Lecture 31

Question 1

what is the chromosome theory of inheritance? Who gave the first evidence? (last name only)

Answer 1

that genes are at specific loci on chromosomes, which undergo separation and independent assortment. Morgan

Question 2

What are linked genes?

Answer 2

genes that are located on the same chromosome, usually assort dependently (relative to each other) during gamete formation

Question 3

Define recombination frequency
What trend does it reveal?
What’s the equation?

Answer 3

Recombination frequency is the distance between genes on the same chromosome, the further they are the GREATER the probability that they will recombine (crossover will occur between them). = number of recombinants / number of total offspring

Question 4

where does crossing over occur on the sex chromosomes?

Answer 4

pseudoautosomal region

Question 5

what are the 2 sex-linked recessive traits that lead to a semi-normal life

Answer 5

red and green color blindness, hemophilia

Question 6

what are the 2 sex linked recessive diseases a woman could get?

Answer 6

color blindness and hemophilia

Question 7

What are the 2 common autosomal aneuploidies? What causes them? Fate of each?

Answer 7

down’s and endward’s (trisomy 18) nondisjunction in MI causes them, Down’s has a sort of shorter life-span, Edward’s die very early

Question 8

What are the 4 somatic cell aneuploidies? Categorize them as disabling, phenotypically present, and not a huge deal

Answer 8

XYY, XXX, XO (Turner syndrome) XXY (klinefelter syndrome). disabling = XO (turner) because they infertile sort of physically disabled women. phenotypically present = XXY (klinefelter) are male and tall, but have feminine faces and voices. not big deal = XYY and XXX

Question 9

what is aneuploidy?

Answer 9

Wrong number of chromosomes

Question 10

what is the mechanism of sex chromosome aneuploid? what are 2 potential causes of this?

Answer 10

Failure of kinetechore microtubules. Could be nondisjunction (no separation) of homologous chromosomes in MI. nondisjunction of sister chrmoatids in MII.

Question 11

why does someone over 40 have a greater chance of a down’s baby?

Answer 11

downs = aneuploidy, which is more prevalant in older women because their eggs were made like 40 years ago, more vulnerable to kinetechore microtubule failure

Question 12

What did pronuclear transplantation of female and male mice embryos show? Why?

Answer 12

male and female genomes are different, have complementary parts that need each other to survive. Due to genomic imprinting

Question 13

What is genomic imprinting? Explain using the Igf2 mice

Answer 13

imprinted region of a genome only expresses 1 allele of the 2 present. only paternal chromosome expresses the growth factor, and only the maternal chromosome expresses the receptor

Question 14

What are the 2 examples of genomic imprinting in humans?

Answer 14

angelman syndrome, prader-willi syndrome

Question 15

How does allelic variation occur? What is an example?

Answer 15

Results from nucleotide changes in alleles that encode cellular proteins. Example = breeding dogs, there were big dogs hundreds of years ago and artificially selected and bred for little ones. the little dogs have allelic variation relative to big dogs

Question 16

What are the 3 traits of a wildtype drosoph? Also known as a “true breeding normal”

Answer 16

gray body, red eyes, normal wings

Question 17

what are the 3 traits of a mutant (“true breeding mutant”)

Answer 17

black body, red eyes, vestigial wings

Question 18

when does crossing over occur between homologous chromosomes?

Answer 18

Prophase 1 of Meiosis 1

Question 19

what would happen if homologous chromosomes did not have crossing over?

Answer 19

M1 would fail

Question 20

what is hemizygocity? which 2 groups have it?

Answer 20

only having 1 allele for an X-linked gene…in men (because they only have 1 X chromosome to begin with) and for flys

Question 21

how do females deal with the fact that they only need the product of 1 allele from an X chromosome? (Name (also called___), effect, when it occurs)

Answer 21

dosage compensation (x inactivation), inactivates 1 X chromosome by 85% (only 15% active), happens in early female embryogenesis

Question 22

what is the mechanism for dosage compensation/x inactivation? there are 2 things

Answer 22

DNA methylation (cant transcribe the genes) and xist (small RNA molecule) covering the inactivated X chromosome

Question 23

what does 1 of a female’s 2 X chromosomes produce (and what does that thing do) to induce dosage compensation?

Answer 23

produces a lot of the RNA molecule XIST. which binds and base pairs along it

Question 24

what is the name of the almost all inactivated X chromosome that has been bound to XIST? When is it visible when the female cell is developing?

Answer 24

barr body, prophase I

Question 25

on the to be inactivated X chromosome of a female happens in the promotor region?

Answer 25

cytosine residues methylated (DNA methylation)

Question 26

Relate “mosaic somatic cell” with “x inactivation”

Answer 26

because the X chromosome can only display 1 allele for a trait, 1 of the chromosomes has to be inactivated: a female tortoiseshell and a calico cat has some cells in which the X chromosome from her mom was inactivated, and some in which the X from her dad was inactivated