chapter 15 the chromosomal basis of inheritance. mendelian inheritance has its physical basis in the...

Chapter 15The Chromosomal Basis of Inheritance


Mendelian inheritance has its physical basis in the behavior of chromosomes during meiosis.


Thomas Hunt Morgan


Thomas Hunt MorganIn the early 1900’s, he was the first scientist to want different varieties of fruit flies to study.


Thomas Hunt MorganA white-eyed mutation showed up in his laboratory.


Thomas Hunt MorganHe bred his white-eyed fruit flies with “wild type” red-eyed fruit flies.


Thomas Hunt MorganF1: all offspring had red eyes

(therefore red is dominant)


Thomas Hunt MorganF2: red:white = 3:1

(as expected)


Thomas Hunt MorganF2: red:white = 3:1

But all the white-eyed flies were male. (very surprising)


Thomas Hunt MorganF2 red:white = 3:1

But all the white-eyed flies were male. (very surprising)

F2♀ red = 100%

F2♂ red:white = 1:1


Thomas Hunt MorganTherefore the gene for white eyes is on the X chromosome.


Thomas Hunt MorganXX = red-eyed female

XX = red-eyed femaleXY = red-eyed male

XY = white-eyed male


Recombination


RecombinationLinked genes tend to be inherited together because they are on the same chromosome.


RecombinationIndependent assortment of chromosomes and crossing over produce genetic recombinations.


RecombinationRecombination can be used to map genes on the chromosome.1 centimorgan = 1% recombination


Sex Chromosomes


Sex ChromosomesSeveral patterns exist.

XX vs. XY

XX vs. X

ZW vs. ZZ

diploid vs. haploid


Barr Bodies


Barr BodiesA mammalian cell needs only one active X chromosome.

In females, one of the two X’s is inactivated


Genomic Imprinting


Genomic ImprintingIndividual genes may also be inactivated. Often this is done preferentially to the maternal or to the paternal copy of the gene.

REPRODUCTIVE COMPETITION BETWEEN MALES AND FEMALES

DAD DAD

MOM MOM MOM

KID KID KID KID KID KID

Easygoing kids make mom’s job easier. Mom has more kids.

DAD DAD

MOM MOM MOM


Difficult kids make mom’s job harder. Moms have fewer kids. Dad’s kids do better.

DAD DAD

MOM MOM MOM


Genomic imprinting allows genes to have different effects based on whether they are passed through mom or through dad.

DAD DAD

MOM MOM MOM



Chromosomal Mutations


Chromosomal MutationsAlterations in chromosome number or structure cause some genetic disorders.


Chromosomal MutationsAneuploidy

Abnormal chromosome number


Chromosomal MutationsPolyploidy

More than two complete sets of chromosomes


Chromosomal MutationsDeletion

Duplication

Inversion

Translocation


Extranuclear Genes


Extranuclear GenesMitochondria and chloroplasts contain some genes


Extranuclear GenesMitochondria and chloroplasts contain some genes.

These exhibit non-Mendelian inheritance (mother line only).

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