Chromosomes

1
Chromosomes

• Chapter 14

2
What is Cytogenetics

• Correlation of an inherited trait to a
  chromosomal anomaly
• Karyotype is a prominent tool
• Established in 1902 by Walter Sutton (Columbia
  University)
• And by German scientist Theodore Boveri

3
Karyotoype
4
Karyotoype
5
Linked Genes

• Biologists realized that there were more traits
  than chromosomes.
• Many genes are linked together on the same
  chromosome (gene linkage).
• Linked genes can only separate by
• Crossing over
• Mutation

6
Sex Chromosomes

• Human cell has 46 chromosomes
• That is 23 pairs
• 22 of the pairs are autosomes
• 1 pair are the sex chromosomes
• Genes on the sex chromosomes determines ones
  gender and other traits
• SRY genes direct development of male parts

7
Sex Chromosomes

• Heterogametic sex 2 different sex chromosomes
  XY
• Males (humans mammals) are heterogametic
• Homogametic sex 2 same sex chromosomes XX
• Females (humans mammals) are homogametic
• Birds, moths and butterflies are opposite

8
X inactivation

• One X inherited by females is largely switched
  off in pre-natal development
• Chosen X is random and can be different from
  other cells in embryo
• Cells arising from this tissue inactivate same X
  chromosome
• Inactivated X creates Barr body
• 1st found by Murray Barr in 1949

9
Sex Linked Traits

• Genes on sex chromosomes that determine traits
  other than sex
• Hemophilia
• Red-Green colorblindness
• Muscular Dystrophy
• Alleles are shown as superscript to sex
  chromosomes

10
Abnormal Chromosome Numbers

• Polyploidy extra set or sets of chromosomes
• Fatal in humans/mammals
• Plants produce larger and hardier fruit and
  flowers

11
Euploid

• Normal chromosome number
• Nondisjunction can produce
• Aneuploid abnormal number of chromosomes
• Trisomy extra chromosome
• Monosomy missing chromosome

12
Autosomal Aneuploid

• Trisomy 21
• Downs Syndrome
• Flat face, large tongue and lips, almond eyes,
  short, wide hands, poor reflex and muscle tone
• Mental retardation varies
• Heart and kidney defects
• Increase incidence with age of mother
• 1 in 3000 if mom under 30
• 1 in 40 if mom is over 45

13
Trisomy 21
14
Sex Chromosome Aneuploids

• Turners Syndrome
• 45 XO
• Female, short, sterile
• Occurs 1 in 2000 live births
• Triplo-X (Super female)
• 47 XXX
• Tall, irregular menstration, learning difficulty
• 1 in 1000 live female births

15
Turners Syndrome
16
Sex Chromosome Aneuploids

• Klinefelters Syndrome
• 47 XXY
• Male, sterile, female secondary sex
  characteristics
• Unusually long arms and legs
• 1 in 800 live male births

17
Klinefelters Syndrome
18
Sex Chromosome Aneuploids

• Super Male
• 47 XYY
• Unusually tall, acne, speech and reading trouble
• Maybe aggressive
• Normal fertility
• 1 in 1000 males
• YO inviable

19
Polygenic Inheritance

• Many genes affect a single trait
• Example Ht, Wt, eye, hair, and skin color