From whom did you get your traits? Parents Mom Dad

What kind of traits do you think you got from your parents? Eye color Hair color Height Nose shape

Which traits do you prefer?

Who are these people?

Who was Gregor Mendel? “Father of Genetics” Performed experiments on pea plants

Why peas? Easy to grow Easily observable traits Male and female reproductive parts on the same flower Pea plants normally reproduce by self- pollination

Self-pollination vs. Cross-pollination Self-pollination – sperm cells in pollen fertilize the egg cells of the same plant Cross-pollination – male pollen fertilizes the female egg cells of another plant

Mendel’s Experiments P generation True-breeding (purebred) pea plants were created by self-pollinating plants for several generations until the offspring had the same traits as the parents

Mendel’s Experiments (CONT’D) First Filial (F1) Generation – offspring of the P generation Mendel then cross-pollinated a purebred tall plant x purebred short plant. RESULT: All tall plants

Mendel’s Experiments (CONT’D) Second filial (F2) generation – offspring of the F1 generation Mendel performed an F1 cross  flowers of the F1 generation were allowed to self- pollinate. RESULT: 3 Tall : 1 Short

Explaining Mendel’s Results Dominant “factor” had masked the corresponding recessive “factor” in the F1 generation  still present but not expressed Reappearance of the recessive “factor” in the F2 generation suggested that at some point the dominant “factor” and the recessive “factor” for plant height separated Mendel suggested that these “factors” separated, or segregated, during gamete formation

Mendel’s Rules of Inheritance 1.Traits are determined by “factors”that are passed from parents to offspring 2.Law of Segregation Alleles are separated during gamete formation 3.Law of Dominance Some alleles are dominant, some alleles are recessive

What are “factors” and alleles? Genes – “factors” that control traits Alleles – different forms of genes (EX: T=tall or t=short)

Genetics Vocabulary Dominant – allele that is expressed Recessive – allele that is not expressed Genotype – genetic makeup of an organism (EX: T t) Phenotype – physical appearance that develops from the genotype (EX: Tall) Homozygous dominant (TT) – organism that has two dominant alleles for a particular trait Homozygous recessive (tt) – organism that has two recessive alleles for a particular trait Heterozygous (Tt) – organism that has two different alleles for the same trait

Punnett Squares Mendel used Punnett squares to predict the possible allele combinations of his crosses –Monohybrid Cross – one “factor” cross involving genes for one trait (EX: plant height) –Dihybrid Cross – two “factor” cross – involve genes for two different traits (EX: seed color and seed shape)

What did this tell Mendel? Mendel’s Law of Independent Assortment - alleles separate independently of one another during gamete formation

Beyond Dominant and Recessive Traits Some alleles are neither dominant nor recessive Many traits are controlled by multiple alleles or multiple genes.

Law of Dominance Some alleles are dominant and some alleles are recessive

Law of Segregation Alleles segregate during the formation of gametes Law of Independent Assortment Alleles for different genes segregate independently of each other during the formation of gametes

Incomplete Dominance One allele is not completely dominant over another allele –EX: Snapdragons Alleles: R – red r – white Phenotype ratio: Why???

Incomplete Dominance One allele is not completely dominant over another allele –EX: Snapdragons Alleles: R – red r – white Phenotype ratio: Why??? Red is NOT completely dominant over white in a heterozygous individual  intermediate phenotype

P F1 F2 RR x rr Rr x Rr 1 RR 2 Rr 1 rr

Codominance “Dominant together” Situation in which two dominant alleles for a gene contribute to the phenotype –Black and white “speckled” chickens –Roan coat color in cows and horses RR – WW – RW – Phenotype Ratio:

Codominance “Dominant together” Situation in which two dominant alleles for a gene contribute to the phenotype –Black and white “speckled” chickens –Roan coat color in cows and horses RR – red WW – white RW – roan Phenotype Ratio: A roan coat consists of a mixture of red and white hair  Both phenotypes are expressed.

Roan Cow

Roan Horse

Speckled Chicken

Multiple Alleles Gene that has 3 or more alleles that are responsible for the same trait Multiple alleles increase the number of possible phenotypes  ***ONLY two alleles can be inherited*** –ABO blood grouping (3 alleles) –Coat color in rabbits (4 alleles)

ABO Blood Grouping I A – dominant allele for type A blood I B – dominant allele for type B blood i – recessive allele for type O blood

ABO Blood Grouping Blood typeGenotype A B AB O NOTE: Blood type AB is also an example of codominance

ABO Blood Grouping Blood typeGenotype AI A I A or I A i BI B I B or I B i ABIAIBIAIB Oii NOTE: Blood type AB is also an example of codominance

ABO Blood Grouping Example Problem If a person that is heterozygous for type A blood has a child with a person that is homozygous for type B blood, what are the possible blood types of the child?

Polygenic Traits Traits that are controlled by more than one gene Genes may be on the same chromosome or different chromosomes –Hair color, skin color, body type, eye color

(Number of dominant alleles shown below each eye color) Eye Color Eye color is known to have a polygenic inheritance pattern, possibly governed by 6 or more genes.

