Chapter 11-3.ppt

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Chapter 11.3

Chromosomes and Human

Heredity

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Karyotype Studies

A Karyotype is an array ofchromosomes created byphotographing themetaphase chromosomes

from one cell, cutting outthe individualchromosomes from thephotograph and liningthem up in order from

largest to smallest,pairing the appropriatehomologouschromosomes. ...

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Karyotype Studies

Notice on this

Karyotype there are 3

copies of the 21st set

of chromosomes This results in downs

syndrome (trisomy

21)

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Nondisjunction at M1

Nondisjunction at M2

Non-disjunction occurs when chromosomes inthe developing gamete (sex cell) fail to separateduring one of the divisions of meiosis. The resultis a sperm or egg cell with either an additionalchromosome, or one that lacks onechromosome. When this sex cell combines withone from the opposite sex, the resulting fetus willhave cells with an extra, or one chromosome

that is lacking. Generally, such fetus' will notdevelop properly and we would say that theresulting baby would have a birth defect.

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Animation of Non-

Disjunction

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Changes in Numbers of Sex

Chromosomes

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Turners Syndrome (0X)

Turner syndrome is agenetic disorder thataffects a girl'sdevelopment. Thecause is a missing orincomplete Xchromosome. Girlswho have it are short,

and their ovaries don'twork properly. Mostare infertile.

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XXX female

Triple X syndrome is a

form of chromosomal

variation characterized by

the presence of an extra

X chromosome in eachcell of a human female.

Usually these woman are

undiagnosed and function

normally

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XXY maleKlinefelters Syndrome

Chromosomal defectin males in whichthere is an extra Xchromosome;manifestations mayincludeunderdevelopedtestes, physical

feminization, sterility,and mentalretardation.

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XYY Male

Most often, this chromosomal change causes nounusual physical features or medical problems.

XYY boys and men are usually taller than

average and several centimeters taller than theirparents and siblings

XYY males have normal sexual developmentand usually have normal fertility. XYY males

may be taller, tend to be wiry-built, and tend tohave severe acne. Minor birth defects -- likepectus, crooked eye, and minor outturning of theelbows, are possible in XYY's.

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OY Chromosome

A person with only one Y chromosome

(45,Y) could not survive or be born alive.

The X chromosome has important genes

on it that would be completely missing insuch a person.

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Fetal Testing - amniocentesis

A sample of amniotic

fluid can be withdrawn

and analyzed (fluid

contains fetal cells). It

is useful for

Diagnosing sex linked

disorders

Chromosomal defects

Sex can also be

determined

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Fetal Testing Chorionic villus

sampling

Tissue is taken from

membrane surrounding

the fetus. Can test for:

(1) Chromosomal

abnormalities.

(2) Some inherited

disorders. Dominant,

Recessive and X-linked

patterns of inheritance.

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Fetal Testing Fetal Blood

sampling A fetal blood sample may betaken to:

diagnose genetic orchromosome abnormalities.

check for and treat severe fetalanemia or other blood problemssuch as Rh disease.

check for fetal oxygen levels.

check for fetal infection.

give certain medications to thefetus.

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Extra Review

REVIEW: Nondisjunction can be caused by_____ .

Answer: Failure of the chromosomes toseparate during meiosis

REVIEW: A gamete affected bynondisjunction would have _____ .a. a change from the normal chromosome

numberb. one extra or one missing chromosomec. the potential for a genetic disorderd. all of the above

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More questions

Amniocentesis involves sampling

Fetal cells in amniotic fluid

The condition occurring when an organism

has a 2n + 1 chromosome composition isknown as

Trisomy

The sex chromosome composition of a

person with Turner syndrome is XO

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Assessment

1. Sex of individual and whether the

proper number of chromosomes are there

2. In homologous pairs from largest to

smallest.

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3.

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4.

Males only receive on X and one Y so

missing sections could contain vital genes

. With females having 2 XX deletion in one

X could be made up for by the other

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Further study

Really interesting information on human

genetics