Chapter 13: Chromosomal Inheritance

Chromosomal Theory of Inheritance

Developed by Sutton and Boveri

Sutton observed chromosomes separating during meiosis

Bovieri showed chromosomes were necessary for embryonic development

Chromal Theory of Inheritance Identified what?

That chromosomes were genetic material responsible for mendelian inheritance

Core Concepts of Chromosomal theory of inheritance

During meiosis chromosomes segregate randomly into gametes, and gametes carry half the genetic material, fertilization restores the full set

T.H Morgan

White eyed gene was found on the X chromosome demonstrating genetic linkage

Linked Genes

Genes tend to be inherited together and are physically located near eachother on the same chromosome-Violating the law of independent assortment

display different offspring rations compared to unlinked genes

Homologous Recombination aka Crossing Over

occurs during prophase 1 of meiosis exchanging genetic material between homo chromosomes

Genetic Linkage Maps

The concept of linkage was further extend to map genes to chromosome position

What does homologous recombination produce?

Produces recombinant chromosomes aka new allele combinations

the closer two genes are the less likely they are to recombine

Cross over between homologous chromosomes

when genes were far apart crossover happened all the time when they were close together it happpened less frequently

Inheritance patterns of unlinked genes

Independently assorted

50% parental type offspring and 50% recombinant offspring

1:1:1:1 ration of phenotypes

Inheritance patterns of linked genes

NOT independently assorted

no recombinant offspring produced, all are parental type

1:1:0:0 ratio of phenotype

What happens if crossover always occurs between homologous chromosomes?

1::1:1 ratio of phenotypes

50% parental type offspring and 50% recombinant offspring

linked genes ACT LIKE independently assorted

Alfred H Sturtevant

The greater distance between 2 genes on a chromosome the more points there are between them where crossing over can occur

Recombination frequency

Recombinants/ total offspring x 100

Recombination frequency

ised to map the relative position of genes on chromosomes

nondisjunction

results when a cell has an abnormal chromosome number due to failure of separation in meiosis leading to gametes with an extra or missing chromosome.

Aneuploidy

the federalization of gametes in which nondisjunction occurs, offspring have an abnormal number of a particular chromosome

Polyploidy

when there are more than 2 complete sets of chromosome in an organism

X chromosome and X Inactivation

1 of the 2 X chromosomes in each cell is randomly inactivated during development

XIST>X-inactive-specific-transcript

Male cats only have 1 X chromosome never exhibit the tortoiseshell color

Trisomy 21

Down Syndrome most common birth defect parental age factor

characteristic facial and limb features

heart defects

Increased risk of leukemia

issues with immune GI and nervous system

social and outgoing

Triple-X Syndrome

Symptoms not usually extreme , extra X chromosome at pair 23, taller than average, increased risk of learning disabilities and delayed development

Turners Syndrome

Female(X) much more severe than XXX , significant issues to heart and kidneys

Growth hormone and estrogen therapy can help treat symptoms

Klinefelters Syndrome

A genetic condition in males characterized by an extra X chromosome (XXY). Symptoms may include reduced testosterone levels, infertility, and learning difficulties. Can be treated not cured with testosterone therapy

Jacobs Syndrome

A genetic condition in males characterized by an extra Y chromosome (XYY). Symptoms may include tall stature and increased risk for autism ; often goes undiagnosed.

cri-du-chat syndrome

A genetic disorder caused by a deletion of part of chromosome 5. It is characterized by a distinctive high-pitched cry, developmental delays, and various physical abnormalities. 5p=petite arm