2. GENETICS Chapter 12

3. GENETICS

4. FATHER OF GENETICS  Monk and Teacher  Experimented with purebred tall and short pea plants  Discovered some of the basic laws of genetics  Studied purebred traits in peas  He died before his work was noticed; Rediscovered in 1900.

5. GENE Sections of DNA that codes for a specific function like producing a certain protein.

6. GENES OCCUR IN PAIRS  There are two copies of every gene.  We have approximately 40,000 pairs of genes.

7. ALLELES  Most genes have two or more variations, called alleles. For example, the gene for flower color for pea plants is either white or purple  Only one of the pair is passed on to offspring from each parent.

8. ALLELES (CONT)

9. CHARACTERS  Alleles are also referred to as characters.  Characters are physical features that are inherited.  Several characteristics of pea plants exist.

10. TRAITS  One of the several possible forms of a character is a trait.  Purple is one of the two possible traits for flower color. What is the contrasting trait?  Round is one of the two possible traits for seed shape. What is the contrasting trait?  Tall is one of the two possible heights. What is the contrasting height?

11. MENDEL’S EXPERIMENT IN REVIEW https://www.youtube.com/watch?v=Mehz7tCxjSE

12. WIDOWS PEAK  This trait is reportedly due to a single gene with a widow’s peak dominant and a straight hairline recessive.  Which do you have?

13. DOMINANT ALWAYS RULES!!! A recessive allele is expressed only when there is no dominant allele present. Scientists use a code of letters to represent the function of alleles. Dominant allele = Capital Letter Recessive allele = Lower case letter

14. DOMINANT  An allele that is fully expressed whenever it is present is called dominant.  Dominance causes a parental characteristic it controls to occur in any offspring

15. RECESSIVE  An allele that is not expressed when a dominant allele is present is called recessive.  Used to describe a gene that produces an effect in an organism only when its matching allele is identical

16. RANDOM SEGREGATION OF ALLELES  Because chromosome pairs split randomly during meiosis, either one of a pair of homologous chromosomes might end up in any one gamete. Chance decides which alleles will be passed on.  In modern terms, the law of segregation holds that when an organism produces gametes, each pair of alleles is separated and each gamete has an equal chance of receiving either one of the alleles.

17. GENOTYPE VS PHENOTYPE  The set of specific combinations of alleles that an individual has for a character is called the genotype.  The detectable trait that results from the genotype ’ s set of alleles is called the phenotype.  Thus, genotype determines phenotype.

18. GENOTYPE VS PHENOTYPE (FLOWER COLOR) file:///Volumes/Holt%20Biology%20NTL/files/ch12/60157.html

19. HETEROZYGOUS VS HOMOZYGOUS  If an individual has two identical alleles of a certain gene, the individual is homozygous for the related character.  If an individual has two different alleles of a certain gene, the individual is heterozygous for the related character.

20. HETEROZYGOUS VS HOMOZYGOUS file:///Volumes/Holt%20Biology%20NTL/files/ch12/60156.html

21. PUNNETT SQUARES  A Punnett square is a model that predicts the likely outcomes of a genetic cross.  A Punnett square shows all of the genotypes that could results from a given cross.  The combination of letters in each box represents one possible genotype in the offspring.

22. PUNNETT SQUARES file:///Volumes/Holt%20Biology%20NTL/files/ch12/60160.html

23. USING PROBABILITY  A Punnett square shows the possible outcomes of a cross, but it can also be used to calculate the probability of each outcome.  Probability is the likelihood that a specific event will occur.  Probability can be calculated and expressed in many ways.  Probability can be expressed in words, as a decimal, as a percentage, or as a fraction.

24. COMPLETE, INCOMPLETE AND CODOMINANCE  Genes that have three or more possible alleles are said to have multiple alleles.  Multiple alleles control the ABO blood groups (blood types) in humans.  Codominance is a condition in which both alleles for the same gene are fully expressed.  The genetics of human blood groups is an example of codominance.

25. When one allele is not completely dominant over another it is called incomplete dominance. INCOMPLETE DOMINANCE

26. A cross between red (RR) and white (WW) four o’clock plants produces pink- colored flowers (RW).

27. In codominance, both alleles contribute to the phenotype. CODOMINANCE

28. In certain varieties of chicken, the allele for black feathers is codominant with the allele for white feathers. WWBB

29. Heterozygous chickens are speckled with both black and white feathers. The black and white colors do not blend to form a new color, but appear separately. BW

30. W BBBB BW BW

31. TYPE OF DOMINANCE? Incomplete Dominance!

32. YOU TELL ME WHICH TYPE OF DOMINANCE… Codominance!

33. TYPE OF DOMINANCE? Incomplete Dominance!

34. SEX LINKED CHROMOSOMES  Sex Chromosomes are the chromosomes responsible for determining the sex of an organism.  These chromosomes carry the genes responsible for sex determination as well as other traits like color blindness.  Males have a genotype of XY, Female have a genotype of XX.  Color blindness is a recessive trait is located on the X chromosome.

35. SEX LINKED CHROMOSOME

36. PEDIGREE  A pedigree can help answer questions about three aspects of inheritance: sex linkage, dominance, and heterozygosity.  A pedigree is graphical chart used to identify the lineage of individuals.  Pedigrees are used in Animal breeding.