1. Gene Linkage and Polyploidy
Chapter 10 Section 3
Gene Linkage and Polyploidy

2. Genetic Recombination
The new combination of genes after crossing over (prophase I) and independent assortment (metaphase I) occur in meiosis
Independent assortment calculated by 2n
n= # of pairs of chromosomes
Humans n= 23, so 2n= 46 for male and female
2n= 246= ~ 70 trillion different recombinations

3. Gene Linkage One exception of Mendel’s Law of Independent Assortment
Chromosomes have multiple genes that code for proteins, said to be linked to one another on the same chromosome and thus usually travel together during meiosis
Drosophila melanogaster- fruit fly study confirmed this
Chromosome maps show the sequence of genes on chromosomes using data

4. Polyploidy
Occurrence of one or more extra sets of all chromosomes in an organism (most are diploid organisms)
Triploid= 3n (3 complete sets of chromosomes)
Earthworms, goldfish, flowering plants
Others
Bread Wheat (6n) Oats (6n) Sugar Cane (8n)

5. Basic Patterns of Human Inheritance

6. Recessive Genetic Disorders Dominant Genetic Disorders
MUST BE HOMOZYGOUS RECESSIVE
Can be a heterozygous carrier and not have the disorder
Cystic Fibrosis
Albinism
Tay-Sachs Disease
Glactosemia
Dominant Genetic Disorders
CAUSED BY DOMINANT ALLELE
Must be homozygous dominant or heterozygous to have disorder
Huntington’s Disease
Acondroplasia

7. Pedigrees
A diagram that traces the inheritance of a particular trait through several generations.
Take note: Male= Square, Female= circle
Colored in shape= expresses trait, or half way colored in is a carrier of trait

8. Dominant Disorder Pedigree
Recessive Disorder Pedigree

9. Genetics – Types of Inheritance

10. Test Cross Tt tt Tt Tt Tt tt Tt Tt t t t
This is done to determine if an organism with a dominant trait is homozygous or heterozygous
Cross the unknown with a __________________.
If any of the offspring are recessive, the unknown must have been __________________.
T T? T t?
t t t Tt tt Tt Tt Tt tt Tt Tt

11. Incomplete Dominance
Produces a phenotype that is an intermediate (a blend) of the dominant trait and the recessive trait in a heterozygote.
Example: In four o’clock flowers, the alleles for red flowers (CR) and white flowers (CW) both influence the phenotype
CRCR = red
CWCW = white
CRCW = pink

12. Codominance Occurs when both alleles for a gene are expressed
Example: Roan horses are a combination of white and red horses
Human example: AB blood type - Type A proteins & type B proteins both show up on blood cells

13. Sickle-cell disease: common of African descent
Chronic pain
Affects RBC and ability to transport oxygen b/c they block circulation in small blood vessel.
Changes in the blood cell shape from round to a “c” shape (sickle)
Heterozygous for trait have BOTH normal and sickle cell shapes, can live a normal life

14. Multiple Alleles
Some traits are determined by more than two alleles. These are multiple allele traits.
Example: Human blood type
Alleles: IA, IB, i
Rh factors (blood protein)
+ is dominant
- is recessive
Blood Type
Possible Genotypes A
IAIA or IAi B
IBIB or IBi AB
IAIB (codominant) O ii
O is the absence of A and B markers and is recessive to A and B
ABO blood group is an example of multiple alleles and codominance

15. Rabbits 4 allele codes for coat color: C, cch, ch, and c
C > cch > ch > c
Can have many different combinations: more alleles equals more possible phenotypes and genotypes
Produces 10 possible genotypes and 4 possible phenotypes
C= dominance
homozygous recessive= cc

16. Epistasis
Variety resulting from one allele hiding the effects of another allele
Labrador retrievers: yellow-black
E= dark
e= light
B= how dark
b= how light
EEbb or Eebb= chocolate lab
eebb or eeBb or eeBB= yellow lab
WHY? Because the “e” masks the effects of the dominant B allele

17. Chromosomes in Humans
Each cell in our body has 46 chromosomes, besides sex cells which have 23
Humans have 23 pairs of chromosomes
22 pairs of autosomes
1 pair of sex chromosomes
Contain genes that determine gender
XX = female, XY = male
Sex-Determination
50% chance for male
50% chance for female
Who determines gender?

