HYS - CH12.1, 12.2 Genetics And Gene Pool Changes

Question 1

How does blood typing demonstrate genes?

Answer 1

Blood type A individuals carry the A antigen on their erythrocytes and have circulating anti-B antibodies.

Blood type B individuals carry the B antigen on their erythrocytes and have circulating anti-A antibodies.

Those with type AB have both antigens and neither antibody; those with type O have neither antigen and both antibodies. That makes type O individuals universal donors and type AB individuals universal recipients.

Question 2

what are male and female chromosomes?

Answer 2

male - XY
female - XX

Question 3

what is a gene locus?

Answer 3

a location on a specific chromosome which is conistent across human beings

Question 4

dominant vs recessive genes

Answer 4

if one copy is needed to express a phenotype– allele is dominant (capital)

of two copies are needed – allele is recessive (lower case)

Question 5

hemizygous, homozygous, heterozygous

Answer 5

homozygous - both alleles are same
heterozygous - alleles are different
hemizygous - only one allele is present for a given gene - as is case for many parts of X chromosome in genotypical males

Question 6

complete dominance

Answer 6

when only one dominant and one recessive allele exist for a given gene. The presence of one dominant allele will mask the recessive allele if present.

Question 7

codominance

Answer 7

When more than one dominant allele exists for a given gene there is codominance.

For example, a person with one allele for the A blood antigen and one allele for the B blood antigen will express both antigens simultaneously

Question 8

incomplete dominance

Answer 8

heterozygote expresses a phenotype that is an intermediate between two homoyzgous genotypes

classic example of incomplete dominance is the mating of certain flowers, in which a red flower crossed with a white flower results in pink flowers

or wavy hair from curly and straight

Question 9

penetrance

Answer 9

**it is the probability that, given a particular genotype, a person will express the phenotype.
**
alleles can be classified by their degree of penetrance, huntingtons disease is caused by an expansion of a repetitive sequence in the huntingtin gene. People with more than 40 sequence repeats have full penetrance - 100 percent show HD symptoms

high penetrance, reduced, low, non penetrance occurs with fewer and fewer sequence repeats

Question 10

expressivity

Answer 10

**different manifestations of the same genotype across the population
**
if expressivity is constant, then all individuals with a given genotype express the same phenotype.

However, if expressivity is variable, then individuals with the same genotype may have different phenotypes.
** Marfan Syndrome - autosomal dominant - 100% penetrant but NOT 100% expressivity - different severity**

Question 11

penetrance vs expressivity

Answer 11

Whereas penetrance is a population parameter (what percentage of individuals with a given genotype express the phenotype?), expressivity reflects the gray area in expression and is more commonly considered at the individual level.

For example, the disease neurofibromatosis type II is an autosomal dominant disease that results from a mutation of the gene NF2 (merlin). Interestingly, a range of phenotypes is associated with carrying the defective allele. **Many patients have debilitating tumors of the vestibulocochlear nerve, which is needed for hearing and balance. Some have cataracts, while others have tumors in the skin called neuromas; still others have spinal lesions. **
variable expressivity ranges from no clinical effect to severe disability

Question 12

mendels first law of segregation tenets

Answer 12

1. genes exist in alternate forms (alleles)
2. an organism has two alleles for each gene - one inherited from each parent
3. 2 alleles segregate during meiosis, resulting in gametes that carrly only one allele for any inherited trait
4. if 2 alleles of an organism are diff, only one will be fully expressed and the other will be silent. The expressed allele is said to be dominant, while the silent allele is recessive. (codominance and incomplete dominance are exceptions)

Question 13

How does meiosis relate to genetics?

Answer 13

the separation of homologous chromosomes during anaphase I of meiosis. By separating—segregating—these chromosomes into different cells, each gamete carries only one allele for any given trait.

Question 14

medels second law of independent assortment

Answer 14

the inheritance of one gene does not affect the inheritance of another gene

this is becuase at the centromere holding sister chromatic the homologous chromsome pair up to form tetrades. Recombination occurs and this allows the inheritance of one gene to be independent of the inheritance of all others

Question 15

why are homologous chromsomes and independent assortment of alleles important?

Answer 15

Both segregation of homologous chromosomes and independent assortment of alleles increase the genetic diversity of gametes and, subsequently, the genetic diversity of offspring. This has been demonstrated to improve the ability of a species to evolve and adapt to environmental stresses.

other ways to increase genetic variability is conjugation and transduction

Question 16

What did Frederick Griffith’s experiment contribute to study of DNA as genetic material?

Answer 16

Two strains of S. pneumoniae were identified: a virulent (disease-causing) strain and a nonvirulent strain. In successive trials, Griffith exposed mice to these strains of bacteria under different conditions and observed whether the mice lived or died, as shown in Figure 12.2.

