GEN BIO: GENETICS

Question 1

Genes

Answer 1

Set of instructions that determine the characteristics of an organism

Question 2

Where are genes located?

Answer 2

On chromosomes

Question 3

Chromosomes

Answer 3

Occur in homologous pairs, consisting of one chromosome from each of two parents, arranged in complementary patterns, and containing genes for the same traits at the same loci on the homologous pairs

Question 4

Alleles

Answer 4

Pairs which genes are found in

Question 5

Homozygous/ purebred

Answer 5

Individual with two identical genes for a trait

Question 6

Law of Dominance

Answer 6

Dominant trait expressed, recessive trait masked
(Dominant gene represented by a capital letter and the recessive trait by a lowercase letter)

Question 7

Heterozygous

Answer 7

-Contain one allele for dominant gene and one allele for recessive gene
-The allele for the dominant gene is expressed and the allele for the recessive gene is hidden

Question 8

Phenotype

Answer 8

Appearance

Question 9

Law of Segregation
1/2

Answer 9

-When two hybrids (heterozygotes) are crossed, the hidden trait becomes segregated and appears in 25% of the offspring.
-This happens because genes separate during meiosis and recombine during fertilization.
-This process can be pictured using a punnet square.

Question 10

Law of Segregation
2/2

Answer 10

-In the genes produced by these individuals, half of the gametes are dominant (T) and half recessive (t) -arranging them on the Punnet square, we see the 25% of the offspring have a genotype of dominant dominant (TT), 50% dominant recessive (Tt) and 25% recessive recessive (tt).
-The phenotype is 75% dominant 25% recessive, because both the pure dominant (TT) and the heterozygote (Tt) exhibit the dominant trait.
-a recessive trait is expressed only if the individual has two recessive genes.

Question 11

Law of Independent Assortment

Answer 11

-Genes on different chromosomes are inherited independently of each other.
-When genes for different traits are on the same chromosome, the traits are linked.
-Some traits do not show a pattern of dominance and the heterozygote for such a trait expresses a mixture of the two traits (codominance)
(Ex. Roan cattle, in which the cattle may be red RR, white WW or roan RW, which is a mixture of red and white fur)

Question 12

How many chromosomes and homologous pairs do humans have?

Answer 12

-Humans have 46 chromosomes, or 23 homologous pairs, of which 22 pairs are autosomes (nonsex chromosomes) and one pair consists of the sex chromosomes (XX or XY)
-XX female
-XY male

Question 13

Autosomes

Answer 13

Nonsex chromosomes (22 pairs out of the 23 are autosomes)

Question 14

Sex-linked traits

Answer 14

-Genes are found only on the X chromosome, but not on the Y
-a male need inherit only one gene for such a trait from his mother for it to be expressed, but a female has to inherit two, one from each parent.
-ex. color blindness and hemophilia

Question 15

DNA (deoxyribonucleic acid)

Answer 15

-what we call the gene
-The model explaining the structure of DNA was first proposed by James Watson and Francis Crick
-To understand the role of DNA in genetics we must understand the structure of DNA

Question 16

Structure of DNA

Answer 16

-Made up of thousands of units called nucleotides
-each nucleotide is composed of a phosphate group (PO4), a five-carbon sugar called deoxyribose, and a nitrogenous base (either adenine, cytosine, guanine , or thymine)
-nucleotides form long chains, which are joined to form a double helix
-two strands of nucleotides are joined by nitrogenous bases connected to each other with hydrogen bonds
-if you think of a DNA molecule as a ladder, the sugar and phosphate units form the uprights, and the pairs of nitrogenous bases are the rungs of the ladder
-bases can bond only in certain combinations—guanine (G) to cytosine (C) and adenine (A) to thymine (T), thus providing four possible pairings CG, GC, AT, TA

Question 17

DNA Replication
Make exact copy of itself

Answer 17

-DNA strand opens or unzips at the base pairs
-free (or unattached) nucleotides are incorporated into the unzipped portion of the DNA, so that complementary base pairs join to form exact duplicates
-ex. if an unzipped strand has a sequence of ATCGA, it attracts nucleotides TAGCT
-the result is 2 replicated DNA molecules that are identical to each other and to the original DNA

Question 18

DNA also serves as a template for the production of messenger RNA (m-RNA)

Answer 18

RNA differs from DNA in that it is single-stranded has the sugar ribose in place of deoxyribose and replaces thymine with uracil

Question 19

Transcription
(General description)

Answer 19

The process of forming m-RNA according to the information contained in the DNA molecule

Question 20

Transcription
(Process)

Answer 20

-The DNA strand opens and acts as a template for the production of RNA
-the base sequence of the DNA strand determines the nucleotide order in the RNA strand
-ex. If the DNA sequence is GCTTAA, the RNA strand is CGAAUU

Question 21

Translation
(Process)

Answer 21

-A molecule of mRNA, which is made in the nucleus, moves out of the nucleus and is attached to a ribosome
-at the ribosome transfer RNA (t-RNA) molecules, which are coded for specific amino acids, line up along the RNA molecule at the ribosome
-in doing so, they align their amino acids according to the code in the m-RNA and form them into proteins
-this mechanism produces proteins according to the information coded in the original DNA molecule

Question 22

Gene Mutations

Answer 22

Changes in the DNA nitrogenous base sequence, causing a change in the protein formed.

Question 23

[gene mutations]
Chromosomal Mutations

Answer 23

-Either the structure or the number of chromosomes changes, resulting in such conditions as polyploidy (in which a full set of chromosomes fails to separate, resulting in an individual that could be 3n) or nondysjunction, in which one chromosome pair fails to separate during meiosis, such as happens in Down syndrome