Download Chapter 12 - Inheritance Patterns and Human Genetics

Chapter 12 - Inheritance Patterns and Human Genetics
I. Chromosomes and Inheritance
A. Terms
1. Autosome- any chromosome but the sex chromosomes
[humans have 44 (22 pairs)]
2. Sex Chromosomes- determine the sex of the organism
 in humans X and Y determine the sex in the offspring
 XX= female
 XY= male
B. Sex Determination (Morgan)
1. Drosophila (fruit fly)
a. 4 pairs homologous chromosomes (1 X/Y pair and 3
autosomal pairs)
b. one pair different in males
1) chromosome same in both sexes called X
shorter, hooked shaped one in male called Y
2) hypothesized them to be sex chromosomes
(determine sex)
c. males XY and females XX
1) male gametes contain X or Y , female only X
2. Sex Linkage (Morgan) (showed that specific gene was on a
chromosome)
a. hypothesized more genes on X since it is larger
b. fruit flies usually have red eyes
(found a male with white eyes)
F2
c. white eyed males X red eyed female (homozygous)
F1 all red eyed
red eyed male
X red eyed female (now will be
heterozygous)
3 red eyed : 1 white eyed (all white eyed were males)
d. hypothesized the gene was on the X chromosome
e. sex linkage - presence of a gene on a sex chromosome
(trait is linked to sex)
1) X linkage and Y linkage (holandric handout)
C. Linkage Groups
1. Morgan sometimes found traits separating independently and
other traits did not
2. linkage group - all the genes located on one chromosome
a. 2 or more genes on same chromosome said to be linked
b. experiments show genes are linked on all chromosomes
P1 GGLL X ggll
F1 GgLl (all gray body, long wing)
GgLl X GgLl
Morgan hypothesized the following:
F2 not linked should be 9:3:3:1
linked should be 3:1
results of cross approximately 3:1 (therefore should be linked), but
cross unexpectedly produced several gray short winged (Ggll) and
several black long winged (ggLl)
3. crossing over
a. Morgan test crossed an F1 with homozygous recessive
GgLl X ggll
some offspring gray, short and some black, long
b. not possible if G and L always inherited together
c. hypothesized alleles on 2 homologous chromosomes
exchanged places (crossing over)
1) occurs in synapsis (prophase I)
2) increases variety in offspring
If either had not been linked…
D. Chromosome Mapping
1. crossing-over showed genes were at fixed positions
on chromosomes
2. genes in a line like a string of beads
3. the farther apart 2 genes are the greater the
frequency of crossing-over
4. results of crossing-over appear in offspring
as new combinations of traits
a. the greater the % of offspring that show
the new comb., the farther apart the genes are
5. breeding experiments can determine how
frequently genes for particular traits are separated
in the offspring
6. chromosome map - shows linear sequence
of genes on chromosome
II. Human Genetics
A. Genetic Traits and Disorders
1. Single allele traits (more than 250)
a. can be due to autosomal recessive or dominant alleles
(Table 12-1 p. 228)
1) cleft chin, freckles, free earlobes, webbed fingers
(dominant)
2) PKU, sickle cell anemia (recessive)
PKU can’t make enzyme to break down amino acid,
phenylalanine - it accumulates, destroys brain cells severe mental retardation
b. genetic marker - short section of DNA that is known to
have close association with particular gene nearby
2. Multiple allele traits
a. controlled by 3 or more alleles of same gene
b. blood type alleles - IA, IB, i
1) IA and IB are codominant (both expressed when
together) and both are dominant to i
2) phenotype
genotype
type A
IAIA : IAi
type B
IBIB: IBi
type AB
IAIB
type O
ii
3) example I A IB X IBi
genotypic ratio
phenotypic ratio
3. Polygenic traits (controlled by 2 or more genes)
a. each gene has a small additive effect
b. continuous variation shown in the trait
1) skin color, eye color, foot size, height, weight,
intelligence
4. Complex Characteristics
a. characters that are influenced strongly by environment
and by genes
b. most complex traits are also polygenetic traits
c. skin color- expose to the sun causes the skin to become
darker, no matter what the genotype is
d. Height- influenced by an unknown # of genes, but also a
person’s nutrition and diseases
e. breast cancer, diabetes, heart disease, stroke, and
schizophrenia
5. X-linked traits
a. color-blindness, hemophilia, Duchenne muscular
dystrophy
b. many other genes code for proteins needed for normal
functions
6. Sex-influenced traits (baldness, beard and breast development)
a. presence of male or female sex hormones influences
expression of certain traits
b. pattern baldness
Pattern baldness
Phenotypes Male
Female
Bald
BB and Bb
BB
Normal hair bb
bb and Bb
*Presence of male hormone causes single B to be expressed (if there are
two “b’s” then imagine that only one will change to “B.”
http://highered.mcgrawhill.com/sites/0073525286/student_view0/chapter4/gie__sexinfluenced_inheritance_-_pattern_baldness_in_humans.html
c. genes on autosomes so both sexes can have same
genotype, but the trait only expressed in one sex
7. Nondisjunction disorders (Fig. 12-3 p. 230) referring to
humans
a. monosomy - 45 chromosomes in zygote (one copy of a
particular chromosome)
b. trisomy - 47 chromosomes in zygote (three copies of a
particular chromosome)
c. Down syndrome - 47 chromosomes (trisomy #21)both
sexes
d. Turner syndrome - 45 chromosomes (XO) - females
e. Klinefelter syndrome - 47 chromosomes (XXY) - males
f. Super female - 47 chromosomes (trisomy of X) (XXX)
g. XYY (males)
Review Questions
C. Detecting Genetic Disorders
1. genetic screening (for those with history of genetic disorders)
- karyotype, examine blood for presence or absence of
certain proteins
2. genetic counseling - medical guidance informing individuals
of potential problems for offspring
3. amniocentesis - some amniotic
fluid removed at 14-16 weeks
(analyze fetal cells and proteins,
make karyotype)
4. chorionic villi sampling - sample of tissue between uterus
and placenta at 8-10 weeks (villi same genetic makeup as
embryo) - make karyotype
5. genetic screening after birth for PKU
6. ultrasound – sonogram (use sound waves)
7. fetoscopy - view fetus, take picture
III. 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)
A. Transfusions
1. concerned with antibodies of recipient
a. antibodies agglutinate (clump) antigens
Type
Antigens
Antibodies
Can receive Can donate
from
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
Picture
B. Rh Factor
1. another antigen on RBC’s
85% Rh + (have antigen)
15% Rh - (no antigen)
2. Rh + blood given to Rh - person
a. Rh - person develops antibodies against Rh antigen
b. little problem on 1st transfusion but subsequent one
could be fatal
C. Erythroblastosis fetalis
(RBC) (destruction) (fetus)
1. mother Rh -, father Rh +, baby Rh +
2. 1st child (Rh +)
a. if any leakage across placenta to uterine blood vessels,
mother will make antibodies against Rh antigen
b. antibodies not made fast enough to affect baby
3. subsequent child (Rh +)
a. antibodies already present will destroy baby’s RBC’s
b. can transfuse baby with Rh - blood in utero (dangerous)
4. Rhogam shot
a. given to mother both before delivery and within 72 hours
of birth of child
b. destroys any Rh + blood antigens mother may have
gotten from child (contains anti Rh antibodies) in order
to prevent mother from making antibodies (making
antibodies could cause anemia, kidney failure, shock in
mother) which would attack baby’s blood cells