Download Standard Biology Chapter 27 Human Genetics

Standard Biology
Chapter 27 Human
Genetics
27.1 The Role of Chromosomes
Very complicated compared to peas!
1
Chromosome Number
Each human sperm and
egg has 23 different
chromosomes
Each human body cell
has 46 chromosomes
(23 pair)
Different organisms
have different number
of chromosomes- most
are paired
(Homologous)
Table 27-1
Chromosome Number
p. 566 (next slide)
2
Chromosome Number
Animal or Plant
#Chromosomes
Body Cell
#Chromosomes
Sex Cell
Red Clover
12
14
16
20
24
38
44
78
6
7
8
10
12
19
22
39
Pea
Onion
Corn
White Pine
Cat
Rabbit
Chicken
3
A Way to Tell Chromosome
Number
Amniocentesis: a look at chromosomes
in fetus



Performed 15-20 weeks gestation
Needle inserted into mother’s abdomen
into amniotic fluid surrounding the fetus.
Some fluid removed which also contains
cells from the fetus.
Cells grown for 10 days, watch for dividing
cells.
4
A Way to Tell Chromosome
Number
Amniocentesis,
cont.


Study the dividing
cells (easy to see
chromosomes as
sister chromatids)
Arrange
chromosomes in a
karyotype
5
Karyotype
Chromosome smear
Karyotype
6
Karyotype
Ordered arrangement of chromosome pairs
by number
Largest is #1, smallest is #22
Match up banding pattern on chromosomes
Can determine sex of fetus by sex
chromosomes



XY is male
XX is female
Y chromosome is much smaller
than X
7
A Way to Tell Chromosome
Number
Chorionic villi
sampling (same idea
as amniocentesis)



Use a piece of the
placenta
Can do earlier in
pregnancy and get
results sooner
May not be as
accurate
8
Sex- A Genetic Trait
Chromosomes # 1-22 are autosomes
Don’t determine sex
Are the same in males and females
Called non sex or body chromosomes
Males are XY so make X sperm and
make Y sperm
Females are XX so only make X eggs
9
Sex- A Genetic Trait
10
Sex- A Genetic Trait
Males determine the sex of the child
11
Standard Biology
Chapter 27 Human
Genetics
27.2 Human Traits
12
Humans have many traits: those
you can see and those you can’t.
13
Survey of Human Traits
Dominant traits


Freckles
Dimples
14
Survey of Human Traits
Recessive traits




Attached ear lobes
Straight hair
Nonroller tongue
Short eyelashes
15
Survey of Human Traits
L=long eyelash trait
l=short eyelash trait
Both parents are heterozygous and
have long eyelashes
Expect 3:1 long to short eyelashes in
offspring or expressed as a %, expect
75% long eyelashes children and 25%
short eyelashes children
16
Survey of Human Traits
L=long eyelash
trait
l=short eyelash
trait
Both parents are
heterozygous and
have long
eyelashes
L
l
L
l
LL
Ll
Ll
ll
17
Incomplete Dominance
One trait not completely dominant over
the other
Heterozygotes show in between trait
Example: Snapdragon flower color
R=red, r=white; Parents are pink
(heterozygous)
18
Incomplete Dominance
19
Incomplete Dominance
Example: Sickle cell
Anemia p. 574


RR=round red blood
cells
R’R’= sickle red
blood cells
20
Incomplete Dominance
Sickle cell Anemia



Serious health
problems because
sickle cells cannot
carry enough oxygen
Causes pain and
fatigue (tiredness)
because sickle cell
block capillaries
Sickle cell Anemia
most in African
Americans
21
Incomplete Dominance
Sickle cell Anemia

RR’= both round and
sickle red blood cells
Usually no health
problems because
enough health red
blood cells to carry
oxygen
22
Blood Types in Humans
Blood Type
Genes
Dominant
Recessive
A
AA or AO
A
O
B
BB or BO
B
O
AB
AB
A and B
none
O
OO
none
O
23
Blood Types in Humans
Three genes: A, B,
and O
A and B are
dominant to O
A and B are
codominant
24
Genes on the X Chromosome
Sex chromosomes carry genes



