What makes you, you?Observable Traits

• Heredity – transmission of characteristics from parent to offspring

• Genetics – scientific study of heredity

Genetics

• Asexual Reproduction – only uses mitotic division; parent and offspring have same genetic information•Some examples: budding, direct outgrowth, fragmentation

Two Types of Reproduction

• Sexual Reproduction – uses meiosis and mitosis; parent and offspring have different genetic information

Two Types of Reproduction

• Two haploid cells (23 chromosomes) unite to form a diploid cell (46 chromosomes) called a zygote.

• Zygote will divide by mitosis and cells will eventually differentiate to form brain cells, heart cells, muscle cells, bone cells, etc.

Sexual Reproduction

• Meiosis – formation of haploid cells• Meiosis is similar to mitosis, but has

a different product.• Mitosis starts with one 46

chromosome cell and gets two identical 46-chromosome cells.

• Meiosis starts with one 46 chromosome cell and gets four different 23-chromosome cells.

Meiosis

• Spermatogenesis – meiosis that produces sperm cells

• Oogenesis – meiosis that produces egg cells

• Meiosis has two cycles when cells divide

• Key events: homologous pairs form; information “crosses over”; each new haploid is different

Meiosis

• Austrian monk• Lived from 1822-1884• Worked in the monastery garden and

began experimenting with pea plants in 1853.

• Why peas?• Short life cycle• Had several observable traits• Most traits only had two forms• Could control pollination• Could grow many at one time

Gregor Mendel

• Mendel began crossing plants with different traits to see what the outcome would be (ex: green seed and yellow seed; round seed and wrinkled seed).

• He realized that certain traits always showed up in the second generation. He called these dominant traits. Traits that could be hidden were called recessive traits.

Mendelian Genetics

• Law of Dominance – Dominant traits show up in the offspring even if a gene for a different trait is also present

• Genes can be paired with a like gene or with a different gene.

Mendelian Genetics

• Homozygous – both genes are the same (also called a purebred)

• Heterozygous – genes are different (also called a hybrid)

• If both genes are dominant – homozygous dominant

• If both genes are recessive – homozygous recessive

Mendelian Genetics

• In order for a recessive trait to be seen, the organism must have both of the recessive genes.

• Alleles are different forms of a gene for a particular trait (color, height, size, etc.).

Mendelian Genetics

• Punnett squares were created by an English biologist named Reginald Punnett in the early 20th century.

• He used them as a way to predict traits of offspring.

• He was one of the first to go deeper into Mendel’s genetic discoveries.

Punnett Squares

• Punnett squares cross the genes of one parent with the genes of the other parent for a particular trait to see what possible traits the offspring could have.

• Punnett squares also allow you to see the genotypes (gene combinations) and phenotypes (physical representation) of parents and offspring.

Punnett Squares

How to use a Punnett square:1. Choose a letter to represent the trait2. Use a capital letter to represent a

dominant trait and a lower case letter to represent a recessive trait** Must be the same letter!!**

3. Determine the genotypes of each parent

Punnett Squares

4. Put the two genes for one parent along the top

5. Put the two genes for the other parent along the left side

6. In each box put the letter above and the letter to the left together (put the capital letter first if they are different)

Punnett Squares

• You can now determine genotype and phenotype ratios by comparing how many are alike to those that are different.

Punnett Squares

• Cross a homozygous tall plant with a homozygous short plant. Tall is dominant to short

1. Use T2. T = dominant, t = recessive3. Homozygous tall = TT, homozygous short = tt

Punnett Square Example

Punnett Square Example4.

Punnett Square Example5.

Punnett Square Example6.

• Genotypes – the actual genes• Phenotypes – how the genes are

expressed

• Genotype of example: Tt• Phenotype of example: Tall

• Genotypic ratio of example: 4:0• Phenotypic ratio of example: 4:0

Punnett Square Example

• Law of Segregation – When hybrids are crossed with each other, the recessive trait segregates, or separates, again in some of the offspring.

• Incomplete dominance – when traits mix or blend instead of one trait being dominant over the other one

More Mendelian Laws

• Law of Independent Assortment – Many traits of an organism are inherited independently of each other

• Since dihybrids (organism with genes hybrid for two traits) follow the law of independent assortment, they can also be shown on a Punnett square. (See example)

More Mendelian Laws

• Example of a dihybrid cross between two pea plants that are heterozygous (RrYy) for seed shape and color. R = round, r = wrinkled, Y = yellow, y = green

Dihybrid Cross

  RY Ry rY ry

RY RRYY RRYy RrYY RrYy

Ry RRYy RRyy RrYy Rryy

rY RrYY RrYy rrYY rrYy

ry RrYy Rryy rrYy rryy

• Traits that follow the law of independent assortment are on different chromosomes.

• Traits on the same chromosome are inherited together and are not separated independently. They are called linkage groups. Ex: hemophilia A and color blindness

More Mendelian Laws

• Multiple Gene Inheritance – occurs when there are more than two different forms (alleles) of a gene for a particular traitEx: Blood type alleles are A, B, and O

• Pleiotropy – one gene affects several unrelated traitsEx: if a certain gene is inherited in cats it can affect fur, eyes, and hearing

Different Types of Gene Inheritance

• Polygenic Inheritance – one trait is controlled by many pairs of genesEx: skin color

• Pleiotropy and polygenic inheritance are considered non-Mendelian traits because they don’t fit the one gene, one trait model.

Different Types of Gene Inheritance

• Walter Sutton – 1902•Gene-chromosome theory•Hypothesized about the existence of genes on chromosomes

• Thomas Hunt Morgan – early 20th century•Existence of sex chromosomes•Used fruit flies for his experiments

Two other geneticists

• XX – female• XY – male

• If a trait is carried on the X chromosome, it is considered a sex-linked trait.

Sex Chromosomes

• Since males only have one X, they will either have a trait or not have it.

• Since females have two Xs, they can have a trait, be a carrier of the trait (without having it), or not be a carrier of the trait (without having it).

Sex Chromosomes

• Eugenics – an attempt to improve the human race through the control of hereditary factors

Eugenics