Lecture 5 and 6- Mendel, Linkage and Sex Determination

Question 1

Describe the law of segregation:

Answer 1

When an organism forms gamtes, only one of the pair of alleles enter the gametes.

Question 2

What is the link between the law of segregation and the meiosis?

Answer 2

When homologous segregate during anaphase 1 alleles segregate as well.

Question 3

Describe the law of independment assortment:

Answer 3

During the formation of gametes, the alleles of one gene segregate from each other independently of one on another gene.

Question 4

What is the link between the law of independment assortment and meiosis?

Answer 4

Independent assortment is the direct consequence of the random orientation of homologous pairs at the metaphase 1 of meiosis.

Question 5

What’s linkage?

Answer 5

If both genes are on the same chromosome they tend to remain associate during meiosis and are said to be linked.

Question 6

What is the mechanism of sex determination in mosquitoes?

Answer 6

In mosquitoes sex is determined by a single locus M (Mm is male and mm is female), this system automatically generates equal number for each sex.

Question 7

What is a karyotipe?

Answer 7

All the different chromosomes contained within a genome.

Question 8

What are autosomes?

Answer 8

Most chromosome in the karyotipe that occur in pairs and are indistinguishable from each other.

Question 9

Describe genetic sex determination in mammals:

Answer 9

The sex is determined by the presence or absence of the Y chromosome.

Question 10

What are the two possible abnormal gametes produced by errors during meiosis in females:

Answer 10

XX o O (No chromosome)

Question 11

If an abnormal gamete XX is fertilized which two possible combination can be formed?

Answer 11

XXX (Sterile female) an XXY (Sterile Male)

Question 12

If an abnormal gamete O is fertilized which two possibile combination can be formed?

Answer 12

OX (sterile female) or OY (Not viable offspring)

Question 13

What is the region on the Y chromosome that confer maleness?

Answer 13

The SRY gene is the gene that confer maleness.

Question 14

Describe genetic sex determination in drosophila:

Answer 14

XX is female and XY is male but abnormal gametes are XO is male and XXY is female because the sex is determined by the ration of X chromosome divided for the number of autosomes.

Question 15

Describe the genetic sex determination in hymenoptera:

Answer 15

The unfertilised egg is haploid and is a male while the fertilised egg is diploid and is female.

Question 16

What is the consequence of the fact that males are hemyzigous for X-Linke genes:

Answer 16

That recessive mutant alleles will always show a phenotype in males.

Question 17

What’s an hemyzigous?

Answer 17

Any gene that is present as a single copy in a diploid organism.

Question 18

Describe sex-linked inheritance:

Answer 18

Inheritance of a gene carried by a sex chromosome.

Question 19

Describe gene dosage compensation in Drosophila:

Answer 19

In drosophila, sinche male have only one copy of most X-linked genes it compensate by doubling the level of gene expression for X chromosome.

Question 20

Describe gene dosage compensation in mammals:

Answer 20

In mammals, female have only one copy of X chromosome active in each cell while the inactive gene is highly condensed (Barr Body).