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