Human heredity is determined by chromosomes and genes. There are 22 pairs of autosomes and one pair of sex chromosomes, which are either XX in females or XY in males. Genes located on the sex chromosomes, including the X chromosome, can be inherited in sex-linked patterns. Pedigree analysis is used to study inheritance patterns by examining traits over multiple generations in families. Autosomal traits can be inherited dominantly, recessively, or multifactorial based on environmental influences. Examples are provided of several genetic disorders and their modes of inheritance.

1. Human heredity
Inheritance of traits

2. Human chromosomes
• 22 pairs of chromosomes called autosomes
• 23rd pair are called the sex chromosomes
• Males as XY determine the sex of the
offspring- ~50% of the time passing X
chromosome (female offspring) and ~50% of
the time a Y (male offspring)

3. Sex chromosomes
• Females- XX
• Males- XY
• Not all genes shared
• Some genes of the X chromosome are not on the Y
• There are a few genes on the Y that are not on the X
• Genes that determine maleness are on the y
Chromosome
• Sex linked genes- are on the sex chromosomes
• Recessive traits on the X chromosomes show up more
often in males- hemizygous

4. Male and Female offspring

6. • Genetic analysis in humans follows a trait for
several generations in a family to determine
how it is inherited- pedigree analysis
• A pedigree shows family information in a chart
form. It cab be used as a toll in deterining
patterns of inheritance and to help identify
disorders.

8. Pedigree analysis

9. Karyotype

10. Spectral karyotyping
• Special karyotyping
• Each chromosome can have it’s own color
• In the near future, each gene can have it’s
own color

11. • Human inheritance involves the interaction of
many genes- polygenic inheritance
• Expression of traits is also affected by the
environment
• Multifactorial traits- genes and the
environment

12. • Heteroygotes for recessive traits are often
identified because their bodies produce half
the amount of gene product, but only
homozygous recessive are affected
• An allele that codes for a genetic disorder
codes for malfunctioning protein or none at all

13. • Recessive disorders can exhibit the most
severe phenotypes because the allele can
remain hidden in the heterozygotes
• A dominant trait that prevented reproduction
would quickly be eliminated from the
population, because it could not be passed on

14. Genetic influences
• Inherited genetic diseases
• Somatic genetic diseases
• Chromosomal aberration

15. • Genetic analysis of inheritance in humans
requires:
– Reconstruction of past histories for families
– Construction of pedigrees and understanding of
inheritance patterns
– Modes of inheritance include autosomal
dominant, autosomal recessive, X and Y linked
inheritance and mitochondrial inheritance

16. Autosomal Recessive
• Cystic fibrosis- mucous production blocks
ducts of certain glands
• Phenylketonuria- excess accumulation of the
amino acid, phenylalanine, in blood to mental
retardation
• Tay-sachs – improper metabolism of nerve
cells causes loss of nerve control
• Sickle cell anemia-

17. Autosomal recessive
• Albinism
– Absence of pigment in skin, hair, and eyes
– All children of affected (homozygous) individuals
will be affected
– Most affected individuals are the children of
unaffected parents

18. Xeroderma Pigmentosum
• Lack of DNA repair
• Sensitivity to UV light
• Skin cancers
• Only about 250 people in the world with this
condition

19. Autosomal Dominant
– Marfan syndrome connective tissue defect; death
by aortic rupture
– Huntington disease- progressive degeneration of
nervous system, dementia, and death
– Porphyria- episodes of mental derangement and
intermittent attacks of pain and dementia

20. Autosomal dominant
• Achondroplasia
– (Dwarfism)
– Associated with
defects in the growth
regions of the long
bones

21. • Polydactyly:
– Extra fingers or toes
• Brachydactyly-
malformed hands or
shortened fingers
– Incomplete
penetration and
variably expressive

22. Sex-linked inheritance
• Females have two X
chromosomes, Males
have an X and Y
• Lack of genetic
equivalence

23. X-linked Recessive
• Color blindness- red or green – insensitivity to
red or green light
• Muscular dystrophy – Duchenne type
progressive, fatal condition

24. X linked inheritance
• Recessive allele
• Ichthyosis
– Results in skin
disorder causing large
dark scales to form
on body

25. Hemophilia
• Inability for blood to
clot due to lack of
clotting factor

26. Additional modes of Inheritance
• Y – linked inheritance from father to son
– Every Y-linked trait is expressed
– Three hundred discovered so far
– Mitochondrial inheritance is from mother to
offspring
• Transmitted through the cytoplasm to the egg
• Involve defects in energy conversion and ATP
production