Unit 6: Genetics and Reproduction

The history

• Gregor Mendel

(1822- 1884) was an Austrian Monk whose studies earned him the title of Father of Genetics.

What is Genetics?• Genetics is the branch of biology that

studies heredity.

• Heredity is the passing of characteristics from parents to offspring.

• Characteristics that are inherited are called traits.

• Sex cells, eggs and sperm are called gametes.

• When the two unite through fertilization, a zygote is formed.

Mendel and the Peas

• Mendel did research using pea plants.

• Normally these plants fertilize themselves: self-pollination.

• If he wanted to, Mendel could take pollen from one plant and fertilize another: cross-pollination.

Mendel was a careful researcher…

• He only studied one trait at a time,

• analyzed his data mathematically,

• worked with true breeding pea plant populations

• and this set him apart from all others who had done heredity research before.

Mendel’s Monohybrid Crosses• A hybrid is the

offspring of parents that have different forms of a trait.

• The crossing of a female tiger and male lion results in the hybrid animal: the lyger.

• The opposite crossing results in tions.

                                                     

The nomencalture

• P stand for parent.• F stand for filial (son

or daughter).• In the example on the

right think of the P1 generation as your grandparents, the F1 generation as yourselves and the F2 generation as an children you may one day have.

Mendel’s experiments1. Mendel crossed true

breeding tall and short pea plants.

2. All the F1 came out tall. They were allowed to self-pollinate.

3. The F2 came out tall 75% of the time and short 25% of the time (3:1 ratio).

4. No matter what trait Mendel studied the numbers came out the same.

The rule of unit factors:

• Mendel concluded that each organism has two factors that control each trait.

• We now know these as genes found on chromosomes.

The rule of dominance:

• One trait is dominant over another. In the case of pea plants, tall is dominant over short.

or…• Short is recessive to

tall.

Alleles

• Alleles are alternative forms of a gene for each variation of a trait of an organism.

• For example height has two alleles in pea plants: short and tall.

The law of segregation

1. Every individual has two alleles of each gene.

2. Their gametes (sex cells) get only one.

3. During fertilization these these randomly pair producing four combinations.

Phenotype vs. Genotype

• Phenotype is the way an organism looks and behaves.

• Genotype is the allele combination the organism contains.

There are 3 main genotypes:

• AA homozygous dominant

• Aa heterozygous

• aa homozygous recessive

It was time for a joke.

                                

          

The law of independent assortment

• Genes for different traits (such as seed color and seed shape) are inherited independently of each other.

Punnett Squares

• In 1905 Reginald Punnett created a simple way to determine phenotype ratios.

• This is now known as the Punnett Square.

Punnett Squares…

Step 1

Step 2

Step 3

Step 4

                                           

Step 5

                                           

Step 6

                                           

Step 7

                                           

Sometimes there’s more

• Occasionally a geneticist wants to study two traits at once.

• A dihybrid cross is done for just that purpose.

When weird stuff happens

• So far we’ve learned about completely dominant alleles.

• For example free earlobes being dominant to attached earlobes.

Incomplete Dominance

• Sometimes traits mix together to create a new allele.

• In picture above the red and white flower were crossed and a pink flower was created.

Codominance

• In codominance the both traits are expressed (can be seen).

• The flower on the right shows codominance because it is the offspring of red and a white flowering plants.

Multiple Alleles

• Sometimes there are many different alleles (variations) for a trait.

• Human hair color, for example, varies greatly. • There are way more than just two alleles.

Polygenic Inheritance

• Some characteristics, such as eye color, are controlled by several genes.

• Sometimes the genes are on the same chromosome.

• Sometimes they are found on different chromosomes.

Polyploidy

• Sometimes organisms have extra chromosomes.

• In animals this is rare and usually results in death or serious defect.

• In plants this usually makes them stronger and bigger.

Determining Sex

Reading a Pedigree

Reading a Karyotype: a picture of an organism’s chromosomes

Genetic Disorders

• Sickle cell anemia• red-green color

blindness• Hemophelia• Down syndrome• Huntington’s diesease

• Turner’s Syndrome• Testicular

Feminization Syndrome

• Klinefelter’s Syndrome

• Jacob’s Synrome• and many more…

Remember…

• In humans…• XX = female

• XY = male

So what’s up with

• XO?

• and XXY?

• and XYY?

• and XY but with TFS?

Turner’s Syndrome 45XO

• Turner’s syndrome affects females only.

• Symptoms:• short• webbed necks• small breasts

Klinefelter’s Syndrome 47 XXY

• Klinefelter’s syndrome affects males only.

• Symptoms• tall• small genitals• small breasts

Jacob’s Syndrome 47 XYY

Testicular Feminization Syndrome 46XY

Meiosis

• is the process via which sex cells are made.

• gametogenesis = spermatogenesis = ovagenesis

• Diploid = regular number of chromosomes (2 copies)

• Haploid = 1 copy of each chromosome