Genetics

Question 1

purines vs pyrimidines

Answer 1

Adenine and Guanine. Larger because they have two ring like structure

Cytosine, thymine, uracil. Smaller because they have a single ring structure.

Question 2

what is DNA composed of

Answer 2

phosphate group (which makes the molecule negative), pentose sugar, nitrogen base (A,G,C,T)

Question 3

Linkage of nucleotides

Answer 3

5’ phosphate (C5) - 3` OH (C3)

• phosphodiester bond (covalent)
• catalysed by a polymerase

Question 4

DNA packaging

Answer 4

Nucleosome- double-stranded DNA loops around 8 histones twice (building block of chromatin)
Chromatin- DNA proteins that condense to form chromosomes during eukaryotic cell division
Histones- positively charged proteins that wrap up DNA through interactions between their positive charges and the negative charges of DNA

Question 5

Human chromosomes

Answer 5

• each chromosomes is made from a single molecule of DNA and proteins (HISTONES)
• 46 chromosomes
• 22 pairs of Autosomes
• 1 pair of sex chromosomes
• diploid (2n) (two complete sets of chromosomes - one from each parent)

Question 6

Interphase

Answer 6

cell grows and DNA is replicated

G0- nondividing differentiated state. Cells may receive signals instructing them to withdraw from the cell cycle and enter G0, or visa versa
G1- longest phase. phase where great cell growth occurs.
S- synthetic phase, replication of DNA.
G2- scan for damages that can be repaired before mitosis. replenishment of energy storages.

Question 7

Miotic phase

Answer 7

MITOSIS:
- prophase- chromosomes start to condense, nucleolus disassembles, miotic spindles start to form (miotic spindles- structure made from microtubules - strong fibres)

• prometaphase- nuclear envelope breaks down, chromosomes fully condense, miotic spindle grow, some of the kinetochore microtubules attach to the chromosomes
• metaphase- spindles line the chromosomes at the metaphase plate. two kinetochores of each chromosome should be attached to microtubules from opposite spindle poles.
• anaphase- kinetochore microtubules pull chromosomes towards poles, the sister chromatids separate from each other (becoming separate chromosomes)
• telophase- chromosomes start to decondense, spindles broken down, nuclear membrane forms (around each set of chromosomes), nucleolus reappears

CYTOKINESIS:
- the division of the cytoplasm to form two new cells (starts in anaphase, finishes after telophase)

Question 8

Meiosis

Answer 8

Prophase I - homologous chromosomes will pair together- chromatid crossover, created non-recombinant chromosomes. These cross over events are the first source of genetic variation

Prometaphase I- Attachment of the spindle fibre microtubules to the kinetochore proteins at the centromeres

Metaphase I- the homologous chromosomes are arranged at the metaphase plate. Independent assortment- 2nd mechanism that introduces variation into gametes.

Anaphase I - the microtubules pull the chromosomes apart

Telophase I and cytokinesis- cell divides in two

Meiosis II- same as meiosis I, except each cell has only one set of chromosomes with 2 chromatids which are separated to generate the daughter cells

Question 9

polyploidy

Answer 9

increase in the complete set of chromosomes

- occurs due to non-disjunction (failure to separate)

Question 10

Aneuploidy

Answer 10

• one or more chromosomes are absent or present
  Occurs due to non-disjunction
  e.g. trisomy for chromosome 21 (down syndrome)

Question 11

central dogma

Answer 11

the process by which the instructions in DNA are converted into a functional product

Question 12

Different types of RNA

Answer 12

mRNA- directs amino acid sequence of polypeptides
tRNA- binds to amino acids and directs them to proper locations within the growing polypeptide chain
rRNA- component of the ribosomes that serve as the site of protein synthesis

Question 13

gene

Answer 13

sequence of nucleotides in DNA or RNA that codes for a molecule that has a function.
Genes are the units of inheritance and are responsible for carrying the genetic information from one generation to another.

Question 14

allele

Answer 14

gene variants that arise by mutation and exist at the same relative locations on homologous chromosomes are called alleles.

Question 15

homozygous vs heterozygous

Answer 15

homozygous have two identical alleles for a specific gene on their homologous chromosomes whereas heterozygous have different alleles.

Question 16

genome

Answer 16

complete set of DNA, including all of its genes. contains all the information needed to build and maintain the organism.

Question 17

Mendel’s law of inheritance

Answer 17

First law- Law of segregation: during gamete formation, the alleles for each gene segregate from each other so that each gamete carries only one allele for each gene.

Second law- Law of independent assortment: genes for different traits can segregate independently during the formation of gametes.

Third law- Law of dominance: some alleles are dominant while others are recessive; an organism with at least one dominant allele will display the effect of the dominant allele.

Question 18

genotype vs phenotype

Answer 18

genotype- all of the organisms genetic information

phenotype- the set of observable physical traits (hair/eye colour…)

Question 19

somatic mutation

Answer 19

can occur in any of the cells of the body except the germ cells (sperm and egg) and therefore are not passed on to progeny

Question 20

germline mutation

Answer 20

any detectable and inheritable variation in the lineage of germ cells. mutations in these cells are transmitted to offspring.

Question 21

SNP

Answer 21

single nucleotide polymorphism- most common type of genetic variation found among people.
- substitution
- deletion
- insertion
- inversion
( not all SNPs or mutations change the final message)