Chapter 15 The Chromosomal

Basis of Inheritance

Timeline

Sutton

Morgan

Fruit Fly

Reasons

Genetic Symbols

Examples Recessive mutation:

w = white eyes w+ = red eyes

Dominant Mutation Cy = Curly wings Cy+ = Normal wings

Morgan Observed:

Morgan crossed

The F1 offspring:

All had red eyes. This suggests that white eyes

is a genetic _________?

F1 X F1 = F2

Morgan discovered:

Fruit Fly Chromosomes

Morgan Discovered

Linked Genes

Body Color and Wing type

Example

b+b vg+vg X bb vgvg

(b+ linked to vg+)

(b linked to vg)

If unlinked: 1:1:1:1 ratio.

If linked: ratio will be altered.

Crossing-Over

If Genes are Linked:

Linkage Strength

Genetic Maps

Comment - only good for genes that are within 50 map units of each other. Why?

Genetic Maps

Sex Linkage in Biology

Chromosomal Basis of Sex in Humans

Human Chromosome Sex

SRY

Sex Linkage

Males

X-linked Disorders

Samples of X-linked patterns:

X-linked Patterns

Comment

Watch how questions with sex linkage are phrased:

Chance of children? Chance of males?

Can Females be color-blind?

Y-linkage

Sex Limited Traits

Sex Influenced Traits

Baldness

Barr Body

Lyon Hypothesis

Examples

Calico Cats XB = black fur XO = orange fur Calico is heterozygous, XB XO.

Question?

Why don’t you find many calico males?

Chromosomal Alterations

Number Alterations

Aneuploidy

Comment

Types of Aneuoploidy

Turner Syndrome

Characteristics

Other Sex Chromosome changes

Kleinfelter Syndrome

George Washington

May have been a Kleinfelter Syndrome individual.

Much taller than average. Produced no children.

Meta female

Super male

Trisomy events

Question?

Why is trisomy more common than monosomy?

Question?

Why is trisomy 21 more common in older mothers?

Polyploid

Question? In plants, even # polyploids

are often fertile, why odd # polyploids are sterile. Why?

Structure Alterations

Result

Translocations

Cri Du Chat Syndrome

Philadelphia Chromosome

Parental Imprinting of Genes

Example:

Cause:

Result

Why have parental imprinting?

Method to detect that TWO different sets of chromosomes are in the zygote.

Experiment

Can fuse nuclei into mouse eggs. If male/male = normal placenta,

abnormal fetus If female/female = abnormal

placenta, normal fetus If male/female = normal placenta

and normal fetus

Extranuclear Inheritance

Result

Mitochondria

Chloroplasts

Variegated Examples

Variegation in African Violets

Comment

Cells can have a mixture of normal and abnormal organelles.

Result - degree of expression of the maternal inherited trait can vary widely.

Summary

Know about linkage and crossing-over.

Sex chromosomes and their pattern of inheritance.

Variations of chromosomes and inheritance patterns.

Summary

Be able to work genetics problems for this chapter.