patterns of Inheritance- HUMAN GENETICS- june 18

any chance that occurs in the DNA sequence of a chromosome

• most are neutral and have no effect

• some are beneficial, while some are harmful

A mutation

causes of mutations

• most are spontaneous

• some are caused by mutagens (environmental conditions)

what does it mean that some mutations are cause by mutagens

environmental conditions that are preventable by limiting exposure to things such as certain chemicals, radiation, UV light

what can be used to identify mutations

Karyotypes

a photographic display of the chromosome from a cell

• blood cell, skin cell, fetal cells, etc.

a karyotype

Cells can be obtained for karyotyping through 

amniocentesis or through chorionic villus sampling

when using amniocentesis to obtain karyotyping, how are the chromosomes found matched up?

by size, shape, and staining pattern

Amniocentesis can be performed during the blank week of pregnancy.

• A needle is inserted into the uterus to obtain fetal cells.

15th to 20th

Chorionic villus sampling (CVS) can be performed as early as the what week week of pregnancy. 

• A suction tube is inserted vaginally to obtain fetal cells.

8th

how many chromosomes should a karytope posses

46

• 22 pairs of homologous autosomes and 1 pair of sex chromomes

an abnormal human karyotype could display

mutations

• abnormal chromosomes or abnormal chromosome number

mutations of chromosome structure

deletions, duplications, inversions and translocations

mutations of chromosome number

Anueploidy

• monosomy

• trisomy

an abnormal chromosome number

aneuploidy

a chromosome is missing

• most are lethal

monosomy

an extra chromosome is present

• some are lethal, while some offspring produced with health issues or disorders

trisomy

the removal or loss of a piece of a chromosome

• can occur in any chromosome when it is being copied

• usually lethal

• karyotype would recognize bc the chromosome would be shorter in length

deletion

a syndrome that results from a deletion in chromosome #5

• not lethal, but a child born with this disorder suffers from mental retardation, has a small head and has a cry like that of a cat. 

• A child with this disorder usually dies in infancy or early childhood.  French for “cry of a cat”.

Cri du chat syndrome

when a segment is repeated twice within one chromosomes

• a piece accidentally gets copied twice

• produces a “look alike chrom.”

• not as harmful, doesnt give rise to disorder or lethality

duplication

when a segment of a chromosome is removed, rotated 180degrees and reinserted in the opposite direction

• occurs when a chromosome is being copied

• not as harmful, typically does not give rise to disorder or lethality

inversion

occurs when there is an exchange of genetic material between two non-homologous chromosomes

• occurs when chromosomes are being copied

• most are lethal

translocation

results from a translocation between chromosome #9 and #22

chronic myelogenous leukemia (CML)

the production of abnormal white blood cells or the absence of their production which prevents a child from having an immune response

leukemia

2n-1=45

disorder that result due to missing chromosome*

monosomy*

2n+1=47

disorders that result due to an extra chromosome*

trisomy*

all aneuploides are due to

nondisjunction

the failure of tetrads to separate into dyads during anaphase I

or

the failure of dyads to separate into individual chromatids during anaphase II *

nondisjunction *

nondisjunction results in the

wrong number of chromosomes in gametes

chromosomes that have nothing to do with an individual’s gender

autosomes

how many pairs of homologous autosomes should a normal human have

22 pairs (44)

syndrome results from having 3 chromosome #13s. 

• It occurs in 1 in 5000 live births.  A child born with this disorder has eye, brain and cardiovascular defects and typically has a cleft palate and hair lip. 

• Death occurs a few days after birth.

Patau’s syndrome - trisomy #13

syndrome results from having 3 chromosome #18s. 

• It occurs in 1 in 10,000 live births. 

• A child born with this disorder has defects in multiple body systems and typically dies a few months after birth.

Edward’s syndrome - Trisomy #18

syndrome results from having 3 chromosome #21s. 

• This occurs in 1 in 700 live births, but can be more frequent depending on the age of the parents. 

• A child born with this disorder can suffer from mild to severe mental retardation. 

• Characteristic features include a round face, slanting eyes, a short stature, thick neck and a protruding tongue. 

• individuals have an increased susceptibility to infections and may have abnormalities of the heart and other organs.  They can survive beyond 40 years of age.

down syndrome - trisomy #21

chromosomes that determine a individual’s gender

• how many should a normal human have

sex chromosomes

• 1 pair (2)

YO

missing a second sex chromosome (X) is lethal. 

• An unborn child dies as a fetus and is spontaneously aborted.

XO

missing a second sex chromosome –

gives rise to a female with Turner’s syndrome. 

• This is the only monosomy disorder that produces a viable offspring

syndrome results due to a missing second sex chromosome. 

• It occurs in 1 in 5000 live births. 

• An individual with syndrome is a female who looks female, but is missing a second X chromosome. 

• She will be short in stature (usually under 5 feet in height), have poor breast development, possess a webbed neck and have under developed ovaries. 

• She is sterile and will not have a menstrual cycle.  Due to a constriction of her aorta, she will ultimately have heart and kidney problems

turner’s syndrome (XO)

trisomies of the sex chromosome

an individual could be born with an extra sex chromosome

an extra sex chromosome (X)– gives rise to a male with Klinefelter’s syndrome

XXY

an extra sex chromosome (X) – gives rise to a female with Triplo-X or Metafemale syndrome.

XXX

an extra sex chromosome (Y) – gives rise to a normal male with no disorder.

XYY

syndrome results from an extra X chromosome. 

• XXY indicates that this individual will be male. 

• It occurs in 1 in 2000 live births.  He will be excessively tall (usually over 6’3” in height), have slight breast development, poor body hair growth and have under developed testes. 

• He will be sterile, but the disorder may go undetected.  20% of individuals with Klinefelter’s syndrome may have mild mental retardation.

klinefelter’s syndrome (XXY)

syndrome results from an extra X chromosome.

• Occurs in 1 in 1000 live births.

• Produces a physically normal female, but with 3 X chromosomes.

• She will be sterile due to under developed ovaries and uterus.  She will not perform menstruation.

• It was once thought that a metafemale would excel in athletics.  This is not true.

Triplo-X or metafemale

a male with an extra Y chromosome effects

no abnormalities- normal male