Transcript Human Heredity Section 14-1

Human Heredity
Sections 14-1 and 14-2
Objectives:
7.2 Interpreting inheritance patterns
shown in graphs and charts
8.5 Relating genetic disorders and disease
to patterns of genetic inheritance
Examples: hemophilia, sickle cell anemia,
Down's syndrome, Tay-Sachs disease,
cystic fibrosis, color blindness,
phenylketonuria (PKU)
Human Chromosomes
• How many chromosomes do we have?
Answer: 46
• How many of those are sex
chromosomes?
Answer: 2
• What are the possible combinations of
sex chromosomes?
Answer: XX or XY
• What are the other chromosomes
called?
Answer: autosomes
Karyotype:
• Def: a picture
of
chromosomes,
taken in
mitosis
metaphase,
and paired up.
• Why would the
picture be
taken at this
point?
Source: http://www.dnalc.org/view/16243Gallery-8-Human-female-karyotype.html
Pedigree Charts
Source:
http://www.citr
uscollege.edu/
lc/archive/biol
ogy/Pages/Ch
apter10Rabitoy.aspx
Pedigree Charts Activities
1. Class Activity: Figure 14-3, p.342
2. Individual Assignment: Problem Solving,
p.343. Add the following questions:
a. Identify the genotype of each individual.
b. Is albinism a dominant or recessive trait?
c. What is the probability of the second-generation
couple having another albino child?
Sex-Linked Genes
• The X chromosome is much larger
than the Y chromosome, carrying
many more genes. (See Figure 14-12,
p.350)
• More than 100 sex-linked genetic
disorders have been mapped to the X
chromosome.
Sex-Linked Genes
• Since males have only one X
chromosome, if an allele for a disorder is
present on that chromosome, the trait will
be expressed.
• Common sex-linked disorders:
1. Colorblindness
a. Color vision is controlled by three genes
on the X chromosome.
b. 1 in 10 males in the U.S. have some form
of colorblindness.
2. Hemophilia – 2 genes on the X chromosome
help control blood clotting (1/10,0000)
3. Duchenne Muscular Dystrophy – (1/3000)
X-Chromosome Inactivation
• Females have two X chromosomes.
• One of those chromosomes is
switched off, becoming a Barr body --a dense (but inactive) region in the
nucleus.
• Males cannot switch off their X
chromosome.
Source:
http://www.123rf.com/photo_2
531003_spotted-cat-with-notail-stands-attentive-andalert.html
Chromosomal Disorders
• Nondisjunction of homologous
chromosomes during _____________,
would give gametes abnormal
numbers of chromosomes.
• When these gametes become diploid
again, the number of chromosomes is
abnormal.
• Some of these zygotes cannot
survive; others produce offspring with
genetic disorders.
Chromosomal Nondisjunction
Source: http://drugline.org/img/term/meiotic-nondisjunction9351_3.JPG
Some Nondisjunction Disorders
1. Down syndrome
a. Autosomal nondisjunction
b. 3 copies of chromosome 21 (“trisomy
21”)
Source:
http://www.buzzle.co
m/articles/teachingchildren-with-downsyndrome.html
Some Nondisjunction Disorders
2. Sex chromosome disorders:
a. Turner’s syndrome – females with only
one X chromosome
1) Fertile
2) Sex organs do not develop at puberty
b. Klinefelter’s syndrome – males with too
many X chromosomes
1) Interferes with meiosis, usually not
permitting reproduction
2) No known cases of babies born
without an X chromosome, so it must
contain genes important for survival.
Some Nondisjunction Disorders
2. Sex chromosome disorders:
c. Y chromosome contains a sexdetermining region necessary to
produce male sexual development
1) Can develop even in the presence of
multiple X chromosomes
2) Will not develop if this region of the Y
chromosome is absent.
DISORDER DETECTIVES ACTIVITY
• http://www.youtube.com/watch?v=th6Njr-qkq0