Biology

Question 1

Know the definitions of independent assortment and crossing over.

Answer 1

Independent Assortment:
Definition: The random distribution of maternal and paternal chromosomes into gametes during meiosis.
Stage of Occurrence: Metaphase I of meiosis.
Effect: Produces genetic variation by shuffling different combinations of chromosomes.
Crossing Over:
Definition: The exchange of genetic material between non-sister chromatids of homologous chromosomes.
Stage of Occurrence: Prophase I of meiosis.
Effect: Produces genetic variation by creating new allele combinations on chromosomes.

Simply: Independent Assortment: Random distribution of homologous chromosomes during Metaphase I
Crossing Over: Exchange of genetic material between homologous chromosomes during Prophase I

Question 2

Know that DNA is a double helix made of nucleotides which consist of the following components:

Answer 2

Phosphate
Deoxyribose Sugar
Base (Adenine [A], Thymine [T], Guanine [G], and Cytosine [C])

Question 3

Understand how to create a complementary strand of DNA using the bases listed above.

Answer 3

A pairs with T
G pairs with C

Question 4

Know the definitions for genes and chromosomes and understand how they link to DNA.

Answer 4

Gene: A segment of DNA that codes for a protein or trait.
Chromosome: A structure made of DNA and protein that contains genes.

Question 5

Know how many autosomes and sex chromosomes humans are supposed to have.

Answer 5

22 pairs of autosomes
1 pair of sex chromosomes (XX or XY)

Question 6

Understand the DNA replication process. Be able to identify the three steps of DNA replication.

Answer 6

Steps: Initiation, Elongation, Termination

1. First, helicase unzips the double helix of DNA by breaking the hydrogen bonds between the nucleotides on opposing strands. SSB or single-stranded binding proteins keep the strands separated and topoisomerase prevents the DNA strand from supercoiling.
2. Second, primase creates a RNA primer on each strand which you can think of as a “helicopter landing platform”. DNA polymerase (III) can then attach to each primer and build 2 new strands of DNA in the 3’-5’ direction. Now, all of this is happening simultaneously as the helicase is unzipping the double helix. Therefore, the DNA polymerase on the 5’-3’-strand has to do it in increments, creating so called Okazaki fragments, while the leading strand can do it in “one go”. For this reason, we call the 3’-5’ strand the “leading strand” and the 5’-3’ strand the “lagging strand”.
3. Finally, RNAse H removes the “excess” RNA primers and DNA polymerase (I) fills in the corresponding DNA. Ligase then glues together all of these fragments into one DNA strand.
   After this whole process you end up with 2 identical new DNA molecules that contain 1 “original” strand and 1 “new” strand. The process is therefore said to be semi-conservative.

Question 7

Be able to explain why DNA replication is semi-conservative.

Answer 7

Each new DNA molecule consists of one old strand and one new strand.

Question 8

Know the difference between genotype and phenotype and be able to determine the genotype and phenotype given some context.

Answer 8

Genotype: The genetic makeup (e.g., AA, Aa, aa)
Phenotype: The physical expression of the genotype (e.g., blue eyes, brown hair)

Question 9

Know what an allele is and be able to identify it on a chromosome.

Answer 9

Allele: A variant form of a gene.

Question 10

Know the difference between dominant and recessive genes and how to represent them using upper and lower case letters.

Answer 10

Dominant: Represented by an uppercase letter (e.g., A)
Recessive: Represented by a lowercase letter (e.g., a)

Question 11

Know the difference between homozygous and heterozygous.

Answer 11

Homozygous: Two identical alleles (e.g., AA or aa)
Heterozygous: Two different alleles (e.g., Aa)

Question 12

Be able to fill in a Punnett square given the phenotype or genotype of two individuals.
Be able to use a Punnett square to determine the phenotypic ratio and the percentage of offspring which will show particular traits.

Answer 12

Yep.

Question 13

Be able to list, label and explain all the stages of mitosis:

Answer 13

Interphase: Cell growth and DNA replication
Prophase: Chromosomes condense, spindle fibers form
Metaphase: Chromosomes line up in the middle
Anaphase: Chromosomes separate to opposite sides
Telophase: Nuclear membranes start to form
Cytokinesis: Cytoplasm divides, forming two cells

Question 14

Know the difference between mitosis and meiosis.

Answer 14

Mitosis: Produces two identical diploid cells

Meiosis: Produces four genetically unique haploid cells

Question 15

Understand why mitosis and meiosis are important for humans.

Answer 15

Mitosis: Growth and tissue repair

Meiosis: Genetic diversity and sexual reproduction

Question 16

Understand the difference between a diploid cell and a haploid cell.

Answer 16

Diploid: Two sets of chromosomes (2n)

Haploid: One set of chromosomes (n)

Question 17

Understand how independent assortment and crossing over contribute to genetic variation.

Answer 17

Yep.

Question 18

Know that a female offspring has two X chromosomes, whereas a male offspring has an X and a Y chromosome.

Answer 18

Yep.

Question 19

Understand how diseases can be sex-linked and how they might be inherited by offspring.

Be able to fill in a Punnett square for sex-linked diseases.

Answer 19

Yep.