Biology 106

Dr. Dudash

Midterm #1

Fall 1999

(30 points) TRUE or FALSE. Fill in the blank with the entire word. 2 points per blank.

1. TRUE Jenkins was a supporter of the "mutationist movement" as an explanation of the diversity of life on earth.

2. FALSE Natural selection can quickly select against a deleterious recessive allele.

3. FALSE Most copies of harmful recessive alleles in a population are carried by individuals that are homozygous for that allele.

4. TRUE Malthus proposed that populations tend to increase at a faster rate than their food supply increases.

5. FALSE During anaphase I homologs line up randomly with regards to which pole they are facing. OCCURS DURING METAPHASE!!!

6. TRUE Natural selection is dependent on the presence of genetic variation in the local population.

7. TRUE A theory in biology is a hypothesis that has been rigorously tested and has a large body of evidence in favor of it's support.

8. FALSE Syngamy is the phase in meiosis where the second reduction division occurs.

9. FALSE Down's syndrome (trisomy 21) is an example of euploidy.

10. FALSE Agamospermy commonly occurs in arthropods.

11. TRUE In humans crossing-over (exchange) of genetic material occurs 2-3 times in each pair of homologous chromosomes during gamete formation.

12. TRUE Viruses are capable of undergoing a form of sexual recombination.

13. TRUE Muller's ratchet demonstrates the importance of recombination in limiting the mutational load of a population.

14. FALSE A genetic cross between an individual of unknown genotype and a homozygous recessive is called a self-cross.

15. TRUE The closer two genes are located on the same chromosome, the less chance there is of crossing over affecting their linkage.

(30 points) MULTIPLE CHOICE Circle the ONE answer that best answers the question or phrase. (3 points each).

1) A homozygous red flower is crossed with a homozygous white flower. The

resulting offspring are pink. This is an example of:

A) Blending inheritance

B) Unequal crossing over

C) Co-dominance

D) Incomplete dominance ANSWER

2) What is the primary reason for including a control within the design of an experiment?

A) To demonstrate in what way the experiment was performed incorrectly.

B) To insure that the results obtained are due to a difference in only one variable. ANSWER

C) To provide more data so that one can perform a more sophisticated analysis.

D) To test the effect of more than one variable.

E) To accumulate more facts that can be reported to other scientists.

3) From the descriptions below, the order that most logically illustrates a sequence of meiosis is which of the following?

1. formation of four new nuclei, each with half the chromosomes

2. alignment of tetrads at the metaphase plate

3. separation of sister chromatids

4. separation of the homologs; no uncoupling of the centromere

5. synapsis; chromosomes moving to the middle of the cell in pairs

A) 1-2-3-4-5

B) 5-4-2-1-3

C) 5-3-2-4-1

D) 4-5-2-1-3

E) 5-2-4-3-1 ANSWER

4) A cell has a diploid chromosome number of 2n = 4. We will designate these four chromosomes as A, B, C, D. Assume meiosis occurs with the formation of homologous pairs AC and BD. How many different types of gametes can be formed?

A) 2 (AB and CD)

B) 3 (AB, BC, and CD)

C) 4 (AB, AD, BC, and CD) ANSWER

D) 5 (AB, AC, AD, BC, and CD)

E) 6 (AB, AC, AD, BC, BD, and CD)

5) A couple who are both carriers for cystic fibrosis have two children who have cystic fibrosis. What is the probability that their next child will be phenotypically normal?

A) 0%

B) 25%

C) 50%

D) 75% ANSWER

E) 100%

6) If inheritance of a human trait is sex-linked (on the X chromosome) and recessive, any of the following could result except that :

A) expression of a trait might skip a generation

B) the trait could be more common in females than males ANSWER

C) all females might become homozygous for the trait

D) the gene for the trait might mutate to a dominant allele

E) females could be a mosaic of two cell types

7) A certain type of grass has a diploid chromosome number of 8. A similar species of grass has a diploid chromosome number of 10. Interspecific hybridizations (matings between the two species) results in sterile hybrids, which can only reproduce vegetatively. The chromosome number of the hybrids would be:

A) 9 ANSWER

B) 16

C) 18

D) 20

E) none of the above

8) The scientific method usually begins with:

A) formulating a testable hypothesis

B) making careful observations ANSWER

C) formulating a theory

D) collecting data

E) conducting a controlled experiment

9) Darwin's confirmation of evolution was supported by which of the following :

A) His ability to artificially select for particular phenotypes of pigeons and plants.

