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Biol 207 > Lecture 12 > Flashcards

Lecture 12 Flashcards

1
Q

Why are some alleles more common in certain populations?

A

The founder effect and the heterozygote advantage

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2
Q

What is the Founder Effect?

A

The loss of genetic variation that occurs when a new population is established by a very small number of individuals from a larger population

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3
Q

What is a Heterozygote Advantage?

A

A single copy of a disease allele confers an advantage. E.g. sickle cell anemia

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4
Q

What can’t physicians use to diagnose genetic crosses of their patients?

A

Mendelian Crosses

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5
Q

What do Physicians use to predict heredity of rare disease?

A

Family histories or pedigrees

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6
Q

What did Polygamy lead to?

A

Rare alleles from small groups to be widely spread

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7
Q

What is the Propositus?

A

The first case of a disease that comes to the attention of a doctor

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8
Q

What are the characteristics of an Autosomal recessive disorder in a pedigree?

A

The parents are unaffected (usually)
It can affect both males and females
Entire generations can be unaffected
More frequency when there is inbreeding

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9
Q

What is the inheritance of PKU?

A

Autosomal Recessive

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10
Q

What occurs in PKU?

A

There is a defect in Phenylalanine hydroxylase, a liver enzyme
Causes buildup of phenylalanine & phenylpyruvic acid in the body which affects the development of neurons

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11
Q

What can manage PKU?

A

Low protein diet

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12
Q

What are the characteristics of pedigrees with autosomal Dominant disorders?

A

Generally the disease appears in the parental generation
Tends to appear in every generation
Affected progeny includes males and females

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13
Q

What causes Pseudoachondroplasia?

A

Mutation in the COMP gene that affects the structural integrity of Cartilage. It is a dominant allele and the allele that causes it is homozygous lethal

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14
Q

What causes Achondroplasia?

A

Mutation in the FGFR3 that is a regulator of bone development. Also homozygous lethal

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15
Q

What is the inheritance of Piebald spotting?

A

Autosomal Dominant

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16
Q

What occurs in Piebald spotting?

A

It affects the migration of melanocytes from dorsal to ventral

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17
Q

What is Penetrance?

A

The proportion of percentage of individuals with a specific allele or allele combination (genotype) that display the corresponding phenotype

18
Q

When can we say something is fully penetrant?

A

When all individuals with this genotype manifest the phenotype

19
Q

When can we say incomplete penetrance?

A

An allele for which a phenotype manifests is less than 100%

20
Q

Why would the same genotype not always give rise to the same phenotype?

A

Environment factors e.g. nutrients, exposure to UV light, altitude
Influence of other alleles/genes
Stochastic events e.g. X inactivation

21
Q

What is Expressivity?

A

The degree to which a given allele influences the phenotype in an individual. It describes the intensity of the phenotype

22
Q

What is the dominance of Polydactyly?

A

Autosomal dominant

23
Q

What are the characteristics of X linked disorders?

A

Males are more common than females
No transmission from father to son
Daughters of affected males are carriers
Affected females have affected fathers and carrier mothers

24
Q

What does is Pseudodominant?

A

In X-linked genes, disease causing recessive alleles in a hemizygous organism/cell

25
Q

What is Hemophilia?

A

The inability to make fibrin which is used in clotting

26
Q

What is the difference between Hemophilia A and B?

A

Hemophilia A patients have a mutation in the F8 gene

Hemophilia B patients have a mutation in the F9 gene

27
Q

What is another way that females can have an X-linked disease?

A

If the X chromosome carrying the wild type allele become deactivated early on in embryogenesis functional mosaicism can occur where the whole organism is mostly the mutated X-chromosome

28
Q

What are the characteristics of X-linked dominant mutations?

A

A female heterozygote transmits to 1/2 of their children
Affected male will transmit to all daughters but not to sons
Affected females may be more common than males
No transmission from father to son

29
Q

What is the inheritance of Fragile X syndrome?

A

X-linked dominant

30
Q

What causes fragile X syndrome?

A

The non-coding region of the FMR1 gene has an increased number of CGG repeats which cause the gene to be turned off (via methylation)

31
Q

What is the Dominance of fragile X syndrome due to?

A

Haploinsufficiency if the wild type allele

32
Q

What are the 3 types of Mosaicism?

A

Repeat Length Mosaicism
Repeat Methylation Mosaicism
X-chromosome inactivation Mosaicism

33
Q

What is Repeat Length Mosaicism?

A

Because full mutations are mitotically unstable some patients have a mixture of cells with repeat lengths ranging from permutation to full mutation

34
Q

What is Repeat Methylation Mosaicism?

A

Some patients have a mixture of cells with and without methylation of CGG repeat

35
Q

What causes repeat sequences in DNA?

A

Strand slippage of the newly synthesized strand which causes the replication machine to believe that it missed nucleotides so it goes back and synthesizes them

36
Q

How do Trinucleotide expansions occur?

A

CAG next to CAG tend to attract to each other which cause the slippage

37
Q

How does Fragile X syndrome occur?

A

There is an increased number of CGG nucleotides in the untranslated region which causes a loss of function of the gene because RNA binding is impaired

38
Q

What is the cause of Huntington disease?

A

Increased CAG produces polyglutamine which give the gene new function through increased transcriptions

39
Q

What is methylation?

A

When a Methyl group is added to a cytosine nucleotide and signals for the associated gene to be transcripted less

40
Q

How does DNA methylation cause gene repression?

A

The methylation marks DNA for repression and this attracts proteins like MeCP2 which recruits other repression proteins that make DNA inaccessible

41
Q

What occurs in Rett Syndrome?

A

In the X-linked dominant disease there is a mutation in the MeCP2 a DNA binding protein that regulates many genes which is critical for brain function and development. Only occurs in females because males die

Biol 207 (14 decks)

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