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

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How many chromosomes do we have?

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Answer: 46 How many of those are sex chromosomes?

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Answer: 2 What are the possible combinations of sex chromosomes?

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Answer: XX or XY What are the other chromosomes called?

Answer: autosomes

Karyotype:

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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.citr

uscollege.edu/ lc/archive/biol ogy/Pages/Ch apter10 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

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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

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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 Dystr ophy – (1/3000)

X-Chromosome Inactivation

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Females have two X chromosomes.

One of those chromosomes is switched off, becoming a Barr body -- a dense (but inactive) region in the nucleus.

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Males cannot switch off their X chromosome.

Source: http://www.123rf.com/photo_2 531003_spotted-cat-with-no tail-stands-attentive-and alert.html

Chromosomal Disorders

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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 syndrome a. Autosomal nondisjunction b.

3 copies of chromosome 21 (“trisomy 21”)

Source: http://www.buzzle.co

m/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 b.

2) Sex organs do not develop at puberty 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