Chapter 11 Inheritance & Heredity

When is a recessive trait expressed?

• When an individual is homozygous recessive for that particular trait

When someone is heterozygous for a trait, they are considered a…carrier

Recessive Genetic Disorders:

• 1. Cystic Fibrosis-1 in 3500-the gene that codes for a specific protein is defective-produces excess mucus-digestive/respiratory problems

2. Albinism:

-1 in 17,000-genes do not produce normal amounts of melanin pigment-skin UV susceptible-lack of color in skin/hair/eyes

http://www.knowlton-family.co.uk/Albinism/Photo.htm

3. Galactosemia:

-1 in 50,000-absence of gene that codes for enzyme that breaks down galactose-mental disabilities-liver/kidney problems

4. Tay-Sachs Disease-1 in 2500-absence of enzyme that breaks down fatty substances-mental disabilities/build up in brain-lipids build up in central nervous system-death usually by age 5

If a disorder is considered to be a dominant genetic

disorder, how many affected alleles do you

have? •1 or 2

Dominant Genetic Disorders:

1. Huntington’s Disease-1 in 10,000-gene affecting neurological function is defective-onset usually in the 40’s-ability to move deteriorates

2. Achondroplasia

-1 in 25,000-gene that affects bone growth is abnormal-short arms/legs-large head

What is a pedigree?

• A diagram that traces the inheritance of a particular trait through several generations

• May or May not show carriers…be careful!– If someone is a carrier, their

genotype must be heterozygous

Common symbols: see board

11.2 Complex Patterns

Mendelian Inheritance: follows typical dominant/recessive rules

Non-Mendelian Inheritance: does NOT follow typical rules

Types of Non-Mendelian Inheritance

A. When traits are inherited in this pattern, the phenotype is intermediate between the two homozygotes. What is this pattern called?

Incomplete DominanceExample: Red x white = pink

Incomplete Dominance

B. What is codominance?:results in both phenotypes being expressed

Example: black x white = black/white spotted

Codominance

How is sickle-cell anemia passed? Heterozygous: lead normal life; may

have a FEW symptoms Homozygous for trait: have full-blown

sickle cell…health issues result because the blood does not transport adequate oxygen.

How are sickle-cell anemia & malaria related to each other?Those that are heterozygous for the sickle-cell trait have a HIGHER resistance to malaria

C. What are ‘traits controlled by more than 2 alleles’ called?

Multiple alleles

Explain how blood types are passed on:ABO blood groups:

IA = type AIB = type Bi = type O

IA & IB are codominant/ i is recessive

Multiple Alleles

What is epistasis?The effect where one

allele hides behind the effects of another allele.

Example: Dog fur*E determines dark pigmentee will have no pigment*B determines how dark

EEbb or Eebb = chocolate browneebb, eeBb, eeBB = yellow coat

How is it determined if something is going to be male or female?

XX vs. XY

What is an autosome? 1st 22 pairs of chromosomes-another name for body cells

What are Barr bodies?-located in nucleus-inactivated chromosomes

D. What are sex-linked traits?:traits controlled by genes located on sex chromosomes (23rd pair)

What gender can get a X-linked trait?Males AND Females.-males are more likely because they only need one affected X to get it, instead of females, which need 2

What gender can get a Y-linked trait?Only males…females do not have Y

Red-green color blindness & hemophilia are both X-linked

E. What is ‘the inheritance pattern of a trait that is controlled by two or more genes’?

Polygenic Inheritance

Name a human trait that is passed through polygenic inheritance:

skin color, hair color, height

Polygenic Inheritance

Give at least 5 examples of external environmental

influences:

1. Sunlight2. Temperature3. Diet4. Exercise5. Water

11.3 What is a karyotype?

A micrograph that shows the pairs of homologous chromosomes-arranged in decreasing size

How many pairs are in a karyotype?

23 pairsHow many of those pairs are autosomes? 22

How many of those pairs are sex chromosomes? 1

What is nondisjunction?

Condition where sister chromatids fail to separate properly

What do you call it when you have one of a particular type of chromosome?

monosomyWhat do you call it when you have three chromosomes of one kind?

trisomy

Down Syndrome is an example of nondisjunction. What is the scientific name for the most common form down syndrome?

Trisomy 21

Trisomy 21 (Down Syndrome)

Other disorders…

Turner’s Syndrome-XO

-female with only one X

-can cause infertility, masculinity symptoms, etc.

Kleinfelter’s Syndrome

-XXY or XXXY, etc.

-male with too many X’s

-Can cause infertily, feminine symptoms