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Chromosomes

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Chromosome Number

All cells in the human body (SOMATIC CELLS) have 46 or 23 pairs of chromosomes

Called the DIPLOID or 2n number

GAMETES (eggs & sperm) have only 23 chromosomes

Called the HAPLOID or 1n number

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Nondisjunction

Chromosomes may fail to separate during meiosis

Resulting gametes may have too few or too many chromosomes

Common Disorders: Down Syndrome – three 21st chromosomes

Turner Syndrome – single X chromosome

Klinefelter’s Syndrome – XXY chromosomes

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Mutations A mutation is a permanent change in the DNA sequence of a

gene. Mutations in a gene's DNA sequence can alter the amino acid sequence of the protein encoded by the gene.

How does this happen? Like words in a sentence, the DNA sequence of each gene determines the amino acid sequence for the protein it encodes. The DNA sequence is interpreted in groups of three nucleotide bases, called codons. Each codon specifies a single amino acid in a protein.

Gene mutations result from changes in a single gene. Chromosomal mutations involve changes in whole chromosomes.

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Gene Mutations Point Mutations – changes in one or a few

nucleotides Substitution THE FAT CAT ATE THE RAT

THE FAT HAT ATE THE RAT

Insertion THE FAT CAT ATE THE RAT

THE FAT CAT XLW ATE THE RAT

Deletion THE FAT CAT ATE THE RAT

THE FAT *** ATE THE RAT

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Gene Mutations Frameshift Mutations – shifts the

reading frame of the genetic message so that the protein may not be able to perform its function. Insertion THE FAT CAT ATE THE RAT

THE FAT HCA TAT ETH ERA T

Deletion THE FAT CAT ATE THE RAT

TEF ATC ATA TET GER AT

H

H

Chromosome Mutations

Changes in number or structure of entire chromosomes . Such mutations may change the locations of genes on chromosomes, and may even change the number of copies of some genes.

Deletions involve the loss of all or parts of a chromosome, while duplication produce extra copies of parts of chromosome. Inversions reverse the direction of parts of chromosomes and translations occur when part of one chromosome breaks off and attaches to another.

Chromosome Mutations Original Chromosome ABC * DEF

Deletion AC * DEF

Duplication ABBC * DEF

Inversion AED * CBF

Translocation ABC * JKL

GHI * DEF

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What Causes Mutations?

There are two ways in which DNA can become mutated:

Mutations can be inherited.

Parent to child

Mutations can be acquired.

Environmental damage

Mistakes when DNA is copied

Sex-Linked Genes Characteristics that are inherited from genes found on the

sex chromosomes. X-linked diseases are those for which the gene is present on

the X chromosome. X-linked diseases show inheritance patterns that differ from

autosomal diseases. This occurs because males only have one copy of the X

chromosome (plus their Y chromosome) and females have two X chromosomes.

Because of this, males and females show different patterns of inheritance and severity of manifestation. While there are both dominant and recessive X-linked diseases, there are some characteristics that are common to X-linked disorders in general

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Sex-Linked Traits Sex Determination

Females – XX

Males – XY

Almost all sex-linked traits are found on the X chromosome

Y chromosome contains very few genes and is mainly involved in sex determination

Sex-Linked Traits It is possible for a

female to be a carrier of an X-linked trait, but not express it

Men will express all X-linked traits they inherit

U.S. National Library of Medicine

X-linked recessive, carrier mother

Unaffected

son

Unaffected

daughter

Affected

son Carrier

daughter

Unaffected

father

Carrier

mother

Carrier

Affected

Unaffected

Example: Color Blindness

Various tests for color blindness.

Pedigree Charts Pedigree charts show a record of the family of an

individual

They can be used to study the transmission of a hereditary condition

They are particularly useful when there are large families and a good family record over several generations.

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Studying human genetics You cannot make humans of different types breed

together

Pedigree charts offer an ethical way of studying human genetics

Today genetic engineering has new tools to offer doctors studying genetic diseases

A genetic counsellor will still use pedigree charts to help determine the distribution of a disease in an affected family

Symbols used in pedigree charts Normal male

Affected male

Normal female

Affected female

Marriage

A marriage with five children, two

daughters and three sons. The eldest

son is affected by the condition.

Eldest child Youngest child

A pedigree chart of a family showing 20 individuals

Generations are identified by Roman numerals

I

II

III

IV

Individuals in each generation are identified by Arabic numerals numbered from the left

Therefore the affected individuals are II3, IV2 and IV3

I

II

III

IV

A DNA fingerprint is a type of restriction map. DNA fingerprints are based on parts of an individual’s

DNA that can by used for identification.

based on noncoding regions of DNA

noncoding regions have repeating DNA sequences

number of repeats differs between people

banding pattern on a gel is a DNA fingerprint

DNA fingerprinting is used for identification.

DNA fingerprinting depends on the probability of a match.

Many people have the same number of repeats in a certain region of DNA.

The probability that two people share identical numbers of repeats in several locations is very small.

(mother) (child 1) (child 2) (father)

Karyotype A picture of chromosomes

Arranged in pairs by size

Chromosomes #1-22 autosomes

Chromosome pair #23 sex chromosomes

Ex. XX = female; XY = male

Karyotype

How is the sex of an individual figured out? X is the symbol for Female and the female carries 2 x

chromosomes

Y is the symbol for male and it carries both an x and a y chromosome

So when conception occurs and cells are divided the end result is X + X = FEMALE

Y + X = MALE Now when there is a missing x chromosome (May be present but

defective)

X + 0 = FEMALE (Turner Syndrome) occurs

When an extra X chromosome is found in the cell

Y + X + X = MALE (Klinefelter Syndrome) occurs

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What chromosomes do all males have that the females don't have?

It’s the Y chromosome

The Y chromosome is responsible for kick starting the process to create a male.

It is the male who determines the sex of the child as he is the only one who carries the Y chromosome.

The male inherits a copy of his fathers genetic material. And it is through this that one can determine his lineage …

King Henry VIII

“King Henry the Eighth, to six wives

he was wedded: One died, one survived,

two divorced, two beheaded."

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Normal Male

28 2n = 46

Normal Female

29 2n = 46

Chromosome Mutations Down Syndrome

Chromosome 21 does not separate correctly.

They have 47 chromosomes in stead of 46.

Children with Down Syndrome develop slower, may have heart and stomach illnesses and vary greatly in their degree of intelligence.

Male, Trisomy 21 (Down’s)

31 2n = 47

Female Down’s Syndrome

32 2n = 47

Klinefelter’s Syndrome

33 2n = 47

Klinefelter Syndrome or XXY Syndrome Klinefelter syndrome is one that affects the male sexual

development.

The characteristics of this disorder include: Small testicles.

Infertility.

Lower testosterone level,

sparse facial and body hair,

taller than average height

may develop a feminine body shape which is caused by the lower level of testosterone.

It happens 1 in every 500 births to 1 in every 1000 births.

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Turner’s Syndrome

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2n = 45

Turner Syndrome Characteristics They are short in stature.

They have webbed necks, low ears , lower hairline , are secondary sex characteristics underdeveloped.

Are often treated with hormone replacement therapy to counteract the lost hormones and simulate puberty.

Turner syndrome is the absence of an X chromosome or by damaged X chromosome.

They may have problems with diabetes, osteoporosis, ear/hearing problems, obesity, kidney and coronary issues.

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Making a Karyotype Cut out the chromosomes

Arrange in pairs by size

Glue the pairs and number the autosomes 1-22

Glue the Sex Chromosomes last

Title it “Male (Disorder)” or “Female (Disorder)”