Chapter 16: Inherited Change

Question 1

How many PAIRS of matching chromosomes do humans have?

Answer 1

22

Question 2

what is the definition of ‘homologous’?

Answer 2

similar in structure and composition

Question 3

what are the non-matching chromosomes in humans?

Answer 3

the sex chromosomes

Question 4

name the two types of chromosomes

Answer 4

sex chromosomes

autosomes (all the other chromosomes)

Question 5

each chromosome has a characteristic set of … which code for different features

Answer 5

genes

Question 6

what is the locus?

Answer 6

the position on the chromosome where genes for particular characteristics are always found

Question 7

definition of a homologous chromosome

Answer 7

pair of chromosomes in a diploid cell that have the same structure as each other, with the same genes at the same loci, and that pair together to form a bivalent during the first division of meiosis

Question 8

definition of a gene

Answer 8

a length of DNA that codes for a particular protein or polypeptide

Question 9

definition of an allele

Answer 9

a particular variety of a gene

Question 10

definition of a locus

Answer 10

the position at which a particular gene is found on a particular chromosome; the same gene is always found a the same locus

Question 11

name the two types of nuclear division

Answer 11

growth and sexual reproduction

Question 12

what type of nuclear division is growth?

Answer 12

mitosis

Question 13

what type of division is sexual reproduction?

Answer 13

meiosis

Question 14

define ‘haploid’

Answer 14

a cell which contains only one complete set of chromosomes

Question 15

events in middle prophase 1

Answer 15

• homologous chromosomes pair up (synapsis)
• each pair is a bivalent
• centrosomes move to opposite ends of the nucleus

Question 16

events in metaphase 1

Answer 16

-bivalents line up across equator of spindle, attatched by centromeres

Question 17

events in late prophase 1

Answer 17

• nuclear envelope breaks up as in mitosis
• crossing over of chromatids may occur
• nucleolus ‘disappears’
• spindle forms

Question 18

events in metaphase 1

Answer 18

-bivalents line up across equator of the spindle, attached by centromeres

Question 19

events in anaphase 1

Answer 19

• centromeres do not divide

- whole chromosomes move towards opposite ends of the spindle, centromeres first, pulled by microtubules

Question 20

events in telophase 1

Answer 20

-nuclear envelope re-forms
-nucleolus re-forns
cytokinesis
-chromosomes reach poles of spindle

Question 21

events in prophase 2

Answer 21

• nuclear envelope and nucleolus disperse

- centrosomes and centrioles replicate and move to opposite poles of the cell

Question 22

events in metaphase 2

Answer 22

chromosomes line up separately across equator of spindle

Question 23

events in anaphase 2

Answer 23

• centromeres divide

- spindle microtubules pull the chromatids to opposite poles

Question 24

events in telophase 2

Answer 24

four haploid daughter cells are formed

Question 25

define 'spermatogenesis'

Answer 25

the formation of male gametes

Question 26

define 'oogenesis'

Answer 26

the formation of female gametes

Question 27

define 'genotype'

Answer 27

the alleles possessed by an organism

Question 28

define 'homozygous'

Answer 28

having two identical alleles of a gene

Question 29

define 'heterozygous'

Answer 29

having two different alleles of a gene

Question 30

what is an 'allele?'

Answer 30

different varieties of the same gene

Question 31

define 'phenotype'

Answer 31

its characteristics, often resulting from an interaction between its genotype and its environment

Question 32

define 'dominant allele'

Answer 32

one whose effect on the phenotype of a heterozygote is identical to its effect in a homozygote

Question 33

define 'recessive allele'

Answer 33

one that is only expressed when no dominant allele is present

Question 34

define 'codominant alleles'

Answer 34

where both alleles have an effect on the phenotype of a heterozygous organism

Question 35

define 'F1 generation'

Answer 35

the offspring resulting from a cross between an organism with a homozygous dominant genotype, and one with a homozygous recessive genotyope

Question 36

define 'F2 generation'

Answer 36

the offspring resulting from a cross between two F1 (heterozygous) organisms

Question 37

define 'test cross'

Answer 37

a genetic cross in which an organism showing a characteristic caused by a dominant allele is crossed with an organism that is homozygous recessive; the phenotypes of the offspring can consequently be a guide to whether the first organism is homozygous or heterozygous

Question 38

define 'linkage'

Answer 38

the presence of two genes that are on the same chromosome, so that they tend to be inherited together and do not assort independently

Question 39

define 'gene mutation'

Answer 39

a change in the structure of a DNA molecule, producing a different allele of a gene

Question 40

what is a 'silent mutation'

Answer 40

a mutation that has no apparent effect on an organism