introduction
DESCRIPTION
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. - PowerPoint PPT PresentationTRANSCRIPT
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)
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.
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
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?
• Using eye color (blue recessive or brown dominant), what conditions would prove that a man is not the father of a child?
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.