Genetics Lecture 2: X Linked And Multifactorial Inheretance

Front 1

Hemizygous

Back 1

Genotype of an individual with only 1 representitive of a chromosome. Usually refers to X chromosome of male.

Front 2

X-Inactivation

Back 2

Inactivation of genes on one X chromosome in somatic cells of females. Occurs early in development. Should be completely random.

Front 3

Skewed X-Inactivation

Back 3

In Females, One X is Inactivated more than another. Can cause problems.

Front 4

Characteristics of X - Linked recessive inheritance

Back 4

1) Mutation of both female Xs or only male X necessary
2) 50% of sons of carrier mothers are affected
3) 50% of daughters of carrier mothers are carriers
4) All daughters of affected males are carriers
5) Carriers may show variable expression of trait based on X-inactivation

Front 5

Characteristics of X linked recessive pedigree

Back 5

1) Number of males affected > Females
2) No male to male transmission
3) Affected males related through female carrier

Front 6

3 types of obligate carriers of X lined recessive disorders

Back 6

1) Mothers of one affected male with a previous family history of disorder.
2) Mothers of more than one affected male
3) All daughters of an affected male

Front 7

3 explanations of x linked recessive disorders in females

Back 7

1) (standard) Female is homozygous for mutant allele
2) Skewed X - Inactivation
3) 45, X karyotype

Front 8

Characteristics of X linked dominant inheritance

Back 8

(are rarer than X recessive)
1) Affected individuals have a 50% chance of having affected children
2) Affected males have all affected daughters and no affected sons.
3) Affected females have 50% affected child (boy or girl).

Front 9

Characteristics of X-linked dominant pedigree

Back 9

1) Affected females are more common than males
2) Many x linked dominant disorders are lethal or more severe to males and affected males might not survive in utero.
3) No male to male transmission
4) All daughters of affected males are affected.

Front 10

Sex-Limited trait

Back 10

Autosomally transmitted trait that is expressed in only one sex even though the determinant gene is not X linked.

Front 11

Sex influenced trait

Back 11

Autosomally transmitted trait that occurs in both sexes but is expressed with widely different frequencies or severity.

Front 12

2 Reasons why x linked dominant disorders are more common in females than males

Back 12

1) 2 x chromosomes = 2x the chance of getting a mutant.
2) X linked dominant disorders are often lethal in utero for males.

Front 13

What are the recurrent risks in multifactorial disorders

Back 13

2-5% (less than single gene disorders but still significant)

Front 14

Multifactorial Disorder

Back 14

A disease caused by the combined effects of several genetic and environmental factors. Are far more common than genetic disorders known to be caused by a single gene.

Front 15

Characteristics of Multifactorial Disorders

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1) familial concentration with no predictable pattern
2) No clear defect of a single gene origin
3) Considerable variation in severity and expression
4) Differences in frequency of occurrence by gender or ethnicity.

Front 16

Regression to the mean

Back 16

Offspring tend to have, on average, less extreme phenotypes than their parents.

Front 17

Continuous v.s. discontinuous traits

Back 17

Continuous trait has a more arbitrary definition of what is normal and what is not. Discontinuous is less or not arbitrary. If threshold is exceeded, a clear disease is present.

Front 18

Degrees of relationship and % genome shared

Back 18

1st = 50%
2nd = 25%
3rd = 12.5%