be passed on to offspring if fertilized
2.
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Somatic mutation
occurs in the organism’s body cells & can affect the organism
ex. Skin cancer & leukemia
are not passed on to offspring
3. Lethal mutation
• causes death (often before birth)
• is not passed on if death occurs before reproduction
4. Beneficial mutation
• result in phenotypes that are beneficial.
• beneficial phenotypes lead to increased reproduction.
Mutation: a change in the DNA sequence.
A) chromosome mutations (affects many genes)
B) gene mutations (one gene)
A) Chromosome mutations:
Cross over errors:
1. Deletion- loss of a piece due to breakage.
2. Inversion- a piece is attached upside down.
3. Translocation- a piece reattaches to a nonhomologous chromosome.
Segregation Error:
1. Nondisjunction- failure of homologous chromosomes
to separate during meiosis.
ex. Down Syndrome = Trisomy 21 (egg usually has 2
of #21)
Chromosome Mutations
nondisjunction
B) Gene mutations/ point
mutationsare nucleotide
differences.
1. Substitution- one
nucleotide is switched for
another.
- ex. sickle cell anemia
2. Frame shift mutationsoccur when nucleotides
are added or removed
either more or fewer than
3 nucleotides at a time.
- addition
- deletion
GENE MUTATION: SUBSTITUTION
ex. Sickle Cell Gene- Hemoglobin
INHERITANCE OF GENETIC
DISEASES follow different
Patterns of Inheritance
1.
2.
3.
4.
Single allele Dominant
Single allele recessive
X-linked
Sex influenced
PEDIGREE ANALYSIS
•
Humans have about 100,000 genes.
•
Most studies are of disease-causing genes.
- easy to track through generations..
•
A pedigree is a family record that shows how a
trait is inherited over several generations.
1. Single allele DOMINANT- need only one
gene to have the disease.
- huntington’s disease (1/10,000) Hh
- dwarfism Dd
- cataracts Cc
- polydactyly Pp
PATTERN: effected individuals in every generation of
both male and female sex.
2. Single allele recessive- The individual needs
two genes to have the disease.
-
Albinism aa
Cystic fibrosis (1/200 whites) cc
Phenylketonuria (1/1800) pp
Hereditary deafness dd
Sickle cell anemia (1/500 African-Americans) sc sc
Tay-Sachs disease (1/1600 European Jews) tt
Pattern: 2 healthy parents have effected child of either sex.
3. X-Linked- women need two genes, men
need only one gene.
- colorblindness XcXc
XcY
-hemophilia (1/7000) XhXh
XhY
-muscular dystrophy (1/10,000) XdXd
XdY
-Icthyosis simplex
-ALD
Pattern: more common in males,
Can kip generations.