Classical Genetics

Question 1

prophase

early prophase and late prophase

Answer 1

the beginning of mitosis when the chromatin begins to form chromosomes

  - centrioles split up and move to opposite poles
  - condensation of chromatin into chromosomes
  - nuclear membrane breaks down

Question 2

metaphase (and prometaphase)

Answer 2

Alignment (ie meeting of the chrms)

- spindle fibres form
 - chromosomes align on metaphase plate
 - spindle fibres attach to centromeres

Prometa: discrete chrms visible; the nuclear envelope fragments

Question 3

anaphase

Answer 3

the shortest phase of mitosis

- spindle fibres contract
 - sister chromatids separate to become daughter chromosomes 
- daughter chromosomes are pulled to opposite poles.

Question 4

telophase

Answer 4

the chromosomes start to unravel

- chromosomes decondense back into chromatin
- new nuclear membranes form

Question 5

cytokinesis

Answer 5

after mitosis is complete (ie when 2 identical nuclei have formed) 2 daughters cells separate

Question 6

euploidy and aneuploidy

Answer 6

having the correct number of chromosomes;

having the incorrect number

Question 7

prophase 1 (very important); prophase 2

Answer 7

PROPHASE I
LEPTOTENE - condensation commences
ZYGOTENE - further condensation, pairing commences
PACHYTENE - further condensation, end of pairing, crossing over ( = chiasma formation)
DIPLOTENE/DIAKINESIS - further condensation, nuclear membrane breaks down
PROPHASE 2 -

Question 8

metaphase 1; metaphase 2

Answer 8

METAPHASE I
-bivalents align on metaphase plate ie in pairs of homologous chrms (cf meta in mitosis in which indiv chrms line up on meta plate)

Question 9

anaphase 1; anaphase 2

Answer 9

ANAPHASE I
- bivalents separate and move toward opposite poles
(disjunction)

Question 10

telophase 1; telophase 2

Answer 10

TELOPHASE I - chromosomes reach poles and new nuclear membranes form

Question 11

meiosis (meiosis 1 and 2)

Answer 11

produces gametes; involves 2 separate divisions, btwn which there is no interphase ie they are back to back

DIVISION II - phrophase II - telphase II are all identical to their mitotic counterparts but involve half the number of chromosomes.

Consequences:
(I) Production of haploid gametes

(II) New combinations of paternally and maternally derived chromosomes
(III) Produces genetic recombination via chiasma formation

This brings about a huge range of variation which allows for natural selection

Question 12

metaphase 1; metaphase 2

Answer 12

METAPHASE I -bivalents align on metaphase plate

Question 13

recombination (also “crossing over” or chiasma/ta)

Answer 13

changes the combination of genes on the chromosomes; with one crossover four possible gene combinations can be produced; one of the mechanisms of maintaining and propagating change and genetic variation

Question 14

inheritance

Answer 14

the heritability of traits

Question 15

allele

Answer 15

a version of a gene; linked with variation

Question 16

uses of genetics

Answer 16

Disease diagnosis and cure (eg haemophilia, cystic fybrosis, sickle cell anaemia, Rh incompatability)
Crop and stock improvement (wheat, figs, peas, dogs, sheep)
Forensics (identity and paternity testing)
Conservation
Systematics (cf phylogeny)
Making sense of the Evolution module

Question 17

systematics

Answer 17

concept of the relationships between species;

based on evolutionary history, in a modern sense; molecular systematics based on genetic features are more reliable

Question 18

chromosome

Answer 18

(literally ‘coloured bodies’ in Latin); a condensed form of proteins and nucleic acids carrying genetic information; visible only during cell division.

Question 19

the gene

Answer 19

from ‘pangen’, a shortening of Darwin’s name for a factor that conveys traits from parent to offspring, a gene is the smallest particle representing one hereditary characteristic; the fundamental physical and functional unit of heredity (from 1909)

Question 20

chromatin

Answer 20

made of nucleic acids and proteins, like chromosomes, but looks different; it is spread out in the nucleus, relaxed

Question 21

(sister) chromatid; daughter chromosome

Answer 21

one of two strands of the chromosome, joined by the centromere;
after they are pulled apart in Anaphase, they become daughter chromosomes

