Introduction to genetics Ch 11 Meiosis Some terms

Introduction to genetics Ch. 11

Meiosis…. Some terms to know • Haploid (1 n)- a cell with only one complete set of chromosomes (gametes or sex cells). Diploid (2 n)- a cell that contains two complete sets of chromosomes. (all other cells) Which are diploid and which are haploid? How do you know sex cells (eggs and sperm) are only haploid?

Homologous Chromosomes come from a Tetrad • Homologous chromosomes are pairs of chromosomes where each one is identical to the other. • A tetrad is a structure containing 4 strands of DNA tightly paired together.

Meiosis • There is a meiosis I and II. Each are the same steps as mitosis. • You begin with one diploid cell and produce 4 haploid. • This gives you many different combinations of genes to be passed on. It’s all chance on the ones you get.

Crossing Over • Occurs during prophase 1 when homologous chromosomes pair up and form tetrads and exchange portions of chromatids.

Meiosis Provides for Genetic Recombination • 1. 28 a Sorting and recombination of genes in sexual reproduction, allows for a great variety of possible gene combinations. • That is why no two people are alike. (Besides identical twins- why? )

1. 46 A great diversity of species increases the chance that at least some living things will survive in the face of large changes in the environment. • Why is this? • So, is diversity good? Give an example.

The Steps…Let’s review. • • Prophase I Metaphase I Anaphase I Telophase I Prophase II Metaphase II Anaphase II Telophase. II • What occurs during each step?

1. 8 c Mitosis vs. Meiosis • Mitosis • Meiosis – Somatic cells – Sex Cells – One cell division – Two cell divisions – Two daughter cells – Four daughter cells with same number of with half chromosomes as parent – Daughter cells are – Daughter cells not identical to parents. – Asexual – Sexual

Genetics • Genetics is the study of heredity. • What is heredity? • Genetics involve traits being passed from one parent to offspring. • What are some traits you got from your parents?

Fertilization • Gametes- Sex Cells – Sperm and Egg Fertilization- process of sperm fertilizing the egg. Zygote- fertilized egg Embryo- zygote- 8 weeks. Fetus- 9 weeks - delivery

Gregor Mendel. . The Father of Genetics • Mendel studied peas for 3 reasons: 1. Structure of pea 2. Presence of distinctive traits. 3. Rapid reproduction cycle. 90 days • What are the male and female parts of a flower? • How do you think he cross fertilized them?

Purebred vs. Hybrids • Since flowers have both male and female (anther in stamen • and ovary in pistol), they are able to self-fertilize. • True-breeding- if org. were allowed to self fertilize, they would have offspring identical to self. • (pure-bred, same genetic traits from each parent) A hybrid is an organism that receives different forms of a genetic trait from each parent.

Generations • P is the Parental Generation. • F 1 - what you get when the parents reproduce. YOU. • F 2 - The offspring of F 1. YOUR KIDS. What are P, F 1 and F 2 in these pictures, assuming everyone is from the same family?

Mendel’s Experiments • He tested 7 traits of the pea pod: 1. 2. 3. 4. 5. 6. 7. Flower Color Flower position Pea color Pea shape Pod color Pod shape Height Mendel’s Peas

Mendel’s Study • Cross pollinated pea plants, taking a stamen and putting that into the pisil of another flower using two pure-bred plants. All of them had yellow peas. • Allowed them to selffertilize. He got 75% yellow and 25% green. • He thought they would blend to form a chartreuse color? Why? • He ended up crossing all 7 traits. See Figure 11 -3.

Mendel’s Results P- Green X yellow F 1 - Yellow F 2 - Green and Yellow

Principles of Inheritance • Chromosome Theory of Heredity states that genes in chromosomes carry the material of inheritance.

1. 21 Genes are coded in DNA molecules and pass information from parents to offspring. • Genes are sections of a • Alleles can be chromosome that code dominate or recessive. for a traits. • Dominate- always • Alleles are one form of expressed. a gene. • Recessive- only – Ie. Eye color can be expressed if no blue, green, brown, etc. dominate is present. – You receive one allele • Let me explain. from your mom and • BB, Bb, bb one from your dad.

Allele Expression • Homozygous dominant- HH (pure) • Heterozygous dominant- Hh (hybrid) • Homozygous recessive- hh (pure) • If H is long hair and h is short hair, which will have long and which short? (on a cat)

Genotype and Phenotype • Genotype represents the genetic make up. HH Hh hh • Phenotype represents the outward expression. Long Hair Short Hair Review of Terms

Mendel’s laws • 1. 22 b Law of Independent • 1. 22 a Law of Assortment states that genes for Segregation states that different traits can segregate into allele pairs segregate gametes randomly and during meiosis. independently of each other. • What does segregate Chromosomes not genes assort mean? independently. • Law of Dominance states that A a the dominant allele is expressed Mom Dad and the recessive allele can be hidden.

Genetics and Predictions • Punnett Squares are used to determine probabilities of outcomes for offspring. • Let’s make one. • What do you get in each box? A • What are the genotypes and phenotypes? a • What are their probabilities? A a

Monohybrid and Dihybrid Crosses • Monohybrid crosses deal with one trait. • Dihybrid crosses deal with 2 traits. • Let’s do one of each. • If R is dominant and is round, and Y is dominant and is yellow and you cross Rr. Yy x Rr. Yy, what do you get?

Test Crosses are used to distinguish between homozygous dominant and heterozygous organisms. You breed an organisms unknown genotype with a homozygous recessive organism. What are the outcomes? Show this is helpful and works! Y=Yellow, y=green Y Y Y y y y

Difficult Predictions • Incomplete Dominance is when two different alleles for the same trait combine. R=red, W=white RW= Pink • Codominance is when both alleles express themselves fully. Blood type. A, B or AB

Polygenic Traits • Polygenic traits are controlled by two or more genes. • Eye color- many genes control the pigment (tone, amount, and position). • Skin tone, hair color, height

Multiple alleles and Pleitropy • Multiple alleles are when three or more alleles are found in the population. • Ie. Rabbits have 4 different alleles for hair color, but each rabbit only has 2 of them. • Blood types • Pleitropy occurs when a single gene affects more than one trait. • Sickle Cell anemia.

Environmental Effects • 1. 1 b Different parts of the genetic instructions are used in the different kinds of cells and are influenced by the cell’s environment and past history. . • Himalayan rabbits fur color is affected by temperature. • Western white butterfly wing coloration is affected by temp. • Japanese goby fish can change its sex back and forth in response to changes in its social environment.

Linked Genes • Genes that are located on the same chromosome, which are inherited together. – Ie. Fruit fly’s red eyes and miniature wings inherited together. – Those closer together, more likely to be inherited together. • It is the chromosomes that assort independently, not the genes.

Genetic Mapping • Researchers have made gene maps that show what traits(alleles) are on what chromosomes and where. • The farther apart the 2 genes are located, the more likely they are to be separated by a crossover. (Cross over more frequently)

Genetics Review • Go to the following link and click on your book. Take the self-test and review the Active Art. • Ch. 11 Review