Genetics lecture 2 Flashcards
(47 cards)
What are the different classifications of human genetic disorders?
- Single gene disorders
- Chromosomal disorder
- Multifactorial or polygenic disorders
- Mitochondrial disorder
What id the law of segregation?
Alleles segregate from each other in the formation of gametes, 1/2 the gametes carry one allele, and the other 1/2 carry the second allele.
At fertilization, gametes are randomly combined
What is the principle of independent assortment?
Genes for different traits assort independently of one another in the formation of gametes
What is the exception to the 2 Mendel’s laws?
The 2 rules only work if each trait is located on a different chromosome and if the traits are independent
How do diploid organisms get their alleles?
Inherit one allele from each parent
What are the different degrees of relatives? What is precent of genes in common in each degree?
- First degree: 50% (parents, sibling and children)
- Second degree: 25% (grandparents, uncles, aunts, nephews, grandchildren, half-siblings)
- Third degree: 12.5% (1st cousins)
What is recurrent risk?
The likelihood that a trait or disorder present in one family member will occur again in other family members in the same or subsequent generations
What are the most common classes of genetic diseases?
- Enzyme defects: almost always recessive
- Defects in receptor proteins
- Transport defects
- Disorders of structural proteins
- Neurodegenerative disorders
- Mitochondrial diseases
What is autosomal dominant inheritance?
- one allele is altered
- homozygous lethal
- no carriers
- most affected individuals are heterozygous
What are the rules of transmission for autosomal dominant disorders?
- Affected individuals are observed in each generation, creating a vertical pattern of inheritance. Affected individuals always have an affected parent
- The recurrence risk is 1/2 of the children born to a single affected parent will be affected
- Unaffected people have normal children
- Both males and females can be affected and can pass the abnormal gene to their offspring
What are the common alterations in dominant disorders?
- Haploinsufficiency
- Gain-of-function
- Dominant-negative effect
What is haploinsufficiency?
Reducted dosage of the wild-type allele is not enough for the normal function of the protein
What is gain-of-function?
The gene product of the mutated allele gains a new abnormal function
What is dominant-negative effect?
The mutated allele (misshapen protein) acts with the gene product of the wild-type allele and inhibits its function
What is autosomal recessive disorder?
- When BOTH alleles are altered
2. Affected individuals inherit one copy from each parent, so both parents are heterozygous for the disease
What are the rules of transmission for autosomal recessive disorders?
- The trait may be found in siblings
- Parents are usually healthy but carry one altered allele
- Horizontal pattern of inheritance
- The recurrence risk is 1/4 of having a second affected child since both parents are heterozygous
- The trait may appear as an isolated event
- Parents of affected children may be related
- Males and females are equally affected
What is special about recessive diseases?
One copy of the gene product is enough to provide the appropriate function. The affected gene is often an enzyme
What is special about X-lined inheritance?
- Since males have only one X chromosome (hemizygous), they can only pass the gene onto their daughters
- X-linked diseases can be dominant or receissive
What are the rules of transmission for X-linked recessive disorders?
- There is no male-to-male transmission; males only pass on the Y chromosome to their sons. Affected males will transmit the gene to all of their daughters
- The disease can skip a generation
- Affected males have phenotypically normal offspring but their daughters are obligated carriers
- Affected males get affected genes from their mothers
- Female carriers will pass the abnormal gene to 1/2 of their offspring. Sons that inherit the gene will be affected and daughters will be carriers like their mothers
- Female carriers may be mildly symptomatic due to unequal inactivation of the X-chromosome
- Unaffected males do not transmit the disorder
- Males only need 1 copy to be affected
What are the characteristics of a dominant X-lined disease?
- Both males and females are affected
- Fathers will pass the gene to ALL of their daughters, but NONE of their sons
- The pattern of inheritance from a mother is the same as autosomal dominant
- Frequently lethal in males
What are some characteristics of mitochondrial inheritance?
Every cell contains mitochondria in the cytoplasm. mtDNA is comprised of a small double stranded circle
Mitochondrial genome is very small and only contains a few genes
Only ova cells contribute mitochondria to the developing embryo. So ONLY females can pass on mitochondrial conditions to their children
What are the rules of transmission for mitochondrial disorders?
- Affected mothers pass the disease to all of her children
- Affected males don’t pass the disease to their children
- Both sexes are equally affected
What are the complications in Medelian inheritance?
Both environmental and genetic factors can influence the expression of a disease and complicate pedigree interpretation
What are the signs that a new mutation has occurred?
A case without a family history where the pehnotype matches a well-known genetic disease
