genetics

Question 1

the 4 nitrogenous base constituents of DNA

Answer 1

**adenine, cytosine, guanine, and thymine, **are commonly represented by their first letters: A, C, G, and T, respectively.

adenine pairs with thymine
guanine pairs with cytosine.

Question 2

Proteins are composed of

Answer 2

polypeptides (intermediate protein compounds), which are composed of sequences of amino acids (organic acids containing NH2 ).

20 different types of amino acids

Amino acids are specified by codons - which are triplets of bases. 64 possible codons and three of 64 signal the end of a gene -
termination codons.

Question 3

complementary base pairing

Answer 3

unpaired base will attract a free nucleotide only if the nucleotide has the proper complementary base.

Complementary base pairing or the consistent pairing of adenine with thymine and of guanine with cytosine, is the key to accurate replication.

Question 4

proteins involved in dna replication

Answer 4

Several different proteins are involved in DNA replication.

DNA polymerase
- travels along the single DNA strand, adding the correct nucleotides to the free end of the new strand.
proofreading: After the new nucleotide has been added to the chain, the DNA polymerase checks to make sure that its base is actually complementary to the template base.

Question 5

RNA differs from DNA in
that …

Answer 5

adenine, cytosine, and
guanine + uracil
rather than thymine

Uracil is structurally very similar to
thymine, so it also can pair with adenine.

Whereas DNA usually occurs as a double strand, RNA usually occurs as a single strand.

The **transport of the DNA code from nucleus to cytoplasm **and the subsequent protein formation involve two basic processes: transcription and translation. Both of these processes are mediated by ribonucleic acid (RNA).

Question 6

Transcription

Answer 6

process by which **RNA is synthesized from a DNA template. **

The result is the formation of **messenger RNA (mRNA) **from the base sequence specified by the DNA molecule.

RNA polymerase binds to a promoter site on the DNA.

Transcription continues until a DNA sequence called a termination sequence is reached. Then
the RNA polymerase detaches from the DNA, and the transcribed mRNA is freed to move out of the nucleus and into the cytoplasm.

Question 7

RNA Splicing

Answer 7

Many of the RNA sequences are removed and the remaining sequences are spliced
together to form the functional mRNA that will migrate to the cytoplasm

excised sequences introns

sequences that are left to code for proteins exons

Question 8

Translation

Answer 8

process by which RNA directs the synthesis of a polypeptide.

However, mRNA cannot code directly for amino acids. Instead, mRNA interacts with transfer RNA (tRNA)

As each codon is processed, an amino acid is translated by the interaction of mRNA and tRNA, which is aided by ribosomes.

Question 9

types of mutation

Answer 9

base pair substitution: in which one base pair is replaced by another. aka missense mutation This substitution sometimes results in a change in amino acid sequence, but because of the redundancy of the genetic code, it may have no consequence.

frameshift mutation: insertion or deletion of one or more base pairs to the DNA molecule. change the entire “reading frame”of the DNA sequence because codons consist of groups of three base pairs. A frameshift mutation thus can greatly alter the resulting amino acid sequence.

Question 10

Chromosomes

Answer 10

somatic cell (all cells other than gametes) has 46 chromosomes in its nucleus. These are diploid cells, chromosomes occur in pairs. 23 pairs of chromosomes per cell.

Gametes are haploid cells: they have one member of each chromosome pair, giving them a total of 23 chromosomes. The process by which these haploid cells are formed from diploid cells is called meiosis.

Question 11

interphase

Answer 11

period of the cell cycle during which the cell is not dividing. The majority of cells are in interphase most of the time.

G1 phase: (gap 1 phase) is the first gap, or growth phase in the cell cycle.
A cell grows and carries out all normal metabolic functions and processes. length of time varies widely between cell types.

S phase: (synthesis phase) is period during which a cell replicates its DNA. 8-10 hrs

G2 phase: is a second gap phase, during which the cell continues to grow and makes the necessary preparations for mitosis. 5 hrs.

G0 phase: cells have temporarily stopped dividing and are resting (a common condition) and cells that have permanently ceased dividing (like nerve cells) are said to be in G0.

Question 12

mitosis

Answer 12

the division of genetic material, during which the cell nucleus breaks down and two new, fully functional, nuclei are formed. 1-2hrs

Prophase:
chromatin into chromosomes, the nuclear envelope break down, chromosomes attach
to spindle fibres by their centromeres. aka loosely packed chromatin coils and condenses into visible chromosomes.

metaphase
sister chromatids, with theirattached microtubules, line up along an imaginary linear plane in the middle of the cell, called the metaphase plate.

anaphase
pairs of sister chromatids are separated from one another,
forming individual chromosomes once again.

telophase.
formation of two new daughter nuclei at either end of the dividing cell.

