as 90715 describe the role of dna in relation to gene expression
Download
Skip this Video
Download Presentation
AS 90715 Describe the role of DNA in relation to gene expression

Loading in 2 Seconds...

play fullscreen
1 / 22

AS 90715 Describe the role of DNA in relation to gene expression - PowerPoint PPT Presentation


  • 70 Views
  • Uploaded on

Part Four…. AS 90715 Describe the role of DNA in relation to gene expression. Determination of Phenotype. Take me to NZQA Documents relating to this standard. Contents. Monhybrid and Dihybrid crosses Incomplete/ Codominant Multiple Alleles and Lethal Genes Linked Genes Recombination

loader
I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
capcha
Download Presentation

PowerPoint Slideshow about ' AS 90715 Describe the role of DNA in relation to gene expression' - hanae-french


An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript
as 90715 describe the role of dna in relation to gene expression
Part Four…

AS 90715Describe the role of DNA in relation to gene expression

Determination of Phenotype

Take me to NZQA Documents relating to this standard

contents
Contents
  • Monhybrid and Dihybrid crosses
  • Incomplete/Codominant
  • Multiple Alleles and Lethal Genes
  • Linked Genes
  • Recombination
  • Chromosome Mapping
  • Sex Linked genes
  • Pedigree charts
  • Pleiotropy and Polygeny
  • Epistasis
  • Epigenetics
some words you may recognise
Some words you may recognise
  • Phenotype
  • Genotype
  • Recessive
  • Dominant
  • Homozygous
  • Heterozygous
  • Punnet Square
  • Allele
  • Gene

R

RR

Red hair

r

Rr

Hair Colour

R

slide4
MONOHYBRID CROSSES

The cross of the F1 generation:

Gametes

Offspring

PP is homozygous dominant

pp is homozygous recessive

Pp is heterozygous

Also called “pure breeding”

The genotype is a description of the genes contained in the individual

The phenotype is a description of its physical appearance (e.g. Purple)

l2 revision
L2 Revision

In bears, white ears are recessive to black

Momma bear (white)

What is the genotype of Momma Bear?

Momma bear=__________

 Poppa bear (black)

What genotypes could Poppa Bear have?

Poppa bear=________ or _______

This is baby bear (white eared).

What is his genotype?

Baby bear =

Can we say something more about Poppa’s genotype?

slide6
DIHYBRID CROSSES

Not linked (not on the same chromosome).

In “Quarks” Two eyes (E) is dominant to one eye and Triangular shape (T) is dominant to Pentagonal.

2 Quarks both EeTt are crossed:

Page 115

alleles that are not dominant and recessive
Alleles that are not dominant and recessive!

In yr 10, yr 11 and yes again in yr 12 we lead you to believe that alleles were either recessive or dominate. But now that you are big grown up yr 13s – it is time we expanded you understanding!

  • Some alleles are:
  • Co-dominate
  • Incomplete dominant
  • Lethal
  • Multiple
  • Linked
  • Sex linked

Yeah sure some alleles are dominant and recessive

incomplete dominance and codominance
Incomplete Dominance and Codominance

In Incomplete Dominance an intermediate phenotype is produced:

In Codominance both alleles are expressed at the same time:

slide9
Multiple Alleles

It is possible to have more than 2 alleles for a particular trait.

Example – In humans the blood group is determined by 3 alleles

A common example is the ABO blood groups in humans:

O is non-functional

A forms a protein with A antigen

B forms a protein with B antigen

A and B are codominant

lethal genes
Lethal Genes

Lethal genes are ones that cause death in the individual. The lethal gene may be dominant or recessive.

In the heterozygous individual there may be some observed difference, e.g. Manx (tailless) cats. Even when dominant the lethal gene may be passed on if it does not have onset until after reproductive age (e.g. Huntington’s).

slide11
LINKED GENES

Linked genes are on the same chromosome.

This means that when cell division occurs the 2 genes are likely to stay together.

So where we might expect a offspring phenotype ratio of 1:1:1:1, we actually get something else.

Two genes B (Bent) and D (Dark) are linked.

For a cross between BbDd and bbdd…

Draw the gametes each could form.

Draw a punnet square for the cross.

Explain these results:

Bent Dark: Bent Light: Straight Dark: Straight Light

24

1

3

22

B and D (and b and d) are linked. The 1 Bbdd and 3 bbDd individuals are due to crossing over. The different numbers are due to random chance.

