Concept 4: Applying the chromosomal basis of inheritance to analysis the effects of alterations in chromosome number or structure.

Campbell: Chapter 15Holtzclaw: pg 111

Please do the following activities on the student media (Chapter 15):

- MP3 tutor: Chromosomal Basis of Inheritance - Activity: Polyploid Plants (relate to speciation (sympatric)!!)

But First… Linked Genes from last class…A blue fly with silver spots is mated with a wild type fly (grey, no spots) and all of the F1 generation are phenotypically wild (grey, no spots). The F1 fly is mated with a blue fly with silver spots (test cross) with the following results for the testcross offspring:1025 wild type

1002 blue with silver spots

352 grey with silver spots

366 blue with no spots

Are the genes for blue and silver spots linked? How do you know? If so, what is the recombination frequency for the genes for blue and silver spots?

But First… Linked Genes from last class…1025 wild type PARENTAL TYPE

1002 blue with silver spots PARENTAL TYPE

352 grey with silver spots RECOMBINANT

366 blue with no spots RECOMBINANT

Are the genes for blue and silver spots linked? YES

How do you know? BECAUSE IF IT WAS TRUE INDEPENDENT ASSORTMENT, THE TEST CROSS OF A DOUBLE HETEROZYGOTE AND THE DOUBLE HOMOZYGOUS RECESSIVE WOULD HAVE PRODUCED A 1:1:1:1 RATIO

However, the genes are not completely linked… in other words, since some recombinants exist… the chromosomes must have recombined via crossing over…

Video Clip

But First… Linked Genes from last class…1025 wild type PARENTAL TYPE

1002 blue with silver spots PARENTAL TYPE

352 grey with silver spots RECOMBINANT

366 blue with no spots RECOMBINANT

If so, what is the recombination frequency for the genes for blue and silver spots?

Recombination frequency = #recombinants/total # of offspring

= (365+366)/(1025+1002+352+366)

= (731)/(2738)

= 0.266

This means that the genes recombine via crossing over 26.6% of the time!

Try This!

Genes A, B, and C are located on the same chromosome. Testcrosses show that the recombination frequency between A and B is 28% and between A and C is 12%. A’s in the middle! Can you determine the linear order of these genes are their relative distance from each other in map units?

Try This!

Genes A, B, and C are located on the same chromosome. Testcrosses show that the recombination frequency between A and B is 28% and between A and C is 12%. Can you determine the linear order of these genes are their relative distance from each other in map units?

40 mu

28mu 12mu

B A C

Learning Intentions

Goal: to analyze mechanisms of chromosomal inheritance

You must know: How the chromosome theory of inheritance

connects the physical movement of chromosomes in meiosis to Mendel’s laws of inheritance

How alteration of chromosome number or structurally altered chromosomes can cause genetic disorders

Alteration of Chromosome Number How? Nondisjuction

Occurs when homologous chromosomes do not separate properly during meiosis II.

Result? Aneuploidy Incorrect number of a chromosome

Trisomic: three copies of the chromosome Monosomic: one copy of the chromosome

OR: Result? Polyploidy More than two complete sets of chromosomes

What happens next? What would the haploid gametes look like?

Down’s Syndrome: aneuploidy

Is this individual trisomic or monosomic?

Tetraploid Mammal! Polyploidy

Rearrangement of Chromosome Structure

Portions of a chromosomes may be lost or rearranged during crossing over Deletion

Fragment is lost. Missing genes. Duplication

Extra fragment. Extra genes. Inversion

Backwards section! May affect genes. Translocation

Moving a piece to a nonhomologous chromosome

Translocation

Chromosaomal Deletion

Example: Cris du Chat Deletion in chromosome 5 in humans Small head, unusual facial features, has a

cry that sounds like mewing of a distressed cat

Death in infancy or early childhood Affects 1 in 20,000 or 50,000 of live births

Try This!

A spermatocyte produces the following four sperm cells:

n + 1 n + 1 n – 1 n – 1

1) These cells are the result of which process?

2) When would this happen?

Try This!

A spermatocyte produces the following four sperm cells:

n + 1 n + 1 n – 1 n – 1

1) These cells are the result of which process? NONDISJUNCTION

2) When would this happen? DURING MEIOSIS I

Learning Intentions

Goal: to analyze mechanisms of chromosomal inheritance

You must know: How the chromosome theory of

inheritance connects the physical movement of chromosomes in meiosis to Mendel’s laws of inheritance

How alteration of chromosome number or structurally altered chromosomes can cause genetic disorders Try Worksheet! You should be able to answer all

questions on pg 112-114 in Holtzclaw