A2 Genetics Unit F215 Genetics

7/21/2019 A2 Genetics Unit F215 Genetics

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A2 Unit F215: Module 1

Control, genomes and environment

Module 1 Cellular control

Genetics

Gregor Mendel the Austrian monk who irst investigated genetics o !lant "reeding#


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A2 Unit F215: Module 1Control, genomes and environment

Module 1 Genetics

$o!ic Tick when

done

%a& '(!lain the termsgenot)!e, !henot)!e, dominant, recessive,

codominance and linkage#

%"& Use genetic diagrams to solve !ro"lems involving se(*linkage#

%c& Use genetic diagrams to solve !ro"lems involving codominance

%d& +escri"e the interactions "etween loci %e!istasis&

%e& redict !henot)!ic ratios in !ro"lems involving e!istasis#

%& Use !redicted !henot)!ic ratios to solve !ro"lems involving e!istasis#

%g& Use the chi*s-uared test to test the signiicance o the dierence

"etween o"served and e(!ected results#

%h& +escri"e the dierences "etween discontinuous and continuous

variation#

%i& '(!lain the "asis o continuous and discontinuous variation with

reerence to the num"er o genes that inluence the variation#

%.& '(!lain that "oth genot)!e and environment contri"ute to

!henot)!ic variation and wh) variation is essential in selection#


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G'/'$0C $'M0/3G4

GENE a length o 6666 that codes or the !roduction o a

66666666666 molecule#

GENETIC CODE

ALLELES dierent formso one gene, e#g777777

LOCUS the positiono a gene on a 666666666666666 and on its

homologous !artner#

GENOTYPE the 2 alleles which an organism !ossesses or a !articulargene, e#g# GG, Gg or gg# %From whom did the organism inherit each one8&

PENOTYPE the e!pressiono the "enot#pee#g# a !erson either has

c)stic i"rosis or not#

DO$INANT onl) oneo this allele needs to "e !resent or the allele

to "e 66666666666666 in the !666666666#

%ECESSI&E twoo these alleles need to "e !resent or7777##

CODO$INANCE 'oth ())e)es (re e*+())# e!pressed in the

,,,,,,,,,, of ( hetero-#"ote.

So 'oth C % /red pi"ment0 (nd

C1

/white pi"ment0 (re e!pressed if to"ether in( "enot#pe. The phenot#pe wi)) therefore 'e222..

LIN3AGE 4 5 or more "enes (re )oc(ted /)inked0 on the s(me

chromosome.

A 6


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Matching airs

1# Gene A $he !osition o a gene on a chromosome#

2# Allele 9 'ach three "ases code or one amino acidand thereore the !rimar) structure#

# Genot)!e C ne orm o a gene#

;# henot)!e + $his allele is e(!ressed even i onl) one is

!resent in the genot)!e#

5# 3ocus ' $wo identical alleles make u! the genot)!e#

# +ominant ? $he 2 alleles or one gene ound on a

homologous !air o chromosomes#

@# ecessive 0 $he e(!ression o the genot)!e#

1# ?eteroB)gous 9oth alleles in the genot)!e are ull)

e(!ressed#

11# ?omoB)gous D $he genot)!e must onl) contain these

alleles i the) are to "e e(!ressed#


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Gregor MendelEs Monoh)"rid Crosses

MendelEs theories were diicult to acce!t ") a scientiic communit) who

knew nothing o chromosomes, genes and +/A, "ack in the latter hal o the

nineteenth centur)# $oda), however, the) can "e ull) e(!lained, i lettersare used to re!resent the alleles which code or the characteristics#

e#g# 0nvestigating $allness and dwarness in !ea !lants#


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$onoh#'rid crosses contin+ed alwa)s draw a genetic diagram

emem"er $wo homoB)gous !ure*"red !arents !roduce heteroB)gous F1

os!ring and mem"ers o the F1 crossed with each other !roduce anF2

generation#

1# ?untington Es chorea is a atal condition o the nervous s)stem caused ") a

dominant allele# Most suerers do not show s)m!toms until over the age o

5# A man with the disease marries and has children in his late 2s# hat is

the !ro"a"ilit) that one o his children will have inherited the condition8

2# A dog "reeder has a +almatian "itch with "lack s!ots# 9lack allele is

dominant over "rown# ?e mated the "itch with a "rown s!otted dog and

she had three "lack and one "rown s!otted !u!!ies# hat was her

genot)!e8

# An F1 generation o geraniums all had red lowers# $he F2 included somewith white lowers#

i& +raw a genetic diagram to show how this was !ossi"le#

ii& hat ratio o red: white would "e e(!ected in the F28


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Using genetic diagrams to solve codominance !ro"lems %!age 12


