Genetics Mendel Father of Genetics 1800 s monk

Genetics

Mendel…. Father of Genetics � 1800 s monk �Studied plant breeding & statistics � 19 th century theories of inheritance : blending �Mendel’s studies showed Particulate inheritance. . �Inheritance of discrete units (genes)

Vocab �Allele – version of a gene �True breeding – both alleles same �Hybrid – produced by crossing 2 true breeding parents (have one of each allele) �P generation : first generation �F 1 generation: offspring of P �F 2 generation: offspring of 2 F 1 individuals

Flower parts 101

Mendel's experiments �Plants self-pollinate �To make crosses Mendel cut off stamens and �cross-pollinated artificially �Each pea seed contains an embryo: �An offspring

F 1 offspring all purple �What does that tell us? �No blending. Only one gene showed up.

To get F 2 offspring cross F 1 x F 1

What does F 2 generation tell us? �White shows back up so…. � 1. must have inherited white gene from purple parent � 2. purple parent must have had 2 copies of gene for color one purple and one white � 3. F 1 s must have gotten one gene from each parent (segregation) � 3. it is possible for one gene to hide another (dominant and recessive genes)

After doing many similar crosses �Mendel determined statistically that which version of a gene (dominant or recessive) �Each parent gave to any given offspring �Was completely random and not linked to what other genes were doing (independent assortment)

Mendel found: � 1) No blending, flowers one color or the other. � 2) All F 1 looked same : called that trait dominant � 3) the other trait was hidden in some of the F 1 s but was passed on to F 2: called that trait recessive � 4) Law of segregation: each parent only gives one of their genes to the offspring hence. . � the 2 parental genes must be separated from each other (segregated from each other) � 5) F 2 crosses led Mendel to formulate the Law of

Descriptors �Since genes(particles) can be hidden use: �Phenotype to describe physical appearance �Genotype to describe genes �In Mendelian Genetics � Dominant genes require 1 copy to be expressed � recessive genes are only expressed if an individual gets 2 copies of the recessive gene

Genotypes �Dominant Traits represented by CAPITAL letters �recessive traits represented by lower case letters �Genotypes: � Homozygous Dominant (AA) � true breeding � Homozygous recessive (aa) � Heterozygous (Aa) hybrid

Punnett squares �Analytical tool for determining probabilities of inheritance �ALL possible Gametes go on top and sides of square …gametes are (1 n) so only one letter �Boxes inside square represent possible offspring �So each must get 2 copies of gene (2 n) so 2 letters

Phenotypes �Ratio of possible offspring in box is … �The probability that type of offspring will be produced � ratio 3 : 1 � 75% smooth : 25% wrinkled

Genotypes �Ratio of possible offspring in box is … �The probability that type of offspring will be produced � ratio 1 : 2 : 1 � 1 SS : 2 Ss : 1 ss

Test Crosses �Done to determine genotype �Cross unknown individual with homo recessive � if any recessive phenotype offspring then. . �Unknown is heterozygous

Types of Crosses �Monohybrid only looks at one gene �Dihybrid looks at probability of inheriting certain alleles of 2 different genes �Each different gene MUST have a different letter of alphabet H = height H = tall h = short C= color C = purple c= white individuals needs 2 of each letter so genotypes: HHCC HHCc HHcc Hh. CC Hh. Cc Hhcc hh. Cc hhcc

Dihybrid Punnett squares �All possible gametes on top �Heterozygous for both traits makes. . � 4 different gametes �Rr. Yy parent makes: �RY or Ry…. r. Y or ry �Each box is a zygote so needs � 2 letter r’s & 2 letter y’s � 2 copies of each gene

�Only parents that are heterozygous for both traits can make 4 different gametes so �Some Punnett squares can be smaller

Multiplication Rule (p 213) �To determine the chances of 2 different events happening together… �Multiply the probabilities of each event � P to get A & B = Probability A x Probability B �Chance to get TTBB �¼ x ¼ = 1/16

�Example Problem : � Tall is dominant to short. � Rigid, inflexible fingers is a recessive trait. � Cold blooded is dominant to warm blooded. �What are your chances of getting a frigid midget with a rigid digit? - both parents are heterozygous for all traits.

Cold blood: ¾ Short: ¼ Rigid: ¼

�Answer : ¾ x ¼ = 3/64

� Addition Rule

Non-Mendelian Genetics = �Any genes that are not straight forward dominant or recessive allele � 1) Incomplete dominance & 2) Co-dominance � 3) Multiple alleles (More than 2 alleles for a gene) � 4) Polygenic traits (traits controlled by more than one gene) � 5) Linked genes – genes that do not assort independently because they are on the same chromosome � 6) Sex linked genes – genes located on X or y

1) Incomplete Dominance �Neither allele completely dominates the other �NO recessive (hidden) allele �Both traits are partially expressed (blending) �Letter symbols… � must be same letter…same gene � must both be capital letters ………. not recessive � use superscripts to differentiate alleles � gene is color so use C � Cw = white Cy = yellow

�Do Punnett squares as normal but heterozygotes show a blended or in-between phenotype �Draw Punnett square for the cross Cw. Cw x Cy. Cy �F 1 will be … �Draw punnett square for F 2

2) Co-Dominance � 2 alleles both fully expressed (NO blending) �Gene for feather color in chickens C � co-dominant alleles for white (Cw) and black (Cb) �Heterozygotes (Cw Cb )have some black feathers and some white feathers (NOT grey)

3) Multiple alleles and Co-Dominance �Human ABO blood types � 3 alleles …. . 2 dominant and one recessive �Gene designated as letter I for �inherited antigenic substance

4) Polygenic traits �Multiple genes determine the phenotype �Example skin color in humans. �Phenotypes show a range of many different each only slightly different from the next. . �Do scientific skills exercise on page 219

5) Linked genes �Linked genes = genes with loci on the same chromosome �Linked alleles more likely to be inherited together than alleles on different chromosomes �The only way liked alleles do NOT end up in the same gamete is if crossing over takes place

6) Sex linked genes �Genes on X or y chromosome �Most often on X �y very small mostly codes for male trait �Writing sex linked genotypes : XX and Xy �Use superscripts to designate alleles �XNXn x XNy

Pedigree Analysis � 1) First step in genetic counseling � 2) Can determine which trait is recessive � a) only recessive alleles can be hidden in one generation and then show up in the next � b) two recessive parents can ONLY have recessive children � 3) Can be used to determine genotypes � a) always know genotype if look recessive � b) if look dominant has at least one…. � c) if parent or child looks recessive …. .

Fork-line Method (Branch Diagram) �Use for Dihybrid or trihybrid cross instead of Punnett square

Forked-line Method Trihybrid

Chromosome Theory of Inheritance �Morgan – first solid evidence �Used fruit flies…good choice because… � produce hundreds of offspring � mature quickly � small /cheap � only 4 chromosomes (3 autosomes, Xy) � mutations created new phenotypes

Morgan’s breakthrough �Natural phenotypes are called wild type (+) �Wild type ff have red eyes �Found mutant male w/ white eyes �Used letter w to represent gene for eye color �And w+ for wild type just w for white �Crossed mutant male with normal femal � w+ x w all F 1 had red eyes so … �Trait is recessive

F 2 generation…. Some white but only males �So differences between sex. �Only difference XX or Xy chromosome

Morgan tried a reciprocal cross �Change which parent has the mutation �All males get white eyes

Supports w gene is on X chromosome �Do Punnett square for X+X+ x Xwy �Do Punnett square for Xw. Xw x X+y �Supports Chromosomal Theory of Inheritance: individual genes are carried by specific chromosomes