ch6- from chromosomes to genes

Question 1

DNA

Answer 1

• a molecule which carries heritable information from one generation to the next.
• packed into units called chromosomes
• the DNA is tightly wound around proteins called histones. (they are positive, stick to wall well)

Question 2

nucleotides

Answer 2

• repeated units formed on DNA
• four types: thymine, guanine, cytosine, adenine.
• A-T- with 2 hydrogen bonds
• G-C- with 3 hydrogen bonds
• makes them complementary

Question 2

Covalent bonds

Answer 2

• strong
• join the phosphates and sugars while nitrogen-containing bases are joined by hydrogen bonds (weak)

Question 2

nucleotide structure

Answer 2

alternating phosphates and deoxyribose sugars form the sides of the ladder, with the bases forming the rungs.

Question 3

gene

Answer 3

a section of DNA which carries coded information for making a protein or an RNA molecule

Question 4

alleles

Answer 4

different versions of a gene
- for some genes only 1 version exists so all individuals will be the same but other genes have multiple alleles and this results in differences between individuals

Question 5

meiosis

Answer 5

• the process of forming haploid cells
• most haploid cells are gametes (egg and sperm cells)
• replication of DNA, then 2 sets of cell division so that the daughter cell contains only one member of each homologous pair and one sex chromosome.

Question 6

chromatids

Answer 6

single stranded chromosome that is copied to become two identical strands.

Question 7

genome

Answer 7

-the genome of an organism is all of its DNA, both coding and non-coding, in a haploid cell.

Question 8

proteome

Answer 8

all of the protein in a cell

Question 9

genomics and proteomics together

Answer 9

result in the development of therapies for people based on their own particular genetics.

Question 10

karyotype

Answer 10

a picture of the chromosomes of an organism where the chromosomes have been paired up and arranged in order of size.

Question 11

autosomes

Answer 11

all of the chromosomes except the sex chromosomes which are X and Y in humans and most mammals.

Question 12

sex chromosomes

Answer 12

carries the gene that determines the sex of the individual

Question 13

eukaryotic chromosomes

Answer 13

-linear and consist of multiple chromosomes (humans have 46)
- organized with histone proteins
- enclosed within nucleus

Question 14

prokaryotic chromosomes

Answer 14

• single and circular
• without histones which is attached to the inside of the plasma membrane.
• contain one or more plasmids

Question 15

meiosis- prior to cell division

Answer 15

single stranded chromosomes are copied to become two identical strands (chromatids)

Question 15

meiosis- stages

Answer 15

• prophase 1
  -synapsis
  -crossing over
• metaphase 1
• anaphase 1
• telophase 1
• prophase 11
• metaphase 11
• anaphase 11
• telophase 11

Question 16

meiosis- prophase 1 (crossing over)

Answer 16

• the two close chromatids wrap around each other.
• contact point is called chiasmata
• the chromosomes at the chiasmata can break and swap pieces in a process called crossing over.
• increase in gamete variation

Question 16

meiosis- anaphase 1

Answer 16

• spindles retract towards the poles of the cell causing the homologous pairs to separate to either side.

Question 16

meiosis- prophase 1 (synapsis)

Answer 16

• ## DNA condenses and chromosomes appear

Question 16

meiosis- metaphase 1

Answer 16

• breakdown of nuclear membrane is completed
• spindle fibers attach to centromeres of the chromosomes
• the homologous pairs move to the equator of the spindle which is fully formed

Question 17

meiosis- prophase 11

Answer 17

• new spindle forms
• DNA condenses, chromosomes appear (double stranded)
• the 2 daughter cells are haploid

Question 18

meiosis- telophase 1

Answer 18

• chromosomes unwind
• spindle breaks down
• nuclear membranes form around chromosomes
  -cytokinesis occurs (the division of the cytoplasm)
• results in 2 haploid cells

Question 19

meiosis- metaphase 11

Answer 19

- the chromosomes line up in single file across the equator of the cell - spindle is connected to the centromere of the chromosome

Question 20

meiosis- telophase 11

Answer 20

- new nuclear membranes form around each bundle of cells - spindle breaks down - chromosomes unwind and disappear - new nucleoli form (RNA) - four separate cells

Question 20

meiosis- anaphase 11

Answer 20

- spindle fibres contract and pull sister chromatids apart

Question 21

role of crossing over

Answer 21

Crossing over produces new combinations of alleles on each chromosome, increasing genetic variation among offspring.

Question 22

role of independent assortment

Answer 22

- how one pair of chromosomes, and hence alleles, separates is independent of how a different pair of different chromosomes separate. - all combinations are possible

Question 23

when non-disjunction occurs

Answer 23

meiosis I- homologous chromosomes fail to separate, leading to gametes with either an extra chromosomes or missing a chromosomes meiosis II- sister chromatids fail to separate, resulting in similar errors with chromosomes numbers in the gametes.

Question 23

non-disjunction

Answer 23

- chromosomes fail to separate properly - results in cells with an abnormal number of chromosomes - an error in cell division

Question 24

chromosomal errors

Answer 24

- duplication - one segment repeated during crossing over - deletion - chromosome way be lost during cell division - inversion - DNA is read backwards - translocation - attached to non-homologous chromosome