2. Gene
Genetic material
Instructions or code for a particular trait or characteristic

3. Allele One of the possible options for a given characteristic or trait
Pea Plant Examples:
flower color is purple or white
height is tall or short
Flowers are terminal or axial

4. Homologous pair
Two chromosomes that contain genes for the same traits at the same locations
One comes from mom, the other from dad
Humans have 22 pairs of homologous and 1 pair of non-homologous chromosomes

5. Probability Chance that a given event will take place
Multiplication rule = to calculate the odds of two or more events occurring at the same time, multiply the probabilities for each independent event

6. Dominant
An allele that can mask or hide the expression of another allele for the same trait
Is represented by a capital (big) letter

8. Recessive
An allele that is masked or hidden when present with another allele for the same trait
Is only expressed when two are inherited
Is represented by a lower case (little) letter

10. Homozygous When the two alleles inherited are the same
Homozygous dominant
Both are dominant alleles
TT = tall tall = a tall plant
Homozygous recessive
Both are recessive alleles
tt = short short = a short plant

11. Heterozygous When the two alleles inherited are different
Only the dominant allele is expressed or visible
Tt = tall short = a tall plant

12. Phenotype
The actual expression of the genes
What you see

13. Genotype The actual alleles present
What genes they inherited for that trait

14. Law of Segregation
Each pair of alleles separate during the formation of the gamete (egg or sperm)
Example: If parent is Tt, the offspring will get either the T or the t- not both Tt
T t

15. Law of Independent Assortment
Each pair of alleles separate independent from other pairs of alleles during the formation of the gamete
Which chromosome goes into a gamete is random
TtPp
TP or Tp or tP or tp

16. Gregor Mendel 19th century Austrian monk
Experimented in breeding pea plants
The father of genetics
Developed terminology used
Stated laws

18. Types of Crosses Individuals
Purebred = have only one allele for a trait TT, tt, PP,pp
Hybrid = have different alleles for a trait Tt or Pp
Crosses
Monohybrid = differ for one trait, TT x tt
Dihybrid = differ for two traits, TTpp x ttPP

19. Punnett Squares
An easy (non-mathematical) way to calculate the probability of the traits for the offspring of two specific individuals

20. Terminology for Crosses
P1 = parent generation
F1 = first generation of children
F2 = second generation of children
F stands for filial, or sons and daughters

21. Monohybrid A cross between two individuals Examines only one trait
Parents have contrasting traits
P1 = Pp x Pp
F1 = 3:1 phenotypic ratio
= 1:2:1 genotypic ratio

22. Test Cross A cross used to determine what genes a parent has
Gametes P ? p Pp ?p
Test Cross
A cross used to determine what genes a parent has
The unknown individual (PP or Pp) is mated with an individual that is homozygous recessive (pp)
Children show the second unknown gene

23. Dihybrid Cross A cross between two individuals
Examines only two traits at the same time
Parents have contrasting traits
P1 = SSYY x ssyy
F1 = SsYy x SsYy
F2 = 9:3:3: phenotypic ratio

24. Incomplete Dominance Alleles are not dominant or recessive
Both alleles are expressed, or blended
Capital letters are used for both alleles, or the same letter with a prime or subscript is used H and H1
Examples:
R = red H = straight hair
r = white H1 = curly hair
Rr = pink HH1 = wavy hair

25. Codominance Both alleles are completely expressed
Neither hides the other
Example: Blood Type
M and N proteins
LM LM produces protein M
LN LN produces protein N
LM LN produces both protein M and N

26. Multiple Alleles Three or more alleles for a given trait exist
Example: A,B,AB and O blood types result from which 2 of 3 genes you inherit
Type A blood results from IAIA or IAi
Type B blood results from IBIB or IBi
Type AB blood results from IAIB
Type O blood results from ii

27. Pleiotropy One gene influences more than 1 trait Example in peas:
One gene determines whether seeds are round or wrinkled
Same gene affects starch metabolism and water absorption

29. Polygenic Inheritance
Results from the interaction of many genes to determine a single phenotype- in other words, many genes work to produce appearance of one trait
Not just 2 or 3 varieties, but a continuous variation or range of phenotypes
The opposite of pleiotropy

30. http://sun. menloschool

32. http://www. specialedprep

33. Linked Genes Are on the same chromosome
Are inherited together because they come as a package

34. Sex-linked
Sex chromosomes the last pair, X & Y
Autosomes
pairs 1-22

36. Sex-linked Examples of human disorders that are sex-linked are:
Hemophilia
Red-green color blindness
Duchennes’s muscular dystrophy
These disorders occur more frequently in men than women, because men only inherit 1 gene for the trait, while women inherit 2

38. Recessive Autosomal Disorders
Phenylketonuria = unable to break down phenylalanine, results in mental retardation
Sickle-cell anemia = abnormal hemoglobin, unable to transport oxygen
Tay-Sachs disease = unable to break down some lipids, causing nerve damage and ultimately death

39. Dominant Autosomal Disorders
Huntington’s disease = mental illness begins in middle age, affecting brain and motor control and leading to total mental and physical incapacity

40. Fraternal Twins
Fraternal twins are the result when two different eggs (ova) are fertilized by two different sperm.
This leads to the development of two separate placentas, each with its own chorion and amnion.
Fraternal twins are more common than identical twins and account for about 2/3 of twin pregnancies.

41. Identical Twins Identical twins develop when a fertilized egg splits.
Depending on when the split occurs will determine if the twins share a placenta, with either one or two chorions and amnions, or if they each develop their own placentas.
In general, the later the spit occurs, the more likely that the twins will share one placenta.

42. Fraternal vs. Identical Twinning
Even after they are born, it is sometimes difficult to know whether twins are identical or fraternal. It can be easier if they:
share one placenta (identical)
are different sexes (fraternal)
have different blood types (fraternal)