Top5-Ch6-P135-146

Question 1

Explain HGPS

Answer 1

• Hutchinson-Gilford Progeria Syndrome (HGPS) causes premature aging
• About 50 patients worldwide
• Fatal by about 13 years of age due to age related organ failure (often coronary problems)
• Dominant autosomal inheritance pattern (usually)
• Caused by mutation in the lamin A (LMNA) gene

Question 2

Study of human inheritance needs three special tools. What are they?

Most phenotypic traits are influenced by both ____ and ______. Difficult to separate the two. Results must be interpreted ______.

Answer 2

1. pedigrees
2. twin studies
3. adoption studies

genotype and environment

prudently

Question 3

What are three difficulties with human genetic study, even though much is know about human anatomy, physiology and biochemistry

Answer 3

1. controlled matings not possible
2. long generation time
3. small numbers of offspring

Question 4

What is a pedigree?

Answer 4

a pictorial representation of a family history, essentially a family tree that outlines the inheritance of one or more characteristics.

See chart attached with symbols used in pedigrees.

Question 5

Explain Autosomal Recessive Traits

Answer 5

• Equal frequency in males and females
• Affected children born from unaffected parents
• Trait seems to skip generations. Only if two parents have it is there chance of 1/4 children getting it.
• More often found in offspring from consanguine matings (mating between closely related people) because there is greater chance of both parents having the recessive allele.
• Affected parents produce affected offspring
• Example: Tay Sachs disease

See chart below of pedigree for this with first cousins marrying to increase likelihood of it being passed on.

Question 6

Explain Autosomal Dominant Traits

Answer 6

• Equal frequency in males and females
• Affected children have an affected parent (unless they carry new mutation, very rare, or unless there is reduced penetrance)
• Trait does not skip generations
• Unaffected persons do not transmit the trait provided that it is fully penetrant.
• Examples: Familial Hypercholesteremia (high cholestorol levels), Waardenburg Syndrome (deafness, fair skin, visual problems and a white forelock)

See attached pedigree analysis

Question 7

Pedigree for Waardenburg syndrome (Autosomal Dominant Trait). See table.

Answer 7

Question 8

Explain X-Linked Recessive Traits

Answer 8

• More often in males than females
• Not transmitted from father to son because Y is passed from father to son.
• Affected sons usually born to unaffected mothers
• Tend to skip generations
• Example: Haemophilia A, is absence of protein necessary for blood to clot.

Question 9

Explain X-Linked Dominant Traits

Answer 9

• Affect both males than females
• Affected males have affected mothers (unless new mutation, very rare)
• Affected males transmit the trait to their daughters
• Example: Hypophosphatemia or familial vitamin-D resistant rickets - people with this disease have symptons that appear like rickets like deformities, stiff joints etc.

Question 10

Explain Y-Linked Traits

Answer 10

• Appear only in males
• Affected fathers transmit the trait to their sons
• Does not skip generations
• Example: maleness

Question 11

Pedigree characteristics of autosomal recessive, autosomal dominant, X-linked recessive, X-linked dominant and Y-linked traits. See table on next page.

Answer 11

Question 12

Dizygotic twins are?

Answer 12

nonidentical twins. Have 50% of their genes in common (as non twin siblings), fertisilised by two different sperm and two separate eggs. Dizygotic twinning tends to run in families and is influenced by hereditary.

Question 13

Monozygotic twins are

Answer 13

identical twins and have 100% of their genes in common. There appears to be little genetic tendency for producing monozygotic twins.

Question 14

Comparisons of mono- and dizygotic twins can separate the influence of ________ in a certain trait

Answer 14

environment

Question 15

Concordance is?

Answer 15

when both members of a twin pair have a trait the twins are said to be concordant. If only one member of the pair has the trait the twins are said to be discordant.

Concordance is the percentage of twin pairs that are concordant for a trait.

Question 16

Higher concordance for monozygotic twins compared with that for dizygotic twins indicates that ______ factors play a role in determining differences in a trait. Low concordance for monozygotic twins indicates that _______ factors play a significant role.

Answer 16

• genetic
• environmental

Question 17

In twin studies for asthma it showed …?

Answer 17

the genetics of asthma showed that genes are an important factor but environment plays an important role as well

Question 18

Twin studies used to study the genetics of obesity showed that _____ are an important factor but _______ plays an important role as well.

Answer 18

1. genes
2. environment

• Genetic research into obesity is done more and more
• 1994, leptin gene was isolated
• Genetic control of bodyweight is very complex

Question 19

1. Adoption studies are a very powerful technique for separating influences of ______ and _____ on a certain trait
2. If adopted children show similarities in a characteristic to their adopted parents, the trait is mainly affected by ________
3. If, on the other hand adopted persons and their biological parents show similarities, these similarities are likely to be due to _____ factors.
4. Adopted children have __ genes in common with their adoptive parents

Answer 19

1. genes and environment
2. environment
3. genetic
4. no

Question 20

In adoption studies it has been shown that three major disorders are influenced by genetics. Name them.

Answer 20

1. Obesity, but genetics was not the only factor
2. A strong genetic influence was also shown in alcoholism. Again, genetic factor was necessary but not always enough.
3. Also show that schizophrenia has a genetic basis

See obesity chart below.