Take out a blank sheet of paper On the paper write : 1.your name (first and last) 2.The date today (5-5-03) 3.The letter of the correct answer to the following question While viewing stained onion root tip cells you notice that distinct chromosomes cannot be observed in most of the cells. This is because most of the cells …..? A.) were destroyed while preparing the slide B.) must be in interphase (G1, S, G2) C.) are undergoing mitosis. D.) are undergoing meiosis.

Asexual and Sexual Reproduction Genetically identical cells are produced from a single parent cell by mitosis.  Fission or Budding Sexual reproduction occurs when new individual is formed through union of two sex cells (gametes).  Produce zygote.  Haploid gametes formed by meiosis in sex organs (gonads).

Asexual and Sexual Reproduction Different Approaches to Sex  Parthogenesis - Virgin birth - Exclusive - Switching  Sexual Reproduction - monoecious / dioecious - Hermaphroditism - Both Sex organs

Sexual Reproduction Sex Determination  In some organisms, environmental conditions can determine sex of offspring. - In mammals, sex is determined early in embryonic development.  Embryonic gonads are indifferent.  Y chromosome produce males.

Animals: Sex Determination

Plant Life Cycle Alternation of generations

Alternation of generations in Gynosperms

Alternation of generations in angiosperms

Comparison between Animal and Plant life cycles Plants gametes divide so individuals are haploid or diploid Animals individuals are diploid and gametes are haploid

Patterns of Inheritance

Pattern of inheritance hypotheses  heredity – the tendency for traits to be passed from parent to offspring “blending” hypothesis – the genetic material of the parents mixes in a manner similar to blending paint. Lamark’s inheritance of acquired characteristics. example a giraffe's neck Mendel’s inheritance of characteristic traits

Mendelian Genetics  Who was Gregor Mendel?  Monk studied science and mathematics at University of Vienna.  Worked with garden peas to study heredity.  Many varieties available  Infrequent version of a trait  Small and easy to grow

What were Mendel’s experiments? Mendel performed simple test crosses  Parent generation P 1 X P 2  First Filial generation F 1  Second Filial generation F 2  In each generation he recorded the phenotype of each individual and the number with each phenotype

How did Mendel derive his rules?  Used pea plants to control parental crosses  Chose only characters that were present or not present.  Started parental cross with true-breeders  Crossed two true- breeders of different varieties – hybridization cross

Dominance: One allele controls the phenotype Dominant phenotype is given by two genotypes: Homozygote and heterozygote: RR and Rr Recessive phenotype is given by one phenotype: Homozygote: rr Mendel’s first observation: Alleles show dominance

Dominant phenotype is given by two genotypes: Homozygote and heterozygote: RR and Rr

 Gene – a discrete unit of heredity Allele – alternate forms of a gene when expressed result in variation within traits  Phenotype – the physical trait expressed  Genotype – the alleles present

 Somatic cells have two alleles of each gene but gametes have only one allele  Alleles of each gene segregate during gamete formation  Principle of allele segregation is Mendel’s first rule  Parent = R r  Gametes = 1/2 R 1/2 r

 Segregation followed by random gamete fusion produces the observed numerical ratios of genotypes  Dominance gives the observed ratios of phenotypes  Segregation followed by random gamete fusion produces the observed numerical ratios of genotypes  Dominance gives the observed ratios of phenotypes

How do scientists predict the probability of inheritance? Punnett Squares  Punnett Squares can be used to visualize crosses between two individuals. Possible gametes of individual are listed along horizontal side. And possible gametes of the other individual are listed along the vertical side.  Genotypes of potential offspring are represented by cells within square.  Frequency expressed as probability.

Genotype R r ovule produced with one allele R and one allele r Genotype r r pollen produced with one allele r and one allele r Punnet’s Square r r r R Rr rr Rr rr

Second Law - Independent Assortment Genes located on different chromosomes are inherited independently of one another. Dihybrid Crosses

YyRr - heterozygous y r y R Y r Y R YyRr - heterozygous Y RY ry Ry r YY RR YY Rr Yy RR Yy Rr YY Rr YY rr Yy Rr Yy rr Yy RRYy Rr yy RR yy Rryy rr yy Rr Yy rr

Parental heterozygous cross phenotypic ratio? YY RR YY Rr Yy RR Yy Rr YY Rr YY rr Yy Rr Yy rr Yy RRYy Rr yy RR yy Rryy rr yy Rr Yy rr Yellow round seeds (any with Y or R) Yellow wrinkled seeds (any with Y and rr) Green round seeds (any with yy and R) Green wrinkled seeds (any with yy and rr)

 Incomplete Dominance Some alleles produce a heterozygote phenotype that is intermediate between those of the parents.

Multiple Alleles  Often each allele has its own effect and the alleles are considered codominant.  Human ABO Blood type  Type A individuals only galactosamine  Type B individuals add only galactose  Type AB individuals add both sugars  Type O individuals add neither sugar  Rh Blood Group  Rh cell surface marker

Epistasis  Epistasis - Interaction between products of two genes where one gene modifies the other gene’s phenotypic expression.  Emerson - To produce pigment, a Zea mays plant must possess at least one functional copy of each enzyme gene.

Epistasis

Sex Linkage A trait determined by a gene on the sex chromosome is said to be sex-linked. In Drosophila, sex is determined by the number of copies of the x chromosome.

Heterozygous for red eye color Eye color gene is carried on the X chromosome X R X r What alleles will the sperm have? What alleles will the eggs have? X R Y X R X r X R YX r Y Offspring phenotypes All females have red eyes ½ of the males have white eyes and ½ the males have red eyes

Mutations in Human Heredity  Mutations are accidental changes in genes. Rare, random, and usually result in recessive alleles.  Pedigrees used to study heredity. Hemophilia - Inherited condition where blood is slow to clot or does not clot at all.  Only expressed when individual has no copies of the normal allele.  Royal Hempohilia - Sex-linked

Sickle-Cell Anemia Sickle-Cell Anemia is a recessive inherited disorder in which afflicted individuals have defective hemoglobin, and thus are unable to properly transport oxygen to tissues. Heterozygotes usually appear normal. Homozygotes have Sickle-Cell, but are resistant to malaria. Copyright © McGraw-Hill Companies Permission required for reproduction or display

Other Disorders Tay-Sachs Incurable heredity disorder which causes brain to deteriorates. Nonfunctional form of hexosaminidas A enzyme. Huntington’s Disease Inherited condition caused by dominant allele causing progressive brain deterioration. Symptoms usually develop late in life.

Genetic Counseling and Therapy Process of identifying parents at risk of producing children with genetic defects and assessing genetic state of early embryos. Amniocentesis Ultrasound Chorionic Villi Sampling

Pedigree Analysis  Mendel’s laws allow us to analyze the genetic information in family records (pedigrees)  From this we can determine the nature of alleles that control traits. From this we can:  deduce whether the trait is dominant or recessive  deduce whether the trait is sex linked  deduce the genotypes of members of the family  predict the phenotypes of future offspring  deduce the genotypes of parents from their offspring phenotypes

In a pedigree, each individual is represented by a symbol The shape, color, and location of the symbol carry information about the sex and phenotype of the individual In a pedigree, each individual is represented by a symbol The shape, color, and location of the symbol carry information about the sex and phenotype of the individual

A dominant allele has a different pattern of inheritance: Trait A dominant A a Only a a for recessive trait expression so both parents have to have a recessive allele