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2# A "udgie ancier "red homoB)gous dark "lue with homoB)gous light "lue

"irds and o"tained all mid*"lue os!ring#

?e needed more mid*"lue, so "red the F1together# '(!lain with a

genetic diagram whether he did the "est thing to !roduce ma(imum

num"ers o mid*"lue#

/ow answer the -uestions 1 and 2 on !age 12=


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ickle cell Anaemia codominant at the cellular level %age 12


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Se! 4 )ink("e

e( in mammals is inherited via a large I and a small 4 chromosome# $here is

little room on the 4 or an) genes other than that or "eing male# 4 however

is dominant to I, so onl) one 4 is needed to "e male# ?owever, linked to the I

are man) genes vital or successul lie# 0 mutations occur to an) o thesegenes then these mutations are carried through to the ne(t generation on

the I chromosome#

$he e(am!le a"ove is the inheritance o haemo!hilia, a condition that

!revents normal "lood clotting# ? is the allele or health) clotting actors,

"ut h codes or the mutation see !ower !oint and !age 12;J125 in the te(t

"ook# Answer -uestions 1, 2 and !age 125#


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Further Kuestions

1# '(!lain wh) a man with haemo!hilia can not !ass it on to his son#

2# $he amil) tree shows the occurrence o a genetic condition called

"rach)dact)l) %short ingers Use the tree to deduce:

a& whether the allele is dominant or recessive

"& i the condition is se( linked#

'(!lain )our answers


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# ne o the genes or coat colour in cats is ound on the I chromosome, "ut

not the 4# $he allele Cgives orange ur, while C9gives "lack# $he two alleles

are codominant, and when "oth are !resent the cat has !atches o orange and

"lack known as tortoiseshell#

a& '(!lain wh) male cats can not "e tortoiseshell#

"& +raw a genetic diagram to show the e(!ected genot)!es and !henot)!es o

the os!ring rom a cross "etween an orange male and a tortoiseshell emale

cat#


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Autosomal linkage %!age 12&

$wo genes "oth on the same chromosome tend to "e inherited together and

are thereore said to "e )inked# $he) usuall) do not show inde!endent

assortment at meta!hase 1 or 2#An e(am!le in humans is the inheritance o the gene locus or A9 "lood

grou!s and the gene locus or nail !atella s)ndrome %/& which causes short

nails and !oorl) ormed knee "ones#

$he loci are ver) close together on the chromosomes as seen in the diagram#

$he ollowing would thereore "e e(!ected to result when "lood grou! and

the s)ndrome are inherited together#


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hat still might rarel) ha!!en during !ro!hase 1, which ma) allow

inde!endent assortment o these alleles8

A worked e(am!le is on !age 12#


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Epist(sis how one gene ma) control the e(!ression o another#

age 12> ke) deinition L

+oes e!istasis reduce or increase !henot)!ic variation8

Kuite oten two or more dierent genes aect the same !henot)!e

%characteristic

?ere is an e(am!le where one gene com!lements another the) work

together#


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orking antagonisticall) %against one another&

$he homoB)gous !resence o a recessive allele %e!istatic allele& ma) !revent

the e(!ression o another allele at a second locus %h)!ostatic allele

/ote the e(am!le o recessive e!istasis as seen in the lower colour o

Galvia#

Another e(am!le is human e)e colour where a gene or "rown melanin !roduction is

re-uired "eore genes or how man) la)ers o melanin are to "e laid down can "e

e(!ressed#

/ow note an e(am!le o dominant e!istasis#


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/ote and learn the three t)!ical e!istatic ratios and answer -uestions 1 ;,

!age 12@#

/ow careull) read !age 12 a"out inheritance o com"s in domestic chickens

and coat colour in mice and then answer the -uestions 1 = %!age 1& in )our

own notes#

Finall) on this to!ic, tr) the stretch and challenge A, 9 and C -uestions#


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Contin+o+s (nd Discontin+o+s &(ri(tion %!age 1


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Genot#pe (nd En:ironment contri'+te to the Phenot#pe

/ow answer -uestion

1 on !age 1=


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Can )ou think o an) o"vious e(am!les and are the) discontinuous or

continuous e(am!les8 Give detail#

Man) o the traits re-uired in agriculture are !ol)genic so the stud) o this

t)!e o genetics is ver) useul or !lant and arm animal "reeders#

ee !ower !oint e(am!les and answer -uestions 1 !age 1=#


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A2 Genetics Unit F215 Genetics

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