Question 22

centromere

Answer 22

protein that joins that two sister chromatids

Question 23

telomere

Answer 23

the ends of the chromatids; their degradation after many cells divisions links with aging and cancer formation

Question 24

shapes of chromosomes: metacentric, acrocentric, telocentric

Answer 24

meta: chromatids joined roughly in the middle by the centromere
acro: joined nearer one end
telo: joined at the end, ie the telomeres

Question 25

karyotype

Answer 25

the full array of chromosomes of an organism; the chromosomes can usually be sorted into pairs of similar shapes and sizes

Question 26

pseudoautosomal regions (Y chrm) - Par1 and Par2

Answer 26

homologous to the X chrm, these allow the Y chrm to “pretend” to be an X during meiosis

Question 27

SRY gene and gene Eif2s3y

Answer 27

switch genes on the Y chrm; these grow the penis and testes and are involved in the production of sperm respectively. (Women have all the genetic material to be male, except for these switches.)
The presence of the SRY gene determines a human’s phenotypic sex. In mammals, this SRY gene is BROKEN in that it is always on, leading to aggression and other dangerous behaviour

Question 28

interphase

Answer 28

non-cell-division, comprising 3 parts: - G1 (period of cell growth before DNA is dup; all the materials needed for gen prod are made); S (period when DNA is dup ie when the chrms are dup); G2 (period after DNA dupd; cell prepares for div)
This always looks the same tho…

Question 29

IPMATC (like “ipmatic”)

also “I play music at the concert”)

Answer 29

mnemonic to remember the cell division cycle/s: interphase, prophase, metaphase, anaphase, telophase and cytokinesis.
To remember the function of each phase, remember:
I is for interlude;
P is for prepare;
M is for meet;
A is for apart;
T is for tear

Question 30

bivalents, ie bivalent chromosomes (meiosis)

Answer 30

homologous chromosomes which align on the metaphase plate during meiosis 1

Question 31

incomplete dominance

Answer 31

three distinct phenotypes are evident. ie the heterozygote has a different phenotype from either homozygote

Question 32

codominance

Answer 32

the phenotype of both alleles are expressed

Question 33

sex-linked disorders

Answer 33

X-linked recessive conditions will be much more common in males than females;

• Fragile X syndrome
• Duchenne’s muscular dystrophy
• Haemophilia
• Red-Green Colourblindness

Inheritance of recessive X-linked traits:

- occurs entirely or primarily in males
- skips generations
- passed from carrier mother to son

Question 34

Hardy-Weinberg Theorem

Answer 34

p^2 + 2pq + q^2 = 1
this gives us the genotypic frequencies: p^2 tells us homozygous dominant; 2pq tells us heterozygous; and q^2 tells us homozygous recessive.
P is the allelic frequency of the dominant allele, and q is the allelic frequency of the recessive allele.
p + q = 1

Question 35

assumptions behind Hardy-Weinberg theorem

Answer 35

1. ) population is large ie >30
2. ) stable gene pool, ie no migration or gene flow
3. ) no mutation (remember achondroplasia coming about by mutation)
4. ) random mating (sexual selection throws this off; this has nothing to do with how using alleles are for survival)
5. ) no natural selection

Question 36

Hardy-Weinberg equilibrium

Answer 36

when the frequencies of alleles in a population remains constant;
this is thrown off by any of the following: evolution, mutation, selective mating, migrating, or extinction

Question 37

random sampling effects (re factors that affect allelic freq over time)

Answer 37

this are all situations that “break” H-W equil due to small sampling sizes:

• genetic drift (random changes in allelic freq in a pop as a result of random variation in the reproductive success; for populations <30)
• bottleneck (occurs when a pop size is drastically reduced and then recovers; like genetic drift affecting a single generation)
• founder effect (a “bottleneck” in space, allelic freq is limited by population/s becoming isolated)

Question 38

selection (re: factors that affect allelic freq over time)

Answer 38

• directional selection (when conditions favour indivs exhibiting one extreme of a phenotypic range; occurs when the environ changes OR when members of a pop migrate)
• stabilising selection (heterozygote advantage; acts against both extreme phenotypes and favours intermediate variants; maintains the status quo, eg birth weight of humans)
• disruptive/ diversifying selection (occurs when conditions favour indivs at both extremes of a phenotypic range over indivs with intermed phenos)