Friday - March 28th 2008

*on whiteboard*

Exam is next friday - April 14th.

1.) New Homework questions for Ch15.

2.) Answers to homework Ch. 14

3.) Practice exam 3

Q & A session on Thursday, April 3rd at 6pm, E112   anatomy/zoology bldg.

 

Here's what we did for notes as far as this class for on the .cam screen:

1:2:1 phenotypic ratio

red, pink, white

 

1:2:1  -Genotypic ratio

Homozygous red, Heterozygous pink, Homozygous white.

 

 

Chapter 15 - Chromosomal basis of Inheritance

 

FISH = Fluorescence in situ hybridization.

• locate genes on chromosomes
• (need to know DNA sequence)
• make a probe of the sequence
• hybridize using DNA DNA base parity and everywhere that sequence is located you can find with a fluorescent tag.

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2 of mendel's Laws:

• Law of Segregation: Dring gamete formation 2 alleles separate.
• Law of Independent assortment: have non-homologous chromosomes and the way one aligns on plate on metaphase one is independent of how the ohters line up on metaphase plate. Its pretty much at random.

 

• The genetic makeup of the gametes is determined by the meiotic segregation patterns of the chromosomes.

WAY EARLY 1900's (1902) Chromosomal theory of inheritance was developed.

• Genes are located on Chromosomes
• the way the chromosomes are distributed during meiosis determines inheritance patterns in the following generation.

 

***QUOTE: "Last time talked about the yellow & round seeds characteristics on the chromosomes themselves now."***

Looking at slide LE 15-2

 

F1 plants heterozygous for charracteristics.

SLIDE 2: DIhybrid cross'

INDEPENDENT ASSORTMENT Rr or RR - whichever.

LAW OF SEGREGATION -

 

KNOW : 9:3:3:1 Dihybrid Cross and independent assortment of Genes

 

Genes that are linked together on the same chromosome.

 

Linkage: genes that are on the same chromosome

 

• 1st solid evidence - developed by Thomas Hunt Morgan (T.H. Morgan - early 1900's)

• bred fruit flies - looked for mutations

   

  Model organisms :

• small & easy to maintain
• breed quickly
• life cycle - 2 weeks
• lots of offspring
• only 4 pairs of chromosomes: 2n = 8,  1n = 4;
• xy sex chromosomes

 

mutation - white eye in a male fly - only.

 

we don't really know what caued the white eye condition so the terminology used it developed was different

(+) plus = wildtype

w = mutation  (white eye so therefore 'w')

 

(scanning electron micrograph) slide - y = 60 genes and of those there are duplicates y = 30 genes without duplicates.

The x chromosomes have thousands of genes and don't necessarily relate to sex determination at all.

---

Humans (mammals) = xy determination system

 

XX = female   XY = male

 

X chr - large, 10000's of genes lots of different traits

Y chr - small, few genes (~60 - 1/2 are duplicates)  --> most of male determining factors

 

xy = Hemizygous- only have one copy of the genes on the x chromosome.

in males - any X-linked gene will be expressed, even if its recessive - that's what they have 'cause that's what they got.

in females - not so, we've got 2 to choose from, threfore

in males, this leads to sex linked characters (diseases)

humans -- colorblindness, hemophelia, muscular dystrophy,

 

Normal female and effected male

A = any X-linked trait

a = recessive x-linked trait

 

Birds = completely opposite - ZW

She's the one with two chromosomes, the males have 2 of same chromosomes.

there's lots of different systems. Crickets have ~ 7 sex chromosomes. wow.

 

Different sex linked traits LE 15-10 Colorblindness = red square

carrier = shaded.

 

ON EXAM: only the males are affected, and the females are carriers

This type of pattern shows its a sex-linked trait.

Could this be female

 

No - female. It's recessive, if parents don't have the trait and one of the children do have the trait then its definitely recessive.

If one of the parents were dominant and had it,  then hard to tell.

 

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IN humans one of the X chromosomes becomes Inactivated.

Which chromosome gets turned off in which cell is entirely random in either x-chromosome.

In cats, coat color (Black + Orange) is on the X chromosomes. (sex linked chr)

 

Cats with both black & orange alleles - X^b X⁰ = tortoise shell phenotype.

Calico cats ==> females