Mendelian Genetics

1
Mendelian Genetics!
2
Mendel

• Studied inherited traits in flowers
• For examplecolor
• His experiment
• What conclusions can you make??

3
Further experiments

• Original Flowers
• Mated the purple flowers and got unusual results
• What can you conclude?

4
Some vocabulary

• P generation (parent)
• F1 generation (first)
• F2 generation (second)

5
Mendels ideas

• Traits come in different versions called
• Alleles there are alternative versions of a gene
  
• ex the gene for flower color has two alleles
• Different alleles vary in the sequence of DNA or
  nucleotides (ACTG) at the specific gene

Rememberyou always have two copies, one from
mom and one from dad
6
Mendels ideas

• Some traits completely mask othersthey dont
  blend
• Dominant trait If two alleles at a locus differ,
  the dominant allele determines the appearance
  (dominates)
• Ex Purple
• Recessive trait When two alleles differ, the
  recessive allele has no noticeable affect on the
  appearance (is hidden)
• Ex White

What is the only way to get a white flower??
7
Mendels Two Laws of Inheritance

• 1. Segregation
• Two alleles for a gene separate (segregate)
  during gamete formation and end up in different
  gametes.

Homologous Chromosomes
Somatic Cell
W
P
Meiosis
Gamete
W
P
8
Explaining what Mendel saw

• Lets work it out using a punnet square, looking
  at all the possible combinations of alleles from
  each generation.
• Dominant trait is always a capital letter
• Recessive trait is always lower case same letter.
• For flower color then P (purple), p (white)
• If one parent is PP and the other is pp, what
  will the offspring look like?

9
P Generation
Offspring are just combinations of parents
gametes
P P
Purple parent
Reproductive cells (egg, sperm)
P
P
Pp
p
Pp
p p
Pp
White Parent
Pp
p
F1 Generation
10
What does this tell us?

• What do these offspring look like? Why?
• Phenotype the physical appearance of a trait
• Ex all purple
• Genotype the genetic makeup of an individual
• Ex all Pp

Pp
Pp
Pp
Pp
F1 Generation
11
F2 generation
What do the offspring look like if both offspring
are Pp? Phenotype ¾ Purple ¼ White Genotype
¼ PP 2/4 or ½ Pp ¼ pp
p
P
P
Pp
PP
p
Pp
pp
12
Genotype vs. Phenotype
13
Genetic vocabulary

• Homozygous when an organism has two of the same
  alleles
• Ex PP, or pp
• Heterozygous when an organism has two different
  alleles
• Ex Pp

14
Mini Quiz

• Cystic Fibrosis is a recessive disorder.
• C normal, c cystic fibrosis
• If one parent is heterozygous for cystic fibrosis
  and the other has cystic fibrosis, what is the
  percent chance that they will have a child with
  cystic fibrosis? Show your work.
• 2. What if both parents are carriers?

15
Mendel also looked at more than on allele at a
time Dihybrids

• Monohybrid One trait at a time ex color
• Dihybrid Observing two traits at a time, ex
  color and shape!
• Color yellow (dominant) or green
• Shape round (dominant) or wrinkled

16
Possible Reproductive cells Every combination
of both genes
17
Mendels Two Laws of Inheritance

• 2. Independent Assortment
• When looking at more than one trait
• Each pair of alleles segregates independently of
  other pairs of alleles during gamete formation.
• (only works if genes are on different
  chromosomes)
• If the parent is YyRr, the possible reproductive
  cells are all combinations
• YR Yr yR yr
• Lets do a problem from your homework

18
Other ways that alleles interact

• Incomplete Dominance
• When the heterozygous condition results in a
  phenotype that is different than the dominant or
  recessive phenotype. (sometimes a combination or
  mix of the two)
• Example Snapdragons
• Red RR
• White WW
• Pink RW makes 50 less color

19

• Incomplete Dominance
• Example

100 Pink
50 Pink
25 white
25 Red
20
Codominance

• Codominance is when both alleles show up equally
  in a phenotype.
• Example Blood types.
• Alleles A, B, O
• A and B are codominant
• This is also an example of multiple alleles.

21
(No Transcript)
22
Blood compatibility

• Universal Donor Type O
• Has no proteins to be recognized by an immune
  system as foreign
• Universal Acceptor Type AB
• An individual with type AB bloods immune system
  will recognize both A and B proteins as its own.

23
Alleles a spectrum of interactions

• B black, b white
• Bb Bb Bb/BW
• Complete Incomplete Codominance
• Dominance Dominance
• Black and white
• Black Grey spots

24
Other vocabPleiotropy

• One gene can affect a number of characteristics
  in an organism
• Not always one gene one discrete trait
• Most genes are pleiotropic, cause multiple
  affects
• Cystic Fibrosis
• Sickle Cell
• Achondroplasia (dwarfism)

25
(No Transcript)
26
Epistasis

• One gene can mask another
• Ex Coat color in mice is determined by 2 genes
• Pigment, C, or no pigment, c
• More pigment (black), B, Less pigment (brown), b
• cc albino

27
Epistasis
28
Polygenic Inheritance

• Most traits are determined by the additive
  effects of 2 or more genes
• Phenotypes are a continuum
• Human traits
• Skin Color
• Height
• Weight
• Eye color
• Intelligence
• Behavior

29
Nature vs. Nurture

• How much is genetic?
• Phenotype can be affected by both genes and the
  environment.
• Ex hydrangeas, human skin color, others?

30
Sex Linked Traits