Ch.9 Patterns of inheritance

1
Ch.9 Patterns of inheritance

• Gregor Mendel

2
Mendels discoveries

• Blending- Hereditary material- Both parents
  contribute genetic material.
• Inheritable factors, genes are passed from
  generation to generation

3
(No Transcript)
4
Pea experiments

• Worked with 7 traits
• Used purebreeding plants first then crossed them.

5
Know the vocabulary

• Homozygous- TT or tt - the same version
• Heterozygous- Tt- two different versions
• Phenotype - What you see ( look like)
• Genotype - The genes TT,Tt, or tt

6
Mendels Pea Crosses
7
Law of independent assortment.

• homologous chromosomes move independently.
• Ex. Chromosome with A or a will go separate from
  chromosome with B or b.

8
Law of Segregation

• Homologous pairs segregate during gamete
  formation(meiosis) and pair again after
  fertilization
• Ex. If a pea is Pp then half the gametes will
  receive a P and half a p.

9
Testcross
10
Dihybrid Cross
11
Incomplete dominance

• Incomplete dominance leads to a blending of
  traits, red white yields pink

12
Codominance
13
Codominance

• Codominance - A and B are both dominant to O but
  not to each other, giving the AB blood type

14
Epistasis

• One gene has an effect on another. C leads to
  deposition of color while B or b leads to color
  BBcc would be white even though the genes code
  for black color.

15
Polygenic inheritance

• Combinations of genes can yield cumulative
  effects. The more dominant alleles the more
  color.

16
Environmental Effects

• Sometimes the environment can change the way a
  gene is expressed, like these hydrangia, and the
  color based on pH of the soil.

17
Pleiotropy

• One gene can have an effect on other parts of the
  body. The sickle cell gene which causes problems
  with blood cells has far reaching affects on the
  body.

18
Sample problems
Mendel crossed short and tall pea plants(purebred
cross) TT x tt P gen. t t T Tt Tt
All offspring are heterozygous T Tt Tt All
are tall (Tt)
19
Mendel crossed round, yellow pea plants to
wrinkled, green pea plants (RRYY x rryy) The
only possible gametes are RY from parent 1 and ry
from parent 2 so ry ry RY RrYy RrYy
All offspring are round RY RrYy RrYy and
yellow (RrYy)
20
Monohybrid Cross -two heterozygotes mated Tt xTt
T t T TT Tt 1TT2Tt1tt t Tt
tt 3 tall 1 short
21
Dihybrid cross Heterozygotes for 2 traits are
crossed RrYy x RrYy You can make the folowing
gametes for each parent RY,Ry,rY,ry, this means a
four by four box as in the next slide
22
Dihybrid Cross
23
Dihybrid crosses can also be done like this
R r Y y R RR
Rr Y YY Yy r Rr rr
y Yy yy Now calculate the chances
of RRYY (1/4 x 1/4) RRYy (1/4 x2/4) RrYY
(2/4 x 1/4) RRyy (1/4 x 1/4) RrYy ( 2/4 x
2/4) Rryy (2/4 x 1/4) rrYY (1/4
x/1/4) rrYy (1/4 x 2/4) rryy (1/4 x 1/4)