Unit 6 notes_1

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6.1- Chromosomes and Meiosis

Somatic cells- These are body cells that make up most of your body tissues and organs.

Ex. Spleen, Kidneys, and eyeballs are made entirely of body cells.

Germ cells- These are cells in your reproductive organs, such as the ovaries or testes.

These develop into gametes.

Gametes are sex cells- eggs in the female and sperm in the male.

Each species has a certain number of chromosomes per cell.

Our body cells hold 46 chromosomes a cell, in 23 pairs.

Cells in organism differ because different genes are expressed.

Your cells have autosomes and sex chromosomes

Our 23 pairs of chromosomes can be divided into two sets: 23 from your mother and 23 from your father.

Homologous chromosomes are two chromosomes- one from the mother, one from the father.

-More importantly, these chromosomes have copies of the same genes, though the two copies may differ.

- Ex. If you have a gene that influences blood cholesterol on chromosome 8, then you will have one copy from your mother and one copy from your father.

One may be associated with high cholesterol levels, one may be associated with low cholesterol levels.

Autosomes are chromosomes that contain genes for characteristics that are not directly related to an organism's sex.

- These are from chromosomes 1-22.

The 23rd chromosomes are made up by your sex chromosomes.

The X- Chromosome contains numerous genes, while the Y-Chromosome contains very few genes.

- Directs development of the testes and other male traits.

Body cells are diploid; gametes are haploid

Sexual reproduction involves the fusion of two gametes that results in offspring that has a genetic mixture of both parents.

The actual fusion of an egg and sperm cell is called fertilization.

The egg and sperm cell need only half the usual number of chromosomes, which means one chromsome for each homologous pair.

A new nuclei is formed

Must have the correct number of chromosomes for an organism to fully develop. after birth.

Diploid means a cell has two copies of each chromosome- One from the father and one from the mother.

Body cells are diploid. 2n=46

Haploid means that a cell has only one copy of each chromosome as fertilization only needs one chromosome per homologous pair.

During fertilization, Egg=X and Sperm= X or Y. Determines the sex of the organism.

Meiosis

Germ cells in your reproductive organs undergo the process of meiosis to form gametes.

Meiosis is a form of nuclear division that divides a diploid cell into haploid cells to get one chromosome instead of two chromosomes.

Process is essential for sexual reproduction.

6.2- Process of Meiosis

Cells go through two rounds of division in meiosis.

Homologous chromsomes are two separate chromosomes, one from your mother and one from your father.

Sister chromatids are half of a duplicated chromosome.

Together, the two chromatids are sister chromatids.

Meiosis 1

There are 4 steps to Meiosis 1 (Refer to book for picture of process):

Prophase 1: Duplicated chromosomes condense; homologous chromosomes begin to pair up

Metaphase 1: Homologous chromosomes line up along the cell equator. Each side of the equator has chromosomes from both parents.

Anaphase 1: The paired homologous chromosomes separate from each other and move toward the opposite sides of the cell.

Telophase 1: Cell undergoes cytokinesis, cell splits into daughter cells.

Meiosis 2

There are 4 steps to Meiosis 2 (5-8) (Refer to book for picture of process if needed)

5. Prophase 2: Centrosomes and centrioles move to opposite sides of the cell.

6. Metaphase 2: Chromosomes align along the cell equator.

7. Anaphase 2: Sister chromatids are pulled apart and move to opposite sides of the cell.

8. Telephase 2: The cell undergoes cytokinesis, ends up with two different sister chromatids in each of the four cells.

6.3- Mendel and Heredity

Mendel laid the groundwork for genetics.

Traits are characteristics that are inherited, such as hair color, paw shape, and hair length.

Traits are hereditary.

Genetics is the study of biological inheritance patterns and variation in organisms.

Mendel's data revealed patterns of inheritance

Experimental Design

The pea flower typically self-pollinates, so the line become genetically uniform.

The line of plants becomes purebred, offspring of purebred parents inherit parental characteristics.

Mendel interfered with the self-pollination process .

Took away male parts of pea plants,

Fertilized female parts of pea plants with pollen from different pea plants.

Because he started with purebred plants, he knows that any variation would have been caused by his experiment.

Results

A cross is the mating of two organisms.

Parent generation: He crossed a purebred white-flowered pea plant with a purebred purple-flowered pea plant. ( Parents give one gene each.)

F1 Generation: Resulted in all purple flowers.

F2 Generation: Resulted in both purple and white flowers.

Means that traits for white flowers did not dissapear, it was masked.

Noticed that there were 3:1 ratios from purple flowers to white flowers in the F2 generation.

Conclusions

Demonstrated that traits are individual units, appear and one point, reappear at the next, never gone masked instead.

Law of segregation

Organisms get two copies of each gene

Organims donate one copy of each gene, so two copies of each gene segregate during the gamete formation.

6.4- Traits, Genes, and Alleles

The same gene can have many versions.

A gene is a piece of DNA that provides insturctions on how to make a specific protein.

Each gene has a locus, a position on a pair homologous chromosomes.

One gene on each chromosome.

An allele is an alternate form of a gene that may occur at a specific locus.

Each parents donates one allele for each gene, one on each of the chromosomes.

Homozygous means that the two alleles are the same at a specific locus.

Ex. Both alleles code for black hair.

Heterozygous means that the two alleles are different at a specific locus. This may mean that the gene has more than one version.

Genes influence the development of traits

A genome is all of an organism's genetic material.

A genotype is the genetic makeup of a certain set of genes.

Genotype of a pea plant includes both genes that code for flower color, even though one of them might be hidden.

A phenotype is the physical characteristics or traits of an organism.

A boy with yellow hair has a phenotype for yellow hair, even though he might have a hidden gene for brown hair.

Dominant and Recessive alleles

Dominant alleles are expressed when there are two different alleles or there are two dominant alleles.

Recessive alleles are the alleles that are only expressed when two recessive alleles are present.

Dominant alleles are not stronger than recessive alleles, they are just being expressed.

6.5- Traits and Probability

A monohybrid cross is a cross that examines the inheritance of only one specific trait.

Dihybrid crosses examine the inheritance of two traits.

The law of independent assortment states that allele pairs separate during gamete formation or meiosis.

Probablity is the likelihood that a particular event will happen.

Crossing over is the exchange of segments between homologous chromosomes.

Increases genetic diversity.

Happens any time a germ cell divides.