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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 3
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 4
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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. 6
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 7
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 H
Deletion THE FAT CAT ATE THE RAT TEF ATC ATA TET GER AT 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 Deletion Duplication Inversion Translocation
ABC * DEF AC * DEF ABBC * DEF AED * CBF 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 12
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 Xlinked traits they inherit
X-linked recessive, carrier mother Unaffected father
Unaffected Affected Carrier
Unaffected son U.S. National Library of Medicine
Carrier mother
Unaffected daughter
Carrier daughter
Affected son
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 A marriage with five children, two
Normal male
Affected male
Normal female
Affected female
Marriage
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 26
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." 27
Normal Male
2n = 46
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Normal Female
2n = 46
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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)
2n = 47
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Female Down’s Syndrome
2n = 47
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Klinefelter’s Syndrome
2n = 47
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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. 34
Turner’s Syndrome
2n = 45 36
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. 37
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)”