The virulent S. pneumonia has a smooth capsule that helps the bacterium evade the immune system and cause disease. He injected this strain into mice, which resulted in death of the mice. Naturally, if the virulent bacteria were killed prior to injection, no disease resulted. Likewise, exposure of the mice to the nonvirulent strain, which has a rough capsule, did not cause disease. However, when both dead virulent bacteria and live nonvirulent bacteria were injected into the mouse, the mouse died and live bacteria with smooth capsules could be found in the mice.

He theorized that the live, nonvirulent bacteria must have acquired the ability to form smooth capsules from the dead virulent bacteria. This was known as the transforming principle.

Question 17

What did the Rockefeller researchers find about the transformation principle?

Answer 17

Oswald avery, colin MacLeod, maclyn McCarty purified a large quantity of the heat killed virulent S strain and seperated the subcellular components of bacteria into different extracts. The addition of one extract to nonvirulent S transformed the bacteria and allows it to kill mouse

When this substance was treated with enzymes known to degrade DNA, the bacteria were not transformed and the mice lived. However, when the substance was treated with enzymes known to degrade proteins, the bacteria were still transformed and the mice died. Thus, the group concluded that the transforming substance must be DNA.

Question 18

What did Hershey and Martha Chase do?

Answer 18

a year before Watson-Crick
Alfred Hershey and Martha Chase worked to confirm the idea that DNA could independently carry genetic information. These scientists created bacteriophages with radiolabeled DNA and protein. One group of bacteriophages contained radiolabeled sulfur, which is found in protein but not in DNA. Another group contained radiolabeled phosphorus, which is found in DNA but not in protein. Each of these bacteriophages was permitted to infect a group of nonlabeled bacteria.

when bacteriophages infect a bacterium, they inject their genetic material into the cell and leave their capsid outside. After the phages and bacteria were incubated, the sample was centrifuged to separate the material that remained outside the cell from the bacterial cells themselves. It was determined that while no radiolabeled protein entered the cells, radiolabeled DNA had. It was known that viruses must enter a cell to cause disease and replicate, so this experiment once again helped confirm that DNA was the heritable genetic material.

Question 19

Epigenetics

Answer 19

Epigenetics is a general term for changes in DNA that do not involve an alteration to the nucleotide sequence. The prefix epi– is Greek for “over” or “above,” so the name suggests regulatory mechanisms that are in addition to the traditional features of inheritance. Epigenetic modifications can include the covalent attachment of different chemical groups to nucleotides and histone proteins, including but not limited to methylation or acetylation. These modifications can be temporary and function to increase or decrease the expression of specific genes.

Question 20

modifications of methylation in DNA and modifications in histons

Answer 20

In general, modifications like methylation of DNA promoter regions tends to decrease the expression of specific genes, whereas modifications of lysines and/or arginines on histones have variable effects on the expression of genes.

Question 21

mutagens

Answer 21

substances causing mutations damadging DNA

Question 22

transposons

Answer 22

elements that can insert and remove themselves from the genome

if a transposon inserts in the middle of a coding sequence the mutation will disrupt the gene

Question 23

nucleotide level mutations

point
frameshift

Answer 23

point mutations - ONE nucleotide is swapped

silent - when change has NO effect on final protein (often on wobble nucleotide)
missense - change results in a DIFF amino acid for the protein
nonsense -when chaneg results in STOP codon amino acid
(premature length)

(UAA, UGA, UAG)

* frameshift mutations when nucleotides are INSERTED or DELETED from genome shifts reading frame of codons
(insertion or deletion mutations)
- premature truncation (nonsense)
- changes in sequence

Question 24

chromosomal mutations

deletion, duplication, inversion, insertion, translocation

Answer 24

large scale mutations in which large segments of DNA are affected

deletion - lost (frameshift)

insertion - segment it moved to a DIFF chromsome
or small insertion (same chrosome is a frameshift)

duplication - copied many times int he genome

inversion - segment REVERSED WITHIN a chromosme

transolcation mutations - when a segment of DNA from one chromosome is swaped with a segment of DNA from DIFF chromsome

Question 25

translocation vs inversion

Answer 25

WITHIN
inversion - segment REVERSED WITHIN a chromosme

DIFF
transolcation mutations - when a segment of DNA from one chromosome is swaped with a segment of DNA from DIFF chromsome

Question 26

inborn errors of metabolism due to detelerious mutations

Answer 26

deficiencies in genes required for metabolism

kids need ealry intervention

phenylketonuria (PKU) has defective phenylanalanine hydrolase which is the enzyme that metabolizes phenylalanine

toxic metabolites accumualte, leanring disability, siezures