Sex Chromosomes, Linked Genes, Organelles

Question 1

Meiosis of gametes

Answer 1

Meiosis of female eggs results in X-bearing eggs only, meiosis in male results in 1:1 ratio of X and Y bearing sperm.

Question 2

Thomas Hunt Morgan

Answer 2

Worked with fruit flies. Found fruit flies with white eyes, crossed them with red-eyed females. White eyes only reappear in the F2 generation and in only 50% of males.

Question 3

X chromosome inheritance in males

Answer 3

All male X chromosome inheritance comes from the mother, which is why females may never present with a mutation but men will, because the men only have one x chromosome. This x chromosome from males is only passed to female daughters.

Question 4

Crisscross Inheritance

Answer 4

The way an X chromosome can alternate between the sexes in sucessive generations

Question 5

Calvin Bridges

Answer 5

When crossing white-eyed females and red-eyed males, he found that very small portion of them were ‘exceptional’. Female with white eyes or male with red eyes. This is due to nondisjunction, failure to separate in anaphase 1. This was the first experimental evidence of nondisjunction.

Question 6

Example of X-linked inheritance

Answer 6

Color blindness in males, 1/20. Hemophilia.

Question 7

Genetic Linkage

Answer 7

Will demonstrate an excess of the original parental genotypes when F1 generation is crossed.

Question 8

Alfred Sturtevant

Answer 8

Discovered genetic linkage in fruit flies. Found that males in the crossed F1 generation had majority of parental genotypes instead of the expected 1:1:1:1 ratio. The minority occured due to crossing over of homologous chromosomes.

Also hypothesized that recombination was due to crossing over between the genes, and the further they were, the more recombination there is.

Question 9

Crossing Over

Answer 9

Results in 2 recombinant and 2 nonrecombinant chromosomes. If crossing over occurs but not between the two linked genes of interest, the result is considered to be 4 nonrecombinant chromosomes. The closer two genes are to one another, the less likely crossing over will occur between them.

Question 10

Genetic Maps

Answer 10

Frequency of recombination can be used as a measure of the distance between genes. Uses a scale where one unit of distance is the distance between genes resulting in 1% recombination. MAP units are additive.

Question 11

SNP

Answer 11

Single Nucleotide polymorphism. A marker that can help detect a mutated gene, but has to be relatively close to the gene in question. Associates the SNP and presence of disease.

Question 12

Y-linked traits

Answer 12

Only males can pass on these tho their male offspring, and Y chromosome lineages can help trace our evolutionary tree. There are very few Y-linked physical traits that follow this line of inheritance.

Question 13

Midochondrial DNA

Answer 13

Inherited through the maternal line, since all organelles and cytoplasm come from the egg cell. All offspring of an affected female will show the trait. Males will never transmit the trait. Midochondrial DNA can also be used to trace human ancestry.

Question 14

Midochondrial Diseases

Answer 14

Often associated with muscle weakness reflecting deficient production of ATP

Question 15

Paternal Inheritance

Answer 15

Derived from the father

Question 16

Biparental Inheritance

Answer 16

Derived from both parents - typically either maternal or paternal predominates.

Question 17

Maternal inheritance

Answer 17

Derived from the mother

Question 18

Recombination Frequency of Two Genes

Answer 18

0% to 50%. 0% means no crossing over took place, and 50% means the genes are so far apart that crossing over between them always takes place. A 50% recombination frequency usually indicates that the genes are not linked, and anything less than that is considered linked.