EXAM 3 - Session 22/Dr. V: Inheritance and Genetic DIsorders

Question 1

Describe characteristics of human chromosomes.

Answer 1

• 23 pairs of chromosomes
• total of 46 chromosomes
• 23 chromosomes from each parent
• 23rd chromosome is sex identifying (female: XX; male: XY)

Question 2

Explain the classical Mendel’s approach to chromosomal inheritance.

Answer 2

• Law of Segregation (Mendel’s First Law)
• Law of Independent Assortment (Inheritance Law)

Question 3

Explain the association/relation between Mendel’s Approach and the Modern Paradigm/model.

Answer 3

The modern paradigm
* agreed with the Law of Segregation
* determined that the Law of Independent Assortment depends on genes linkage and crossing-over/recombination

Question 4

Describe Gregor Mendel.

Answer 4

• 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

Question 5

Define the Law of Segregation (Mendel’s First Law)

Answer 5

• 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

Question 6

Define monohybrid cross.

Answer 6

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

Question 7

Define the Law of Independent Assortment (Inheritance Law)

Answer 7

The inhertance of an allele for one gene does not influence the allele recieved for a different gene.

Question 8

Define dihybrid cross.

Answer 8

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

cat color and tail size are inherited independently

Question 9

What were Sutton’s findings?

Answer 9

Observed that gene inheritance patterns paralleled behavior of chromosomes during cell division.
* proposed that genes are located in chromosomes

Question 10

Which experiments proved that genetic information is stored in the form of DNA?

Answer 10

• Griffith’s experiements
• Avery et al
• Hershey-Chase

Question 11

Explain Griffith’s experiments.

Answer 11

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

Question 12

Explain the findings of Avery et al.

Answer 12

Decided to determine what the transforming principle was made of
* DNA

Question 13

Explain the Hershey-Chase experiement.

Answer 13

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.

Question 14

Describe the function of chromatin.

Answer 14

• 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

Question 15

Explain gene linkage.

Answer 15

All genes on a single chromasome are inherited as a single linked group

Question 16

Describe the inheritance ratio for linked genes.

Answer 16

Dihybrid cross
* second generation of offspring (F2) have two linked traits
* 3:1 ratio

Color of the flower is linked to the color of the circle (red:red and white:blue)

Question 17

Compare the inheritance ratio between independent versus linked genes.
(cross of heterozygote to a homozygous recessive)

Answer 17

Independent:
* 1(1:1):1(1:1)

Linked:
* 1:1 ratio

Question 18

Explain crossing-over

Answer 18

Unlinks genes and produces new allele combinations on chromosomes
result: offspring have recombinant chromosomes

Question 19

Describe the characteristics of female sex-determining chromosomes.

Answer 19

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.

Question 20

Define genetic disorder versus genetic disease.

Answer 20

Genetic disorder - condition caused by abnormalities in genes or chromosomes.
Genetic disease - diseases present in all cells of the body and present since conception.

Question 21

Describe aneuploidy.

Answer 21

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

Ex. 3 chromosomes in c'some 21

Question 22

Explain the results of monosomy X0

Answer 22

• 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

Question 23

Explain the results of monosomy Y0.

Answer 23

• Lethal in embryonic development

Question 24

Explain the results in Trisomy XXX (female).

Answer 24

• no detectable problems
• fertile and bear normal children
• may produce 2 Barr bodies

Question 25

Explain the results of Trisomy XXY (male).

Answer 25

• 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

Question 26

Explain the results of Trisomy XXY (male).

Answer 26

• 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

Question 27

Explain the result of Trisomy XYY (male).

Answer 27

• jacobs syndrome
• generally fertile
• increase vertical stature
• higher incidence among incarcerated males and those in mental institutions; social maladjustment.

Question 28

What are the two types of single gene disorder categories?

Answer 28

• Autosomal dominant
• Autosomal recessive

Question 29

Describe autosomal dominant disorders.

Answer 29

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.

Question 30

Describe autosomal recessive disorders.

Answer 30

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

Question 31

Describe X-linked dominant disorders.

Answer 31

• 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

Question 32

Describe X-linked recessive disorders.

Answer 32

• 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

Question 33

Describe Y-linked disorders.

Answer 33

Caused by mutations on the Y chromosome
* only males can get them

Question 34

Describe mitocondrial inheritance disease.

Answer 34

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

Question 35

Describe multifactoral and polygenic disorders.

Answer 35

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