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Introduction to genetics

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1 Introduction to genetics
Ch. 11

2 Meiosis….Some terms to know
Haploid (1n)- a cell with only one complete set of chromosomes (gametes or sex cells). Diploid (2n)- 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?

3 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.

4 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.


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

7 Meiosis Provides for Genetic Recombination
1.28a 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?)

8 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.

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


11 1.8c Mitosis vs. Meiosis Mitosis Somatic cells One cell division
Two daughter cells with same number of chromosomes as parent. Daughter cells are identical to parent. Asexual Meiosis Sex Cells Two cell divisions Four daughter cells with half chromosomes as parent Daughter cells not identical to parents. Sexual

12 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?

13 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

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

15 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.

16 Generations P is the Parental Generation.
F1- what you get when the parents reproduce. YOU. F2- The offspring of F1. YOUR KIDS. What are P, F1 and F2 in these pictures, assuming everyone is from the same family?

17 Mendel’s Experiments He tested 7 traits of the pea pod: Flower Color
Flower position Pea color Pea shape Pod color Pod shape Height Mendel’s Peas

18 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 self-fertilize. 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.

19 Mendel’s Results P- Green X yellow F1- Yellow F2- Green and Yellow

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

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

22 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)

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

24 Mendel’s laws 1.22b Law of Independent Assortment states that genes for different traits can segregate into gametes randomly and independently of each other. Chromosomes not genes assort independently. Law of Dominance states that the dominant allele is expressed and the recessive allele can be hidden. 1.22a Law of Segregation states that allele pairs segregate during meiosis. What does segregate mean? A a A a Mom Dad

25 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? What are the genotypes and phenotypes? What are their probabilities? A a A a

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

27 Test Crosses 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 how this is helpful and works! Y Y y y Y y y y Y=Yellow, y=green

28 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

29 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

30 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.

31 Environmental Effects
1.1b 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. .

32 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.

33 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)

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

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