Page 110

slide12
RECOMBINATION

B

A

B

A

A

B

A

B

A

b

B

a

a

b

a

b

a

a

b

b

Recombination (crossing over) during meiosis increases gamete variation.

1. Homologous chromosomes line up

3. Meiotic division

Expected gamete

Recombinants

2. Chiasma forms, segments swap

Expected gamete

4. Mitotic division

The closer the genes, the more likely they stay together

Page 111

slide13
No. of recombinants

Crossover value (%) =

 100

No. of offspring

CHROMOSOME MAPPING

We can “map” the distance between 2 genes by comparing how often the cross over.

Low cross over value = not often recombined = close together

Page 114

slide14
SEX LINKED GENES

Carried on the X-chromosome.

As opposed to autosomal.

Males only have 1 allele – more susceptible to recessive diseases, e.g. colour blindness. DO NOT SAY WHAT YOU SEE.

X is normal, Xcis colour blind. Y carries no information.

So… XX is a normal female

What other possibilities can you have?

Explain why it is less common for women to be colour blind.

XcX = normal female XcXc = colour blind female

XY = normal male XcY = colour blind male

slide15
In cats one aspect of coat colour is controlled by a sex-linked gene with alleles that are codominant.

These 2 females (XoXo) and (XbXb) are crossed with a male (XbY)…

Draw Punnett squares to find the offspring of each cross.

What is the XbXo offspring called?

How do we get male Tortoiseshell?

Page 121-2

slide16
PEDIGREE CHARTS

Dead

Males

Normal

Affected (but not dead – yet)

Females

Page 128-9

slide17
GENE-GENE INTERACTIONS

Pleiotropy: One gene ( one protein) controls many phenotypes

40% of cats with white fur and blue eyes are deaf.

Marfan syndrome: one gene is responsible for thinness, joint hyper mobility, limb elongation, lens dislocation, and increased susceptibility to heart disease.

The p53 gene directs damaged cells to stop reproducing, thereby resulting in cell death… helps avert cancer. BUT it also suppresses the division of stem cells, preventing replacement of deteriorating tissues during aging.

Polygeny: Many genes control one phenotype (e.g. Human skin colour, cat coat colour)

Epistasis:Two genes interact, mask, or modify. There are a number of types…

Lab manual page 133

slide18
EPISTASIS

PC

Pc

pC

pc

ppCC

PPcc

PC

Pc

PpCc

pC

pc

One gene alters the outcome of another

Substance

Product A

Product B

Enzyme 1

Enzyme 2

Complementary genes: Both need to be present for either to work.

In a flower, 2 genes control the production of a purple pigment. The intermediate product has no colour.

White

White

Purple

Gene P

Gene C

Can we cross 2 white plants to get purple offspring?

What will the genotype ratio of the dihybrid cross be?

9:7

Think 9:3:3:1, but group the last 3 sets.

slide19
Supplementary genes:the second gene adds more to the first.

Coat color in Labrador retrievers: two genes (B and E)

A black dogis B_E_

Yellow

Brown

Black

Gene E

Gene B

  • What are the genotypes of two black parental dogs that, when mated, produce black puppies, yellow puppies and brown puppies?
  • b. What proportions of black and yellow puppies do you expect from this cross?
  • c. This cross is an example of a what type of gene interaction?

Lab manual page 135/6

slide20
COLLABORATION

This is where 2 genes interact to make a product different to that which either could make independently.

The most common example is comb types in chickens.

rose

Gene P

Gene R

single

Walnut

Gene P

pea

Gene R

rrpp

rrP_

R_pp

R_P_

See more chickens…

Page 132

Summary 138

slide21
EPIGENETICS

This is where gene expression is affected without changing the underlying DNA code.

e.g. a zygote (toti-potent) becomes more and more specialised by turning different genes on or off.

e.g. Genomic Imprinting.

Some genes can be activated or silenced depending on which parent they came from. The ‘switch’ used to silence or activate a gene is often methylation of cytosines – this inhibits that region of the DNA.

slide22
GENE-ENVIRONMENT INTERACTIONS

This is where gene expression is affected by the environment.

Some organisms are affected by temperature, altitude or the presence of members of the opposite sex or competitors/predators.

Page 125-6 (opt)

ad