EXAM 3 - Session 22/Dr. V: Inheritance and Genetic DIsorders Flashcards
Describe characteristics of human chromosomes.
- 23 pairs of chromosomes
- total of 46 chromosomes
- 23 chromosomes from each parent
- 23rd chromosome is sex identifying (female: XX; male: XY)
Explain the classical Mendel’s approach to chromosomal inheritance.
- Law of Segregation (Mendel’s First Law)
- Law of Independent Assortment (Inheritance Law)
Explain the association/relation between Mendel’s Approach and the Modern Paradigm/model.
The modern paradigm
* agreed with the Law of Segregation
* determined that the Law of Independent Assortment depends on genes linkage and crossing-over/recombination
Describe Gregor Mendel.
- Austrian monk
- discovered the basic principles of heredity through experiments in his garden
- his studies became the foundation of modern genetics and the study of heredity
Define the Law of Segregation (Mendel’s First Law)
- Alternative versions of genes account for variations in inherited characteristics
- For each characteristic, an organism inherits two alleles (one from each parent)
- the two alleles for each characteristic segregate during gamete production
Define monohybrid cross.
Genetic cross between homozygous parents with different alleles for a specific gene.
* One trait is studied
* predicted phenotypes of F2 –> 3:1
* importance: determine dominance relationship of alleles
Define the Law of Independent Assortment (Inheritance Law)
The inhertance of an allele for one gene does not influence the allele recieved for a different gene.
Define dihybrid cross.
A cross between parents with two different alleles for two genes of interest.
* Two traits studied
* predicted phenotype of F2 –> 9:3:3:1
* importance: assessing independent assortment of alleles
What were Sutton’s findings?
Observed that gene inheritance patterns paralleled behavior of chromosomes during cell division.
* proposed that genes are located in chromosomes
Which experiments proved that genetic information is stored in the form of DNA?
- Griffith’s experiements
- Avery et al
- Hershey-Chase
Explain Griffith’s experiments.
Injected mice with various mixtures of bacteria
* virulent and avirulent streptococcus pneumoniae bacteria
* In a mixture of avirulent bacteria and heat’killed virulent bacteria –> mouse died –> bc of genetic material (transforming principle) that allowed the capsule sugars to form –> make virulent bacteria in the mouse
Explain the findings of Avery et al.
Decided to determine what the transforming principle was made of
* DNA
Explain the Hershey-Chase experiement.
Determine if the entire phage particle entered the bacteria cell or if only one component of the phage (DNA) entered the cell.
* If only one component enters the cell –> the component must be the DNA
DNA was labeled with P52 - PHOSPHORUS
PROTEIN was labeled with S53 - sulfur
Previous experiments were inconclusive because –> could not distinguish between phage material actually inside the bacterium and material attached to the cell surface.
* Hershey-Chase halted the infection before completion and agitated in a blender
* blending would detach the phage material on the surface –> seperate surface material with material inside cell.
Describe the function of chromatin.
- Package DNA into a smaller volume to fit into cell.
- Strengthen DNA to allow for meiosis and mitosis
- Serve as the mechanism to control expression
Explain gene linkage.
All genes on a single chromasome are inherited as a single linked group
Describe the inheritance ratio for linked genes.
Dihybrid cross
* second generation of offspring (F2) have two linked traits
* 3:1 ratio
Compare the inheritance ratio between independent versus linked genes.
(cross of heterozygote to a homozygous recessive)
Independent:
* 1(1:1):1(1:1)
Linked:
* 1:1 ratio
Explain crossing-over
Unlinks genes and produces new allele combinations on chromosomes
result: offspring have recombinant chromosomes
Describe the characteristics of female sex-determining chromosomes.
Females inherit two X-chromosomes, but only 1 is active
* during female development, one X chromosome per cell condenses into a compact object - Barr body
* Genes on the Barr body are usually not expressed
* Barr-body chromosome is reactivated in ovarian cells that produce ova.
Define genetic disorder versus genetic disease.
Genetic disorder - condition caused by abnormalities in genes or chromosomes.
Genetic disease - diseases present in all cells of the body and present since conception.
Describe aneuploidy.
Changes in chromosome number due to non-disjunction during meiosis
* chromosome doesn’t seperate properly in Meiosis 1 –> causes extra chromosome or missing chromosome in gametes
Explain the results of monosomy X0
- Turner syndrome
- Absence of secondary sexual development and sterility
- more often the result of non-disjunction in sperm (75%) than in egg formation
- Doesn’t produce Barr bodies
Explain the results of monosomy Y0.
- Lethal in embryonic development
Explain the results in Trisomy XXX (female).
- no detectable problems
- fertile and bear normal children
- may produce 2 Barr bodies
Explain the results of Trisomy XXY (male).
- kleinfelter syndrome
- mixed secondary development at puberty and low sperm production leasing to sterility –> testes and prostate gland are smaller than normal
- generally taller and heavier than average males
- 2/3 of extra X’s come from the egg
Explain the results of Trisomy XXY (male).
- kleinfelter syndrome
- mixed secondary development at puberty and low sperm production leasing to sterility –> testes and prostate gland are smaller than normal
- generally taller and heavier than average males
- 2/3 of extra X’s come from the egg
Explain the result of Trisomy XYY (male).
- jacobs syndrome
- generally fertile
- increase vertical stature
- higher incidence among incarcerated males and those in mental institutions; social maladjustment.
What are the two types of single gene disorder categories?
- Autosomal dominant
- Autosomal recessive
Describe autosomal dominant disorders.
Only one mutated copy of the gene is necessary for a person to be affected by an autosomal dominant disorder.
* Huntington disease
Each affected person usually has one affected parent
* off spring will have 50% chance of inheriting mutated gene.
Describe autosomal recessive disorders.
Two copies of the gene must be mutated for a person to be affected by an autosomal recessive disorder.
* affected individual usually has two unaffected parents who each carry one copy of the mutated gene –> 25% chance of a child with the disorder.
* cyatic fibrosis, sickle cell anemia, tay-sachs, spinal muscular atrophy, and dry earwax
Describe X-linked dominant disorders.
- Affected males pass the condition to their daughters but none to their sons.
- Affected heterozygous females married to unaffected males pass the condition to 50% of their sons and daughters
Describe X-linked recessive disorders.
- Disease phenotype more often seen in males than females
- All the daughters of an affected male are “carriers” (if mother is not a carrier)
- Affected male will not pass to sons
Describe Y-linked disorders.
Caused by mutations on the Y chromosome
* only males can get them
Describe mitocondrial inheritance disease.
AKA maternal inheritance –> applies to genes in mitochondrial DNA.
* Since only egg cells contribute mitochondria to the developing embryo, only females can pass on mitochondrial conditions to their children.
* Leigh syndrome and Leber’s hereditary optic neuropathy
Describe multifactoral and polygenic disorders.
Associated with the effects of multiple genes in combination with lifestyle and envrionmental factors.
* do not have clear-cut pattern of inheritance
* difficult to determine likelihood of passing disorder to offspring
