Stages of mitosis

    • Condensation of chromosomes that consist of paired chromatids (prophase)
    • Alignment of chromosomes at cellís equator (metaphase)
    • Splitting of chromosomes into chromatids (anaphase)
    • Chromatids migrated to opposite ends of the cell (telophase)
    • (Cytokenisis, Replication) Review Animation

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What are the genotypes and phenotypes of the offspring of a Heterozygous smooth pea crossed with a Wrinkled pea?
  -   Homozygous smooth peas produce only "S" gametes
  -   Heterozygous smooth peas produce "S" & "s" gametes
  -   Pure wrinkled peas produce only "s" gametes

First, what gametes are produced by each parent?

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The Punnett square must include both parent's gametes
 

S

gamete

s

gamete

s

gamete

Ss

smooth

ss

wrinkled

s

gamete

Ss

smooth

ss

wrinkled
The genotypes are ½ homozygous recessive & ½ heterozygous
The phenotypes are ½ wrinkled & ½ smooth

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What if Mendel had crossed a smooth pea with a wrinkled pea and had gotten 50% - 50% mix?
 

?

gamete

?

gamete

s

gamete

??

??

s

gamete

??

??

Is the smooth pea homozygous (SS) or heterozygous (Ss)?

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Finally, we can use the Punnett square to consider two characters simultaneously
  -   S (smooth) is dominant to s (wrinkled)
  -   Y (yellow) is dominant to y (green)
  -   Let's cross 2 heterozygous pea plants
FIRST: what kinds of gametes can they produce?

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SY

gamete

sY

gamete

Sy

gamete

sy

gamete

SY

gamete

SSYY

SsYY

SSYy

SsYy

sY

gamete

SsYY

ssYY

SsYy

ssYy

Sy

gamete

SSYy

SsYy

SSyy

Ssyy

sy

gamete

SsYy

ssYy

Ssyy

ssyy

Why is sexual reproduction necessary?

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  -   What are the four phenotypes?
  -   What is the ratio of the phenotypes?

Smooth Yellow 9
Smooth Green 3
Wrinkled Yellow 3
Wrinkled Green 1


This (Mendelian Genetics) only works if the color and wrinkledness genes are on different chromosomes; i.e., the are not "linked."

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