Unit 6: Genetics and Reproduction

Cell Growth and Reproduction The bigger a cell gets, the smaller its surface area to volume ratio becomes.

Volume vs. Surface Area 6cm 2 : 1 cm 3 = 6 24cm 2 : 8cm 3 = 3 96cm 2 : 64 cm 3 = 1.5

Cell Growth and Reproduction If a cell became too big it would take too long for wastes from the middle to make it all the way out through the membrane. Also it would take way too long for nutrients to reach from the surface all the way to the middle.

Chromosome Two identical chromatids (sisters) are held together by a centromere. The tips are called telomeres.

The Cell Cycle is the sequence of growth and division of a cell.

Interphase The majority of a cell’s life is spent in the growth period known as interphase. DNA gets duplicated (copied) during this time.

Mitosis is the process by which two daughter cells are formed, each containing a complete set of chromosomes.

Step 1. Prophase It is the longest step. The long stringy chromatin coils up into chromosomes.

Step 1. Prophase (cont’d) The nucleus disappears; the nuclear envelope and nucleolus dissolve. The centrioles migrate to opposite poles and the spindle forms.

Step 2. Metaphase The doubled chromosomes become attached to the spindle fibers by their centromeres.

Step 2. Metaphase (cont’d) The chromosomes are pulled by the spindle fibers to the middle (equator).

Step 3. Anaphase The centromeres split apart. The microtubules of the spindle fibers shorten. The sister chromatids separate.

Step 4. Telophase Chromatids reach the opposite sides (poles) of the cell. Chromosomes unwind into chromatin. Spindle breaks down.

Step 4. Telophase (cont’d) The nuclear envelope and nucleolus reform. A new double membrane begins to form between the two nuclei.

Cytokinesis After mitosis, the cell’s cytoplasm divides during this stage. In animals, the cells simply pinch off.

Cytokinesis In plant cells a cell plate is laid down and the plasma membrane and cell wall form on either side of it.

Meiosis is the process via which sex cells are made. gametogenesis = spermatogenesis = ovagenesis Sex cells = gametes

Meiosis (cont’d) Diploid = regular number of chromosomes (2 copies) Haploid = 1 copy of each chromosome

The history Gregor Mendel ( ) 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.

What is Genetics? (2) 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.

Mendel and the Peas (cont’d) 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,

Mendel as a researcher (cont’d) 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 nomenclature P stand for parent. F stand for filial (son or daughter). P 1 = grandparents F 1 = parents F 2 = kids

Mendel’s experiments 1.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.

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 dominance: One trait is dominant over another. In the case of pea plants, tall is dominant over short. or… Short is recessive to tall.

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 law of segregation 1.Every individual has two alleles of each gene. 2.Their gametes get only one. 3.During fertilization these randomly pair producing four combinations.

The law of independent assortment Genes for different traits are inherited independently of each other.

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.

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.

Punnett Squares In 1905 Reginald Punnett created a simple way to determine phenotype ratios. This is now known as the Punnett Square.

Step 1

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

Codominance In codominance 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 AS?

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 Tall Acne (body and face) Predisposition to criminal insanity/behavior

Androgen Insensitivity Syndrome 46XY Externally female Blind vaginas Testes located inside Infertile Cannot produce nor ingest male hormones Formerly known as Testicular Feminization Syndrome