Genetics Part II

1
Genetics Part II

• 9B

2
Testing for Genetic Disorders

• Amniocentesis
• Chorionic Villus Sampling
• Ultrasound
• Blood Test for AFP

3
Amniocentesis

• Sample the fluid (amnion) around
• the fetus which contains millions of fetal cells

4
Chorionic Villus Sampling

• a needle is passed into the developing placenta
  sac (at this stage the placenta is called
  chorion).

5
Ultrasound
Transducer put on abdomen emits
ultrasounds Reflected waves show a continuous
image
6
Ultrasound Images
7
Blood Test for AFP

• AFP alpha-fetoprotein
• Excess could be an indicator of a neural tube
  disorder such as spina bifida

8
What the numbers mean
9
Incomplete Dominance

• R red
• And r white
• Rr pink
• (in between)

10
What is the phenotypic ratio?

• 100 pink

11

• With codominance, a cross between organisms with
  two different phenotypes produces offspring with
  a third phenotype in which both of the parental
  traits appear together. 

12
CODOMINANCE

• homozygous white cow X a roan bull 

RESULT 50 roan RW 50 white WW
13

• With codominance, a cross between organisms with
  two different phenotypes produces offspring with
  a third phenotype in which both of the parental
  traits appear together. 
• EXAMPLE ABO blood types

14
What would codominance look like to cross a white
hen and black rooster?

15
Black and white spotted
16
Co-Dominance

• Both alleles are fully expressed in the
  heterozygous phenotype
• May result in a mosaic or patchwork pattern
• Both alleles are dominant, and are represented
  with symbols like IB and IW

IBIB
IBIW
IWIW
17
Co-Dominance
IW
IB
IB
IBIB
IBIW
IW
IWIW
IBIW

• Phenotypic ratio is 121 (black checkered
  white)
• Genotypic ratio is 121 (IBIB IBIW IWIW)

18
POLYGENIC TRAITS

• Many traits such as height
• Shape
• Weight
• Color
• metabolic rate
• are governed by the cumulative effects of many
  genes.

19
Polygenic Skin Color
20
Pleiotropy

• the effect of a single gene on more than one
  characteristics

Cats that are white with blue eyes are often
deaf, white cats with a blue and a
yellow-orange eye are deaf on the side with the
blue eye. Sickle-cell anemia SS sickle cell
AS resistant to malaria
21
Fruit Flies
Drosophila melanogaster
22
Why use Fruit Flies?

• 1. Keep in small containers with corn meal and
  molasses
• 2. Grow new generation in 2 weeks
• 3. Only 8 chromosomes

23
Fruit Flies

• Drosophila is 2n 8
• 3 pairs of autosomes
• 1 pair of sex chromosomes
• Has XY system of sex determination

24
4 pairs of chromosomes
25
Wild Type Drosophilia
Red eyes Long, straight wings Antennae stick out
front 6 legs Brownish body
26
Drosophilia Mutation Can you recognize what it
is?

• Short Wing

27
Drosophilia Mutation Can you recognize what it
is?

• Yellow body

28
Drosophilia Mutation Can you recognize what it
is?

• Ebony (black) body

29
Drosophilia Mutation Can you recognize what it
is?

• White-eyed

30
Drosophilia Mutation Can you recognize what it
is?

• Leg-headed

31
Drosophilia Mutation Can you recognize what it
is?

• Curly winged

32
Morgan Hunt

• Nobel Prize in medicine 1933 on his work on
  heredity with the fruit flies

33
Morgans Lab

• His FLY ROOM lab

34
Linked Genes

• How do you know?
• If on the same chromosome, these genes tend to be
  inherited together.
• If you notice certain traits show up together
  more often than expected
• Do not exhibit independent assortment

35
Fruit Fly Linked Genes

• gene for body color Bgray
• bblack
• gene for wing length Slong
• s short (vestigial)

• EXPECT (no crossover)
• 50 gray bodies, long wings50 black bodies,
  short wings

36
Linked Fruit Fly Genes

• BbSs (Gray long) x bbss (black short)
• 41.5 gray bodies, long wings41.5 black bodies,
  short wings8.5 gray bodies, short wings8.5
  black bodies, long wings
• 17 recombinants

37
Used for Mapping Genes

• The closer the genes are to one another, the less
  frequently they recombine
• Crossing over frequency is proportional to
  distance between genes

38

• "map unit" 1 recombination frequency

39
What is sequence of genes on chromosome?

• If b vg are 17 map units,
• b cn are 9 map units,
• vg cn are 9.5 map units

• Correct sequence is
• b-cn-vg

40
Linked Genes exampleTurken
41
Blue Eggs and Silkie Rooster
42
SEX CHROMOSOMES

• Humans X and Y
• Grasshoppers and Crickets X and O
• Butterflies, fish, and birds eggs determine the
  sex (carries either Z or W) males ZZ females ZW
• Ants and Bees sex determined by chromosome number
  (females are diploid and males are haploid)

43
SRY GONAD SWITCH

• Y chromosome
• Triggers testes development
• In its absence, the person develops ovaries

44
Both in Same Organism

• Monoecious plants that have both egg and sperm
• Hermaphroditic animals that have both egg and
  sperm

45
Sex-linked Punnett Squares

• Note No trait on Y
• KEYH normal
• And h hemophilia

46
What is the genotypic ratio?

• KEY H normal
• And h hemophilia
• 50 males normal
• 50 males hemo
• 50 girls hemo
• 50 girls normal