1. Patterns in Inherited Traits
Chapter 13

2. Alleles and Traits Blending inheritance
Example: Black and white horse will produce _________offspring
Failed to explain how traits disappear over several generations and then _________________unaltered generations later
Charles Darwin did not accept this idea
Gregor Mendel (____________________)
Started breeding thousands of _______________________
Kept detailed record of how traits passed from one ____________________to the next
Began to formulate how _________________works

3. Mendel’s Experiments Garden pea plant is ________-fertilizing
The flowers produce male and female _____________
The experiments
Controlled the pairings between individuals, by removing ___________________, with specific traits and observed traits of their _______________________
______________fertilized plants and collected _____________
Recorded traits of new pea plants

4. Mendel’s Experiments
Started with garden pea plants that “bred true” for a particular trait _________________________________________________
Cross-fertilized pea plants with different traits and offspring appeared in ___________________________________
Concluded (correctly) that hereditary information is passed in discrete units

5. Inheritance in modern terms
Locus: _______________________________________________
Homozygous: ____________________________________________
Heterozygous: ___________________________________________
Hybrids are _____________offspring of a cross between individuals that breed true for different forms of a trait
Dominant: Effect masks that of a recessive allele paired with it
represented by italic _____________letters
Recessive: Effect is masked by a dominant allele paired with it
represented by italic _____________________letters
Genotype: ______________________________________________
Phenotype: _________________________________

8. Allele distribution into gametes
A homozygous dominant pea plant with two alleles (____) has purple flowers, and a homozygous recessive pea plant with two alleles (___) has white flowers
If these ______________plants are crossed (PP × pp), all offspring will be _____________________
All ____________________(F1) offspring will be heterozygous
Genotype = _______
Phenotype = __________________________

9. DNA replication meiosis I meiosis II zygote (Pp)1 2
meiosis II 3
gametes (P)
gametes (p)
zygote (Pp)

10. Punnet square
A grid used to predict the _____________ and _________________ outcome of a cross
female gametes
male gametes

11. Testcross __________________________________________________
An individual that has a dominant trait (but an unknown genotype [PP/Pp]) is crossed with one that is homozygous recessive_________
Results?

12. Monohybrid cross
Breeding experiment in which individuals identically ____________________for _______gene are crossed (Pp×Pp)
Frequency of traits among offspring in the ________________ offers information about the dominance relationship between the alleles
First generation = _______
Second generation = ________
Results? (Ratio, %)

13. Mendel’s Seven Pea Plant Traits

14. Monohybrid cross

15. Law of segregation
The 3:1 phenotype ratios in F2 offspring of monohybrid crosses became the basis of ___________________________
_______cells carry pairs of genes on each pair of __________________________________
The two genes of each pair are ______________from each other during meiosis so that they end up on ___________ gametes

16. Dihybrid cross
Individuals ___________________for alleles of _______genes (dihybrids) are crossed, and the traits of the offspring are observed
Frequency of traits among the _____________offers information about the ___________relationships between the paired alleles

17. Dihybrid cross
Punnett square
One parent plant that breeds true for purple flowers and tall stems (______) is crossed with one that breeds true for white flowers and short stems (________)
Each plant makes only one type of gamete (________)
All F1 offspring will be dihybrids (________) and have purple flowers and tall stems
PT×pt

18. Dihybrid cross
Punnett square
The result of two F1 plants crossing: a dihybrid cross (PpTt × PpTt)
Four types of gametes can combine in sixteen possible ways

19. Dihybrid cross
In F2 plants, four phenotypes result in a ratio of ____________
_________________________________
Go back and check results!

20. Law of Independent Assortment
Mendel discovered the 9:3:3:1 ratio in his dihybrid experiments
Each trait still kept its individual 3:1 ratio
Each trait sorted into gametes ______________of other traits
During meiosis, members of a pair of genes on homologous chromosomes get distributed into gametes independently of other gene pairs

21. Contribution of Crossovers
How two genes get sorted into gametes depends on if they are found on same chromosome
Random assortment
Genes on one chromosome assort into gametes independent of genes on other chromosomes
Linkage group – all genes on a chromosome
Genes that are far apart on a chromosome tend to assort into gametes independently
Genes very close together on a chromosome are linked
They do not assort independently because crossing over rarely happens between them

22. Patterns of Inheritance
Simple/Complete dominance
A dominant allele fully masks the expression of a recessive one
Other patterns of inheritance are not so simple:
Codominance
Incomplete dominance
Epistasis
Pleiotropy

23. Codominance
Two alleles that are both fully expressed in heterozygous individuals
Multiple allele systems – gene for which three or more alleles persist in a population
Example: an ABO gene for blood type, human hair/eye color.

24. Codominance The A and the B allele are codominant when paired
Which two of the three alleles of the ABO gene you have determines your blood type
The A and the B allele are codominant when paired
Genotype AB = blood type AB
The O allele is recessive when paired with either A or B
Genotype AA or AO = blood type A
Genotype BB or BO= blood type B
Genotype OO = blood type O

25. AA or AO BB or BO
Genotype: AB OO
Phenotype: A AB B O

26. Incomplete dominance One allele is not fully dominant over another
The heterozygous phenotype is between the two homozygous phenotypes (example: red×white=pink)
In snapdragons, one allele (R) encodes an enzyme that makes a red pigment, and allele (r) makes no pigment
RR = red; Rr = pink; rr = white
A cross between two pink (Rr × Rr) yields red, pink, and white in a 1:2:1 ratio

27. Epistasis
The effect in which a trait is influenced by the products of multiple genes
Example: Fur color in dogs
B=__________, b=___________
E=colour in fur, e=reduced colour in fur

28. Pleiotropy __________________________________________________
Mutations in pleiotropic genes are associated with complex genetic disorders
Sickle-cell anaemia: a severe hereditary form of anemia (deficiency of red blood cells) in which a mutated form of ________________distorts the red blood cells into a crescent shape at low oxygen levels
Cystic fibrosis: a hereditary disorder affecting the _______________. It causes the production of abnormally thick __________, leading to the blockage of the pancreatic ducts, intestines, and bronchi and often resulting in ________________________.
Marfan syndrome: a hereditary disorder of ____________________, resulting in abnormally long and thin digits and also frequently in optical and cardiovascular defects

29. Environment and Phenotype
Epigenetic research is revealing that environment can influence phenotype
Some examples of environmental effects
______________________________
_______________________________
________________________________
_______________________

30. Short tandem repeats
Some genes have regions of DNA in which a series of two to six nucleotides is repeated hundreds or thousands of times in a row
Example: 12 alleles of homeotic gene that influence face length in dogs
___________________________________________________

31. Continuous variation Some traits appear in two or three forms
Example: _________________________________________
Others occur in a range of small differences
Example: __________________________________________
The more genes and environmental factors that influence a trait, the more continuous the variation
If a trait varies continuously, it will have ________________ curve

32. Cystic fibrosis Most common fatal genetic disorder in the U.S.
Most CF patients live no more than _______________
The CFTR gene encodes a protein
Protein moves chloride ions out of ________________________
Binds disease-causing bacteria
Occurs in people __________________for a mutated allele of CFTR gene (______________________)
The allele of CF has a 3 base pair deletion
Called ΔF508 because protein is missing the normal 508th amino acid
People with CF inherit 2 copies of ΔF508
The deletion causes mucus to accumulate, making breathing difficult