More on Inherited Traits and DNA

Question 1

What is the chromosome theory of inheritance?

Answer 1

There are specific genes that are connected to specific chromosomes. Mendel’s factors (genes) are linked to chromosomes.

Question 2

Why did Thomas Hunt Morgan choose fruit flies in his experiments?

Answer 2

• only 4 pairs of chromosomes (2n=8 - 3 pairs autosomes, 1 pair sex chromosomes)
• lots of offspring (more possibilities for genetic variation)
• inexpensive and small
• mature and breed quickly because their lifespans are about 2 weeks

Question 3

1. Wild type and mutant phenotype (definition)

2. What were the wild type and mutant phenotype of the flies?

Answer 3

wild type: the common trait in a population (red eyes)

mutant phenotype: uncommon trait (white eyes)

Question 4

How are X and Y chromosomes different?

Answer 4

• Y creates boy/ X creates girl
• Y = smaller (only have genes - 75 - for sperm production)
• X = 1000 genes

Question 5

X linked chromosome and Y linked chromosome

Answer 5

genes on X and genes on Y

Question 6

hemizygous

Answer 6

a male needs only one copy of the allele

Question 7

Why are males more likely to get recessive disorders?

Answer 7

Because they always take the gene of the mom, so if she has the disease or is a carrier, the son will have it

Question 8

X inactivation

Answer 8

• only happens in girls (with 2 X chromosomes)
• which chromosome is turned off differs in each cell
• when a chromosome is “turned off” and condensed into a Barr Body early in embryotic development under the nuclear membrane

Question 9

mosaic

Answer 9

when there is a combination of dominant and recessive traits expressed by the maternal and paternal X chromosomes

Question 10

What is an example of a mosaic/X inactivation?

Answer 10

Tortoise shell cat- orange and black expressed in different cells

Question 11

What is the experiment with the black vestigial and gray normal flies representing?

Answer 11

recombination frequencies

Question 12

recombination frequencies

Answer 12

percent of recombinant offspring from a breeding

Question 13

When breeding the parents and offspring from the gray normal and black vestigial experiment, some of the offspring turned out black normal and gray vestigial. Why did this happen?

Answer 13

recombinant offspring from crossing over of the DNA at the chiasmata during meiosis

Question 14

What are recombination frequencies used for in the fly experiments?

Answer 14

gene maps- the location of the genes relative to each other

Question 15

What theory did Morgan come up with from the recombination frequencies and the gene maps?

Answer 15

the closer together the genes are on a chromosome, the more likely they’ll be inherited together and the farther they are, the more likely they’ll be recombined

Question 16

Why do we care where genes are located?

Answer 16

• predetermines the recombinant offspring

- helps to diagnose disease

Question 17

What is nondisjunction?

Answer 17

chromosomes do not separate properly during meiosis because the mitotic spindle breaks (happens in old women when eggs start to age)

Question 18

What is aneuploidy?

Answer 18

wrong number of chromosomes which mostly results in miscarriage (genetic screen)

Question 19

trisomy and monosomy

Answer 19

tri- extra chromosome (2n+1)

mono- missing chromosome (2n-1)

Question 20

Give an example of trisomy.

Answer 20

Trisomy 21 = Down Syndrome (speech slurred, heart defects, wider face and smaller ears, sterile…)
-a collection of traits caused by nondisjunction

Question 21

polyploid

Answer 21

more than one set of chromosomes, natural in plants (fruits and grains), ex) strawberries are octaploid

Question 22

What is genetically modified fruit?

Answer 22

seedless, sterile, bigger

Question 23

Explain the anatomy of a plant.

Answer 23

fruit- ripened ovary

seed- fertilized egg (zygote)

Question 24

Name the structural alterations of chromosomes.

Answer 24

deletion- when a portion of a chromosome breaks off (malformation of vocal chords)
duplication- copied portion of a chromosome
translocation- a portion breaks off and reattaches to a non-homologous chromosome (different chromosome)
-reciprocal translocation- 2 parts swap places on non-homologous chromosomes
inversion- when a chromosome breaks off, flips, and reattaches to the same chromosome but the gene will now be in a different order

Question 25

Is aneuploidy more dangerous in autosomes or sex chromosomes?

Answer 25

autosomes

Question 26

Why is DNA important?

Answer 26

• life cannot exist without it because it is the instructions for protein synthesis
• central dogma of biology- DNA is how traits get passed from one generation to the next (every organism needs it)

Question 27

What is the official name of fruit flies?

Answer 27

Drosophilia Melanogaster

Question 28

Explain the history of DNA and chromosomes.

Answer 28

Mendel (4 observations) → Thomas Hunt Morgan (Chromosome Theory of Inheritance, 1907 with Drosophilia Melanogaster → studied red eyes and white eyes - x linked traits) → Griffith and Hershey/Chase (DNA is the material of inheritance, not proteins - viruses and bacteria) → Wilkins and Franklin (show DNA is a double helix through x-ray) and Chargaff 1953 (ratio of A and T is same, ratio of C and G is same - they occur in pairs) → Watson and Crick made model of DNA, got glory from others’ research

Question 29

By what process do traits get passed down?

Answer 29

meiosis

Question 30

Describe the structure of DNA.

Answer 30

double helix ladder, antiparallel strands (3’ = sugar, 5’ = phosphate), nucleotides- phosphate, sugar, nitrogenous bases (adenine, thymine, guanine, cytosine), complementary base pair (A & T with 2 bonds, C & G with 3 bonds), semi-conservative

Question 31

How does semi-conservative replication help prevent mutations in DNA?

Answer 31

It makes more healthy stands of DNA than damaged ones.

Question 32

Chromatin

Answer 32

loose DNA

Question 33

When is DNA replicated?

Answer 33

S phase

Question 34

When is DNA condensed into chromosomes?

Answer 34

mitosis

Question 35

What structure hold the two sister chromatids together?

Answer 35

centromere

Question 36

Explain DNA replication.

Answer 36

Replication starts at origins of replication because helicase is attracted to certain bases on a strip of DNA. Helicase is an enzyme that separates and untwists the DNA by breaking the hydrogen bonds. The area where it does this is called a replication fork. Meanwhile, topoisomerase attaches a bit ahead of helicase and relieves strain on the DNA by breaking and rejoining the strands. As helicase opens the DNA, bubbles of the 2 strands are created. Each parental strand is called a template. Single-strand binding proteins attach to either strand, making sure the strands do not reconnect. DNA polymerase is used to attach free nucleotides to the template. However, polymerases must go in a 5’ → 3’ direction because DNA is antiparallel to each other, ending with a phosphate (5’) on one end and a sugar (3’) on the other end. The 2 stands are called leading and lagging strands. In a leading strand, primase attaches one RNA primer onto the template. Then, the polymerase continues fluidly down the DNA strand, creating a daughter strand. In a lagging strand, several RNA primers are attached to the template. DNA polymerase then attaches complementary bases to the template in fragments. These fragments are called Okazaki fragments. On both the leading and lagging strands, DNA polymerase then replaces the RNA primer with DNA nucleotides. DNA ligase then joins the fragments. This entire process continues until the bubbles merge into each other. When 2 daughter strands have been formed, DNA polymerases run themselves along the DNA to find errors in the replicated DNA. This prevents mutations. Mismatch repair occur when enzymes remove and replace incorrectly paired nucleotides that have resulted from replication errors.