+ All Categories
Home > Documents > Chapter 15 Chromosomal Basis of Inheritance. Mendel’s inheritance with independent assortment.

Chapter 15 Chromosomal Basis of Inheritance. Mendel’s inheritance with independent assortment.

Date post: 17-Jan-2016
Category:
Upload: melinda-lamb
View: 223 times
Download: 0 times
Share this document with a friend
27
Chapter 15 Chromosomal Basis of Inheritance
Transcript
Page 1: Chapter 15 Chromosomal Basis of Inheritance. Mendel’s inheritance with independent assortment.

Chapter 15

Chromosomal Basis of Inheritance

Page 2: Chapter 15 Chromosomal Basis of Inheritance. Mendel’s inheritance with independent assortment.

Mendel’s inheritance with independent assortment

Page 3: Chapter 15 Chromosomal Basis of Inheritance. Mendel’s inheritance with independent assortment.
Page 4: Chapter 15 Chromosomal Basis of Inheritance. Mendel’s inheritance with independent assortment.

Mendel had factors, we now know these factors were

specific genes at specific loci, (locations) on specific

chromosomes. This is the chromosome theory of

inheritance.

Page 5: Chapter 15 Chromosomal Basis of Inheritance. Mendel’s inheritance with independent assortment.

Morgan’s experiments with Fruit Flies

A.Morgan used fruit flies to trace a gene to a specific chromosome

Page 6: Chapter 15 Chromosomal Basis of Inheritance. Mendel’s inheritance with independent assortment.

1. Drosophila Melangaster – wildtype phenotype = most common and mutant phenotypes = caused by mutations of the wildtype gene.2. Sex-linked- using the gene for white eyes Morgan found that if a female had the trait and mated to a male with wildtype, only her sons would be white-eyed.

Page 7: Chapter 15 Chromosomal Basis of Inheritance. Mendel’s inheritance with independent assortment.

Sex Linkage

This meant the gene must be on the X and not the Y.

A daughter would receive the wildtype X from the father which would override the faulty X from mom.

Page 8: Chapter 15 Chromosomal Basis of Inheritance. Mendel’s inheritance with independent assortment.

Linked genes – genes close together on the same chromosome

• Morgan found that flies have linked genes for body color and wing size.

• Gray and normal wings were wildtype, black and vestigal wings were mutant types.

• Gray flies with vestigal wings and black flies with normal wings are much harder to breed than the ones in b.

Page 9: Chapter 15 Chromosomal Basis of Inheritance. Mendel’s inheritance with independent assortment.

Independent assortmentGenes which are not linked sort

independent of one another.When they come together in a zygote it is called recombination.

a. A frequency of 50% or more recombination means the genes are not linked

b. Linked genes do not sort independently, they travel together, making recombination percentages low.

Page 10: Chapter 15 Chromosomal Basis of Inheritance. Mendel’s inheritance with independent assortment.

Recombination information can be used to map the genes on a

chromosome.

• The measurements are called centimorgans

• If the recombination frequency between cn and b is 9%, cn and vg 9.5%, b and vg 17% the map would look like this;

• 17 centimorgans

b cn vg

Page 11: Chapter 15 Chromosomal Basis of Inheritance. Mendel’s inheritance with independent assortment.

• If the genes are far apart they behave as if they were on different chromosomes

• This slide shows recombination during meiosis.

Page 12: Chapter 15 Chromosomal Basis of Inheritance. Mendel’s inheritance with independent assortment.

Recombination calculations

Page 13: Chapter 15 Chromosomal Basis of Inheritance. Mendel’s inheritance with independent assortment.

Sex chromosomes

A. In humans XX is female and XY is male

1. The SRY gene has been shown to trigger the development into a male fetus at about 2 months old.

2. SRY probably regulates other genes

3. Some XX male and XY females exist with mutated SRY genes

Page 14: Chapter 15 Chromosomal Basis of Inheritance. Mendel’s inheritance with independent assortment.

Sex-linked

• Genes on the X chromosome will only be present in one copy in males, as they only have one X and the Y does not contain the same genes.

Page 15: Chapter 15 Chromosomal Basis of Inheritance. Mendel’s inheritance with independent assortment.

Hemophilia

Page 16: Chapter 15 Chromosomal Basis of Inheritance. Mendel’s inheritance with independent assortment.

Males are said to be hemizygous for these traits

a. Colorblindness is an example of a non- lethal sex-linked trait- females can acquire it from their father (colorblind) and mother (carrier).

b. Duchene muscular dystrophy – weakening of the muscles,1/3500 males- usually die by 20s

c. Hemophilia- absence of certain clotting factors.

Page 17: Chapter 15 Chromosomal Basis of Inheritance. Mendel’s inheritance with independent assortment.

X inactivation- ch.17

• In females one X becomes inactivated and condenses into a Barr body, which one is inactive is random, and will be different in different cells.

Page 18: Chapter 15 Chromosomal Basis of Inheritance. Mendel’s inheritance with independent assortment.

Errors

A.Nondisjunction- when meiosis is not accurate and some cells are missing a chromosome (anueploidy) and one has too many chromosomes(polyploidy)

Page 19: Chapter 15 Chromosomal Basis of Inheritance. Mendel’s inheritance with independent assortment.

Turner’s

Page 20: Chapter 15 Chromosomal Basis of Inheritance. Mendel’s inheritance with independent assortment.

Metafemale

Page 21: Chapter 15 Chromosomal Basis of Inheritance. Mendel’s inheritance with independent assortment.

Down’s Syndrome-1/700 births trisomy 21

Page 22: Chapter 15 Chromosomal Basis of Inheritance. Mendel’s inheritance with independent assortment.

Klinefelter – XXY, XXXY

Page 23: Chapter 15 Chromosomal Basis of Inheritance. Mendel’s inheritance with independent assortment.

XYY

Page 24: Chapter 15 Chromosomal Basis of Inheritance. Mendel’s inheritance with independent assortment.

Other nondisjunctions

• Metafemale - XXX2. Turner – X0

Page 25: Chapter 15 Chromosomal Basis of Inheritance. Mendel’s inheritance with independent assortment.

Other errorsA. Deletions – Chromosome fragment is lost

1. Cri-du-chat- chromosome 5B.Duplication – chromosome fragment attached to homologueC.Inversion – reverse orientation of fragment on chromosomeD.Translocation – fragment on a nonhomologue

1. Implications of cancer - CML

Page 26: Chapter 15 Chromosomal Basis of Inheritance. Mendel’s inheritance with independent assortment.

Imprinting

• Genomic imprinting – One active copy either maternal or paternal.

• Fragile X – caused in part by maternal imprinting.

Page 27: Chapter 15 Chromosomal Basis of Inheritance. Mendel’s inheritance with independent assortment.

Extranuclear genes

A. Small circular DNA in mitochondria and chloroplasts

B. Maternal inheritance is the rule


Recommended