Chapter 15 The Chromosomal Basis of Inheritance

Timeline

Sutton

Morgan

Fruit Fly

Life Cycle u Egg u Larva u Pupa u Adult

Reasons

Fruit Fly Chromosomes

Genetic Symbols

Examples u Recessive mutation: u w = white eyes u w+ = red eyes u Dominant Mutation u Cy = Curly wings u Cy+ = Normal wings

Morgan Observed:

Morgan crossed

The F1 offspring: u All had red eyes. u 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

u 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 u Watch how questions with sex linkage are phrased: u Chance of children? u Chance of males?

Can Females be color-blind?

Y-linkage

Sex Limited Traits

Sex Influenced Traits

Baldness

Barr Body

Lyon Hypothesis

Examples

Calico Cats u X B = black fur u X O = orange fur u Calico is heterozygous, X B X O.

Question? u Why don’t you find many calico males?

Chromosomal Alterations

Number Alterations

Aneuploidy

Comment

Types of Aneuoploidy

Turner Syndrome

Characteristics

Question u Why are Turner Individuals usually sterile

Other Sex Chromosome changes

Kleinfelter Syndrome

George Washington u May have been a Kleinfelter Syndrome individual. u Much taller than average. u Produced no children.

Meta female

Super male

Trisomy events

Question? u Why is trisomy more common than monosomy?

Question? u Why is trisomy 21 more common in older mothers?

Polyploid

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

Experiment u Can fuse nuclei into mouse eggs. u If male/male = normal placenta, abnormal fetus u If female/female = abnormal placenta, normal fetus u If male/female = normal placenta and normal fetus

Extranuclear Inheritance

Result

Mitochondria

Chloroplasts

Variegated Examples

Variegation in African Violets

Comment u Cells can have a mixture of normal and abnormal organelles. u Result - degree of expression of the maternal inherited trait can vary widely.

Summary u Know about linkage and crossing-over. u Sex chromosomes and their pattern of inheritance. u Variations of chromosomes and inheritance patterns.

Summary u Be able to work genetics problems for this chapter.