Introduction

Introduction

• Genetics: the study of the transfer of traits and hereditary material from parents to offspring.

• Asexual reproduction: The offspring is exactly copy of the parent. Only one parent is involved.

• Sexual reproduction: Two parents are involved.-Genes from 2 organisms (parents) of the same species get mixed.

sex cells = gametes = sperm and ova

• What is the purpose of sexual reproduction?– Greater variety

• Why are animals diploid (2 copies of each chromosome)?– Most of “genetics” is based on the fact that animals

have 2 copies of each gene.

• What is the purpose of meiosis:– To keep the chromosome number constant

•

• Diploid (2n): having 2 sets of chromosomes• Haploid (1n): having 1 set of chromosomes• Homologous chromosomes have the same

genes.

Meiosis

• Meiosis is cell division which produces gametes.• Meiosis cuts the chromosome number in half.

-Example: a human body cell has 46 chromosomes and a human sex cell has 23 chromosomes

• Meiosis occurs after DNA replication, and contains two cell divisions ( Meiosis I and Meiosis II), with no Interphase between them.

Meiosis l – homologous chromosomes separateThis results in 2 daughter cells that are NOT the same

(DON’T NEED TO KNOW ALL DETAILS)

Meiosis ll – similar to mitosis: sister chromatids separate

(DON’T NEED TO KNOW ALL DETAILS)

Crossing over provides more genetic variation

Occurs at prophase of Meiosis I

Genetics

Gregor Mendel observed pea plants with different traits ( flower color, plant size, pea shape..)

Self-pollination

• Most plants produce both sperm and ova• Pea plants can self-pollinate.• Self pollination leads eventually to pure –bred

plants.• Pure-bred plants produce offspring exactly like

themselves (if self-pollinated). • Mendel crossed various pure-bred plants.

Life Cycle of the Pea Plant

Cross-Pollinated Plants

Dominant and Recessive Traits

• A dominant trait overshadows a recessive trait.

• Mendel crossed yellow seeds x green seeds. All offspring had yellow seeds. He did not get plants with green seeds.

• P – parental generation• F1- first filial generation (from 2 purebred

parents)• F2- second filial generation (F1 X F1)

Mendel then crossed the F1 offspring among themselves. In the F2, he got 3/4 yellow seeded plants and ¼ green seeded plants.

• There are 2 alternative forms of a gene, one for green seeds and one for yellow seeds. These 2 forms are called alleles.

• Peas have 2 alleles of each gene.• Yellow is dominant and green is recessive.

Mendel’s conclusions

Modern Genetics

• Genes are segments of DNA on a chromosome that make a particular protein that is responsible for a particular trait (seed color, skin color, eye color, type of hair, etc.)

• Homozygous is an organism with two identical alleles of a gene for a given character:

- YY (yellow) or yy (green).• Heterozygous is an organism that has

different alleles for a character: Yy. Only the dominant gene will be expressed.

• Phenotype is an expressed, observable trait.– Example: color of the seed, yellow phenotype and

green phenotype.

• Genotype is the combination of specific alleles in the offspring.- Example: YY and Yy genotypes for yellow color,

and yy genotype for green color.

The Punnett Square

• It demonstrates simple genetic possibilities and probabilities in chart form.• Parent’s alleles are placed on both sides of the chart

The Punnett Square

F2 Phenotype and genotype ratio

Phenotype ratio in a Dihybrid Cross(DON’T NEED TO KNOW DETAILS)

The Law of Independent Assortment

• The traits are not stuck together. They sort independently.

Probabilities• Rule: probabilities of events that must happen at the same time are multiplied

• Coin: H-head h-tails1. Coin # 1 H probability ½ ( 50%) Coin #2 H probability ½ (50%)• Probability for HH: ½ x ½ = ¼ ( 25%)

2. Probability for hh: (25%) 3. Probability for Hh: (25%) 4. Probability for hH: (25%) 5. Hh and hH are basically the same. To calculate the probability of one

head and one tail, add the two separate probabilities. • ¼ + ¼ = 2/4 (50%)

• In a 4-person card game in which all the cards are dealt out, what is your chance of getting the king of spades?

• What is your chance of getting the king and ace of spades?

• What is your chance of getting the queen, king and ace of spades?

Pedigree Chart-Genetic History of a Person Carrying a

Mutation

• Using eye color (blue recessive or brown dominant), what conditions would prove that a man is not the father of a child?

Answer

• If child has brown eyes, and both man and mother have blue eyes.

Polygenetic Inheritance

• More then one gene determines a particular trait. Examples: wheat grain color, skin color, body height.

• Such a trait exist in a range (it does not come in just two variations).

Sex Determination

• X and Y chromosomes are a pair, but they do not carry the same genes. The Y chromosome is much smaller.

• XY - male individual• XX - female individual• So the Y chromosome makes a person a male• Females have 2 X chromosomes, but males have only 1.

Genes linked to the X sex chromosome

• Sex chromosomes also carry genes for other traits. The X chromosome carries many more genes than the Y chromosome.

• Since a male has only one X chromosome, all genes on that chromosome will be expressed.

• A bad gene on the X chromosome is much more likely to be expressed in a male than in a female.

• My father was color blind (X-linked recessive).1.I am not, but do I have to worry that my

children will get my father’s color blind gene from me?

2.If I had a sister, would she have to worry about this?