1. Chapter 9: Heredity
AP Biology Exam Review

2. MENDEL’S PRINCIPLES
Alternate version of genes (alleles) cause variations in inherited characteristics among offspring.
For each character, every organism inherits one allele from each parent.
If 2 alleles are different, the dominant allele will be fully expressed; the recessive allele will have no noticeable effect on offspring’s appearance.
Law of Segregation: the 2 alleles for each character separate during gamete formation.

3. P (parental) generation = true breeding plants
P1 (first filial) generation = offspring
P2 (second filial) generation = F1 offspring

4. Alleles: alternate versions of a gene

5. 7 characters in pea plants
Dominant vs. Recessive (expressed) or (hidden)

6. Law of Segregation

7. dominant (P), recessive (p)
homozygous = 2 same alleles (PP or pp)
heterozygous = 2 different alleles (Pp)

8. Phenotype: expressed physical traits
Genotype: genetic make-up

9. Testcross: determine if dominant trait is homozygous or heterozygous by crossing with recessive (pp)

10. Law of Independent Assortment:
Each pair of alleles segregates (separates) independently during gamete formation
Eg. color is separate from shape

11. Monohybrid cross: study 1 character
eg. flower color
Dihybrid cross: study 2 characters
eg. flower color & seed shape

12. The laws of probability govern Mendelian inheritance
Rule of Multiplication:
probability that 2+ independent events will occur together in a specific combination  multiply probabilities of each event
Ex. 1: probability of throwing 2 sixes
1/6 x 1/6 = 1/36
Ex. 2: probability of having 5 boys in a row
½ x ½ x ½ x ½ x ½ = 1/32
Ex. 3: If cross AABbCc x AaBbCc, probability of offspring with AaBbcc is:
Answer: ½ x ½ x ¼ = 1/16

13. The laws of probability govern Mendelian inheritance
Rule of Addition:
Probability that 2+ mutually exclusive events will occur  add together individual probabilities
Ex. 1: chances of throwing a die that will land on 4 or 5?
1/6 + 1/6 = 1/3

16. Blood Typing Phenotype (Blood Group) Genotype(s) Type A IAIA or IAi
IBIB or IBi
Type AB
IAIB
Type O ii

17. Blood Transfusions Blood transfusions must match blood type
Mixing of foreign blood  clumping  death
Rh factor: protein found on RBC’s (Rh+ = has protein, Rh- = no protein)

18. Nature and Nurture: both genetic and environmental factors influence phenotype
Hydrangea flowers vary in shade and intensity of color depending on acidity and aluminum content of the soil.

19. Mendelian Inheritance in Humans
Pedigree: diagram that shows the relationship between parents/offspring across 2+ generations
Woman =
Man =
Trait expressed:

20. Genetic Testing May be used on a fetus to detect genetic disorders
Amniocentesis: remove amniotic fluid around fetus to culture for karyotype
Chorionic villus sampling: insert narrow tube in cervix to extract sample of placenta with fetal cells for karyotype

21. Genetic Disorders Autosomal Recessive Autosomal Dominant
Cystic fibrosis (CF)
Tay-Sachs disease
Sickle-cell disease
Phenylketonuria (PKU)
Huntington’s disease (HD)
Lethal dominant allele

22. Chromosome theory of inheritance:
Genes have specific locations (loci) on chromosomes
Chromosomes segregate and assort independently
Chromosomes tagged to reveal a specific gene (yellow).

23. Sex-linked genes Sex-linked gene on X or Y Females (XX), male (XY)
Eggs = X, sperm = X or Y
Fathers pass X-linked genes to daughters, but not sons
Males express recessive trait on the single X (hemizygous)
Females can be affected or carrier

24. Transmission of sex-linked recessive traits

25. Sex-linked disorders Colorblindness Duchenne muscular dystrophy
Hemophilia

26. X-Inactivation
Barr body = inactive X chromosome; regulate gene dosage in females during embryonic development
Cats: allele for fur color is on X
Only female cats can be tortoiseshell or calico.

27. Human development Y chromosome required for development of testes
Embryo gonads indifferent at 2 months
SRY gene: sex-determining region of Y
Codes for protein that regulates other genes

28. Genetic Recombination: production of offspring with new combo of genes from parents
If offspring look like parents  parental types
If different from parents  recombinants

29. If results do not follow Mendel’s Law of Independent Assortment, then the genes are probably linked

30. Linked genes: located on same chromosome and tend to be inherited together during cell division

31. Crossing over: explains why some linked genes get separated during meiosis
the further apart 2 genes on same chromosome, the higher the probability of crossing over and the higher the recombination frequency

32. Calculating recombination frequency

33. Linkage Map: genetic map that is based on % of cross-over events
1 map unit = 1% recombination frequency
Express relative distances along chromosome
50% recombination = far apart on same chromosome or on 2 different chromosomes

34. Nondisjunction: chromosomes fail to separate properly in Meiosis I or Meiosis II

35. Nondisjunction Aneuploidy: incorrect # chromosomes
Monosomy (1 copy) or Trisomy (3 copies)
Polyploidy: 2+ complete sets of chromosomes; 3n or 4n
Rare in animals, frequent in plants
A tetraploid mammal. Scientists think this species may have arisen when an ancestor doubled its chromosome # by errors in mitosis or meiosis.

36. Chromosomal Mutations

37. Chromosomal Mutations

38. Exceptions to Mendelian inheritance
Genomic imprinting: phenotypic effect of gene depends on whether from M or F parent
Silence genes by adding methyl groups to DNA (methylation)

39. Exceptions to Mendelian inheritance
Some genes located in organelles
Mitochondria, chloroplasts, plastids
Contain small circular DNA
Mitochondria = maternal inheritance (eggs)
Variegated (striped or spotted) leaves result from mutations in pigment genes in plastids, which generally are inherited from the maternal parent.