Chapter 4 - Dhruv Patel Chapter 4 Sex determination and...

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Dhruv Patel Chapter 4 Sex determination and sex-linked characteristics 1. Sex determination a. The mechanism by which sex of an organism is determined b. Determined by genes i. Various gonads- Ovaries (females) testis (male) ii. Development of internal reproductive organs iii. Development of external reproductive organs iv. Development of secondary sexual characteristics c. Sex Chromosomes i. Chromosomes that differ between males and females ii. Humans (xx- female)(xy-male) d. Autosomes i. Genes that do not play a role in sex determination ii. Same for males and females iii. May have genes for secondary sex characteristics but they need to be turned on by the sex chromosomes 2. Sex determination in Protenor Bugs a. First case of chromosomal sex determination b. They have a single sex chromosome: X c. Females have two x chromosomes i. XX plus 2 of each of six autosomes (2n=14) d. Males have only 1 X chromosome i. X0 plus 2 of each of the 6 autosomes (2n-1=13) 3. XY sex determination a. Seen in both Humans and Drosophila i. Females are XX 1. Known as Homogametic sex ii. Males are XY 1. Known as Heterogametic sex iii. Humans have 7 genes on their y chromosome, and crossing over does not occur between the sex chromosomes( though some similar genetics sequences) b. There can be extra sex chromosomes that effect the organism (study chart) Sex Chromosomes Humans Mouse Drosophila XO ♀(sterile) ♀(fertile) ♂(sterile) XXX ♀(fertile) ? ♀(sterile) XXY ♂(sterile) ♂(sterile) ♀(fertile) XYY ♂(fertile) ? ♂(fertile) i. There is no evidence that having an extra y chromosome will cause more aggression 4. Sex Determination in Drosophila a. The fruit fly has 8 chromosomes (6 autosomes) 1 pair of sex chromosomes b. The sex is determined by the X to A ratio
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Dhruv Patel Chapter 4 Sex determination and sex-linked characteristics i. A is a complete set of autosomes c. If the X:A ratio is > 2/3, the female-determining genes on the X chromosomes win and fly will be a female. d. If the X:A ratio is < 2/3 , the male-determining genes on the autosomes win and the fly will be a male. e. A lot of x compared to autosomes will make you female 5. Sex determination rule in mammals a. General rule i. If a Y chromosome is present- Male ii. If a Y chromosome is absent- Female b. Actual Rule i. The Y chromosome contains the Sex determining Region Y Gene (SRY Gene) 1. The gene encodes for Testis Determining Factor- TDF 2. If TDF is absent ovaries and estrogen develop 3. If TDF is present Testis; Testosterone; malaria inhibiting hormone, and dihydrotestosterone are produced
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This note was uploaded on 06/28/2011 for the course BY 210 taught by Professor Powell during the Summer '08 term at University of Alabama at Birmingham.

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Chapter 4 - Dhruv Patel Chapter 4 Sex determination and...

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