HUMAN GENETICS

Chromosomes and Sex Determination Autosomes – chromosomes that appear identical in males and females –1 st – 22 nd sets of chromosomes Sex chromosomes – determine gender and appear different in males and females –23 rd set of chromosomes Male  XY Female  XX

Chromosomes and Sex Determination Each sperm cell receives either an X or Y chromosome Each egg cell receives an X chromosome

Chromosomes and Sex Determination Each sperm cell receives either an X or Y chromosome Each egg cell receives an X chromosome XX X Y

Chromosomes and Sex Determination Each sperm cell receives either an X or Y chromosome Each egg cell receives an X chromosome XX XXX YXY

Chromosomes and Sex Determination Each sperm cell receives either an X or Y chromosome Each egg cell receives an X chromosome Therefore, gender is ALWAYS determined by the male gamete. XX XXX YXY

Genetics and Human pedigrees Humans have few offspring Pedigrees do not show clear proportions Geneticists use pedigrees to determine whether a rare allele is dominant or recessive. –If a recessive allele is rare in the general population, it is unlikely that two people that marry will both carry it unless they are related (e.g., cousins). –Different alleles arise through mutations – changes in a gene Harmful  genetic disorder Neutral  most are recessive – not physically expressed in a heterozygous individual Beneficial  source of the variation a species needs in order to adapt to changing conditions and evolve over time

What is a pedigree? Family tree that traces the inheritance patterns of particular traits from generation to generation Square is male circle is female Filled in=affected Pp pp Pp ppPp pp Pp PP or Pp pp First generation (grandparents) Second generation (parents plus aunts and uncles) Third generation (two sisters) Ff ffFf ff Ff ff FF or Ff ff FF or Ff Widow’s peak No Widow’s peak Attached earlobe Free earlobe (a) Dominant trait (widow’s peak) (b) Recessive trait (attached earlobe)

Sex-Linked Disorders Disorders linked to genes located on a sex chromosome MOST are located on the X chromosome Y chromosome is very small and contains few genes

X-Linked Recessive Genetic Disorders

X-Linked Recessive Disorders Appear much more often in males than females Daughters who are heterozygous are carriers Mutant phenotype can skip a generation if it passes from a male to his daughter XY X X

X-Linked Recessive Disorders Appear much more often in males than females Daughters who are heterozygous are carriers Mutant phenotype can skip a generation if it passes from a male to his daughter XHXH Y XHXH XhXh

X-Linked Recessive Disorders Appear much more often in males than females Daughters who are heterozygous are carriers Mutant phenotype can skip a generation if it passes from a male to his daughter XHXH Y XHXH X H X H Y XhXh XHXhXHXh X h Y

X-Linked Recessive Disorders ALL males that inherit the affected gene will have the disorder ONLY females pass on the affected gene to males – WHY? Males get the affected X chromosome from their mother XHXH Y XHXH X H X H Y XhXh XHXhXHXh X h Y

X-Linked Recessive Disorders How would a female inherit the disorder? XY XHXH X H XX H Y XhXh XhXhXhXh X h Y

X-Linked Recessive Disorders How would a female inherit the disorder? Father must have the disease and the mother must be at least a carrier. XhXh Y XHXH X H X h X H Y XhXh XhXhXhXh X h Y

Colorblindness Mutation that causes the failure to make some of the pigments necessary for color vision XBXB XbXb XbXb X B X b X b YX B YX b Y

Colorblindness

WHAT NUMBERS DO YOU SEE?

NOW WHAT NUMBER DO YOU SEE???

WHAT NUMBERS DO YOU SEE?

CHROMOSOME DISORDERS CAUSED BY NONDISJUNCTION

WHAT IS NONDISJUNCTION? NONDISJUNCTION – error in meiosis in which homologous chromosomes fail to separate Produces gametes that contain abnormal numbers of chromosomes –Some with TWO copies of a chromosome –Some with NO copy of a chromosome

Nondisjunction

Diagnosis of Chromosomal Disorders Cells in metaphase can be fixed in order to characterize the chromosomes Karyotype: individual chromosomes can be recognized by length, position of centromere, and banding patterns are arranged in order

Down Syndrome

SEX CHROMOSOME DISORDERS CAUSED BY NONDISJUNCTION Turner’s syndrome  XO female Klinefelter’s syndrome  XXY male Jacob’s syndrome  XYY male Triple X syndrome  XXX female

Klinefelter’s Syndrome (47, XXY)

Turner’s Syndrome (45, XO)

Klinefelter’s vs. Turner’s

Turner’s Syndrome (45, XO) A rare chromosomal disorder of females  1 in 2500 Short stature Lack of sexual development at puberty  sterile

Klinefelter’s Syndrome (47, XXY) 1 in 700 to 1 in 1000 males are born with this condition About half show lower IQ, slower development Most are sterile