Question 13

cytokinesis

Answer 13

divides the cytoplasm into two distinctive cells.

The cleavage furrow is a contractile band made up of microfilaments that
forms around the midline of the cell during cytokinesis.

This contractile band squeezes the two cells apart until they finally separate.

Two new cells are now formed.

One of these cells (the “stem cell”) enters its own cell cycle; able to grow
and divide again at some future time.
The other cell transforms into the functional cell of the tissue, typically
replacing an “old” cell there.

Question 14

after DNA replication but before cell division, each cell actually
contains # copies of each chromosome

Answer 14

after DNA replication but before cell division, each cell actually
contains two copies of each chromosome.

Each copy of the chromosome is referred to as a sister chromatid and is physically bound to the other copy. The centromere is the structure that attaches one sister chromatid to another.

Because a human cell has 46 chromosomes, during this phase,
there are 92 chromatids (46 × 2) in the cell.

Question 15

genotype vs phenotype vs karyotype

Answer 15

Genotype - An individual’s complete genetic makeup

Phenotype - The characteristics that the genes express, whether they are
physical, behavioral, or biochemical.

A karyotype is an individual’s
complete set of chromosomes.
The term also refers to a lab-produced image of a person’s chromosomes isolated from an individual cell and arranged in numerical order.

Question 16

inheritance: homozygous vs heterozygous

Answer 16

Homozygous state -
a person can have two identical alleles for a single gene

Heterozygous state-
a person has two different alleles. The two alleles can interact in several different ways

Question 17

dominant vs recessive inheritance

Answer 17

dominant gene is observable

The expression of an allele can be dominant, the activity of this
gene will mask the expression of a recessive, allele.

Sometimes dominance is complete; at other times, it is incomplete.

Question 18

codominance

Answer 18

A classic example of codominance in humans is ABO blood type:

People are blood type A if they have an allele for an enzyme that facilitates the production of surface antigen A on their erythrocytes. This allele is designated IA.

People are blood type B if they express an enzyme for the production of surface antigen B.

People who have alleles for both enzymes (IA and IB) produce both surface antigens A and B. As a result, they are blood type AB.

Because the effect of both alleles (or enzymes) is observed, we say that the IA and IB alleles are codominant.

Question 19

chromatin

Answer 19

the substance that gives the nucleus a granular appearance

Question 20

Genes are composed of

Answer 20

sequences of deoxyribonucleic acid (DNA), a primary constituent of chromosomes;

proteins, such as histones, that cause the DNA to coil into a highly compressed structure

Question 21

nucleotide

Answer 21

DNA subunit—consisting of one deoxyribose molecule, one phosphate group, and
one base —is called a nucleotide.

Question 22

karyotype

Answer 22

karyotype is an individual’s
complete set of chromosomes.
The term also refers to a
laboratory-produced image of a
person’s chromosomes isolated
from an individual cell and
arranged in numerical order.

Question 23

Gen 1 AA + aa

Answer 23

all second gen A dominant

Question 24

Generation parents: Aa + Aa

Answer 24

AA, Aa, aA (which is the same as Aa), and aa.

75% dominant
25% recessive

Question 25

What about crosses that involve multiple traits?

Answer 25

independent assortment states that the members of one pair
of genes (alleles) from a parent will sort independently from other pairs of genes during the formation of gametes.

Question 26

Autosomal Dominant Inheritance

Answer 26

When the dominant allele is located on one of the 22 pairs of autosomes (non-sex chromosomes), we refer to its inheritance pattern as autosomal dominant.

one parent is heterozygous for this disorder (and who therefore has neurofibromatosis), Nn, and one parent is homozygous for the normal gene, nn. every child of this couple would have a 50% chance of inheriting neurofibromatosis.

Question 27

autosomal recessive

Answer 27

a genetic disorder is inherited in an autosomal recessive pattern, the
disorder corresponds to the recessive phenotype.

Heterozygous individuals will not display symptoms of this disorder,
because their unaffected gene will compensate. Such an individual is called a carrier.

Question 28

X-linked dominant.

Answer 28

abnormal allele for a gene that occurs on the X chromosome is dominant
over the normal allele, the pattern is described as X-linked dominant.

X-linked recessive inheritance is much more common because females can
be carriers of the disease yet still have a normal phenotype.

Question 29

incomplete dominance

Answer 29

offspring express a heterozygous phenotype that is intermediate between one parent’s homozygous dominant trait and the other parent’s homozygous recessive trait.

Question 30

Codominance

Answer 30

Characterized by the equal, distinct, and simultaneous expression of both parents’ different alleles. This pattern differs from the intermediate, blended features seen in
incomplete dominance.