18. Dosage Compensation
Females= 22 pairs of autosomes and 1 pair of X chromosomes
Males= 22 pairs of autosomes and one X and one Y chromosome
Do females have more dosages?
no, randomly one of the X chromosomes stop working in each cell of female’s body (dosage compensation)
Calico Cats- orange fur spots
Barr Bodies- dark stain
on cells
DIFFERENT SIZES
X chromosomes help development of M and F
Y chromosome help development of just male

19. Sex Linked Traits
Genes located on the X chromosome are X-linked genes.
Genes located on the Y chromosome are Y-linked genes.
Sex-linked traits are coded for by an allele on a sex chromosome.
More on X chromosome because it’s larger
Because males only have one X chromosome, if they carry a recessive allele on the X chromosome, they exhibit the trait.
Examples: color-blindness, hemophilia

20. Red-green color blindness
Recessive X-linked trait
8% of males in US
dad= not a carrier b/c
he does not have the “b” allele
mom=carrier b/c has recessive allele (b)
Only possible offspring that can have red-green colorblindness is MALE

21. Hemophilia- delayed blood clotting

22. Polygenic Traits
Many phenotypic traits come from the interaction of multiple pairs of genes
skin color, height, eye color, finger prints
Bell curve shows that the more the dominant allele occurs, the less the extreme phenotypes will occur

23. Environmental Influences
Can effect the appearance of organisms:
Sunlight
Water
Temperature

24. Twin Studies Identical twins= genetically the same
If a trait is inherited, the both will have it
Concordance Rate
If a trait is cause by environmental factors, they may not both have it

25. Chromosomes and Human Heredity
Chapter 11 Section 3

26. Karyotype Studies
The study of whole chromosomes by using images of chromosomes stained during metaphase.
Stains= identify marks on homologous chromosomes
Placed in decreasing size to produce a micrograph (karyotype)
22 autosomes matched together
1 pair of nonmatching sex chromosomes

27. Telomeres Protective protein end capping chromosomes
Possibly linked to aging and cancer

28. Nondisjunction Down’s Syndrome -Trisomy 21
Cell division during which sister chromatids fail to separate properly

29. During meiosis cells do not get the right number of chromosomes and when they divided the resulting cells do not get the correct number either
Can be extra sets or lack of sets of chromosomes
3 sets= trisomy
1 set= monosomy

30. Trisomy- Down Syndrome
Extra chromosome 21 (“Trisomy 21”)
1/800 Americans
60% chance if mom
is 45+
Characteristics
distinct facial features
short stature
heart defects
mental disabilities

31. Nondisjunction Sex Chromosomes
Occurs in both autosomes and sex chromosomes

32. Fetal Testing

33. Mutations Germ-cell mutations occur in gametes
Affect offspring only
Somatic-cell mutations occur in body cells
Affect the organism only, not inherited
Lethal mutations cause death, often before birth
Some mutations are beneficial and give an organism an evolutionary advantage.

34. Chromosome Mutations Deletion – loss of a piece due to breakage
Inversion – a piece breaks off, flips, and reattaches
Translocation – a piece breaks off and reattaches to a nonhomologous chromosome

35. Chromosome Mutations
Nondisjunction – a chromosome fails to separate from its homologue during meiosis
One gamete gets an extra copy, the other gets no copies
Example: Down’s syndrome is caused by 3 copies of the 21st chromosome

36. Gene Mutations Point Mutation – A mutation in a single nucleotide
Substitution – one nucleotide changed for another
C = A instead of C = G
Frameshift Mutation – Results when all of the codons are changed due to an addition or deletion of a nucleotide
Addition – one nucleotide added
Deletion – one nucleotide removed