Genetics Notes

Review… DNA contains information on how to make you. You are made of proteins which are made of amino acids.

Why do you look similar to your parents? How do your traits get passed on to your children?

Cell reproduction Mitosis: a body cell divides to form two identical cells.

Steps: 1. DNA duplicates so there are 2 copies. 2. DNA coils into chromosomes.

3. Nuclear membrane disappears, centrioles make spindle fibers 4. Chromosomes line up in the middle of the cell, attached to spindle fibers

5. Chromosomes split apart and are pulled towards poles of cell. 6. Cell pinches in half, forming 2 cells.

Draw pictures. (6 circles) 1. Interphase: normal cell life, DNA duplicates.

2. Prophase: Nuclear membrane disappears, Chromosomes form, Centrioles make spindle fibers.

3. Metaphase: chromosomes line up in the middle of the cell.

4. Chromosomes split apart and migrate toward poles

5. New nuclei form, cell pinches in half forming two cells.

Mitosis occurs when your body grows and repairs.

All cells come from pre-existing cells. Your skin cells have the same DNA as your brain cells. Why do they look different?

Cell differentiation Stem cells = generic body cells As you develop your stem cells specialize and turn into specific body cells like skin, muscle, hair… Only certain genes are used in a specific cell… the rest are “turned off”. (epigenetics)

DNA = deoxyribose nucleic acid Gene = a section of DNA Chromosome = coiled up DNA

Humans have 46 chromosomes Bullfrogs have 26 chromosomes Fruit Flies have 8 chromosomes Carp = 104 Cat = 38 Dog = 78 Ant = 2 Fern = 1200

Chromosomes: Humans have 23 pairs of chromosomes. 46 Total. Half come from mom, half come from dad. The matching pairs from mom and dad are called homologous chromosomes.

Chromosome anatomy:

Passing traits to your children… Meiosis: cell division which reduces the number of chromosomes by half. End product: sperm and egg cells Why? ½ + ½ = 1

Steps of Meiosis 1. DNA duplicates 2. DNA coils into chromosomes, nuclear membrane disappears 3. Chromosomes line up in middle as homologous pairs.

4. Chromosomes separate and migrate to opposite poles. 5. Cell splits into two 6. Chromosomes line up in middle (single file this time) 7. Chromosomes split and migrate to poles. 8. Cells split. End product… 4 cells with half the number of chromosomes.

Egg formation = oogenesis

Sperm formation = spermatogenesis

History of genetics People have observed that children look like their parents. What substance and what mechanism allows this to occur?

Mendel A monk/scientist who lived in Czechoslovakia. He studied pea plant traits.

Mendel’s experiment… What do you think happened when he bred/crossed a tall plant and a short plant? ____________ P (parent) generation = Tall and Short F1 (first filial) generation = All tall F2 (second filial) generation = 3 tall to 1 short

Why were there no short plants in the F1 generation? Tall is dominant…

Dominant Genes: Overpowers recessive trait. Is seen Use capital letters to represent dominance.

Recessive traits: Are overpowered by dominant genes Only seen if both traits are recessive Lower case letters represent recessive traits.

Law of segregation: Each parent gives one copy of their genes.

Traits have 2 genes per trait. One from mom, one from dad… P = TT x tt F1 = Tt, Tt F2 = TT, Tt, tT, tt

Heterozygous The trait has two different genes. Hybrid Tt, Yy, etc.

Homozygous: The trait has two of the same gene Purebred Homozygous dominant = TT Homozygous recessive = tt

Genotype What your genes are… TT or Tt or tt

Phenotype What your appearance is. What is expressed. Tall or short

Allele: A variation of a gene… Blue eyes or brown eyes Tall or short Green or yellow seeds TT or tt

Probability: Probability of coin landing heads side up? Probability of offspring being short…

Punnett squares:

Human traits that are simple dominance/recessive Widow’s peak PTC paper tasting Attached and free earlobes Bent or straight pinkies Hitch-hikers or straight thumb Cleft chin Freckles Dimples

Not all traits are so simple… Co-dominance: both alleles are dominant therefore both are expressed. Example…..Blood type: Type A is dominant Type B is dominant If you get both, then you have type AB

Roan coloring: both red and white hairs are dominant so both are expressed.

Blending or Incomplete dominance Neither trait is dominant and an intermediate form is expressed. Red x White  Pink

Multiple alleles: Some traits are controlled by more than just two alleles Blood types have three alleles A, B, and O Cat hair color has three alleles Black, Chocolate, and Cinnamon

Sex linked traits: Males have 22 autosomes (body chromosomes and 1 sex chromosome = Y Females have 22 autosomes and 1 sex chromosome = X

The X chromosome contains about 2000 genes compared to 86 genes on the Y chromosome.

Some traits are located only on the X chromosome and not the Y chromosome. Hemophilia Colorblindness

Pedigree Charts A pedigree chart is a diagram that shows the occurrence of phenotypes of a particular gene from one generation to the next. The trait can be determined to be Autosomal recessive Autosomal dominant X-linked recessive

Occurrence of Hemophilia

How to make a pedigree chart…

What can we determine about this trait?

Calico Cats Fur color in cats is controlled by several genes. Orange fur is dominant and black fur is recessive. These alleles are located on the X chromosome. Only one X chromosome functions in each cell, the other is “turned off”.

When the cat is still developing, one of the two X chromosomes in the cell gets “turned off” and the “on” chromosome expresses its traits. Either chromosome can be turned on or off. The result is some areas are black and some are orange.

Usually only females can be calico.

Crossing Over Occurs during Meiosis Creates genetic variation

Mutations A change in DNA

Gene Expression Changes in your environment can cause genes to be expressed or not. Snowshoe hair Siamese cats jsp?cntn_id=116369&media_id=66293 &org=NSF jsp?cntn_id=116369&media_id=66293 &org=NSF

Karyotype A picture of your chromosomes. Arranged according to size #1-23

Nondisjunction An uneven split of chromosomes during meiosis. Example: Down Syndrome

Polyploidy Extra sets of chromosomes Occurs due to nondisjunction Plants work well with extra chromosomes, animals do not.