chapter 6-8

Question 1

what are chromosomes

Answer 1

Chromosomes are condensed single molecules of DNA with associated proteins.

Question 2

what are genes

Answer 2

Genes are sequences of bases located on chromosomes that code for specific proteins. These proteins control a particular characteristic or trait of the organism.

Question 3

what are alleles

Answer 3

alleles the different forms of a particular gene

Question 4

what is a genome

Answer 4

A genome is the complete set of genetic instructions for an organism; it is the total DNA of an organism.

Question 5

Telocentric

Answer 5

Centromere is positioned at the tip of the chromosome

No p arms

Question 6

crossing over

Answer 6

involving the exchange of corresponding segments of non-sister chromatids of homologous chromosomes

Question 7

independent assortment

Answer 7

formation of random chromosome combinations during meiosis that contributes towards producing variation

Question 8

stages of meiosis

Answer 8

interphase:
-dna rep
-growth

prophase:
-chromosomes condense
-crossing over
-nuclear envelope degrades

metaphase:
line up along the equator of the cell

anaphase:
they are separated from each other and their centromeres are pulled to opposite poles of the cell by spindle fibres

telophase:
a nuclear envelope reforms around each set of chromosomes (cytokinesis)

anaphase 2:
replicated chromosomes are separated into single stranded ones by the spindle fibres pulling sister chromatids

telophase 2:
forming 4 haploid daughter cells

Question 9

incomplete dominance

Answer 9

“blending” Pink flowers

Question 10

codominance

Answer 10

equal expression AB blood type

Question 11

epigenetics

Answer 11

the study of changes in organisms caused by modifications of gene expression rather than alteration of the genetic code itself
Epigenetic factors can change how DNA in cells is packaged or how it is labelled.

Packaging of DNA in cells may be tight or may be open (see subtopic 6.2). Genes in segments of DNA that are tightly packaged are silenced, while genes in segments of DNA with open packaging are active and translated into protein.

Labelling DNA is like adding a ‘tag’ that does not alter the base sequences of genes, but can either silence genes or make them active.

Question 12

hemizygous

Answer 12

a person who has only one copy of a gene rather than the usual two copies.

Question 13

monohybrid cross

Answer 13

monohybrid cross a cross in which alleles of only one gene are involved

Question 14

linkage group

Answer 14

linkage group genes that are physically close to each other on a chromosome and are likely to be inherited together as a single unit

Question 15

linked genes

Answer 15

Are two gene loci linked?
This can be explored by a particular test cross of a known double heterozygote (AaBb) with a double
homozygous recessive (aabb).
 If the two gene loci are not linked, the genes will assort independently, and the outcome of
the test cross will be four classes of offspring in equal proportions.

 If the two gene loci are linked, the outcome of the test cross can reveal that linkage. There
will be four classes of offspring but the proportions of these will not be equal. Instead, there
will be an excess of offspring from parental gametes and a deficiency of offspring from
recombinant gametes.

Because the loci of two linked genes are physically close, the particular combination of alleles of the
genes that are present on parental chromosomes tend to be inherited together more often than
alternative combinations. These combinations of alleles can, however, be broken by crossing over
during meiosis so that new combinations of alleles are generated. The chance that this occurs
depends on the distance between the two linked genes.

Question 16

Chiasma

Answer 16

Chiasma is the point of contact between two non-sister chromosomes belonging to the homologous chromosomes.

Question 17

haploid and diploid cells

Answer 17

Haploid refers to the presence of a single set of chromosomes in an organism’s cells. Sexually reproducing organisms are diploid (having two sets of chromosomes, one from each parent).

Question 18

test cross

Answer 18

test cross a cross used to determine the genotype of an individual with an unknown genotype by crossing it to an individual with a homozygous recessive genotype

Question 19

dihybrid

Answer 19

A dihybrid cross involves the alleles of two different genes

Question 20

zygote

Answer 20

zygote, fertilized egg cell that results from the union of a female gamete (egg, or ovum) with a male gamete (sperm).

a cell formed by the union of two gametes

Question 21

Nucleotide

Answer 21

Nucleotides refer to the foundation of nucleic acids such as the polymers DNA and RNA. It is basically composed of a sugar molecule connected to a phosphate group of the nitrogen-containing bases.

Question 22

Polypeptide

Answer 22

They are the building blocks of proteins

Question 23

Non-disjunction

Answer 23

a pair of homologous chromosomes has failed to separate or segregate at anaphase so that both chromosomes of the pair pass to the same daughter cell.