Chapter 13: Modern Understandings of Inheritance

Question 1

Who is the person whose work influenced modern genetics?

Answer 1

Gregor Mendel

Question 2

Chromosomal Theory of Inheritance

(Background Info)

Answer 2

-Proposed before there was any direct evidence that traits were carried on chromosomes
-Scientists, Boveri and Sutton, independently discovered that chromosomes occur in matched maternal and paternal pairs that segregate in meiosis
-They were supported by Eleanor Carothers demonstrating independent assortment of chromosomes in grasshoppers

Question 3

Chromosomal Theory of Inheritance

Answer 3

• During Meiosis, chromosome pairs migrate as discrete structures
  -Chromosome sorting from each homologous pair into pre-gametes appear to be random
• Each parent synthesizes gametes that contain only half their chromosomal complement
• Even though male and female gametes (sperm and egg) differ in size and morphology, they have the same number of chromosomes, suggesting equal genetic contributions from each parent
• The gametic chromosomes combine during fertilization to produce offspring that have the same number of chromosomes as their parents

Question 4

Can traits be sex-linked?

Answer 4

Yes, T.H. Morgan showed that the white eye mutant allele was inherited along with sex (the x chromsome)

This sex linkage was the first demostration that genes were on chromosomes

Question 5

The concept of linkage was further extended to map genes to chromesome positons, what is this called?

Answer 5

Genetic Linkage Maps

Question 6

Do traits segregate on the same chromosome?

Answer 6

Yes, however, far apart traits segregated independently.

Traits closer together segregated less often than independence predicted

Cross over between homologous chromosomes was the mechanism that segregated genes on the same chromosome. When genes were far apart
crossover happened all the time. When the were close together cross over happened less frequently.

Question 7

Linked genes

Answer 7

They are located close to each other on the same chromosome and tend to be inherited together.

They display different offspring ratios compared to unlinked genes

Question 8

Independent assortment occurs when?

Answer 8

During Meiosis

Question 9

What type of genes are independently assorted?

Answer 9

Unlinked genes

Question 10

Inheritance patterns of unlinked genes

Answer 10

• 50% parental type offspring and 50% recombinant offsprings
• 1:1:1:1 ratio of phenotypes

Question 11

What type of genes are NOT independently assorted?

Answer 11

Linked Genes

Question 12

Inheritance Patterns of linked genes

Answer 12

• No recombinant offsprings, all are parental type
• 1:1:0:0 ratio of phenotypes

Question 13

Inheritance Patterns of linked genes

if crossover always occur between homologous chromosomes

Answer 13

• 1:1:1:1 ratio of phenotypes
• 50% parental type offspring and 50% recombinant offsprings
• linked genes** ACT LIKE** independently assorted.

Question 14

Recombination Frequency

Answer 14

is the frequency in which a single chromosomal crossover will take place between two genes during meiosis

(recombinants/ total offspring) x 100 = recombination frequency %

Question 15

What is a Linkage Map?

Answer 15

• Recombination frequencies can be used to map the relative position of geneson chromosomes
• So, a diagram where relative gene locations are

Question 16

Genetic Linkage Mapping

Answer 16

• Recombination frequency was a function
  of distance between genes.
• Recombination of 1% was chosen as a
  unit equal to one genetic map unit (gmu)
  also named a Centimorgan in honor of T.H. Morgan

Question 17

When does abjunction occur?

Answer 17

Nonjunction occur when homologous chromosomes or sister chromatids fail to separate during Meiosis, resulting in an abnormal number of chromosomes. Occurs during either Meiosis I or Meiosis II

Question 18

Sex Chromosome Abjunction

(example used is cat fur coat colors)

Answer 18

In cats, the fur coat color in on the x chromosome, in the development of
female cats, one of the two X
chromosomes is randomly
inactivated in each cell, resulting in
a tortoiseshell pattern if the cat has
two different alleles for coat color. Because of this male cats cannot have tortoiseshell pattern fur coat

Question 19

Cri-du-chat syndrome- deletion of chromosome

Answer 19

A human genetic disorder resulting from a chromosomal recombination mutuation that causes a deletion of a portion of chromosome 5

Question 20

What type of inversion include the centromere?

Answer 20

Pericentric Inversion

Question 21

A pericentric inversion can…

Answer 21

Change the relative lengths of the chromosome arms

paracentric inversion cannot do this

Question 22

Homologous Pairing: When one chromosome undergoes an inversion, but the other one does not, what must the other chromosome do?

Answer 22

The chromosome must form an inverted loop to retain point for point interaction during synapsis

This inversion pairing is essential to maintaining gene alignment during Meiosis and to allow for recombination

Question 23

Reciprocal translocation mutations

Answer 23

Non-homologous chromosomes may also exchange material

Question 24

When does a reciprocal translocation occur?

Answer 24

Occurs when another segment of DNA is transferred fromm one chromosome to another nonhomologous chromosome