B) The observation that sea shells occurred on mountain tops.

C).The finding of fossils in the earth's strata.

D) The finding that different species filled similar roles in different parts of the world.

E) all of the above. ANSWER

10) Which of the following is true of a species that has a chromosome number of 2n = 16?

A) The species is diploid with 32 chromosomes.

B) The species has 16 different types of chromosomes.

C) There are 16 homologous pairs.

D) A gamete from this species has 8 chromosomes. ANSWER

E) A and C

(20 points) DEFINE (3 pts.) and provide an EXAMPLE (1 pt.) for each term (4 pts. each)

1) Individual Fitness: INDIVIDUAL FITNESS IS ULTIMATELY DEFINED AS BOTH THE QUANTITY AND QUALITY OF PROGENY PRODUCED BY AN INDIVIDUAL TOWARDS THE NEXT GENERATION

ANY EXAMPLE THAT DEMONSTRATE AN INDIVIDUAL'S FECUNDITY IS ACCEPTABLE HERE.

2) Polygenic Inheritance:

LECTURE: THE INHERITANCE OF A TRAIT IS CONTROLLED BY MANY GENES.

OR

(THAT ACT ADDITIVELY - I HAVE ASSUMED THIS IN LECTURE AND NOT MADE A BIG DEAL OF THIS BUT IT IS PART OF THE DEFN. IN THE TEXT). IF STUDENTS RESPOND WITH THE DEFN FROM LECTURE - THAT IS FINE.

EXAMPLES INCLUDE, SKIN PIGMENTATION, HEIGHT, WEIGHT, MUSCULATURE, INTELLIGENCE, HAIR COLOR , HUMAN BLOOD GROUP.

3) Natural Selection: ONLY MENTION SURVIVAL = 1 PT, NEED GENETIC BASIS AND DIFFERENTIAL REPRO FOR FULL CREDIT.

LECTURE:

-MORE OFFSPRING ARE PRODUCED THAT CAN THEMSELVES REPRODUCE

-VARIATION EXISTS AMONG INDIVIDUALS IN SURVIVAL AND REPRODUCTION

-VARIATION IS HERITABLE (GENETIC BASIS) FROM PARENTS TO OFFSPRING

-DIFFERENCES IN SURVIVAL AND REPRODUCTION ARE GENETICALLY BASED LEADING TO DIFFERENCES EXPRESSED BY INDIVIDUALS/PHENOTYPES IN THE LOCAL POPULATION/ENVIRONMENT!

OR

DEFN IN TEXT = DIFFERENTIAL SUCCESS IN REPRODUCTION OF DIFFERENT PHENOTYPES RESULTING FROM THE INTERACTION OF ORGANISMS WITH THEIR ENVIRONMENT. EVOLUTION OCCURS WHEN NATURAL SELECTION CAUSES CHANGES IN RELATIVE FREQUENCIES OF ALLELES IN THE GENE POOL.

MANY EXAMPLES, BISTON BETULARIA, DARWIN'S FINCHES, AND OTHERS IN THE TEXT OR FROM LECTURE.

4) Mendel's Law of Independent Assortment:

LECTURE: GENES FOR DIFFERENT TRAITS ASSORT INDEPENDENTLY TO GAMETES UNLESS THEY ARE ON THE SAME CHROMOSOME (LINKED).

OR

TEXT: INDEPENDENT SEGREGATION OF EACH PAIR OF ALLELES DURING GAMETE FORMATION .

EXAMPLE: THE STUDENTS MAY DRAW A FIGURE ILLUSTRATING THIS - OR THEY CAN DESCRIBE AN EXAMPLE.

5) Anisogamy: THE EVOLUTION OF DIFFERENT SIZED GAMETES. ONE SMALLER AND MORE MOTILE (SPERM OR POLLEN-MALE) AND ONE LARGER AND LESS MOTILE (EGG OR OVULE- FEMALE). extra info: WE HAVE DATA DEMONSTRATING THAT LARGER FEMALE GAMETE SIZE CORRELATES POSITIVELY TO LARGER ZYGOTE SIZE AND AN INCREASED PROBABILITY OF SURVIVAL OF THE ZYGOTE. EX., ANY ORGANISM EXHIBITING ANISOGAMY.

