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Human HereditySections 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/16243-Gallery-8-Human-female-karyotype.html
Pedigree Charts
Source: http://www.citruscollege.edu/lc/archive/biology/Pages/Chapter10-Rabitoy.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_2531003_spotted-cat-with-no-tail-stands-attentive-and-alert.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-nondisjunction-9351_3.JPG
Some Nondisjunction Disorders
1. Down syndromea. Autosomal nondisjunction
b. 3 copies of chromosome 21 (“trisomy 21”)
Source: http://www.buzzle.com/articles/teaching-children-with-down-syndrome.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 sex-
determining 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