Genetics

1
Genetics

• Lab 3

2
Genes Alleles

• Gene Basic unit of heredity. A short sequence
  of DNA that codes for a polypeptide.
• Example the gene that codes for flower color in
  peas.
• Allele one of two or more forms of a gene.
• Example purple or white for flower color in
  peas.

3
Dominant vs. Recessive

• Dominant allele that controls the appearance of
  heterozygotes.
• Example an individual with alleles for purple
  and white will appear purple.
• Recessive allele that is masked in the presence
  of a dominant allele.
• Example white flowers only appear when only
  white alleles are present.

4
Dominant vs. Recessive

• Co-dominant heterozygotes appear to be
  intermediate between the two homozygous forms.
• Example legs in dragons.
• LL 4 legs Ll 2 legs ll 0 legs.

5
Homozygous vs. Heterozygous

• Homozygous both alleles are the same.
• Hom. Recessive shows recessive trait.
• pp pea flowers appear white.
• Hom. Dominant shows dominant trait.
• PP pea flowers appear purple.
• Heterozygous two different alleles.
• Pp pea flowers appear purple.
• Ll dragons have 2 legs.

6
Genotype vs. Phenotype

• Genotype which ALLELES are actually present.
• PP, Pp, pp
• Phenotype what the organisms LOOKS like.
• Purple, white

7
Punnett Square

• A purple flowered plant PP is crossed with a
  white flowered plant pp. PP x pp.
• PP can pass on only one of the two alleles P or
  P.
• pp can pass on only one of the two alleles p or
  p.

8
Punnett Square
PP x pp
P
P
p
Pp
Pp
Genotype All Pp
p
Pp
Pp
Phenotype all Purple
9
Monohybrid Cross

• Monohybrid cross examines how one trait is
  passed on when both parents are heterozygous for
  the trait.

10
Monohybrid Cross Punnett Square
Pp x Pp
P
p
PP
Pp
P
Genotype 1PP2Pp1pp
Pp
pp
p
Phenotype 3 purple 1 white
11
Dihybrid Cross

• Dihybrid cross examines how two traits are
  passed on when both parents are heterozygous for
  both traits.
• Flower color in peas
• P allele is dominant for purple flowers.
• p allele is recessive for white flowers.
• Plant height in peas
• T allele is dominant for tall plants.
• t allele is recessive for short plants.

12
Dihybrid Cross - PpTt x PpTt

• Each parent is the same and can donate the same
  alleles.
• PpTt P with T PT
• PpTt P with t Pt
• PpTt p with T pT
• PpTt p with t pt

13
Dihybrid Cross - PpTt x PpTt
PT
Pt
pT
pt
PT
PPTT
PPTt
PpTT
PpTt
Pt
PPTt
PpTt
Pptt
PPtt
Genotypes
pT
PpTT
PpTt
ppTt
ppTT
pt
PpTt
Pptt
ppTt
pptt
14
Dihybrid Cross - PpTt x PpTt

• Phenotypes
• 9 purple, tall (P_T_)
• 3 purple, short (P_tt)
• 3 white, tall (ppT_)
• 1 white, short (pptt)