X chromosome has many genes because it
is a large chromosome
Y chromosome has few genes because it
is a small chromosome
X chromosome and Y chromosome do
have the same genes
25
Genes on the X Chromosome
Females are XX have 2 copies of each gene
Males are XY have 1 copy of X genes and 1
copy of Y genes
26
Color Blindness
27
Color Blindness
Color blindness gene
on X chromosome p.
576
Red and green shades
look alike
Females 2 copies of
color blindness gene;
color blind if both
copies are recessive
(cc)/ not color blind if
heterozygous (Cc) or if
homozygous dominant
(CC)
28
Color Blindness
Males 1 copy of color blindness gene;
color blind if the one is recessive (c)/
not color blind if the one gene is
dominant (C)
Males are more likely to be color blind
Females are carriers when they are
heterozygous (Cc)
Example: Normal male (XCY), female
carrier (XCXc)
29
Color Blindness
Example:
Normal male
(XCY)
XC
XC
XCX
C
female carrier
(XCXc)
Y
XCY
XC
XCXc
XcY
30
Color Blindness
XC
Example:
Color blind male
(XcY),
Xc
female carrier
(XCXc)
Y
XCXc
XCY
Xc
XcXc
XcY
50% color blind females
50% color blind males
31
Color Blindness
This is called a sex-linked genes
because it is located on the X
chromosome
Another sex linked gene is hemophilia
(blood clotting disorder)
32
Standard Biology
Chapter 27 Human
Genetics
27.3 Genetic Disorders
About 600 babies born each day in the U.S. with a disorder,
some are genetic disorders.
33
Errors in Chromosome Number
Can happen if baby has more than 46
chromosomes
Can happen if baby has less than 46
chromosomes
Can happen if sperm or
egg have more or less
than 23 chromosomes
34
Errors in Chromosome Number
Error happens
during meiosis
when sister
chromatids don’t
separate correctly;
get one sex cell with
22 the other with 24
chromosomes
Can happen to any
of your
chromosomes
35
Down Syndrome (Trisomy 21)
3 copies of
chromosome #21
36
Down Syndrome (Trisomy 21)
mental retardation, heart problems, facial
abnormalities
37
Down Syndrome (Trisomy 21)
1 in 700 births
Increasing
incidence with
increasing age of
mother
38
Turner’s Syndrome
Female with only 1 X
chromosome (X0)
No neck, short,
mental retardation,
do not develop
secondary sex
characteristics
1 in 5000 births
39
Genetic Disorders and Sex
Chromosomes
Hemophilia



Failure of blood to
clot
Bruising
Significant in royal
families of Europe
(Russia)
40
Genetic Disorders and Sex
Chromosomes
Color blindness

Cannot distinguish red/green shades
41
Genetic Disorders and
Autosomes
Dyslexia (dominant
gene)


“Word blindness”
See and/or write
letters and words
backwards, difficult
to learn to read
42
Genetic Disorders and
Autosomes
PKUphenylketonuria


Amino acid
phenylalanine can’t
breakdown in body,
builds up causing
mental retardation
Now tested at birth
and babies are given
special diet with low
levels of this amino
acid
43
Genetic Counseling
Looks at family history to determine
genetic disorder
Use of genetics to predict and explain
traits in children
Genetic counselor- person trained to
interpret medical information and
counsel patients
44
Genetic Counseling
Answer questions:






How did the baby get this
disorder?
If the baby is healthy,
does it have a problem
gene?
Is the trait dominant or
recessive?
What will happen to
baby’s health as it gets
older?
What are the chances
that future children will
have the trait?
What medical treatment
is available?
45
Genetic Counseling
Genetic counselors use a pedigree (diagram
of family history) that can show how a
certain trait is passed along in a family
46
Cystic Fibrosis
Recessive genetic
disorder
Symptoms of disease:
excess and thick
mucus, respiratory
problems and digestive
problems
Child with the disease
1 in 4 chance if parents
are heterozygous
F
f
F
FF
Ff
f
Ff
ff
47
Cystic Fibrosis Pedigree
1
II
III
IV
2
1
I
1
2
3
5
4
3
2
1
4
2
3
4
5
48
Pedigree Analysis
Are females
Are males
Shaded in circles and squares are
affected individuals
Roman Numerals (I – IV) are
generations
Lines across
represent
mating
Lines down represent offspring
49
Understanding the Pedigree
Count the number of affected males and
affected females. If most males and few or
no females most likely sex linked trait.
Look at the affected individuals. If every
individual with the trait has a parent with the
trait then this trait is dominant. If nonaffected parents produce an offspring with
the trait then it is recessive.
Determine the phenotype and genotype of
every individual
50
Understanding the Pedigree
Affected males: 1
Means not sex
linked
Affected females: 2
No affected individual has parent with the
trait, means recessive
All affected individuals would be
homozygous recessive, aa
All parents of affected individuals would be
heterozygous, Aa
Siblings of affected individuals would be
heterozygous (Aa) or homozygous dominant
(AA)
51
Cystic Fibrosis Pedigree
I
II
III
IV
1
2
Aa
Aa
1
2
3
?
Aa
aa
5
4
?
?
1
2
3
4
?
?
Aa
Aa
1
2
?
aa
3
4
?
aa
5
?
? Would be AA or Aa
52