(20 points) SHORT ANSWER In the space provided, supply a concise answer to the following questions.

1. Stalk eyed flies look like regular flies, but their eyes are spread apart, located at the end of stalks. In some species, males with wider eyespans (distance between their eyes) attract more females and win more fights (and are able to successfully mate more often) than do males with shorter eye spans.

(4 points)

a) Assuming that an increase in eyespan is not detrimental to these flies' health or survival, what pattern/type of selection across many generations does this scenario represent? (1 point)

DIRECTIONAL SELECTION : 1/2 point for sexual selection

b) Label the axes, and draw onto this diagram what the new distribution would look like after many generations of this described selection. (3 points)

FREQUENCY

1 point each axis

1 point for the graph

1/2 pt NARROW WIDE

SMALL LARGE

1/2 pt EYESPAN

2. Please answer the following. (6 points)

a) What hypothesis of inheritance did Mendel 's work disprove? (2 points)

BLENDING INHERITANCE

b) Give an example of a cross where this theory is disproven (as Mendel demonstrated) showing both phenotype and genotype. (4 points)

GOAL IS TO DEMONSTRATE THE RECOVERY OF A PARENTAL PHENOTYPE (PURPLE (WW) X WHITE (ww) IN THE F2) OR THE OCCURRENCE OF A NEW PHENOTYPE ( IN THE CASE OF A HET. PURPLE X HET. PURPLE). THE BLENDING HYPOTHESIS PREDICTS THAT ALL FLOWERS WOULD BE PURPLE.

FOR EX.,

Heterozygous individuals (Ww) for the flower color alleles mate and

produce offspring. The result of this cross will show a proportion of 3

purple flowers (WW, 2Ww) to each 1 white flower (ww). The blending

hypothesis predicts that all flowers would be purple.

GENOTYPE 1 WW, 2 WW, 1 ww

PHENOTYPE 3 PURPLE TO 1 WHITE

ALSO FIG. 14.2 PG 241 - DEMØNSTRATES A CROSS THROUGH THE F2.

FIG. 14.4 PG 242

FIG. 14.5 PG 14.5- phenotype vs. genotype

3. A brown-haired, brown-eyed father and brown-haired, brown-eyed mother have a

blonde, blue-eyed child. If we assume for simplicity that brown hair (B) is dominant and blonde (b)

recessive, and if brown eyes (E) are dominant and blue eyes (e) recessive. (4 points)

a) What must the parents' genotypes be? (1 point)

BOTH parents must be heterozygous, BbEe

b) For these two parents, what is the probability that they would produce a

blonde, blue-eyed child? (1.5 point)

1/16 mom: 1/2 blue * 1/2 blonde = 1/4

dad: 1/2 blue * 1/2 blonde = 1/4

1/4 * 1/4 = 1/16

c) What is the probability that they would produce a brown-haired, blue-eyed

child? (1.5 point)

3/16 3/4 brown * 1/4 blue = 3/16

4. Feather color in budgies (bird) is determined by two different genes that affect pigmentation of the outer feather and its core. Y_B_ is green; yyB_ is blue; Y_bb is yellow, and yybb is white. The inheritance of feather color in budgies is an example of what genetic phenomena? (2 points)

EPISTASIS

5. Discuss two ways that the evolution of "sex" may be adaptive. (4 points)

1. REMOVE DISADVANTAGEOUS MUTATIONS THROUGH RECOMBINATION AND CROSSING OVER.

2. BRING TOGETHER FAVORABLE COMBINATIONS OF GENES FOR A PARTICULAR ENVIRONMENT.

3. PERHAPS EVOLVED AS A DNA REPAIR MECHANISM THROUGH MEIOSIS. DNA REPAIR REQUIRES MEIOSIS.

4. CAN GENERATE GREATER GENETIC VARIATION IN A POPULATION VIA RECOMBINATION AND CROSSING OVER.

5. INCREASED GENETIC DIVERSITY ALLOWS A QUICKER RESPONSE TO SELECTIVE PRESSURES IN ANY GIVEN ENVIRONMENT. LEADS TO DIFFERENTIAL SURVIVAL AND REPRODUCTION AMONG INDIVIDUALS IN CHANGING HABITAT. NATURAL SELECTION CAN ONLY ACT ON THE GENETIC VARIATION THAT EXISTS WITHIN A LOCAL BREEDING POPULATION.

1 point for the name of the mechanism

1 point for how it works