Eduard Strasburger

Walther Flemming

Meiosis & Mitosis

I.

Animation 3.2

Animation 3.3

II.

Genes exist, come in pairs

Gametes – only 1 gene copy

pair of copies SEGREGATE

alleles combine randomly

In offspring

Each gamete – only 1 gene copy

START

A / a

a+ / a

Genes exist, come in pairs Gametes – only 1 gene copy

pair of copies SEGREGATE

What aboutsecond law?

Animation 5.1a

Mendel’s 2nd Law:Genes segregate independently

אין תלות בין גנים בסגרגציה )הפרדה(

Recombinant Parental Recombinant Parental

Parental

R/r Y/y

If we have a third genefor seed size –big>small:

B/b, and TRI-hybrids

¾of these seeds will be big

¼of these seeds will be small

¾of these seeds will be big

¼of these seeds will be small

¾of these seeds will be big

¼of these seeds will be small

¾of these seeds will be big

¼of these seeds will be small

27/64

9/64

9/64

3/64

9/64

3/64

3/64

1/6464/64

9

3

3

1

YY

Yyyy

If we look at theGENOTYPE ratios-

With a second genefor seed texture–

round/wrinkled:

1/4 of these seeds will be RR2/4 of these seeds will be Rr

1/4 of these seeds will be rr

1/4 of these seeds will be RR2/4 of these seeds will be Rr

1/4 of these seeds will be rr

1/4 of these seeds will be RR2/4 of these seeds will be Rr

1/4 of these seeds will be rr

1/162/161/16

2/164/162/16

1/162/161/1616/16

Genotype ratios: 1:2:1:2:4:2:1:2:1Phenotype ratios: 9:3:3:1

• Mendel’s rules are relevant for organisms that sexually reproduce: diploid/haploid

–Plants, Animals, many Monera…

Those that ‘do’meiosis

Sex chromosomes: The breakthrough to the chromosomal theory of inheritance

III-IV

Nettie Stevens Thomas H.

Morgan

Thomas H. Morgan

Board

Reciprocal

White RedMothers Fathers

Red WhiteDaughters Sons

習字 書道

המופיליה

F6

F7

אחיות כנשאיות – לא חולות

To be a male: Fly: ratio of X chromosomes to autosomes = 1

Man: Presence of Y chromosome

Barr body

For ‘dosage compensation’, 1 X chromosome is condensed, silenced in females

Y?

Y linked trait??

First Second (reciprocal)

MammalsFruitflies Moth

s

Homogametic Heterogametic Heterogametic Homogametic