1. Inheritance Principles and Human Genetics
BioH - Chapter 11

2. Genetics Vocabulary Review
Genes – units of information about heritable traits
Homologous chromosomes – similar chromosomes received from male and female that line up next to each during MetaphaseI in meiosis
Alleles – different forms of a gene
Locus – location on a chromosome where specific genes are found
Linkage – when genes on a chromosome “stay together” even during crossing-over
Genetic recombination – the “recombining” of genes as a result of crossing-over

3. Chromosomes Thomas Hunt Morgan Studied fruit flies
Found X and Y chromosomes
After the “rediscovery” of Mendel’s pea plants research – Morgan studied fruit flies in the early 1900’s

4. Karyotypes
Karyotyping is a process that allows chromosomes to be presented in an orderly, easily compared manner
This karyotype is of a female (XX)

5. Sex chromosomes (X, Y) Autosomes
Contain genes that determine the sex (gender) of an individual
Autosomes
Not directly involved in determining the sex of an individual
Different organisms, different number X Y
The X chromosome contains over 800 genes. The Y chromosome contains less than 50 genes (as of 2010).

6. Sex determination Sex-determination Region Y (SRY)
Sperm has equal chance of receiving X or Y
Egg only receives X
XX – female
XY - male
Totally RANDOM
process
Sex-determination Region Y (SRY)
Found in mammalian Y chromosome
Gene codes protein to cause
gonads to develop testes

7. Gene location Sex-linked
Traits coded for by an allele on a sex chromosome
Could be on X or Y chromosome
More X-linked genes because X is much larger
If male carries a recessive allele on the X chromosome, it will exhibit the trait
Ex. Hemophilia (blood disorder)
Studying sex-linked traits allowed a better understanding of where genes are located on chromosomes

8. Linked genes Traits that are inherited together Makes a linkage group
This happens because they are found close to each other in the same chromosome and not as easily genetically recombined by “crossing-over”

9. Chromosome Map
A diagram that shows the linear order of genes on a chromosome
Map unit – frequency of crossing over of 1%.

10. Mutations Germ-cell mutations Somatic-cell mutations
Occur in gametes (may not be expressed until offspring)
Somatic-cell mutations
Occur in body cells
May affect organs
Skin cancer and leukemia
Lethal mutations
Cause death, often before birth
Either mutation may affect “control genes” that cause changes to many other genes

11. Inheritance of Traits Pedigrees
A diagram showing how a trait is inherited over several generations

12. Russian Royal Family & hemophilia
Genetic abnormality – rare, uncommon trait version
Genetic disorder – inherited condition causing medical disorders
Syndrome – recognized set of disorders that characterize a disorder

13. Patterns of Inheritance
If a trait is
Autosomal
Appears in both sexes equally
Dominant
Every individual with the trait will have parents with the trait
BB or Bb (dominant trait will show)
bb (recessive trait will show)
Recessive
1, 2, or no parent with the trait
Bb X Bb will not show mutation but can produce children for the recessive allele (bb)
Bb (carrier)

14. Genetic Trait and Disorders
Single-Allele traits
Controlled by a single allele of a gene
More 200 human traits
Huntington’s disease
Forgetfulness and irritability

15. Gene Inheritance & Disorders
Polygenic Inheritance
Traits are influence by more than one gene
Skin color
3 to 6 genes
Genes control amount of melanin
Eye color, height, hair color

16. Complex characters Influenced both by environment and genes
Skin color, breast cancer, height

17. Multiple Alleles Codominance Genes with 3 or more alleles
ABO blood groups
IA, IB, and I
IA and IB are codominant
Codominance
Both alleles are expressed
IAIB is type AB

18. Incomplete dominance
Trait that is displayed is intermediate between the two parents.
Hair type
Curly (CC) X Straight (cc)= Wavy hair (Cc)

19. X-linked Genes are linked to x-chromosome Colorblindness Recessive
Unable to distinguish certain colors, eg. green or red

20. Sex-influence traits
Males and females can show different phenotypes even with same genotypes
Autosomal
Type of Baldness
Dominant in males
Recessive in females

21. Chromosomal disorders
Chromosome problems, not genes
Duplication – a repeat of
several gene sequences on
the same chromosome
Deletion – loss of a
chromosome
segment

22. Inversion – gene sequence separated from chromosome, reinserted into same place, but in reverse
Translocation –
transfer of
one chromosome
part to a
non-homologous chromosome

23. Chromosome number disorders
Nondisjunction – one or more pairs of chromosomes fail to separate during mitosis or meiosis (produces condition known as aneuploidy – more or less chromosomes than the parental number)
Down Syndrome – one extra chromosome at #21

24. Sex Chromosome number changes
Turner syndrome – inheriting only one X chromosome with no additional X or Y chromosome
Most X0 zygotes
spontaneously abort
0.01–0.04% of
females
Non-functional ovaries
(infertile)
Short height
Normal intelligence

25. Kleinfelter Syndrome – one extra X chromosome with normal XY (XXY)
% of males
Conditions develop after puberty
Smaller testes - usually sterile (not always)
Taller than normal
Normal intelligence
Very subtle phenotype characteristics

26. XYY Condition – extra Y chromosome as result of non-disjunction
0.1% of males
Taller than average
Mild retardation

27. Detection Amnioncentesis
Removal of amniotic fluid from the amnion, the sac surrounding the fetus
Between 14 – 16 week of pregnancy

28. Chorionic villi sampling
Cells derived from the zygote that grow between uterus and placenta
Between 8th and 10th week

29. Genetic counseling
Informing a person or couple about their genetic makeup
Form of medical guidance about problems that might affect their offspring

30. Treatment Usually treat symptoms Gene therapy
Replacement of defective genes with a healthy one
Somatic cell gene therapy (body cells)
Germ cell gene therapy (eggs or sperms)
Poses risks and ethical issues